11

Lumbar syndrome

  Definition and Prevalence

Lumbar syndrome is not only an important medical entity but also has a considerable effect on society at large, both because of its high frequency and because it usually arises in middle age and thus strikes patients at the high point of their occupational productivity. The symptoms most often arise in the patient’s late twenties and reach their highest age-related prevalence around age 40 (Fig. 11.1). This is also the age at which most operations for lumbar disk prolapses are required. As will be discussed in Chapter 12, the disks have a special biomechanical constellation at this age, in which the nucleus pulposus still has a high turgor pressure, but the mechanical resistance of the anulus fibrosus has already begun to decline. Because of these properties, centrally located disk tissue can become displaced outward. Further information on the point prevalence and the annual and lifetime prevalence of back pain (which can largely be equated with the epidemiology of lumbar syndromes) can be found in Chapter 3.

Etiology. The regularly observed statistical features of lumbar disk syndromes are few. Acute low back pain and sciatica often seems to develop spontaneously, without any recognizable external cause. The relationship between lumbar syndrome and heavy or light physical labor is discussed in Chapter 17. The incidence of certain other types of illness (e.g., ulcer disease) is known to vary seasonally; the incidence of lumbar syndrome is somewhat lower in the spring, but relatively constant at other times of the year.

  Special Anatomy of the Lumbar Motion Segments

Lumbar Disks

The lumbar spine generally has five freely mobile lumbar vertebral bodies, four lumbar intervertebral disks, and one disk each at the thoracolumbar and lumbosacral junctions. The lumbar disks increase in size from cranial to caudal, with the exception of the lowest (lumbosacral) intervertebral disk, which is about one-third thinner than the next disk above it. The biconvex shape of the disks is at its most pronounced in the lumbar region of the spine. The disks are higher ventrally than dorsally to an extent that depends on the degree of the lumbar lordosis. This ventral-to-dorsal difference is greatest in the lumbosacral (L5/S1) intervertebral disk, whose cross-section on a lateral image is trapezoidal in shape (Fig. 11.2).

Intervertebral Foramina

The anatomical relationships of the intervertebral disks and intervertebral foramina with the corresponding spinal nerve roots are of particular importance in the lumbar spine. As shown in Fig. 11.3, the intervertebral foramina are found at the level of the disk. The spinal ganglia and ventral roots lie more ventrally than in the thoracic region and are thus immediately adjacent to the disk. The bony border of the intervertebral foramen formed by the dorsolateral edge of the vertebra becomes more prominent superiorly, particularly in the upper portion of the intervertebral foramen, through which the nerve root travels. The caliber of the lumbar nerve roots increases as one moves caudally, with the L5 nerve roots being the thickest—approximately five times thicker than the L1 roots.

The intervertebral foramina of the lumbar spine are dorsally delimited by the facets of the intervertebral joints. The joint spaces of the L1–L4 joints are sagittally oriented, but the articular surfaces at the lumbosacral junction lie in the frontal plane, as in the thoracic spine. As a result, the lumbosacral intervertebral foramen is smaller than the rest. Variations and differences between the two sides are common. Changes at the joint facets and altered positions of the intervertebral joints can narrow the intervertebral foramen from its dorsal aspect.

An increasing degree of importance is currently being ascribed to the width of the lumbar spinal canal in the frontal and sagittal planes as a contributing factor in the generation of low back pain and nerve root irritation. If the lumbar spinal canal is narrow, either congenitally or for an acquired cause, even a mild alteration of the contour of the intervertebral disks dorsally delimiting the canal can produce symptoms.

Ventral Epidural Space

The ventral epidural space of the lumbar region, lying between the posterior edge of the vertebral body and the ventral dura mater, contains a thin peridural membrane that has veins running within it (Fick 1904, Dommisse 1974, Schellinger et al. 1990, Wiltse et al. 1993, Ludwig 2004). Extradiscal disk fragments (sequestra) can be displaced under this membrane; in such cases, discography reveals contrast medium occupying a round area in the epidural space, either cranial or caudal to the level of the disk, without any other epidural contrast medium. The MRI appearance is of a round shadow covered with a membrane. At operation, the surgeon must open this membrane to gain access to the disk fragment (Fig. 11.4).

The space between the ventral epidural membrane and the posterior edge of the vertebral body is delimited medially by the relatively tightly adjacent posterior longitudinal ligament and laterally at infradiscal levels by the pedicle. At supradiscal levels its lateral boundary is formed by the adherence of the connective tissue layer to the vertebral body.

Hematomas can collect in the ventral epidural space and can be confused with submembranous disk fragments (Wiltse et al. 1993) (Figs. 11.4, 11.5).

Ligamentum Flavum

Venous System

The vessels of the vertebral venous system can also play a role in the generation or worsening of disk-related symptoms. The valveless veins of the spinal canal form an uninterrupted anastomotic chain running from the skull base to the sacrum. The degree of filling of the veins depends on the position of the body. The veins are tautly distended if the individual sits or lies prone. As our intraoperative measurements have shown, the degree of filling of the lumbar epidural veins depends on the central venous pressure (Ghazwinian and Krämer 1974). The degree of filling and the central venous pressure are lowest in the kneeling position. During lumbar disk surgery, the epidural venous plexus appears as a collection of flat strands containing only a small amount of blood; as a result, electrocoagulation is usually not necessary for hemostasis within the spinal canal. The studies of Clemens (1970) and Crock (1983, 1994, 2002) showed that the vertebral venous system not only plays a local role as the draining vasculature of the vertebral arches and the spinous and transverse processes, but also communicates with the interior of the skull by way of the emissary veins. The venous plexuses of the spine are also a venous pathway connecting the superior and inferior venae cavae. Together with the azygos system, they form a collateral venous circulation that operates beyond the local level, coming into play physiologically whenever the venous pressure is elevated in the thoracic, abdominal, or intracranial cavities—as when the individual coughs, sneezes, or presses. This partly explains why disk-related symptoms often worsen when these events occur.

Numerical Variations and Transitional Vertebrae

The clinical importance of malformations and developmental anomalies of the lumbar spine and their causative role in disk-related symptoms are generally overstated. Numerical variations are of practical clinical importance, e.g., in the designation and identification of segments. The number of ribless lumbar vertebrae above the sacrum should be counted. If there are only four, the term “sacralization” is often used; if there are six, “lumbarization.” It is clear, however, that sacralization or lumbarization can only be determined from the enumeration of all vertebrae in a complete radiological image series. It is therefore preferable to avoid these terms and use only the designation “transitional vertebra.” The numbering of the spinal nerve roots in numerical variations of the lumbar vertebrae is shown in Fig. 11.6. In such cases, one should count downward from L1—the first ribless vertebra—rather than upward from the sacrum. For example, if there are six free lumbar vertebral bodies, a disk prolapse between L5 and L6 produces an L1 syndrome. On the other hand, if there are only four free lumbar vertebrae, then a prolapse between the fourth vertebra and the sacrum usually produces an L5 syndrome.

Transitional vertebrae have characteristics of both of the neighboring regions. Lumbosacral transitional vertebrae may have free transverse processes, or they may be connected to the sacrum either rigidly or through joints. The intervertebral disk can take on many different transitional forms (Fig. 11.7).

As long as the transitional vertebra is symmetrical, having the same types of structures on both sides, no symptoms are to be expected. Abnormal mechanical statics of the spine arise only when the transitional vertebra is asymmetrical, e.g., when a free transverse process is present on one side and a rigid or articular connection to the sacrum is present on the other (Fig. 11.7). Asymmetrically shaped lateral masses of transitional vertebrae that have lumbosacral joints on both sides can also produce tilting of the transitional vertebra, resulting in a low-lying lumbar scoliosis. In such cases, the disks at higher levels are subject to an asymmetrical mechanical stress, by which they may become pathologically affected.

Topographical Relationships Between the Spinal Nerve Roots and Disks in the Lumbar Spinal Canal

The long caudal spinal nerves as they course through the lumbar spinal canal below L1/2, together with the filum terminale (the caudal continuation of the spinal cord, which extends to the second sacral vertebra), are known collectively as the cauda equina (“horse’s tail”).

The direction in which the nerve roots run after exiting the dural sac depends on the level of the segment. The further caudally the nerve root must travel to reach the corresponding intervertebral foramen, the more acute the angle it makes with the dural sac as it exits from it. It follows that the topographical relationship between the nerve root and the disk is different in each lumbar motion segment (Fig. 11.8). The origin of the L4 nerve root is found at the level of the L3 vertebral body. The L5 root, however, exits the dural sac at the level of the lower edge of the L4 vertebral body, and the S1 root at the lower edge of the L5 vertebral body. An L4/L5 disk prolapse generally impinges on the L5 nerve root. The L4 root is affected only if the prolapse is very large and laterally displaced, because the L4 root runs above the level of the intervertebral disk.

A lateral prolapse of the L5/S1 intervertebral disk can simultaneously impinge on the L5 and S1 nerve roots even if the prolapse is small. The L5 nerve root, as it passes through the upper portion of the L5/S1 intervertebral foramen, is immediately adjacent to the outer lamellae of the intervertebral disk. The root has very little freedom to move within the foramen. Only the lowest two lumbar nerve roots, which lie in the lowest two lumbar motion segments, are in direct contact with the corresponding intervertebral disks. It is here that the danger of compression by disk tissue is greatest.

Radiological/Surgical Subdivisions of the Lumbar Motion Segments

The AP projection provides the best topographical overview of a lumbar motion segment. It also corresponds to the surgeon’s view, albeit rotated by 90°. The successive transverse anatomical planes, from cranial to caudal, are called levels, and the successive sagittal planes, from medial to lateral, are called zones (Fig. 11.9).

Levels. The levels are defined from caudal to cranial in relation to the borders of the intervertebral space and the pedicles on the anterior wall of the spinal canal. Practically speaking, the intervertebral disk is the main orienting structure in radiology and disk surgery, because it is easy to identify both on radiological images and in the operative field.

The discal level is delimited by the upper end plate of the vertebral body below the disk in question and by the lower end plate of the vertebral body above it.

The supradiscal level is above the discal level and extends upward to the lower edge of the pedicles, i.e., to approximately the level of the middle of the upper vertebral body.

The infradiscal level is below the discal level and extends downward to the lower edge of the pedicles of the lower vertebral body.

Zones. The division of a lumbar segment as seen on a transverse radiological image (CT, MRI) into successive sagittal zones, from medial to lateral, differs depending on the craniocaudal level. At the discal level, the segment is divided into medial, paramedial, and lateral zones, without any further landmarks for orientation.

The medial zone has a right and a left half. The center of the paramedial zone corresponds to the central point of the interlaminar operative field after removal of the ligamentum flavum. All pathological findings in the immediate vicinity are described as paramedial, those nearer to the midline are medial and those further from the midline are lateral. The transition from the paramedial to the lateral zone is indicated by the medial border of the pedicles of the vertebral bodies above and below.

The same division is operative at supra- and infradiscal levels. The medial and paramedial parts of the vertebra lie between the pedicles, and the lateral part of the vertebra is the part lying lateral to the medial border of the pedicle. Thus, the pedicle itself and the infrapedicular zone corresponding to the upper portion of the intervertebral foramen lie in the lateral zone of the vertebra.

A disk herniation cannot lie in the lateral zone at the infradiscal level, because the lateral zone is occupied here by the pedicle. Lateral disk herniations at discal and supradiscal levels are located within the intervertebral foramen.

Frontal aspect, with roots. Myelography displays the dural sac and the roots exiting from it in a frontal view, projected over the vertebral bodies and disks. A similar view can be obtained by MRI. These views correspond to the view into the operative field at surgery.

In the lower lumbar motion segments, each root traverses an intervertebral disk before exiting the spinal canal through the intervertebral foramen under the pedicle of the segment below. Each lumbar interlaminar window contains two roots (Fig. 11.10):

The traversing root lies in the paramedial zone at the discal level and is usually affected by paramedial disk prolapses and protrusions. The exiting root is found laterally, above (cranial to) the disk.

The exiting nerve root is derived from the segment above and exits the spinal canal under the correspondingly numbered pedicle. Cranially dislocated prolapses can compress the exiting root at the supradiscal (infrapedicular) level intraforaminally (i.e., in the lateral zone).

For the purposes of description and documentation of radiological and intraoperative findings, not only the cardinal directions cranial, caudal, medial, and lateral but also the intermediate directions craniomedial, craniolateral, caudomedial, and caudolateral sheould be used. Directions can also be designated using clockface notation (Fig. 11.11). In an operative report, not only the direction in which the disk fragment is located, but also its distance from the site of perforation should be mentioned.

The next most common direction of migration is cranial (to 3 or 9 o’clock). Craniolateral dislocation (to 4 or 8 o’clock), i.e., intraforaminal disk prolapse, is relatively rare, as is lateral prolapse (to 6 o’clock).

Sagittal MRI sections give the best view of prolapsed disk tissue. The tissue may lie at the level of the disk, or else it may be cranially or caudally dislocated to a greater or lesser extent or lie behind the vertebral body. It is usually possible to tell from which disk the fragment originated (the “donor disk” or disk of origin). One can also determine the position of the disk fragment along the medial-to-lateral axis by viewing sagittal sections taken in different planes. Laterally and craniolaterally dislocated fragments lie within the foramen and compress the exiting root. Fragments that are dislocated in any other direction compress the traversing root (Fig. 11.12).

The lateral (sagittal) view is useful not only for prolapse localization, but also for determination of the segment. The radiographic image that is normally taken intraoperatively with a needle lying between two spinous processes must be correlated with the preoperatively obtained MR image showing the prolapse in order to confirm that surgery is being carried out at the right level. Rudimentary and transitional disks look different in MRI than in a conventional lateral radiograph. Errors in counting can be avoided by using terms such as the “last” or “second last” disk, rather than “L5/S1,” etc.

Overlapping laminae. The laminae cover the discal level to an extent that increases as one goes up the spine. This fact must be borne in mind when operating on the lumbar spine via an interlaminar approach, with a view of the spine from the side. Thus, while flavectomy at the L5/S1 level immediately exposes the level of the disk. Flavectomy exposes only the infradiscal level at L4/5 and even more so at L3/4, etc., so that that the discal level comes into view only after removal of the lower portion of the upper lamina (Fig. 11.13).

Transverse (axial, horizontal) sections of the lumbar motion segments are obtained by CT or MRI (Fig. 11.14). One can determine the level of any section from the sequential alternation of disks and vertebral bodies (or of pedicles and intervertebral foramina) across the series of transverse sections; reference to a lateral scout view (“topogram”) is thus not necessary. The remaining posterior elements—joints, spinous processes, and transverse processes—have highly variable shapes and add nothing to segment localization except confusion. The two sides of a transverse section look different in the presence of scoliosis or if the section is improperly aligned (i.e., not really transverse).

A transverse section at the discal level displays the disk, possibly accompanied by partially sectioned portions of the upper and lower vertebral body end plates, as well as the intervertebral foramen. At the supradiscal level, the vertebral body and foramen are seen next to each other; an infradiscal section shows the vertebral body and the pedicle, but not the foramen.

At the supradiscal level, the exiting roots are seen laterally and the traversing roots are seen paramedially. The exiting roots are usually cut obliquely. Intraforaminal disk prolapses lie in the vicinity of the exiting roots and can be mistaken for them (the exiting roots, too, can be mistaken for disk prolapses).

The division of the transverse sections at different levels into zones is the same as that described above for the frontal view (Fig. 11.15). The center of the paramedial zone is located between the midline and the lateral border of the disk and usually corresponds to the center of the operative field in the interlaminar approach. The medial edge of the pedicle, as seen in an infradiscal section (which contains the pedicle), defines the border of the lateral zone. Medial prolapses and protrusions can be more pronounced on either the right or the left side.

  Special Biomechanics of the Lumbar Spine

Mechanical Stress on the Lumbar Disks

Beyond the general biomechanical properties of motion segments that were discussed earlier in Chapter 4, the lumbar spine has a number of special properties that are relevant to the causation of disk disease and to its prevention.

The human upright stance puts great stress on the lower spinal segments in particular. At these levels, the weight of the entire body above must be carried on a surface with an area of only a few square centimeters. Moreover, when the upper body deviates from the mid-line, the mechanical stress is multiplied many times over.

There are many ways of measuring the mechanical stress on the spine in different postures and when an individual lifts or carries heavy loads. Quantification is rendered difficult by the general impossibility of putting a measuring instrument directly into the spine in a living individual. Usually, therefore, we must resort to theoretical models or indirect measurements for most information of this type. Analytical models are used to determine the overall stress on the spine by calculating all of the individual forces that are placed upon it (Fig. 11.16). Stress on the spine is a complex matter, as the spine does diverse tasks and has a complicated mechanical structure. Muscles must exert force to counteract the forces acting upon the spine and keep the body mechanically stable.

Methods of Measuring Stress on the Lumbar Motion Segments

Theoretical models provide a simple, analytic approach toward an initial rough estimation of the biomechanical condition of the spine under static or dynamic stress (Schultz and Anderson 1981, McGill 1992). Extensive calculations have been carried out using computer simulation models (Chaffin 1969, 1988; Nussbaum and Chaffin 1996, Parniapour et al. 1997). Finite element models can be used to obtain further information on specific parameters such as deformation, stretching or pressure in individual components of the motion segment (Shirazi 1991, Goel et al. 1993, Wang et al. 2000, Zander et al. 2001) (Fig. 11.17).

The complex overall system, with all of its individual components, can be modeled only in a simplified fashion because of the limitations of computing capacity. The input parameters of computational models must include anatomical, biomechanical, and biological data and materials constants; not all of these parameters can be adequately measured or estimated by other methods, and therefore not all of the inputs to computational models can be considered reliable. The validity of such models, then, is limited by the simplifications and assumptions that they incorporate. The results of computation should always be checked against experimentally measured findings (Fig. 11.18).

Electromyography (EMG) provides information on individual muscle activity and also, if the experimental setup is held constant from muscle to muscle, a rough picture of the distribution of activity among different muscles. The surface electrodes that are usually used can yield no information about deeper muscles. Thin needle electrodes inserted deeply into the muscle yield direct information about the local situation at the site of the needle tip; thus, these electrodes, though much less commonly used in practice, are also much more informative. Andersson et al. (1974) reported the findings of intradiscal pressure measurements, some of which were made simultaneously with EMG. Unfortunately, it remains impossible to infer absolute muscle strength from the EMG data alone. This task requires more complex optimization algorithms, whose validity is still a matter of hypothesis (Parniapour et al. 1997). In any case, it has been conclusively shown with this method that a kyphotic sitting position requires less muscle activity then a consciously effected lordosis (Dolan et al. 1988, Betz et al. 2001).

Biomechanical measurements can be made indirectly in vivo with the aid of measuring devices located in implanted material, such as the implants used in fusion operations on the lower lumbar spine. These implants, when properly equipped, serve as measuring instruments in themselves. Such methods can be used only in a limited number of cases because of the enormous experimental effort required and the high demands that they place on the patient’s readiness to cooperate. Measurements of this type on external fixators provided the first demonstration that these implants are not under any greater stress during sitting than during standing (Wilke et al. 1992). The experimental set-up was taken a step further with the fitting of measuring instruments on internal fixators (Rohlmann et al. 1999, 2000, 2001) (Fig. 11.19). Rohlmann et al. (2004) report the measured stresses in the internal fixators of 10 patients in various bodily positions and during the performance of various activities. The stresses that were measured in the sitting position were approximately 10% lower than during standing and very much lower than during walking. The type of furniture that the patients sat on (stool, office chair, exercise ball, kneeling stool) made little difference with respect to stress. Office chairs with a backrest that could be inclined backward led to less stress on the implants than conventional office chairs. A comparison of the measured implant stresses with the intradiscal pressures measured in one of the experimental subjects revealed close agreement between these two variables for many activities, as long as the measured value of each variable in the standing position was used as a reference.

The most reliable in-vivo data are derived from intradiscal pressure measurements of the type first reported by Nachemson and colleagues (Nachemson and Morris 1964, Nachemson 1966, Nachemson and Elfstrom 1970, Nachemson et al. 1986). These investigators inserted a needle with an integrated pressure-sensitive polyethylene membrane into the disk space and connected it to a measuring instrument employing the nanometer principle. The intradiscal pressure was usually measured in the L3/4 disk. The results were normalized to the intradiscal pressure in each subject while standing (which was assigned the value 100%). These measurements showed a marked increase of intradiscal pressure, by about 50%, when the subjects bent forward. If they additionally held weights in their hands, the pressure rose by a further 70–220% of the reference value.

More recent studies on disk stress in the lower lumbar motion segments have replicated Nachemson’s measurements with updated measuring techniques and extended them to further positions and movements of the spine (Wilke et al. 1998, 1999, 2001, 2004). The intradiscal pressure was measured with a flexible pressure gauge with a constant diameter of 1.5 mm that was surgically inserted directly into the nucleus pulposus of the L4/5 disk under sterile conditions (Figs. 11.20, 11.21). Signals were transmitted through a wireless connection to a computer in order to allow the subjects full freedom of movement. Over a period of 24 h, pressures were measured during the following positions and movements, among others: various lying positions, sitting positions on a normal chair, in an armchair, and on an exercise ball (also called a gym ball, Swiss ball, or Pezzi ball), sneezing, laughing, walking, climbing stairs, lifting weights. The pressure changes taking place overnight because of hydration of the disks in the lying position was measured over a 7 h period.

In relaxed standing, the pressure lay reproducibly between 0.48 and 0.5 MPa. Abdominal pressing raised it to 0.92 MPa and marked forward bending to 1.1 MPa.

In sitting, the pressure varied markedly depending on the degree of support from the back- or armrests (Figs. 11.22, 11.23). Sitting on a chair with a normal, straight back produced a pressure of 0.45–0.5 MPa. Active extension of the lumbar spine raised the pressure to 0.55 MPa. In the sitting position, too, forward bending produced a continual increase in pressure up to a maximum value of 0.83 MPa in maximal flexion, e.g., while tying shoelaces. Pressure in the sitting position could be markedly reduced by leaning back comfortably in an armchair. Relaxed reclining brought the pressure as low as 0.27 MPa.

In walking, the intradiscal pressure was measured at values between 0.53 and 0.65 MPa. The difference between slow and fast walking, or between walking in tennis shoes or barefoot, was small. In jogging, the pressure oscillated between 0.35 and 0.95 MPa. Jogging in tennis shoes lowered the pressure spikes by only a small amount, to 0.85 MPa.

The highest pressure values of all (2.3 MPa) were measured during biomechanically incorrect lifting of a full case of beer weighing 19.8 kg. Incorrect lifting in this case involved a rounded back and straight knees, rather than the correct method of keeping the back straight and bending at the hip and knee, as is taught in back school; correct lifting reduced the peak pressure during lifting to 1.7 MPa. When the case was held against the body at chest height, the pressure was 1.1 MPa; when it was held at the same height but at arm’s length (ca. 60 cm) from the upper body, the pressure was 1.8 MPa (Fig. 11.24).

Conclusions. The findings of these more recent studies agreed with the results of Nachemson et al. (1964) with respect to the pressure values during standing, lying, lifting, and carrying. In particular, the pressure differences between lifting with a straight back and flexed knees vs. a rounded back and extended knees were reproduced with the newer methods. These important results of the older and newer studies measuring intradiscal pressure confirm rules 2 and 3 of back school (see Table 14.1): keep the back straight and kneel to lift. Incorrect lifting of a heavy weight, such as a 20kg case of beer, with rounded back and straight knees raised the intradiscal pressure to 450% of its initial value in the newer studies. This very high value was not matched even during trampolining. If the case was held correctly, however, with flexed knees and a straight back, as taught in back school, the intradiscal pressure rose only to 340% of its initial value. Finally, when the case, after being lifted, was held as close as possible to the body and the subject assumed a mildly lordotic posture, the pressure was only 200% of the value in normal standing.

On the other hand, the marked pressure differences that Nachemson et al. (1964) found in standing vs. sitting, or in lying in different positions, were not confirmed in the more recent studies. It could not be confirmed, for example, that comfortable (relaxed) sitting actually raises the intradiscal pressure by 40%. The current studies show rather that sitting in this position lowers the pressure by 10%; this could be demonstrated both with high-precision stadiometric measurements and with instrumented internal fixators (Rohlmann et al. 2000). The earlier finding that the intradiscal pressure was three times as high in the lateral decubitus position as in the supine position could not be replicated either; the current studies show only a small difference.

The new findings on the relaxed sitting position are of great importance. Relaxed sitting with diagonal positioning of the back and “deposition” of the upper body on the backrest lowers pressure markedly, and the subject also feels this reduction of pressure to be comfortable. As soon as the subject rose from the relaxed sitting position to the upright position, there was a marked increase of pressure in the lumbar disk (Fig. 11.25). Thus, even while seated, the individual can improve diffusion, and thus the nutritive process, within the intervertebral disks by regularly alternating between the upright and relaxed sitting positions (Fig. 11.26).

The differences between the newer measurements and those of Nachemson et al. (1964) are probably due to the different measuring techniques. Nachemson et al. (1964) integrated their measuring devices into a stiff cannula that could be bent, e.g., by muscle tension or displacement, which might have given rise to false signals and thus to incorrect measured values. The pressure gauges that are currently used cannot be bent out of shape, because they are flexible along their entire length. The only nonflexible element is the 7 mm metal tip, which, after implantation, is located completely within the nucleus pulposus, where it is exposed to hydrostatic and therefore equally distributed pressure. The new findings are confirmed by their excellent agreement with measurements made on external fixator implants (Wilke et al. 1992) and stadiometric measurements (van Deursen 2001).

  Special Pathological Anatomy and Pathophysiology

Protrusions and Prolapses

A disk protrusion is a bulging of a disk whose anulus fibrosus is more or less well preserved. A disk prolapse is a disk herniation with perforation of the anulus fibrosus. Even in the case of a prolapse perforating the anulus fibrosus, the disk material outside the anulus may still be enclosed in a thin membrane. In the case of a disk protrusion, in which the disk tissue is displaced within the disk, the fibrous ring around it is largely intact (grade I or II dislocation) (see Fig. 11.31). Intradiscally injected contrast medium remains within the disk and does not flow into the epidural space. A protrusion (bulging) in this sense corresponds to the usual Anglo-American terms, “contained” or “bulging” disk (Fig. 11.27). Farfan (1996) calls it “intradiscal loose islands of disk material.”

A covered prolapse (grade III dislocation, see Fig. 11.31) is one in which the displaced disk tissue has perforated the anulus fibrosus but is still covered by a thin membrane, the so-called ventral epidural membrane (Ludwig 2004). Fragments that find their way under this membrane or under part of the posterior longitudinal ligament, which becomes thinner laterally, are called submembranous or subligamentous sequestra (fragments) and correspond to the covered perforations found at surgery. The term “herniation” can also be used correctly in this situation, because the displaced tissue is still covered by a tissue layer. When contrast medium is injected into the disk (discography), it fills the space occupied by the prolapsed tissue, which sometimes extends to supra- or infradiscal levels.

The disk tissue that lies outside the disk space, but remains covered, still remains in communication with the intervertebral space by way of its path of exit and is therefore in an exceptional situation from the biochemical point of view as well. The displaced disk tissue remains a part of the osmotic system of the intervertebral disk, i.e., it is still nourished by diffusion by way of the pressure-dependent fluid shifts within the disk. This tissue, therefore, does not shrink as rapidly as a fragment lying freely within the spinal canal, which is exposed to the enzymatic activity of the lymphatic fluid, among other influences. Furthermore, the still-covered disk tissue outside the intervertebral space continues to participate in the normal fluctuations of consistency and volume affecting the disk.

As long as there is still a strong layer of anulus fibrosus over the disk protrusion, the protruding tissue may still be able to find its way back into the center of the disk (unless it is a so-called incarcerated fragment). This possibility is exploited by a number of therapeutic techniques, e.g., traction, step positioning and movement therapy.

A distinction must be drawn between disk protrusion through outward displacement of the centrally located, mobile disk tissue and simple outward bulging of the anulus fibrosus in a totally degenerated disk (Fig. 11.28).

Anulus fibrosus bulges of this type are often found at multiple segmental levels simultaneously and become more pronounced with axial loading and backward bending. They play a role in the narrowing of the spinal canal in lumbar spinal stenosis, particularly when they are located at the level of the upper edge of the ascending facet.

Prolapse

A disk prolapse involves complete perforation of the anulus fibrosus and the ventral epidural membrane. The dislocated disk tissue lies more or less free within the spinal epidural space; the perforation is no longer covered. Intradiscally injected contrast medium flows into the epidural space and distributes itself within it. The intraspinal fragment may still be contiguous with the disk (grade IV dislocation) and thus be located “half inside and half outside.” A free fragment (grade V dislocation) lies free in the epidural space and has no connection to the disk.

Once it has perforated the posterior border of the disk, the dislocated disk tissue can travel in any direction. In general, the prolapsed material migrates laterally and caudally along the nerve root, compressing it from the ventral side. The root is thereby raised and pressed against the posterior wall of the spinal canal (lamina, ligamentum flavum). The prolapsed tissue can also migrate cranially or further caudally to compress a nerve root at an adjacent level.

Every large operative series contains not just standard situations like these, but exceptional cases as well. If the prolapsed material migrates medially, the contralateral nerve root can be compressed: sciatica on alternating sides is the result (Fig. 11.29). The material can also migrate around the dura mater to compress the nerve root from the dorsal side (Fig. 11.30). Very rarely, hard sequestrated fragments can perforate the ventral dura mater of the lumbar sac and present as an intradural or intrathecal fragment. Such cases have been reported by Roda et al. (1982), Lee (1983), Griss (1984), Kasch (1986), Yildizhan and Okten (1991), McCulloch (1998), and Postacchini (1999).

The classification of disk protrusions and prolapses by grade of dislocation (I–V) is shown in Fig. 11.31. The grade of dislocation, together with the clinical findings, determines the most advisable form of treatment; intradiscal therapy may still be possible, or an open operation may be necessary (Figs. 11.32–11.37).

When the disk tissue is no longer subject to intradiscal pressure, it takes up fluid, according to the relation discussed in Chapter 4, thereby swelling up and increasing markedly in volume. This occurs because of the laws of osmosis and the intrinsic turgor of disk tissue. We have been able to show, in experiments on dissected specimens of disk tissue (Krämer 1973), that the volume of a disk prolapse induced by identical mechanical conditions is greater in hypo- or isotonic solution than in hypertonic solution. Nevertheless, neither this experiment nor others carried out on operatively removed disk tissue (Wittenberg et al. 1990) revealed any significant shrinkage of prolapsed tissue when exposed to hypertonic solution.

Fluid uptake by prolapsed tissue can be demonstrated by MRI: on a T2-weighted image, the prolapsed tissue has higher signal intensity than the disk from which it emerged (Fig. 11.38).

Prolapsed disk tissue in the epidural space remains swollen for several weeks. As mentioned in the discussion of the osmotic system in Chapter 4, the capacity for hydration and dehydration of disk tissue depends on its proteoglycan content. Nucleus pulposus tissue can take up more fluid than anulus fibrosus or cartilaginous end-plate tissue.

Its water content and volume decrease and the pressure on the nerves diminishes. Depolymerization and enzymatic degradation of the hydrophilic molecules in the disk fragment causes it to lose turgor. These processes can be verified at surgery: freshly prolapsed tissue (removed only a short time after the onset of symptoms) has more pronounced turgor than old extradiscal fragments, which are said in surgeons’ jargon to be “pulpy.”

Aside from osmotic swelling and shrinkage, extradiscal fragments are also enzymatically degraded.

The disk and the nerve root are indeed part of the same motion segment, as far as their function is concerned, yet they are composed of very different types of tissue that arise from different primordial layers during embryonic development. The mechanical impingement and biochemical influence of disk tissue on epidural neural structures induce an inflammatory reaction that accelerates the degradation of the disk tissue. Small fragments are directly enzymatically resorbed by phagocytosis. It is therefore necessary, when a free fragment is to be surgically removed, to verify by a pre-operative MRI scan that it is in fact still there. In some cases, persistent neurological deficits are not due to the persistence of compressive disk tissue but are rather the residua of past nerve compression.

Larger disk fragments are degraded by vascularization and connective-tissue organization from the surrounding epidural fat. Nucleus pulposus tissue is more easily degraded by macrophages and T cells than anulus fibrosus tissue. According to our own studies (Owczarek and Schmidt 1994) and others reported in the literature (McCulloch 1998, Postacchini 1999), once a disk prolapse has been spontaneously resorbed, follow-up CT and MRI scans reveal no significant degree of scarring or adhesion formation in the spinal canal.

Large fragments, i.e., those that occupy more than one-third of the cross-sectional area of the spinal canal, are less likely to be resorbed in an acceptably short period of time than smaller fragments. Parts of the anulus fibrosus and the cartilaginous end plates are resorbed more slowly than parts of the nucleus pulposus. Hard disk fragments therefore more commonly require surgery and also cause more intense pain (Krämer, Herdmann, and Krämer 2005, Willburger 2005). Supra- and infradiscal fragments are resorbed more rapidly because they are surrounded by the well-vascularized ventral epidural membrane and the posterior wall of the vertebral body. The farther away the fragment is from the donor disk, the more likely it is to be spontaneously resorbed. If it is located in the concavity of the posterior surface of the vertebral body, the disk prolapse also exerts less pressure on the dura mater and nerve roots. The fragment has less of an opportunity to avoid impingement on these structures if the spinal canal is narrow and if the fragment is located within the foramen. Our group has published reports on the spontaneous course of lumbar disk prolapses that have been successfully managed conservatively, as observed in serial CT and MRI scans (Owczarek and Schmidt 1994, Krämer and Wilke 1988, Krämer, Hermann, and Krämer 2005), and so have many others (Koeller et al. 1984, Saal and Saal 1989, Hirabayashi et al. 1990, Saal and Herzog 1990, Yutaka et al. 1993, Donelson et al. 1997, Martikainen 1998, Trasimeni 1998, Fergusson 1999, Aelart 2004, Nakagawa 2004) (see also Chapter 12).

In some cases, total resorption of the prolapsed fragment is accompanied by complete remission of the clinical signs and symptoms; in other cases, the clinical findings regress partly or completely despite unchanged findings on CT or MRI. The prolapsed tissue usually becomes calcified. In such cases, the patient’s condition tends to improve after a shorter or longer follow-up interval.

Disk Slackening and Instability

Disk slackening and instability do not necessarily imply the presence of clinical signs and symptoms. These conditions become clinically relevant only when pain and disability arise as a result of instability (see Chapter 6). If disk slackening and instability are present in combination with the associated clinical manifestations, the term “clinical instability” can be used (White and Panjabi 1978, Frymoyer et al. 1979, Kirkaldy-Willis 1984, Farfan 1996, Krismer et al. 1997). Instability leads to insufficiency of the lumbar erector spinae muscles, excess stress on the intervertebral joints, and sometimes manifestations of nerve root irritation. Disk slackening also plays a role in the pathogenesis of lumbar spinal stenosis.

In its initial stages, disk slackening can be compensated for by the abdominal and erector spinae muscles when the spine is under normal amounts of stress. If the functional reserve capacity of these muscles is exceeded, however, signs of insufficiency appear. The most commonly affected muscles are the deep and superficial erector spinae muscles of the lumbar motion segments, though the proximal muscles of the lower limbs can also be affected. Not just the muscles, but also the intervertebral joints are subjected to increased stress by disk slackening. The intervertebral joints of the lumbar spine already have a greater range of normal positions than those elsewhere in the spine because of the marked pressure and volume fluctuations of the lumbar disks (Fig. 11.39).

If the lumbar disks are also slack and subject to greater than normal fluctuations in volume, abnormal and excessive stress on the lumbar intervertebral joints can result, producing arthrogenic symptoms after long periods of mechanical loading followed by unloading. If the joints are subject to abnormal or excessive stress for a long time because of disk slackening, spondylarthrosis can develop (arthrosis deformans).

Displacement of the vertebral bodies with respect to one another can also come about because of disk slackening. Dorsoventral dislocation was called pseudospondylolisthesis in the nomenclature of Schmorl and Junghanns (1968)—“pseudo,“ because the articular facets are fully intact in this condition, as opposed to genuine isthmic spondylolisthesis. The most commonly used term in current clinical parlance is degenerative spondylolisthesis. Rotatory spondylolisthesis is usually due to disk slackening in combination with scoliosis, though it can also occur in the absence of scoliosis.

Sciatica can also be produced by slackening of intervertebral disks without any displacement of disk tissue (Benini 1976, Krämer, Herdmann, and Krämer 2005). In a slackened motion segment, the disk is of less than normal height and the lumbar vertebrae are displaced to some extent in relation to one another. The intervertebral foramina are narrowed, producing nerve root compression, mainly when the disk loses height dorsally and the vertebral body above is simultaneously posteriorly displaced with respect to the one below. The intervertebral foramen between them is then narrowed ventrally by the posterior border of the upper vertebra and by the upper portion of the articular facet of the lower vertebra. The lateral and oblique views of a myelogram or myelographic MRI scan will then reveal indentations in the column of contrast medium (spinal canal stenosis).

Returning the lumbar lordosis to its normal shape through relaxing positions and postures thus plays a major role in the treatment and prophylaxis of disk disease (Fig. 11.40).

Clinical course. Disk slackening and its clinical manifestations are present during a transient, though sometimes quite prolonged, phase in the course of disk degeneration. As the disks progressively dry out and become fibrotic with advancing age, the abnormal movements and displacements of the motion segment also diminish, so that the symptoms gradually disappear— unless the bony changes at the intervertebral joints have lead to narrowing of the spinal canal, i.e., spinal canal stenosis.

Bony Deformation

This situation is often not recognized because the objective clinical signs and changes on CT and MRI are not very pronounced. It can be remedied only by surgical removal of the osteophytes and freeing of the nerve roots from the surrounding tissue (rhizolysis). In spondylarthrosis, osteophytic reactions also arise at the edges of the intervertebral joints. If they jut into the spinal canal, they cause degenerative spinal canal stenosis. Because the lumbar intervertebral joints are part of the dorsal wall of the intervertebral foramina, spondylarthrosis can also cause foraminal stenosis. As mentioned above, bony deformation alone is not clinically relevant; symptoms are produced only when the segment is also slack.

  Clinical Features of Lumbar Syndromes

Introduction

Diagnostic techniques that have been recently developed or improved (EMG, CT, and MRI) now permit better differentiation of the disease manifestations in lumbar syndrome. MRI images of the soft-tissue structures in the lumbar spinal canal are steadily improving in quality. Such images have already revealed that displacement of the dural sac and nerve roots by disk protrusions and deformation of the spinal canal play the most important role in the generation of low back pain and sciatica. The lower two lumbar motion segments are most commonly affected.

Symptoms

Pain is the most important symptom of lumbar syndrome. What the patient says about the onset, development, and responsiveness of the pain provides important clues to the diagnosis. Objective signs are often mild or absent despite severe pain; thus, physicians often have difficulty assessing the situation correctly, especially (but not only) in the medicolegal setting. Moreover, the physician often sees the patient for the first time only after the pain has begun to diminish in intensity, or during an asymptomatic interval.

 

Table 11.1 Typical characteristics of the pain of discogenic lumbar syndrome

Sudden onset
Fluctuating course
Positional dependence
Intensification by coughing, sneezing, pressing

 

The patient can usually describe the localization and character of the pain so precisely that the diagnosis of “lumbar syndrome” can be given on the basis of the history alone. When objectifiable neurological deficits are lacking, the only evidence for lumbar root syndrome is the typical band of pain in the lower limb, whose precise location is also an important clue to the affected segment. The patient complains of numbness or sensory irritative manifestations such as a pins-and-needles sensation or the feeling that the limb has “gone to sleep.” The severity of the pain is, in general, proportional to the pressure exerted on the nerve root, until the area supplied by the root becomes entirely anesthetic and analgetic when the nerve is maximally compressed.

Disk-related symptoms in the lumbar region generally develop over a short time; in most cases, their onset is sudden (Table 11.1). Many patients attribute the onset of the pain to a particular event, perhaps because of a natural desire for a plausible explanation. The events most commonly mentioned in medicolegal assessments are faulty lifting and rotatory movements of the trunk.

More than half of the patients who were interrogated by questionnaire in specialized practices and in our outpatient clinic (Fig. 11.41) reported no particular event before the onset of the pain to which the pain could be attributed. Their sciatica or lumbago appeared to strike them out of a clear blue sky. Accidents and other mechanical forces of the types commonly discussed in medicolegal cases played a numerically insignificant role in this group of nonmedicolegal patients.

The character and radiation of the pain in lumbar syndromes are subject to continuous change: pain lying deep in the low back moves to one buttock or to the sacroiliac region on one side. Sciatica sometimes arises, too, initially only in the thigh, then later radiating all the way down to the foot. The low back pain may entirely disappear, leaving only sciatica in the lower limb (sciatica without low back pain). The reverse type of varying course is seen when the pain moves proximally, reflecting a centralization phenomenon (McKenzie 1987): sciatica changes to isolated low back pain (Fig. 11.42).

The positional dependence of disk-related symptoms is more pronounced in the lumbar region than anywhere else in the spine because of the marked fluctuations of intradiscal pressure and the changing relative positions of the neural structures and the posterior border of the disk that accompany postural shifts. Both low back pain and sciatica are functions of the position of the lumbar motion segments and the mechanical demands placed on them. This is also reflected in the circadian variation of symptoms. Aside from intradiscal pressure, another important question is whether the patient is able to assume a stress-reducing position. If this is not possible, the pain intensifies even when the patient lies down with a lordotic posture of the lumbar spine, e.g., in the prone or flat supine position. Forward bending or sitting in a chair raises the intradiscal pressure considerably, though many patients are asymptomatic when they sit because this posture widens the intervertebral foramina. Only when the patient sits up, increasing the lumbar lordosis, does the slackened posterior portion of the disk get caught in the “nutcracker” of the posterior vertebral body edges and protrude toward the dura mater and nerve roots. This situation arises at night, too, when the patient shifts from the kyphotic lateral decubitus to the flat supine or prone position. Most patients are most comfortable when lying with flexed hip and knee joints, either on their back or on the side (the “fetal” position).

Other patients, however, say that they feel relief only when they are prone or bending backward. The asymptomatic, stress-reducing position thus differs from patient to patient depending on the site of the protrusion or prolapse.

The exacerbation of pain by coughing, sneezing, or pressing is a common feature of all disk-related symptoms in the lumbar region. The importance of the valve-less epidural venous plexus in the spinal canal and its relation to intraabdominal and intrathoracic pressure has already been discussed in Chapter 4. Nachemson (1976), in his measurements of intradiscal pressure, found that abdominal pressing raises the pressure in the lumbar disks to a considerable extent. Patients are aware of, and fear, these elevations of pressure and assume all possible pressure-reducing positions when abdominal pressing is unavoidable. The dependence of the pain on position and on pressing is subject to change at different times of day and also over the course of the illness. Any reported bladder or bowel symptoms or sexual dysfunction can be an important clue to a possible partial cauda equine syndrome; any weakness of the dorsiflexors of the feet and toes, or of the gluteal and calf muscles, may indicate a motor disturbance of a type that often accompanies sciatica.

Findings of Clinical Examination

The standing patient is first asked to bend forward and to the sides and to rotate the trunk actively, and then these same movements are tested passively. A limited range of motion to one side is found. Lateral bending is not as severely restricted as forward and backward bending. The abnormal posture and limited range of motion of the trunk may sometimes be only mild or even absent, e.g., in the asymptomatic interval of a lumbar syndrome or with a far lateral S1 disk protrusion. Painful limitation of motion of the lumbar spine is often not evident until the patient is asked to bend laterally while keeping the trunk bent slightly forward. If the physician suspects that a limited range of forward bending may have a nonorganic cause (e.g., in medicolegal situations or possible psychogenic overlay), a kneeling test can be done at this point (see Chapter 13): if the patient still cannot bend forward (at the hip joint) when kneeling on a chair, a position in which the sciatic nerves and ischiocrural muscles are relaxed rather than stretched, then the limited range of motion is probably of nonorganic origin.

Next, the patient is asked to stand, and to take several steps, when standing on tiptoe and then on the heels; this will reveal any possible weakness of the foot dorsiflexors (L5) or calf muscles (S1).

The remainder of the examination is carried out with patient lying down. Lumbar spasm often disappears when the patient is horizontal, because the trunk muscles no longer have a stabilizing, antigravity task to do. The supine position with mildly flexed hips and knees is usually the most comfortable position for the patient (the maximally stress-reducing position). Patients find it unpleasant to lie flat in the prone position.

With the patient prone, the physician should palpate the spinous processes and ascertain whether there is any tenderness of the affected motion segment to gentle shaking or percussion. Because the lumbar intervertebral joints are sagittally oriented, lateral shaking of the spinous process will always produce movement of the vertebral bodies above and below as well; thus, this part of the examination cannot be considered segmentally specific.

Paraspinous tenderness is more informative: in thin and not particularly well-muscled patients, one may be able to exert pressure on the ligamentum flavum and the nerve root lying directly under it by deep palpation with one finger. The soft tissues between the laminae may be depressed by this maneuver to such an extent that the nerve root is squeezed between them and a disk protrusion lying anterior to it in the spinal canal (Fig. 11.43), resulting in the provocation of the patient’s typical local and sciatic pain. This pain on deep palpation is still more intense if it is evoked when the patient’s back is in a lordotic posture, with flexed hip joints, in the kneeling, squatting, or lateral decubitus position, because these positions increase the height of the interlaminar window.

Keeping the patient prone, the physician proceeds to test the ability of the hip joints to be hyperextended, checking for the provocation of pain on femoral nerve stretching, the so-called “reverse Lasègue sign” that indicates a disk protrusion at a higher level (Fig. 11.44).

Certain parts of the neurological examination can now be carried out while the patient remains prone, starting with sensory testing in the dorsally located dermatomes. The physician asks the patient to tense the gluteal musculature and palpates for any difference in muscle tone that may indicate the presence of an S1 syndrome. The prone position is also suitable for testing of active knee flexion, which can be impaired in higher lumbar root syndromes.

The supine position. After determining that the range of motion of all joints (including rotation at the hips) is free, the physician tests for the presence of the Lasègue sign; this can be done either by raising the straight lower limb or by extending the knee when the limb is already flexed at the hip.

No matter which of these two methods is used, Lasègue’s test consists of hip flexion at a right angle combined with knee extension. If this provokes pain in the back radiating down into the sciatic distribution, the Lasègue sign is said to be positive; the clinician must differentiate among locally induced back pain, classic radicular pain, and the dull discomfort that accompanies stretching of the hamstrings. Lasègue (1864) was also the first to observe that patients with sciatica keep the foot in a plantar flexed position and complain of increased pain when it is dorsiflexed (Fig. 11.45). In common medical parlance, the term “positive Lasègue sign” can also refer to the provocation of pain by raising of the straight lower limb; this is the “straight-leg raising test” often mentioned in the Anglo-American literature. The provocation of pain by this maneuver was first described as a typical finding in sciatica by Forst, a pupil of Lasègue (cited in Finneson 1980).

Straight-leg raising displaces the L4, L5, and S1 spinal nerves by up to 5mm and stretches them by 2–4% (Smith et al. 1993).

The straight lower limb can normally be raised to 70–90° by passive flexion at the hip, with some variability between individuals and depending on age. Limb raising is limited by a feeling of tension in the ischiocrural muscles, but no unusual feeling normally arises from the sciatic nerve during this maneuver. Sciatica is provoked only when the sciatic nerve is irritated or if it is less than normally mobile, or already under stretch, in the region of the nerve roots.

The sensitivity and specificity of the Lasègue sign have been investigated by Edgar (1995), Andersson and Deyo (1996), Hogen et al. (1996), Igarashi et al. (2004), and Summers et al. (2005). In their systematic review of the literature, Walter et al. (2000) concluded that the specificity of the Lasègue sign is low. Thus, pain on straight-leg raising should only be considered to be of diagnostic value in the context of other accompanying manifestations of lumbar syndrome.

Depending on the site of the displaced disk tissue, radicular pain may also be induced or intensified by raising of the contralateral lower limb, i.e., the one that is not painful (contralateral Lasègue sign). This is sometimes the case when the prolapse is medially situated and compresses the nerve from the caudal side (Fig. 11.46).

Straight-leg raising will also be painful in pathological conditions affecting the hip and sacroiliac joints. To rule out these potential sources of pain, one can do the sciatic nerve test (Fig. 11.45c): The straight lower limb is raised to the point at which pain begins to be felt and then lowered till the pain just disappears. If mild passive dorsiflexion of the foot at this point induces pain again, then it can be regarded as certain that a sciatic nerve syndrome is present. Dorsiflexion stretches the tibial nerve by about 1–2 cm. This maneuver does not induce pain originating in the hip or sacroiliac joints, because it causes no additional movement in these joints.

In the popliteal fossa pressure test, the straight leg is raised to the point at which pain begins to be felt, and then the knee is flexed and placed on the physician’s shoulder. Pressure from the physician’s thumb in the patient’s popliteal fossa provokes sudden sciatic pain if the nerve is under tension (Fig. 11.47).

The pain-provoking effect of sciatic nerve stretch in patients with lumbar syndrome is also exploited in the straight-leg sitting test (see Chapter 13). The patient is unable to sit up on a flat surface, e.g., in bed or on an examining table, with the knees extended. This objective sign of the intensity of pain is of particular value in medicolegal assessment: because straight-leg raising is a commonly known medical test, patients will often indicate the presence of severe pain when the leg is raised only to 20° or 30°, but will then be able to converse normally with the physician when sitting up in bed with the knees extended. The same applies to the sciatic nerve stretching test in the sitting position, the so-called “reclination test”: the patient sits up in a chair without leaning back and the examiner raises the patient’s calf. If the patient then leans back because of pain, the test is positive (Fig. 11.48).

Some useful diagnostic evidence can already be obtained at the start of the examination when the examiner observes the patient during toe-standing, heelstanding, toe-walking, and heel-walking. The motor dysfunction may be so mild that the patient does not notice it. Fibrillation may be seen in affected muscle groups. The magnitude of the motor deficit is generally proportional to the pressure on the nerve root. Large muscles are only mildly weakened in monosegmental lumbar irritative syndromes, even when a nerve root is massively compressed. The quadriceps, for example, is supplied by the L3, L4, and L5 nerve roots, but the extensor hallucis longus is supplied only by L5. An L3/4 disk prolapse compressing the L4 root produces quadriceps weakness that is evident only during active knee extension, but an L4/5 prolapse compressing the L5 root produces marked loss of strength of the foot dorsiflexors (i.e., a foot drop). Thus, the knee flexors and extensors should always be tested, but the most important tests are of the raw strength of the plantar flexors and dorsiflexors of the feet and, specifically, of the big toes (Fig. 11.49).

Although motor testing often yields unexpected findings for both the physician and the patient, the findings of sensory testing are often already partly implicit in the clinical history itself (complaints of numbness, etc.). Because disk-related nerve root syndromes generally impair sensation only superficially, sensory testing can be restricted to directed testing with a pin-wheel, needle, cotton-wool pad, or similar object. Just as in motor testing, dermatomal overlap (particularly in the proximal portion of the lower limb) often precludes reliable assignment of a sensory deficit to a single segment.

Bradford and Spurling (1950) reported a surgical series of S1 rhizotomy (complete transection of the S1 root within its dural sleeve) on a number of patients. They found that this produced a different distribution of hypesthetic areas in the thigh and leg in each patient. The various dermatome charts that are available also differ from one another; the classic ones are those of Foerster (1933), Tilney and Riley (1938) and Keegan (1943).

Neurophysiologic Testing—EMG

Plain Radiographs

In the AP view, one first counts the lumbar vertebrae and notes any transitional vertebrae, which are of clinical importance only in the case of an asymmetrically anchored lumbosacral vertebra causing asymmetrical stress on the disks lying above it (see p. 28). One should also note whether the upper and lower end plates are parallel, as they should be, and inspect the shape and location of the oval shadows representing the pedicles seen on end. In torsion scoliosis, for example, these are projected toward the concave side, and they may be blurry or absent if the pedicles are involved by a neoplastic or infectious process.

Disk collapse and lumbar hyperlordosis cause adjacent spinous processes of the middle and upper lumbar spine to touch one another, leading to reactive sclerosis and, sometimes, clinical symptoms (Baastrup disease) (Fig. 11.50).

The width and borders of the interlaminar windows are of importance for epidural and perineural injections and can be seen in their projections on an AP view, so that the physician can determine the optimal puncture site in advance. Spina bifida occulta, if present, should be mentioned in the radiography report for the sake of completeness but is of no biomechanical significance for the motion segment or for the generation of disk-related symptoms. The lateral view of the lumbar spine is more informative than the AP view (Fig. 11.51).

Just as in the cervical spine, straightening of the lumbar spine cannot always be interpreted as evidence of an acute disk syndrome, because the normal lordosis can also be abolished voluntarily. When radiographs are taken with the patient lying on one side and flexing the hip and knee joints, as is often done, the lumbar lordosis is often considerably reduced in any case. Findings of greater significance include marked narrowing of the intervertebral spaces in young adults; lateral, rotational, or dorsoventral displacement of the vertebral bodies with respect to one another without interruption of the articular processes (pseudospondylolisthesis in the terminology of Schmorl and Junghanns 1968); and exophytes on the posterior edge of the vertebral column.

If such changes are found in the plain lateral radiographic view, one should proceed to obtain oblique, spot, and tomographic views. Particularly when there is a question of spondylolysis and spondylolisthesis, oblique views should not be omitted. These also show intervertebral joint arthrosis, with characteristic telescoping of the joints due to degenerative disk collapse (Fig. 11.52).

The notochordal remnants and juvenile developmental anomalies to which so much attention is often paid are actually clinically unimportant and imply nothing more than possible weakness of the structures bordering the intervertebral disks, which might create a predisposition to disk disease. Not every protrusion seen in the posterior silhouette of the vertebral column on a plain lateral radiograph is a dorsal osteophyte; a large lateral osteophyte may also be projected over the spinal canal (Fig. 11.53). This situation can only be clarified with a CT or MRI scan.

Lumbar Myelography

The lumbar subarachnoid space is a compartment filled with cerebrospinal fluid (CSF) that is contained between the arachnoid membrane lying just under the spinal dura mater and the pia mater surrounding the spinal cord and nerve roots. The space between the spinal dura mater and the arachnoid membrane is only virtual under normal circumstances. The dural sac containing the subarachnoid space extends caudally to the S2 vertebral level. In the lumbar region, the CSF of the sub-arachnoid space surrounds the nerve rootlets of the cauda equina; CSF continues to surround the nerve roots in nerve root sleeves that extend into the intervertebral foramina.

 

Table 11.2 Indications for lumbar spine CT

Trauma
Spondylolisthesis
Spinal canal stenosis
Spondylitis
Tumors
Disk herniation
Post-discographic CT

 

Myelography has become a much less important diagnostic technique for the assessment of disk disease since the introduction of CT and MRI. It is now possible to display the CSF-containing spaces with MR myelography in much the same way that they were displayed with conventional myelography. Furthermore, MRI displays the soft tissues neighboring the CSF spaces, including disk protrusions and prolapses, which myelography does not. Thus, myelography is currently used only for a narrow range of indications, e.g., when a patient suffers from acute cauda equine syndrome and all lumbar segments must be examined radiographically but an MRI scanner is not available.

The combination of myelography with post-myelographic CT has also largely fallen out of use because of the improved display of intraspinal structures with MRI. Practically the only advantage that myelography has over other procedures is that CSF is always obtained as a part of the procedure and can be analyzed in the laboratory for the differential diagnosis of a variety of neurological diseases.

In conclusion, myelography has largely gone out of use, being supeseded by CT and MRI, in accordance with the MIRACLE principle stated in Chapter 1. In comparison with these newer techniques, it is more invasive, has a greater risk of complications, and generally provides less information, at least in the diagnostic evaluation of disk disease.

CT

In combination with discography (“disco-CT”), CT can still be used to advantage in the diagnostic evaluation of disk protrusions and subligamentous prolapses. A disco-CT can be helpful in differential diagnosis, particularly for the choice of the optimal intradiscal therapeutic technique (Table 11.2). Its main disadvantage is that the invasive procedure of disk puncture has to be carried out twice: once for diagnostic purposes and then later, after evaluation of the CT images, for therapeutic purposes in a second sitting. A CT scan of the lumbar spine can also be useful as part of a comprehensive assessment in medicolegal cases, if warranted by the clinical findings.

The findings of degenerative spinal change that are revealed by CT have the same significance as those revealed by plain radiographs and myelography: these radiological findings are of no pathological significance and do not imply a need for surgical intervention except when they are closely correlated with the patient’s clinical manifestations.

Positioning. A CT scan of the lumbar spine is obtained with the patient supine. Roentgen rays emitted by rotating tubes, oriented in all radial directions perpendicular to the long axis of the body, are sensed by detectors placed opposite the tubes. The resulting data are processed by computer to generate a cross-sectional image in the transverse (horizontal) plane. The lumbar spine should be as straight as possible, i.e., the lumbar lordosis should be reduced as much as possible, so that the planes of section will be parallel to the vertebral bodies and disks. This is achieved by positioning the patient with the knees flexed and the pelvis tilted backward (Fig. 11.54). This method of compensating for the lumbar lordosis is not adequate at the L5/S1 level, for which one can additionally tilt the imaging plane by 20° by tilting the gantry of the CT scanner.

Once the patient is properly positioned, the position must be maintained for the duration of scanning, which takes a few minutes, so that the individual cross-sectional images will correspond correctly to the planes of section indicated on the scout view or topogram of the lumbar spine that is obtained at the beginning. The planes indicated by lines in the scout view are numbered with the numbers of the corresponding transverse (horizontal) images in the study.

The sequence of cross-sectional images and their interpretation. The distance between cross-sectional images can be chosen at will; the images should be more closely spaced at levels near the intervertebral disks than elsewhere. The mid-level of the vertebral body at the height of the pedicles is generally not imaged, to reduce cost and radiation exposure, even though free fragments can be found at this level, just as at other levels.

The cross-sectional images generated by computer are always displayed in the same way (Fig. 11.55).

Further computer processing enables the reconstruction of a more familiar-appearing AP or lateral view of the spine from the horizontal CT sections. In principle, a reconstruction of the images in the sagittal or frontal planes can yield no further information than is already present in the horizontal images, from which the findings can be read directly. It therefore seems a better idea to get adequate practice in the interpretation of the cross-sectional horizontal images, rather than routinely obtain reconstructed views. The horizontal images are easy to interpret as long as they are displayed one after the other in sequence, from cranial to caudal or the other way round, and are adequately labeled. In any case, the pathological finding in question, generally a disk protrusion or prolapse, will only be clearly visible in two or three individual sections.

Signs of tissue displacement. Displaced disk tissue always pushes some of the ventral epidural fat aside, producing an asymmetrical configuration of the fat. It must be borne in mind, however, that epidural fat may be absent, e.g., because of spinal canal stenosis (see below), postoperative adhesions and scoliosis, or simply advanced age. The most important radiological finding is the displacement or loss of contour of a nerve root together with indentation of the dural sac. The differential diagnosis includes asymmetry of the nerve root origins from the dural sac and scoliosis causing the CT plane to be angulated rather than truly transverse in relation to the spine.

When dislocated disk tissue protrudes into the spinal canal, the indication for surgery or intradiscal treatment depends to a large extent on whether the finding is a protrusion with a preserved anulus fibrosus or a prolapse perforating the outer layer of the fibrous border of the disk. Discography provides an unequivocal answer to this question, but CT can also be very helpful. Disk protrusions have a symmetrical base and a greater ratio of base width to height than prolapses; prolapses, on the other hand, jut further into the epidural space from a relatively narrow base and tend to have an irregular surface with a pointed tip, producing a triangular outline (Fig. 11.56).

Even very broad prolapses seen on CT do not necessarily require invasive treatment. Their management should always be based on the clinical findings (Figs. 11.57–11.62).

A further means of distinguishing different types of soft tissue from one another in CT scans is the systemic (i.e., intravenous) administration of contrast medium. The theoretical basis for this is the fact that well-perfused tissue will take up contrast medium to a greater extent than tissue that is only poorly perfused or not at all, such as a fresh disk prolapse. Contrast-enhanced CT scans are mainly useful for the detection of recurrent disk prolapse within peridural scar tissue. Fresh, well-perfused scar tissue naturally takes up more contrast medium than old, fibrotic sheets of scar in which old disk-derived tissue has become incorporated.

Diagnostic Study of the CSF

Discography

The diagnostic accuracy of lumbar discography, when it is employed in this way, is 83% (Hudgins 1977) (Fig. 11.63). Discography is also a useful supplement to CT scanning in many cases, because it provides special information about the location and size of any dorsally displaced disk fragments. Discography yields information about the disease process beyond the findings that can be appreciated visually on radiographs: if the disk is closed (not perforated), the injection pressure and injectable volume of fluid indicate the size of the intradiscal cavity system and the extent of disk degeneration (Fig. 11.64). Injection of the affected disk generally reproduces or intensifies the patient’s typical radiating pain, similarly to the cervical spine distension test (memory pain).

The interpretation of contrast medium patterns. In general, a lateral radiographic view suffices to show whether the contrast medium injected into the disk remains in the center of the disk or flows out of it through a narrow connecting pathway into the epidural space. To localize a fragment more precisely, additional oblique views are needed (Fig. 11.65). The contrast medium injected into the interior of the disk spreads out in different patterns depending on the size and type of the intradiscal cavity system. The contrast medium depot may appear rounded or branch out irregularly toward the periphery. These intradiscal contrast medium patterns are of little clinical importance, however, because from a certain age onward nearly all lumbar disks display degenerative tears and branching of greater or lesser severity. The only findings that should truly be considered pathological with reference to a possible indication for surgery are contrast medium reflux into the epidural space and the presence of a tissue fragment.

Such fragments are often covered by a thin layer composed of the outer lamellae of the anulus fibrosus, the posterior longitudinal ligament, and/or the ventral epidural membrane. The hernia-like sac around the fragment may take up so much contrast medium that the fragment itself can no longer be seen.

Corresponding to the diverse pathoanatomical operative findings in patients with lumbar disk prolapses, discography can reveal almost any conceivable pattern of contrast medium, a fact that makes interpretation rather difficult (Fig. 11.66). If the lateral and oblique radiographs after discography do not provide sufficient information about the site of a disk fragment, a CT scan of the affected segment can be obtained about 2 h later (so-called CT discography). This technique is especially suitable for the demonstration of intraforaminal protrusions (Jackson and Glah 1987, Kornberg 1987, Schulitz et al. 1988).

MRI

Technical procedure. Just as in CT, the patient lies supine with slightly flexed legs and must remain in the same position throughout the study. The scout scan and sectional images in the transverse plane are analogous to their CT counterparts. The patient’s right side is always on the left side of the image (cf. Fig. 11.54, p. 173).

Advantages. MRI is the diagnostic imaging method of choice for lumbar disk disease because it enables imaging of the entire lumbar spine, in multiple planes of section, with better differentiation of various types of soft tissue from one another than CT. A particular advantage is the absolute harmlessness of the technique, which has now been fully documented.

The advantage of MRI for disk surgery is that it can be used to generate images of all of the lumbar motion segments in a single study. It is thus much harder to overlook dislocated disk fragments or simultaneous disk prolapses at other levels in an MRI scan as compared to CT, which is routinely used to image only two or three lumbar segments at a time.

Table 11.4 Indications for lumbar spine MRI

Disk herniation
Post-discotic syndrome
Differential diagnosis of other neurological diseases

The resolution of the technique is such that prolapsed disk tissue and the dural sac are well demarcated from one another. The indentation of the dural sac by a disk prolapse resembles what is seen in a lateral myelographic image. Furthermore, the prolapsed tissue is seen in fine detail. Well-hydrated nucleus pulposus tissue has a high signal intensity, equivalent to that of CSF, in T2-weighted images. Portions of the anulus fibrosus, the cartilaginous end plates, and the posterior longitudinal ligament have a low signal intensity in all signal weightings because of their low water content (Table 11.3).

A well-hydrated free fragment in the epidural space can be treated conservatively at first, as long as no major neurologic deficit is present, because it can be expected to shrink rapidly in volume now that the nucleus pulposus tissue within it is no longer in contact with the intradiscal osmotic system. On the other hand, hard, cartilaginous fragments, which usually produce severe pain, are unlikely to shrink over time and one should not wait too long before removing these surgically.

In addition, MRI enables quantitative assessment of degenerative changes of the disks, particularly their water content. We have found that the human intervertebral disk contains more water in the morning than in the evening. This finding reveals the operation of an osmotic system within the disks (see Chapter 4).

We know from pathoanatomical studies and clinical experience in discography that disk degeneration is not synonymous with disk-related symptoms. Findings on MRI within 12 weeks of the inception of serious low back pain are highly unlikely to represent any new structural change (Carragee 2006). Thus, it is wrong to attach too much importance to the radiological finding of degenerative dehydration of disk tissue with consequent bulging of the anulus fibrosus. On the contrary, the hypointense, poorly hydrated degenerated disks seen on an MRI scan (“black disks”) bode fewer problems for the future than the bright, well-hydrated disks that still have a normal turgor pressure (see Fig. 11.68).

CT or MRI?

The indications for lumbar spine MRI in disk disease are determined mainly by considerations of availability and cost. The entire diagnostic spectrum can be covered by CT, occasionally supplemented with myelography (Table 11. 4).

The special advantages of MRI have to do with the localization and differentiation of dislocated fragments in theepiduralspace.A surgeon should not operate on a disk without a preoperative MRI scan, particularly if microsurgery is to be done through a small incision. MRI is also much better than CT and myelography at distinguishing postoperative scar tissue from residual or recurrent prolapses. Likewise, it is better for the differential diagnosis of other neurological diseases in the lumbar region. All other questions, particularly those concerning bony structures, are better answered by CT (Table 11.5).

Findings in Disk Degeneration

The strengths of MRI are particularly easy to appreciate when MRI and CT scans of the same patient are compared. The surgeon obtains clear information about how far and in what direction the spinal canal must be explored so that all sequestrated fragments can be removed. The designation of locations in the lumbar and epidural space with a conventional scheme of levels and zones enables radiologists and surgeons to communicate effectively and unambiguously about the MRI findings. In addition to precise localization, MRI also yields information about the consistency and water content of disk tissue. When interpreting MRI scans, however, the clinician must be aware that the perifocal edema surrounding dislocated pieces of disk tissue makes the degree of impingement on neighboring structures appear more extensive, and more impressive, than it really is. Medial protrusions and prolapses seen in sagittal MRI views often seem to occupy the entire spinal canal.

Beyond the changes in the disk, there are also corresponding changes in the neighboring vertebral bodies, expressed not only as spondylosis and osteochondrosis, which can be seen even in plain radiographs or CT scans, but also as a variable appearance of the spongiosa. The MRI abnormalities of the bone marrow space of the neighboring vertebrae were classified by Modic (1985) into three types, representing stages that cannot always be sharply distinguished from one another (Fig. 11.67):

Type I: ingrowth of vascularized, contrast-enhancing tissue into the neighboring bone marrow, with increased signal intensity on T2-weighted images and decreased signal intensity on T1-weighted images.

Type II: fatty degeneration of the bone marrow with increased signal intensity on T1-weighted images and moderately increased signal intensity or isointense signal on T2-weighted images.

1. L2/3 Protrusion and Prolapse, MRI and CT (Fig. 11.68)

Clinical presentation. This 44-year-old man reported feeling a sudden snap in his back while getting up from a low chair 4 weeks ago, and thereafter severe back pain radiating into the lateral aspect of both thighs. The pain persisted despite 3 weeks of conservative treatment, and he was admitted to hospital. Examination revealed a sciatic postural deformity with the torso inclined slightly to the right. There were no motor deficits, and the deep tendon reflexes were normal. The Lasègue sign was positive on the right at 30°.

MRI and CT. These study sequences are shown in Fig. 11.68.

Findings. The L3/4 and L5/S1 intervertebral discs are of markedly diminished signal intensity in the T2 image. There is a broad-based, asymmetrical posterior displacement of disk tissue of relatively high signal intensity at level L2/3 (c, →), which compresses on the dural sac (a–c). There is also a circumscribed posterior displacement of disk tissue in the median zone at the L5/S1 level (a, b, d), without compression the dural sac. The CT findings at L5/S1 are consistent with the MRI findings, but the CT additionally shows clear evidence of calcification or ossification (e, →).

Diagnosis. Protrusion (grade II dislocation) of the L2/3 intervertebral disk and old medial prolapse of the L5/S1 intervertebral disk.

2. L5/S1 Protrusion and Prolapse, Modic II Signs (Fig. 11.69)

Clinical presentation. This 40-year-old man complained of low back pain and left-sided sciatica of 3 months’ duration. The band of pain corresponded to the left S1 segment. The pain was of moderate intensity; he was able to sleep at night, and he felt pain during the day only with certain movements. Examination revealed a diminished left Achilles tendon reflex and a positive Lasègue sign on the left at 60°.

MRI. The study sequences are shown in Fig. 11.69.

Findings. Disk degeneration is present in the last two segments, which are of diminished signal intensity and diminished height (a, b). Marked changes (Modic type II) are seen in the superior and inferior end plates at L4/5. The L4/5 disk and especially the L5/S1 disk (a–c) are posteriorly displaced, narrowing the left caudal intervertebral foramen (e, →). The subligamentous portions of the disk are of relatively high signal intensity in the T2 image (e, →). The left S1 nerve root is thickened (a, b, f, →).

Diagnosis. Broad-based disk protrusion at L4/5 (dislocation grade II) and prolapse at L5/S1 (dislocation grade V).

Treatment. Because the pain was relatively mild, conservative treatment was provided.

Clinical course. The treatment included epidural perineural injections on the left side in segment L5/S1, cube positioning (with hips and knees flexed), and physiotherapy. The symptoms improved, and the patient returned to his office job.

Comments. Neither the clinical findings nor the MRI findings are particularly severe. Some of the denser tissue in the left lateral recess of S1 corresponds to the left S1 nerve root, which is thickened because of edema. Modic type II changes of the upper and lower end plates of L4/5, of no clinical importance.

3. L4/5, Prolapse with Supradiscal Extension, Modic II Signs (Fig. 11.70)

Clinical presentation. This 61-year-old man had suffered from back pain, with occasional radiation into the legs, for several years. In the week leading up to presentation, the pain had become increasingly severe and radiated into the right leg in an L4 and L5 dermatomal pattern, with some radiation into the anterior aspect of the thigh as well. Physical examination revealed limping on the right side due to pain and a positive Lasègue sign on the right at 60°. The right Achilles tendon reflex and patellar reflex were slightly diminished.

MRI. The study sequences are shown in Fig. 11.70.

Findings. The last two intervertebral discs are of diminished height and signal intensity on the T1- and T2-weighted images, and there is a zone of increased signal intensity in the end plates (a, b). There is disk tissue lying posterior to the L4 vertebra (a, b, arrowhead) and retaining only tenuous contact with the intervertebral disk (a, →). This tissue fills the entire right L4 lateral recess (c) and masks the right L4 nerve root (→ = left L4 nerve root). The MIP reconstruction (d) shows the topographic relationship of the prolapse (P), the L4 nerve root (→), and the L5 nerve root (→).

Diagnosis. Right paramedial L4/5 disk prolapse with supradiscal fragment (dislocation grade V). Osteochondrosis at L4/5 and L5/S1 with Modic type II bone marrow changes.

Treatment. Surgery was recommended because of the severe pain and the massive fragment, despite the absence of a motor deficit.

Operative findings. Half of the inferior margin of the L4 lamina was removed to reveal a massive free fragment compressing the intrathecal portion of the L5 nerve root medially and the exiting L4 nerve root laterally. The L4/5 intervertebral space was so narrow that it did not admit insertion of a disk rongeur.

4. L3/4, Prolapse with Supradiscal Extension and Modic I Signs (Fig. 11.71)

Clinical presentation. This 52-year-old man complained of severe back pain of 3 weeks’ duration. The pain had initially radiated into the anterior aspect of his right thigh, but then radiated laterally in a band corresponding to the proximal portion of the right L5 dermatome. A marked ipsilateral sciatic postural deformity was present (i.e., the torso was inclined to the right). The Lasègue sign was positive at 30° on both sides.

EMG. There was evidence of nerve root irritation at the L3 and L4 levels, without any sign of florid denervation or a functionally relevant deficit.

MRI. The study sequences are shown in Fig. 11.71.

Findings. The lowest three intervertebral discs are of diminished signal intensity. A circumscribed subligamentous posterior displacement of disk tissue is seen at the L3/4 level, and the annuloligamentous complex (→) is well demarcated. The extruded disk tissue extends cranially as far as the middle of the posterior margin of the L3 vertebral body and is continuous with the parent disk (a, b). The dural sac is markedly compressed (a–c). A circumscribed edematous area in the posterobasal portion of the L3 vertebral body (a, c, →) is consistent with Modic type I bone marrow changes.

Comments. The L3/4 extrusion at disk level initially caused severe pain referable to the L3 and L4 nerve roots as it migrated into the concavity of the posterior wall of the vertebral body. The pain later became less severe. The extruded fragment was not sequestrated in the epidural space, but rather lay beneath the epidural membrane of the L3 vertebra, as can be seen from its relatively broad-based bulging into the epidural space, with a smooth margin (Fig. 11.71c). There are no nerve roots in the median and paramedian zones of the supra-discal level of the L3/4 segment; a disk prolapse at this level affects only the intrathecal nerve roots.

5. L4/5, After Previous Surgery, Modic Type II Upper and Lower End-Plate Changes (Fig. 11.72)

Clinical presentation. This 58-year-old woman had undergone disk surgery 2 years previously. Pain in the left leg resolved after surgery, but returned 3 months later and persisted. The pain radiated into the L5 dermatome and occasionally also the S1 dermatome. The Lasègue sign was positive on the left at 30° and on the right at 60°. There was no neurologic deficit.

MRI. The study sequences are shown in Fig. 11.72.

Findings. There is soft tissue formation in the left L4/5 intervertebral foramen, with marked contrast enhancement (c, d, →). The spinal ganglion is only vaguely distinguishable in the contrast-enhanced images (d, →). There is marked dural enhancement, mainly posteriorly (d, →). The sagittal images show a lack of fat signal at the infrapedicular (a, b, →) and infradiscal levels (a, b, →).The L4/5 intervertebral disk is severely degenerated, with accompanying Modic type II degenerative changes in the upper and lower end plates.

Diagnosis. Scarring and granulomatous changes due to previous surgery in the left L4/5 intervertebral foramen and on the posterior aspect of the dura mater. No evidence of recurrent disk prolapse.

Treatment. This patient suffered from postdiscectomy syndrome. Conservative treatment was initially provided, with epidural perineural injections, physiotherapy, and a flexion orthosis.

Clinical course. Conservative treatment yielded no significant improvement. As leg pain was the primary symptom, neurolysis was recommended.

Comments. This patient had a typical postdiscectomy syndrome. There was no evidence of recurrent disk prolapse. Extensive postoperative scarring was present, both in the spinal canal and in the paraspinous musculature. As the radicular symptoms were more prominent than the back pain, neurolysis and fat-pad insertion was preferred to spinal fusion as the surgical treatment.

6. L1/2, Protrusion, Multisegmental Degeneration with Modic Type II Changes (Fig. 11.73)

Clinical presentation. This 60-year-old man had suffered from back pain for 20 years. There had been recurrent episodes of severe low back pain, occasionally radiating along either the anterior or the posterior aspect of the thighs.

MRI. The study sequences are shown in Fig. 11.73.

Findings. All of the lumbar intervertebral discs are of markedly diminished signal intensity, with varying reductions in height and disk protrusions of varying severity. There is a marked reduction of disk height at L1/2, where mild retrolisthesis and posterior osteophytes (b, →) are also seen. There are circumscribed areas of Modic type II degeneration in the upper and lower end plates. There is a broad-based posterior displacement of the disk, most severe in the lateral zones, causing marked bilateral stenosis of the intervertebral foramina, while the posterior surface of the disk remains concave (c, →) and the dural sac and the conus medullaris within it are, therefore, not compressed.

  Clinical Syndromes

Classification of Lumbar Syndromes

Lumbar syndromes can be classified into three categories (Table 11.6): simple low back pain, back and leg pain, and alarming spinal syndromes (Nachemson and Jonsson 2000, Waddell 2004, German Back Pain Guidelines 2006). This threefold classification corresponds to the scheme of the Spine Working Group (now called the Spine Section) of the German Society of Orthopedics and Orthopedic Surgery, which divides lumbar syndromes into local lumbar syndrome, lumbar root syndrome, and differential diagnoses with alarming manifestations (Krämer 2004).

In accordance with this threefold classification, the following sections will deal with

local lumbar syndrome

lumbar root syndrome

the differential diagnosis of low back pain, with discussion of the serious conditions, both intrinsic and extrinsic to the spine, that can cause it.

No precise epidemiologic data are available on the relative frequency of simple and complicated low back pain, back and leg pain, and alarming spinal symptoms. Waddell (1993) estimated that 93% of patients suffer from low back pain alone, 5% from back and leg pain, and 2% from alarming symptoms; similar estimates were given by Bogduk (2000), Casser (2001), and Nachemson (2004). Nonspecific low back pain should not be viewed as a homogenous condition. Outcomes can be improved when subgrouping is used to guide treatment decision-making (Brennan 2006)

Local Lumbar Syndrome, Low Back Pain

Local lumbar syndrome is characterized by positionally dependent low back pain, spasm of the lumbar erector spinae muscles, and restricted range of motion of the lumbar spine. There is no segmental radiation of pain into the lower limbs (Table 11.7). The symptoms arise from degenerative changes of the lower lumbar motion segments leading to mechanical irritation of the posterior longitudinal ligament, the intervertebral joint capsules, and the spinal periosteum. The sensory fibers of the meningeal and dorsal branches of the spinal nerve are mainly affected. Reflex spasm of the erector spinae muscles of the back is unpleasant and painful. These muscles are innervated by the dorsal branches of the lumbosacral spinal nerves. It is not possible to identify the particular segment that is involved when pain arises through irritation of a dorsal branch, unlike when it arises through irritation of a ventral branch (sciatica).

Table 11.7 Major manifestations of local lumbar syndrome

Positionally dependent low back pain
Spasm of the lumbar erector spinae muscles
Painful limitation of motion of the lumbar spine
Pain on percussion and shaking of the lumbar spinous processes

Local lumbar syndromes are by far the commonest type of disk-related symptom in the entire spine. They are even more frequent than local cervical syndromes. Patients with only mild local lumbar syndrome (so-called simple low back pain) rarely consult a physician because their symptoms resolve spontaneously in a short time and respond well to treatments that are commonly known to the general public, such as the application of heat of any type and suitable positioning. Only when the pain is very severe, lasts longer than usual, or recurs frequently and at ever shorter intervals does the patient start to worry and seek medical help.

Classification. Local lumbar syndromes are subdivided into acute and chronic types based on the pattern of major symptoms. It is of therapeutic importance whether the patient is suffering from discogenic lumbago or from chronic low back pain of arthroligamentous origin. The most important clues to the diagnosis are to be found in the clinical history, as in all disk-related conditions.

Lumbago, Discogenic Back Pain

The main cause of lumbago is intradiscal tissue displacement with irritation of the posterior longitudinal ligament (cf. Fig. 11.27a). The main zone of pain is located in the lower lumbar region and over the sacrum, either in the midline or somewhat lateral to it. The pain may also spread diffusely, on an autonomic basis, in the ventral or cranial direction. There may be pseudoradicular radiation of pain to the thigh muscles (cf. Fig. 8.5). In addition to lumbago of sudden onset associated with a particular movement, there is also a rarer form that gradually increases in severity and that takes a few hours to reach its peak.

The major finding on clinical examination is the abnormal, rigidly held posture of the lumbar spine (Fig. 11.74). Flexion of the trunk is impossible; any flexion that the patient may be able to carry out occurs only at the hip joints, while the lumbar spine remains completely rigid. The patient can rise from the examining table only with a characteristic lateral rolling movement, using the buttocks as a fulcrum.

The lower lumbar spinal processes are tender to deep pressure and percussion. Straight-leg raising in the supine position worsens low back pain. There are no positive neurological findings.

The abnormal posture depends on the site of the lesion; it may consist of a rigid extension (kyphosis) of the lumbar spine combined with inclination to the right or left side. This abnormal posture is also the only positive radiological finding. When stress is taken off the low back, i.e., when the patient lies with the hips and knees lightly flexed, the pain is usually absent and the abnormal posture disappears.

It is mainly younger patients who suffer from lumbago, because their intervertebral disks are more likely to undergo intradiscal tissue displacement.

The attacks of pain are usually of brief duration at first and tend to resolve spontaneously. Their further course is unpredictable. Attacks of lumbago in youth and middle age may remain the only manifestation of disk degeneration. Often, however, they represent the beginning of a chronic, recurrent lumbar disk syndrome that expresses itself in its further course with frequent attacks of low back pain and sciatica.

Low Back Pain of Arthroligamentous Origin

Characteristics and etiology. Long-lasting and recurrent low back pain constitutes the chronic form of local lumbar syndrome. The major symptoms of local lumbar syndrome are often of only mild intensity, arise gradually, and subside slowly. Low back pain of arthroligamentous origin can be regularly provoked by certain positions, e.g., prolonged sitting, standing, or sometimes even lying, and ameliorated by changes of position. Lumbago, in contrast, is of sudden onset and is not induced or ameliorated by positional changes. Chronic, recurrent low back pain is usually thought to be due to changes of the elasticity and volume of the lumbar disks with secondary effects on the joints, ligaments and muscles. Because these manifestations arise only when disk degeneration has reached an advanced stage, chronic low back pain generally arises only after age 35–40. Depending on the position that induces it, the pain can be designated as low back pain in flexion or in extension, or else as lumbar kyphosis pain or low back pain in hyperextension (facet syndrome).

Facet Syndrome

Most facet syndromes are stress-related, with symptoms worsening over the course of the day. The pain disappears when the patient lies flat with mildly flexed hips and knees (Helbig and Lee 1988). In many individuals, postural weakness while standing leads to hyperlordosis of the spine that becomes painful in a very short time. In this position, the facet joints are subject to excessive stress, and the spinal canal and the intervertebral foramina are relatively narrow. The low back pain may even be associated with radicular symptoms (see Fig. 11.39). Low back pain in hyperlordosis arises after prolonged walking and standing, particularly when the individual wears high-heeled shoes, indirectly producing forward tilting of the pelvis and hyperlordosis of the spine. The pain of hyperlordosis can also be induced or exacerbated when the lumbar lordosis is increased by downhill walking or by activities requiring the individual to lean backward, e.g., hanging up laundry, looking at pictures, or any type of work above the head.

Other types of stress-related pain are due to gradual loss of height of the intervertebral disks and fatigue of the truncal musculature over the course of the day. The disks become less elastic as they shrink. The remaining components of the lumbar motion segments, mainly the intervertebral joints and ligaments, are subject to excessive or inappropriate stress and give rise to pain mediated by the meningeal branch of the spinal nerve.

The pain of facet syndrome originates in the lumbar intervertebral joints and is felt in the low back with radiation into the buttocks, groin, lower abdomen, thighs, and occasionally the scrotum. Patients describe it as diffuse and widespread and demonstrate its localization by laying the hand flat over the affected area, unlike patients with radicular syndromes, who can draw the borders of the affected dermatome with one finger. Examination reveals tenderness to shaking and percussion over the affected segments. Not all of the intervertebral joints are affected to the same extent, and the diagnostic assessment must therefore include segmental examination, with testing for pain on rotation, flexion, and extension of the lumbar spine (Fig. 11.75).

The Sacroiliac Joint and Sacroiliac Joint Syndrome

The sacroiliac joint can be considered functionally and neuroanatomically as the lowest pair of facets. Kiessling (1993) studied the neuroanatomy of the sacroiliac joint and found a pattern of innervation resembling that of the lumbar intervertebral joints. Spontaneous pain and tenderness to pressure can be found on the iliac crest, at the greater trochanter, and in the groin over the origin of the iliopsoas muscle.

A special test of the sacroiliac joint consists of palpation of the posterior iliac spine during movement to check for the so-called forward bending phenomenon. Normally, the two posterior iliac spines are at the same height both before the patient bends forward and afterward. A difference in height at the end of forward flexion is considered pathological (Fig. 11.76).

The diagnosis of facet pain or sacroiliac joint pain is strongly suggested by the generation of pain in the low back and leg with the so-called “figure 4” maneuver, in which the lumbar spine is passively brought into lordosis when the examiner maximally abducts and externally rotates the patient’s hip (Fig. 11.77). The diagnosis is further confirmed by the reduction or elimination of the pain upon injection of local anesthetic into the capsule of the affected joint (facet infiltration, see p. 243).

Facet syndrome and sacroiliac joint syndrome with stress-related low back pain have a fluctuating course. The frequency and intensity of the pain depend on bodily activity and posture: patients can largely prevent the emergence of symptoms by regularly alternating between sitting, standing, and lying positions and avoiding abrupt movements. On the other hand, biochemical and biomechanical involutional processes in disk tissue that are still poorly understood can cause the symptoms to arise and subside suddenly and unpredictably, because any change in the disk necessarily brings about an altered position of the intervertebral joints.

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