Spondylolisthesis
Spondylolisthesis is defined as the forward slippage of one vertebra on its adjacent caudal segment. Derived from the Greek words for “vertebra” and “to slip or slide,” spondylolisthesis has been recognized since the late 18th century, when it was first described by obstetricians as a barrier to passage of the fetus through the birth canal.
Spondylolisthesis is one of the most variable conditions affecting the pediatric spine. Its severity ranges from an asymptomatic, coincidental radiographic finding to a disabling deformity that produces severe postural and gait disturbances, pain, and neurologic impairment affecting the lower extremities, bowel, and bladder. Just as symptoms can vary, so does the radiographic severity of the slippage, which ranges from no anterior displacement to complete dislocation of L5 in front of the sacrum (termed spondyloptosis ). Controversy regarding treatment in severe cases is gradually resolving because of recent improvements in classification from the understanding of spinopelvic sagittal balance, enabling a more intuitive treatment algorithm to be developed.
Classification
Historically, spondylolisthesis cases have been divided into congenital and acquired types. Recognition of cases in which the pars interarticularis is fractured (termed spondylolysis ), with slippage occurring through the fracture, or cases in which the pars is not fractured but elongated and the abnormal lumbosacral anatomy allows forward slippage became the basis for the well-known Wiltse classification. Five types, based on the radiographic findings and age at onset, have been described ( Table 14-1 ). The remaining discussion in this chapter will be limited essentially to types I and II.
| Type | Description | Description |
|---|---|---|
| I | Dysplastic (congenital or developmental) | Anatomic predisposition to slippage from dysplastic L5-S1 articulation; may have intact pars interarticularis or elongation of pars with forward slippage; lysis of pars may be present because of abnormal stresses from dysplastic L5-S1 facets and sacrum |
| II | Isthmic (spondylolytic) | Stress fracture or elongation of pars interarticularis, with forward slippage through fracture; posterior elements remain in situ |
| III | Degenerative | Manifests in adulthood; associated with degenerative segmental intervertebral instability |
| IV | Posttraumatic | Acute fracture of posterior elements other than pars; slippage of cephalic vertebra by displacement of the fracture |
| V | Pathologic | Attenuation of pars from generalized or localized bony pathologic process (e.g., osteogenesis imperfecta, osteopetrosis, connective tissue diseases such as Ehlers-Danlos syndrome) |
Marchetti and Bartolozzi have amplified the Wiltse classification. They termed type I slips as developmental and subdivided them into a high-grade dysplastic spondylolisthesis, which results in lumbosacral kyphosis, and a low-grade dysplastic type, in which the slippage is purely translational, the vertebral end-plates remain relatively parallel, and there is no associated vertebral or sacral deformity associated with kyphosis. Differentiation of these two types has implications for the potential for slip progression, risk for neurologic involvement, choices for surgical treatment, and sometimes the rate of healing after surgical fusion. Those termed as acquired (Wiltse type II) slips were associated with traumatic or degenerative processes, usually stress fracture of the isthmus, and were distinguished from dysplastic (developmental) types by absence of bony changes.
Most recently, the Spinal Deformity Study Group (SDSG) has developed a classification incorporating and emphasizing sagittal spinopelvic balance, in part because of difficulty in reproducibly classifying the degree of dysplasia. Six types of spondylolisthesis are now recognized, based on the grade of slip and spinopelvic alignment, using measurements of pelvic incidence (PI), sacral slope (SS), pelvic tilt (PT), and the C7 sagittal plumbline (parameters described later, under “Radiographic Findings”). Three types of low-grade spondylolisthesis (Meyerding grades 0 to 2, slip < 50%) are described, based on pelvic incidence: low (type 1), normal (type 2), and high (type 3). High-grade spondylolisthesis (Meyerding grade ≥ 3, slip ≥ 50%) includes type 4 (balanced sacropelvis), type 5 (retroverted sacropelvis with balanced spine), and type 6 (retroverted sacropelvis with unbalanced spine; Fig. 14-1 ). Currently, the system has been validated as having modest to good interobserver and intraobserver reliability and ultimately strives to guide surgical treatment.
Pathoanatomy
Dysplastic Spondylolisthesis (Wiltse Type I)
The dysplastic form of spondylolisthesis occurs only at the L5-S1 level and is caused by primary congenital dysplasia of the L5-S1 facet joints ( Fig. 14-2 ). Typically, the inferior facet of L5 is dysplastic and the sacral facet absent. Its congenital nature is supported by frequent association with spina bifida occulta of L5 and the sacrum. The anatomic incompetence of this facet joint allows the slipping (listhesis) to begin. Without lysis or elongation of the pars, such forward vertebral slipping beyond 25% would almost certainly produce a neurologic deficit as the posterior neural arch impinges on the dura (see Fig. 14-2 ), producing symptoms in childhood. Otherwise, the slip may remain asymptomatic until early adolescence and the prepubertal growth spurt, when leg pain and hamstring spasm result in gait disturbances, with or without back pain. Dysplastic spondylolisthesis is more common in females and has an increased incidence in first-degree relatives of patients, suggesting a genetic cause that results in the congenitally incompetent facet.
A pars defect (lysis) along with a congenitally abnormal L5-S1 articulation is to be differentiated from the Wiltse type II (acquired) slip, in which the L5-S1 articulation is anatomically normal but a stress fracture occurs and the slip displaces through the stress fracture. In the presence of an isthmic defect or pars elongation in a dysplastic slip, the displacement can become severe, but without neurologic sequelae, because the dural sac is not impinged by the posterior elements.
An abnormal sacral dome and end-plate may also predispose the patient to translation with kyphosis. Biomechanical weakness and “epiphyseal” disruption to the sacral end-plate, similar to the proximal medial tibial epiphysis of infantile Blount disease or the physeal disruption of slipped capital femoral epiphysis, have been described. *
* References .
This type of primary sacral deformity ( Fig. 14-3 ) in susceptible individuals may produce a growth disturbance contributing to the onset of the deformity that becomes important during the prepubertal growth spurt. Furthermore, such weakness of the sacral end-plate may become critical when stressed by shear forces in the upright posture in patients with increased PI, SS, and lumbar lordosis (see later discussion under “Radiographic Findings”). A higher PI may predispose for slipping (see Fig. 14-3, B ) through a combination of shearing postural forces imposed on a congenitally abnormal sacral dome, the preexisting conditions for the high dysplastic grade of Marchetti and Bartolozzi. An interesting report has noted that the rounded sacrum deformity in young children can reverse when the child’s activities are limited. This observed remodeling supports the theory of primary sacral dome dysplasia as a cause of spondylolisthesis.
Isthmic Spondylolisthesis (Wiltse Type II)
The isthmic type of spondylolisthesis (termed acquired traumatic in the Marchetti-Bartolozzi classification) is a more common and benign form that rarely produces significant neurologic findings or gait disturbance ( Fig. 14-4 ). Pars stress fracture, or spondylolysis, is fairly common, reported to be 4.4% at 6 years of age and 6% at 18 years. A study of lumbar spine computed tomography (CT) scans in asymptomatic patients has noted rates in the general population of 5.7% and 3.1% of spondylolysis and spondylolisthesis, respectively. Spondylolysis is most prevalent at L5, accounting for 87% of all stress fractures, followed by lysis at L4 (10%) and L3 (3%). Both familial and racial predispositions toward isthmic spondylolisthesis have been observed. The incidence of isthmic spondylolisthesis seems to stabilize in adulthood, during which the degenerative type of spondylolisthesis predominates.
Acquired pars defects appear to have mechanical causes. The pars region is the weakest area of the neural arch and is susceptible to fatigue fracture. Histologic analyses of fetal and stillborn vertebrae have confirmed trabecular and cortical irregularity of the lumbosacral pars interarticularis caused by ossific nucleus irregularity. This histologic peculiarity may act as a stress riser in the lower lumbar vertebrae. Equally important may be anatomic parameters restricting excursion of the lumbosacral facets. In particular, spondylolytic specimens from the Hamann-Todd collection at the Cleveland Museum of Natural History have demonstrated that the pars of L5 is subject to increased contact stress during normal extension movement. This has been found in specimens in which the lumbar interfacet transverse distance does not increase appropriately between L4 and S1, thus limiting facet glide during the extension of L4-5 and L5-S1 and pinching the pars from above and below, producing a fatigue fracture. This supports the proposed “nutcracker” mechanism of spondylolysis and is seen in patients with a relatively low pelvic incidence and sacral slope (see Fig. 14-4, B and later, “Radiographic Findings”), who consequently have a relatively horizontal L5 disk.
Pars defects have not been observed in newborns or nonambulatory patients, thus supporting the Marchetti-Bartolozzi contention that this form of spondylolisthesis is more accurately termed acquired. Pars lysis or elongation does not occur in primates that do not have an upright bipedal gait. The presence of lumbar lordosis, which is unique to humans, is thought to be necessary for spondylolisthesis to occur. Both flexion and extension forces have been implicated in the production of these stress fractures. The increased incidence of isthmic spondylolytic defects in athletes who perform repetitive lumbar hyperextension (e.g., gymnasts, football linemen, cricket bowlers) confirms this mechanism. Spondylolisthesis occurs more frequently if L5 has short transverse processes and is high riding relative to the iliac crest. This susceptibility to spondylolisthesis may occur because the L5 vertebral body is hypermobile when it is not anchored deeply in the pelvis, with strong ligaments attached to longer transverse processes.
An acquired isthmic spondylolysis in a juvenile patient can progress to a listhesis as a result of shear forces during upright gait, as described for patients with the shear mechanism of spondylolysis. An anterior force on L5 is produced and increases as the spine is flexed, especially in patients with an increased PI and SS (see Fig. 14-3, B ). The posterior muscle attachments that act on the laminae and spinous process hold this part of the neural arch in place and thus tend to separate or distract the spondylolysis further. With a strong anterior deflection force, a slip between the sacral apophysis and end-plate may also occur and allow anterior translation and rotation of the slipping vertebra. Thus, an acquired isthmic spondylolysis in a growing child can progress to a significant spondylolisthesis, even in the absence of congenital dysplasia of the lumbosacral facets.
Other Types of Spondylolisthesis
Degenerative spondylolisthesis, which occurs in adults, will not be discussed in this chapter. Similarly, traumatic spondylolisthesis, a rare condition resulting from significant spinal trauma, is more appropriately discussed under the management of spinal injuries. Pathologic spondylolisthesis is treated in the same fashion as nonpathologic spondylolisthesis of the same grade and severity or in conjunction with a global thoracolumbar deformity associated with a syndrome or skeletal dysplasia. Treatment must take into account that the underlying bone pathology or abnormal connective tissue may make pseudarthrosis more likely and treatment failure more frequent.
Clinical Features
The age at onset is probably the most important determinant of symptoms and the need for treatment. The more severe dysplastic types usually present at an earlier age because of greater instability of the lumbosacral junction, producing neurologic symptoms. Children may not have pain but demonstrate deformity and gait abnormalities from lumbosacral instability as the only neurologic signs.
Spondylolysis is generally manifested as low back pain only. This is not surprising considering that the lysis produced by a stress fracture in, for example, an adolescent gymnast produces no slippage and hence no neurologic risk. Pain may radiate to the buttocks and posterior of the thighs from mechanical instability, and it is usually aggravated by flexion and extension activities. Mechanical low back pain symptoms are always a cause for suspicion in a child or adolescent and mandate radiography, especially in a susceptible athlete or dancer.
Physical examination may actually be normal in patients with spondylolysis or a low-grade (<50%) listhesis. A listhesis may present a palpable step-off at the lumbosacral junction, and back pain may be elicited by standing hyperextension stress. As the degree of listhesis increases, more obvious physical findings can be appreciated, including a postural disturbance of flexed hips and knees combined with sacral prominence posteriorly and hyperlordosis proximal to the slip. Hamstring tightness, thought to be caused by lumbosacral instability and subsequent rotation of the sacrum into a more vertical position producing a retroverted pelvis, rather than being caused by actual nerve root or dural impingement, may result in a distorted gait as a result of the individual’s inability to take a normal stride. The individual may also have to walk on tiptoes because of the flexed hip and knee positions ( Fig. 14-5 ). In a severe disturbance, the individual may actually walk sideways in a bizarre fashion because the hamstrings are so tight that no forward stride can be taken at all. Straight-leg raising with the patient supine on an examining table may be dramatically limited. Because of the vertical position of the sacrum and pelvis, a backward pelvic tilt and an abdominal crease may be obvious cosmetic complaints, with the prominence of the sacrum posteriorly producing the so-called heart-shaped buttocks. An olisthetic scoliosis producing marked spinal decompensation with hyperlordosis can be observed (see Fig. 14-5 ) and is often rigid, having been produced by the irritative phenomenon of the slip, and is a measure of how severe the spondylolisthetic crisis has become.
L5 or S1 root weakness, including a motor weakness or the loss of an ankle jerk reflex, may be present. Bowel and bladder function must be evaluated by history, including, for example, questions about incontinence and decreased frequency of urination. Sacral sensation and rectal tone are important evaluations of cauda equina function. Patients undergoing surgical treatment should have these functions evaluated preoperatively. If the patient reports infrequent urination, bladder capacity should be determined by cystometrography and urologic consultation.
Radiographic Findings
The diagnosis of spondylolysis or spondylolisthesis is made from a standing lateral radiograph of the lumbosacral junction ( Fig. 14-6 ; see Fig. 14-2 ). A standing radiograph is emphasized to measure displacement and the true angulation of the lumbosacral junction, if present. The femoral heads should be visible on the lateral radiograph to measure pelvic incidence and tilt. In general, the degree of translational displacement, lumbosacral kyphosis, as measured by the slip angle (see Fig. 14-7, C ), and the spinopelvic balance, together with the clinical findings, usually determine the course of treatment.
A unilateral pars defect may be difficult to see on a single lateral plain film. In this case, oblique radiographs may be obtained. Proper positioning is confirmed by identification of the so-called Scotty dog head and neck outline (the articular processes, superior and inferior, and the pars in between) at levels adjacent to the level of interest (see Fig. 14-6, B ). Oblique views may show the defect, elongation, or sclerosis suggestive of a chronic stress reaction. A defect that is wide and has a smooth edge suggests a long-standing chronic lesion, whereas an irregular edge suggests a more acute process. If the clinical situation suggests acuteness, such as a recent injury producing back pain, a bone scan or single-photon emission computed tomography (SPECT) scan may be “hot” and confirm an acute lesion (see Fig. 14-4, D and E ). In these recent fractures, an attempt to heal the lesion by external immobilization is justified. CT is occasionally necessary to diagnose occult pars lesions that cannot be seen on plain films ( Fig. 14-6, D to F ). Thin, 1.5-mm sections are recommended to observe the lysis. CT scans with three-dimensional reconstruction can be useful in the preoperative evaluation of patients with severe dysplastic spondylolisthesis to characterize the pathologic anatomy more precisely.
Disk herniation in association with spondylolisthesis has been reported in as many as 25% of patients at the next level above the slip and in 15% at the level of the listhesis itself. Magnetic resonance imaging (MRI) may therefore clarify the clinical picture in a patient with L5 radicular symptoms and minimal listhesis or in a patient with radicular symptoms not correlating with the level of the slippage. MRI is also useful to rule out other causes of lumbosacral dysfunction, such as tumor or infection, and may demonstrate a slipped vertebral apophysis, if present.
The radiographic parameters of the deformity define the severity and need for treatment, with increasing severity of slip parameters correlated to worsening quality of life questionnaire scores. Anterior translation, the listhesis of L5 on S1, is measured by the method of Taillard ( Fig. 14-7, A ) or described by the classic Meyerding grades ( see Fig. 14-7, B ). The lumbosacral kyphosis, or sagittal rotation, is measured by the slip angle (see Fig. 14-7, C ), for which several methods of measurement have been described. We prefer to construct the slip angle from the tangential line of the upper end-plate of L5 because the lower end-plate of L5, the site originally described, is usually deformed and rounded and often cannot be identified on a postoperative radiograph when fusion has occurred spontaneously or surgically. The cephalic end-plate of L5 is consistently present and undeformed and thus is better suited for this measurement. The body of L5 may become trapezoidal, a response to impression by the dome of the sacrum, and such distortion indicates a more severe deformity.
Because of the lumbosacral kyphosis, a standing or even supine anteroposterior (AP) radiograph of the sacrum will be difficult to interpret because of the superimposition of L5 and the sacrum (Napoleon’s hat sign; see Fig. 14-2, B ). To eliminate this superimposition, evaluate for spina bifida occulta, and most importantly evaluate the quality of the postoperative fusion mass accurately, a Ferguson view of the sacrum is recommended. The Ferguson view ( Fig. 14-8 ) is an outlet view of the pelvis and thus shows the L5 and S1 bodies in their true AP position.
As noted earlier (see “Classification”), the importance of sagittal spinopelvic balance in determining pathogenesis, prognosis, and treatment guidelines has been recently emphasized and confirmed. PI, PT, and SS are descriptive radiographic angles used to describe the sagittal relationships ( Fig. 14-9 ). PI, the angle created by a line from the midpoint of the sacral end-plate to the center of rotation of the femoral heads and a line perpendicular to the sacral end-plate drawn from its midpoint (see Fig. 14-9, A ), is a fundamental anatomic relationship specific and constant for an individual subject. It describes pelvic morphology and ultimately lumbar lordosis and thoracic kyphosis in the upright position. PI remains constant during childhood and then increases in adolescence until reaching a maximal value, which is constant in adulthood. The degree of pelvic incidence is unaffected by posture; it is constant whether supine, sitting, or standing. PT is the angle between a line joining the midpoint of the sacral end-plate to the center of the femoral heads and the vertical line, whereas SS is the angle between the tangent to the sacral end-plate and the horizontal (see Fig. 14-9, B and C ). These two angles, measured with respect to the horizontal and vertical axes, describe the orientation of the pelvis in the sagittal plane and vary according to a person’s posture. PI is the arithmetic sum of SS and PT.
Studies of normal subjects have documented a link among PI, SS, and lumbar lordosis and thoracic kyphosis, with the latter spinal parameters adjusting to keep the head and trunk balanced over the femoral heads. Thus, as PI increases, SS and lumbar lordosis increase to maintain sagittal balance. Patients with spondylolisthesis have a greater PI than controls, suggesting that an increased PI can predispose to spondylolisthesis.
Typically, normal subjects have a PI of approximately 50 degrees, whereas patients with spondylolisthesis have a PI of 70 to 79 degrees, with PI increasing as slip severity worsens. Unfortunately, the actual prediction of progression of listhesis, and thus the use of an abnormal PI as an indication for surgery, has not been proved. In contrast, slip percentage, Meyerding grade, and slip angle have been shown to be predictive of progression.
The concept of spinopelvic balance has been further refined, describing the pelvis as balanced or unbalanced (retroverted), with the spine unbalanced or balanced ( Fig. 14-10 ; see Fig. 14-1 ). The ultimate goal is to differentiate which patients might benefit from surgical reduction of a spondylolisthesis versus those for whom it is unnecessary (see later, “ Surgical Methods: High-Grade Spondylolisthesis ”). The balanced pelvis is one in which compensatory increased lumbar lordosis and decreased thoracic kyphosis of the spine are adequate to maintain an adequate C7 plumbline or normal sagittal balance. In the unbalanced, or retroverted, pelvis, there is such a high PI because of increased pelvic tilt (visualized as an anterior position of the femoral heads relative to the sacrum) that the spine cannot accommodate the associated high L5 incidence angle, leading to positive forward balance (see Fig. 14-1 ). This positive balance, indicating an unbalanced spine, occurs when the C7 plumbline falls anterior to the femoral heads on the standing lateral radiograph. The spine is balanced when the plumbline falls on or posterior to the femoral heads.
Measurement of L5 incidence (see Fig. 14-9, D ) has been shown to correlate with the outcome of spondylolisthesis treatment and was found to improve along with the slip angle in patients who had subjective improvement postoperatively. PI, PT, and SS may be affected minimally by surgical treatment. Thus, although pelvic morphology is not altered by clinically successful surgery, spinal balance measures (slip angle, L5 incidence, lumbar lordosis) seem to improve and correlate with outcome.
Prognosis and Natural History
Once the diagnosis of spondylolisthesis or spondylolysis has been made, the risk of progression is the main determinant of treatment. Although younger patients might seem to have a greater risk of deformity progression, long-term studies (>45 years) have not found predictive value in the age, percentage of slippage, lumbar index (lordosis), or slip angle at initial evaluation. Only Seitsalo and co-workers have found prognostic value in the initial percentage of slippage. The adolescent growth spurt continues to be a period of interest because significant progression of translation or kyphotic deformity is uncommon after maturity in a patient with mild deformity (<50% slip).
PI is now regarded as a key prognostic parameter. Because PI is often abnormally high in high-grade listhesis, one may conclude that the risk of progression in low-grade listhesis (<50% slip) in patients with a low or normal PI (e.g., patients with the nutcracker mechanism; see Fig. 14-4 ) is low compared with the shear mechanism in patients in whom the PI is higher. Similarly, patients with a retroverted pelvis and increased PT are extremely likely to progress, even with a balanced spine, because of the biomechanical forces that promote continued listhesis and lumbosacral kyphosis (see Fig. 14-3 ).
The natural history of untreated spondylolisthesis may leave patients with some impairment, influencing job choice, avoidance of heavy lifting, and choice of recreational activities. In lower grade slips (<30%), progression is unexpected unless the patient is immature, and even then progression occurs rarely in isthmic (acquired) defects. Conservative treatment of low-grade slips has been reported to yield the same results as operative treatment, and in general the progression of listhesis is mild and has no correlation with later symptoms on long-term follow-up, which have been attributed primarily to disk degeneration. Thus, prophylactic treatment of lower grade spondylolisthesis to avoid later progression of slippage does not appear to be justified, especially when a low incidence of progression is expected, and the spinopelvic parameters (low or normal PI) are favorable. Although patients with spondylolisthesis may have disk degeneration and other low back impairment as adults, these problems do not appear to be caused by progression of the deformity, which in some series is not altered by the presence of fusion in situ. Patients with long follow-up were often treated in an era when the fusion techniques were questionable, thus raising doubts about the outcome data. Finally, the controversy surrounding the need for more aggressive treatment of higher grade spondylolisthesis stems from favorable or unfavorable interpretation of long-term natural history studies and the results of in situ posterior fusion.
Treatment
Spondylolysis
Asymptomatic Spondylolysis
Asymptomatic spondylolysis is common, and the diagnosis is made coincidentally during investigation of other problems (e.g., scoliosis). An asymptomatic patient needs no treatment and may not need follow-up to check for progression. No restrictions on activity are necessary but if the patient is younger than 10 years, the possibility of progression should be discussed and the patient counseled to return for reevaluation should symptoms occur. It has been our experience that patients with acquired spondylolysis who are asymptomatic do not need regular follow-up to check for progression because progression of deformity is rare (5% of patients) and will be accompanied by the onset of symptoms.
Symptomatic Spondylolysis
Symptomatic spondylolysis may require treatment of transient low back pain. The level of treatment may depend on determination of whether the stress fracture is acute or relatively chronic. As noted, radionuclide scintigraphy or SPECT may be useful to determine the chronicity of the lytic defect and if the bone scan is hot (see Fig. 14-4 ), immobilization with a thoracolumbosacral orthosis (TLSO) or cast may be attempted in an effort to heal the defect. With attention to the early diagnosis of so-called stress injuries of the pars, thought to be a prodromal event occurring before plain radiographs show an actual lysis, SPECT has proven to be the most sensitive diagnostic test for presumed impending spondylolysis. Rest and immobilization appear to prevent progression to a pars defect if instituted on discovery of a hot SPECT scan but before actual radiographic lysis. Unilateral pars lesions, as might be expected, heal more readily than bilateral ones.
Documentation of healing of an acute spondylolytic defect, especially a bilateral pars defect, by nonoperative means is rare. Fujii and colleagues have found that early-stage L4 lesions heal radiographically almost 90% of the time, whereas only 45% of early-stage L5 lesions heal with nonoperative treatment. Later stage lesions in L4 or L5 rarely healed. This most extensive report (134 patients) of acquired symptomatic pars defects justifies an attempt to heal an acute stress fracture by immobilization and rest.
For patients with severe back pain, external immobilization for 3 to 6 months may be the most effective way to resolve the symptoms. Curtailing inciting activities is most important for patients with symptoms related to athletics. Although abdominal- and back-strengthening exercises are often prescribed, many adolescent athletes are already in excellent physical condition, and such exercises seem superfluous. Rest, avoidance of inciting activities, use of antiinflammatory pain medication, and application of a brace in extreme situations usually resolve the acute symptoms. Whether the lysis actually heals radiographically does not seem to affect the resolution of symptoms in most patients. Meta-analyses have focused on studies of the nonoperative treatment of spondylolysis, including grade I spondylolisthesis in children, and have demonstrated an 84% success rate of nonoperative treatment at 1 year; however, it was also found that bracing did not appear to influence the outcome.
Once the patient is asymptomatic, a full return to all activities without restriction is permitted. Follow-up is unnecessary unless symptoms recur. If symptoms recur after return to a higher level of activity, two treatment options must be discussed with the patient—abandonment of the activity that produces symptoms or possible surgical treatment to repair the lytic defect or eliminate movement at the spondylolytic segment with a one-level fusion.
Direct Repair.
Direct repair of the lytic defect has the apparent advantage of avoiding fusion. A prerequisite to defect repair is ensuring that disk herniation or other pathology (e.g., osteoid osteoma, apophyseal avulsion) is not present. Several methods of direct pars repair have been reported, including screw fixation across the defect, compression wiring between the transverse and spinous processes ( Fig. 14-11 ) or between pedicle screws and the spinous process, and combinations of pedicle screw and laminar hook constructs. Radiographic union can be achieved in 80% to 90% of patients with appropriate indications, with good or excellent clinical results in 80%. Direct repair of the pars is probably best suited to a lytic defect of L4 or above because limited L5-S1 fusion for an L5 defect carries little morbidity or loss of motion. Repair of a spondylolytic defect may be destined to fail clinically if there is any preoperative evidence of disk degeneration; thus, MRI evaluation of the involved disk is mandatory before repairing a spondylolytic defect. Direct repair is also more likely to succeed in a patient younger than 30 years. The advantage of a wiring technique is that the implant takes up little space; thus, the pars defect may be thoroughly curetted and débrided and the lamina, transverse process, and spinous process thoroughly decorticated before bone-grafting the defect and tightening the compression wire. However, the biomechanical soundness of wiring has been questioned. More effective compression across the defect is achieved with a pedicle screw–laminar claw technique, with increased stiffness and fatigue resistance arising from the solid rod connecting the two points of fixation. Unfortunately, healing of the pars defect cannot be assessed radiographically because of the volume of metal in the screw-claw technique.
Low-Grade Spondylolisthesis
Low-grade spondylolisthesis (<50% slip) may be treated similarly to that for spondylolysis without slippage, provided that dysplastic features or a high PI–high SS alignment (SDSG type 3) are absent (see Fig. 14-3 ). Age at onset, with children younger than 10 years being at increased risk in dysplastic cases, should also be taken into consideration.
Isthmic (Acquired) Spondylolisthesis
An asymptomatic patient with isthmic (acquired) spondylolisthesis of low grade (SDSG type 1 or 2), without dysplastic features (low or normal PI < 60 degrees), needs no active treatment. Patients younger than 10 years can be monitored radiographically at 6-month intervals for maximum surveillance, with regular follow-up abandoned once they are near puberty (11 years for girls, 13 for boys).
Symptomatic patients with isthmic spondylolisthesis often can be managed nonoperatively. As with spondylolysis without slip, approximately 60% of patients will become asymptomatic with nonoperative treatment and as many as 83% will be asymptomatic at long-term follow-up. Return to full activity on resolution after exercise and spine-stabilizing techniques is frequently possible. The athletic adolescent must be carefully educated concerning identification of recurrent symptoms and the need for prophylactic spine exercises for the indefinite future. If symptoms recur despite maximal physical therapy and nonoperative protection, the adolescent must choose between abandoning the provocative activity or undergoing surgical treatment.
Dysplastic Spondylolisthesis
If dysplastic changes are present, especially in patients with a high PI (>60 degrees; SDSG type 3 shear mechanism), close follow-up is recommended, and prophylactic fusion should be considered. Fusion is particularly indicated in patients with listhesis without lysis (see Fig. 14-2 ) because of the increased possibility of neurologic deficit from forward slippage and constriction of the cauda equina. If the patient has a low-grade deformity but a high PI and SS, and slip angle greater than 10 degrees, early fusion may be indicated, with consideration of kyphosis reduction.
The unique pathology associated with dysplastic spondylolisthesis without lysis frequently results in incapacitating back and leg pain and often neurologic deficit as a consequence of encroachment on the cauda equina (see Fig. 14-2 ). Once such symptoms have occurred, nonoperative treatment is rarely successful. Dysplastic spondylolisthesis without lysis is more likely to require surgical treatment than isthmic spondylolisthesis with a slip of the same magnitude.
For a low-grade spondylolisthesis, with or without lumbosacral kyphosis, the standard surgical treatment has historically been in situ fusion, performed via a Wiltse paraspinal approach, with an autogenous bone graft placed between the transverse processes of L5 (or sometimes L4) and sacral ala. Although no prospective randomized trials comparing operative with nonoperative treatment have been performed to date, most retrospective reviews have indicated that in symptomatic patients in whom nonoperative treatment fails, in situ posterolateral fusion improves the natural history by eliminating pain and in most patients stabilizes the radiographic and neurologic situations.
Preoperative assessment should include evaluation of cauda equina function, including a rectal examination for sacral sensation and sphincter motor tone, especially if there are other neurologic findings, such as motor loss. The same examiner who assesses the patient preoperatively should be available postoperatively to detect partial loss of sphincter tone if any question of cauda equina problems arises. Surgical positioning mandates careful placement of the patient prone, on chest rolls only. Cauda equina syndrome can occur on a frame that does not support the abdomen because of further forward vertebral slipping as the abdomen hangs free between posts of the frame under anesthesia. Root or dermatomal monitoring (evoked electromyography) may alert the surgeon to cauda equina dysfunction. Motor potential monitoring is also used during manipulation of L5 or S1 nerve roots.
Technique of In Situ Fusion.
The classic method described by Wiltse and associates uses a midline skin incision with two paramedian incisions in the fascia approximately 5 cm lateral to the midline to split the paraspinous muscles bluntly and approach the articular facets and transverse processes from a more lateral direction ( Fig. 14-12 ). The bony elements of the sacral ala and the facet joints of L5-S1 are exposed from the lateral to the medial aspect, with the midline ligamentous structures being retained for stability. Exposure of L4 should be avoided unless fusion to that level is desired, but it should not be necessary for most low-grade slips. The L5 segment should be exposed from the tip of the transverse process to halfway up the base of the spinous process, if present. The sacral ala should be exposed in a subperiosteal plane as anteriorly as possible because the more anterior the bone graft can be placed, the more it is under compression. Decortication of the sacral ala and facet and transverse processes of L5 (and L4) is best accomplished with a high-speed dental burr. Because pounding with a mallet may increase the likelihood of postoperative cauda equina syndrome, routine use of a gouge is not recommended when less traumatic decortication is possible. Ample autogenous bone graft is placed from the transverse process of L5 to the most anterior area of the sacrum. A flap of bone from the ala can be raised and turned toward L5 before the bone graft is placed. The incision is closed with running sutures placed in the superficial lumbodorsal fascia bilaterally.
Postoperative care varies from no immobilization at all to a cast or TLSO. There is little evidence that immobilization increases the fusion rate, but postoperative management of the patient may be easier with some type of orthosis for comfort.
Destabilization of midline structures is avoided by use of the Wiltse technique. Exposure of the loose L5 lamina through a midline approach is unnecessary and may be useless to achieve fusion; exposure is indicated only when L5 is to be removed for decompression or the pars defect is to be repaired as part of the fusion procedure. The destabilization produced by such exposure and removal may be responsible in part for the reported continued progression of slippage after in situ fusion.
Although further slippage after in situ fusion is more likely related to the degree of dysplastic changes (kyphosis, high PI–high SS), removal of midline structures during posterolateral transverse process fusion mandates some form of internal fixation or postoperative immobilization (cast) because of the instability created.
The results of intertransverse process fusion have shown rates of 83% to 95% successful fusion, with 75% to 100% excellent or good clinical outcomes.
Because of these results, the bilateral transverse process fusion procedure of Wiltse is considered to be a gold standard operation for spondylolisthesis, especially in a low-grade deformity. In adolescents and young adults with radicular symptoms (e.g., leg pain), these symptoms frequently resolve simply by achieving solid fusion. †
† References .
Decompression of spondylolisthesis is rarely necessary in adolescents because of the likelihood that symptoms will resolve after arthrodesis. Indications for decompression with the index procedure include an objective motor neurologic deficit, not merely radicular symptoms or tight hamstrings. If cauda equina syndrome complicates an in situ fusion procedure, the recommended management is immediate decompression by sacroplasty.Decompression includes removal of the loose L5 lamina (Gill procedure), but it must not stop there. Appropriate decompression of the L5 nerve root, for example, requires removal of local hypertrophic callus and fibrotic tissue in the region of the pedicle. This callus is the offending compressing material, and mere removal of the loose L5 laminar segment is insufficient for this purpose.
If decompression is performed as part of the index procedure, a meticulous fusion that includes internal fixation may be superior to a noninstrumented in situ fusion ( Fig. 14-13 ) because of the destabilization and thus risk of progression of an unprotected in situ fusion. Decompression commits the surgeon to external immobilization (possibly recumbent) or internal fixation to maintain position. In an uncooperative patient (e.g., one with mental retardation or autism) or a patient with pathologic bone (e.g., osteogenesis imperfecta), internal fixation for stabilization offers definite advantages over noninstrumented fusion (see Fig. 14-13 ).
The goal of in situ fusion is to obtain a solid fusion. Surprisingly, several reports have indicated that a satisfactory outcome can still be achieved, even though the quality of the fusion mass is suspect. Evaluation of the postoperative fusion mass is an important part of evaluating a patient with incomplete resolution of symptoms to determine whether an actual pseudarthrosis is present or whether a patient with a solid fusion should undergo decompression. Fusion mass grading is done on a Ferguson AP view postoperatively (see Fig. 14-8 ) and if a poor fusion mass is seen, a poorer clinical result is not unexpected. On the other hand, if a solid fusion mass is noted, further evaluation with MRI to rule out disk herniation and evaluate dural effacement by the posterior edge of the sacrum is indicated. Finally, recurrence of mechanical symptoms in the presence of a radiographically solid fusion should raise the possibility of a new spondylolysis occurring at the next segment cephalic to the fusion mass ( Fig. 14-14 ).
High-Grade Spondylolisthesis
Few conditions have caused as much controversy regarding treatment as high-grade spondylolisthesis (>50% slip), primarily because of the high incidence of complications associated with instrumented reduction. ‡
‡ References .
Consequently, interest in precise indications for reduction, as well as concepts such as partial reduction, have emerged to attempt to resolve the controversy while providing satisfactory outcomes. Discovery of a high-grade dysplastic spondylolisthesis without symptoms is unusual ( Fig. 14-15 ), and although nonoperative treatment, including observation, may be carefully attempted in such an asymptomatic patient, surgical treatment will eventually be necessary.
The usual clinical presentation, described earlier (see Fig. 14-5 ), is difficult not to recognize quickly, especially if significant hyperextension of the thoracolumbar spine above the lumbosacral kyphosis is present. Irritative olisthetic scoliosis may also be present. The patient may be in positive sagittal balance, with the C7 vertical axis falling well anterior to the sacrum. An objective neurologic deficit may be present, but more likely the neurologic compromise is represented by the gait and postural abnormalities. As with any spondylolisthesis being considered for treatment, determination of cauda equina function is essential.
Radiographically, the L5-S1 translation by definition exceeds 50%, but lumbosacral kyphosis (slip angle > 20 degrees) is also present. The L5 body will appear to be falling off the anterior edge of the sacrum, with a trapezoidal deformity of L5 and rounding off of the sacrum indicating chronicity. Spondyloptosis, the end stage of the process, exists when the L5 body lies in the front of the sacrum and below a horizontal line from the top of the sacral dome ( Fig. 14-16 ).
More importantly, however, is the determination of the spinopelvic parameters to differentiate between whether the pelvis is balanced or retroverted (unbalanced) and whether the spine is balanced or unbalanced (positive C7 plumbline anterior to the femoral heads; see Figs. 14-1 and 14-10 ). Based on the outcome of reduction for high-grade slips, the importance of these distinctions in spinopelvic parameters is now accepted, with evidence to support reduction techniques for cases with a retroverted (unbalanced) pelvis featuring low SS and high PT, along with the PI more than 60 degrees or an L5 incidence more than 45 degrees.
The need for reduction to achieve solid fusion, neurologic stabilization and resolution, and prevention of later progression or recurrence has not been confirmed to date because of a lack of high-level evidence studies and the finding that there has so far been no demonstrable difference in clinical outcomes of patients treated in situ versus with reduction. §
§ References .
However, the retrospective multicenter study of Labelle and associates demonstrating the restoration of sacropelvic balance following repositioning (reduction) of L5, and indirectly improving the outcome by this restoration because of the better quality of life for balanced patients, may now change attitudes toward the value of at least partial reduction.Lumbosacral kyphosis, the key deformity, can be corrected by a variety of means, from traction and corrective casting to posterior instrumented reductions with pedicle screw instrumentation or the use of sublaminar wiring ( Video 14-1 
). ‖ Proponents of reduction have maintained that the incidence of pseudarthrosis and slip progression is decreased by biomechanical restoration of lumbosacral alignment and that reduction may produce orthopaedic decompression of stretched nerve roots and dura. Also, improved sagittal plane balance and reduction in lumbar hyperlordosis are achieved if the reduction is maintained.
‖ References .
A selective approach to surgical reduction based on the concept of spinopelvic balance discussed earlier has now been suggested. Retrospective data have suggested that reduction of the unbalanced pelvis leads to clinically significant improvements in SS, PT, and L5 incidence angle (slip angle) and corresponding improvement in the normal spine sagittal profile. On the other hand, reduction of the preoperatively balanced pelvis yields relatively no change in these parameters and therefore theoretically provides little benefit. Based on these findings, a tentative treatment algorithm for the surgical treatment of spondylolisthesis has been proposed ( Table 14-2 ). With the exception of complete spondyloptosis, all reductions are partial—again, primarily out of respect for the risk of neurologic complication—with emphasis on the correction of the slip angle and an improved L5 incidence (see Figs. 14-9 and 14-10, B ).Related posts:
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