Disk-related diseases have a high point prevalence as well as a high annual and lifetime prevalence and are, therefore, frequently the subject of medicolegal assessments by physicians. Indeed, they account for 60% of all such assessments, followed by disorders affecting the lower limbs (30%) and upper limbs (10%). Even when the primary damage is in a limb, e.g. after amputation or after stabilization of a joint, the affected individuals usually claim additional disability because of secondary effects on the spine. Disk disease commonly gives rise to claims of inability to work, inability to pursue one’s present occupation, and loss of earning capacity, as well as claims of occupational or accidental injury.

Pre-existing degenerative disease, the fluctuating nature of the clinical manifestations, and the lack of objective correlates to the pain all complicate the task of medicolegal assessment of disk disease. Because of the diversity of possible interpretations in this area, the judicial process is often protracted, and assessments are often met with counter-assessments and overriding assessments. A further difficulty arises from the fact that, with the exception of small children, all humans have some degree of degenerative disease of the intervertebral disks.

Everyone who suffers from sudden-onset back pain attributes it to some external event, from a natural tendency to believe that everything must have a cause. Overexertion, faulty posture, or trauma is blamed for the pain. Questions of this type arise in all assessments of possible occupational or accidental injury, and the assessors’ opinions are varied. It is sometimes stated that the disks are actually quite robust and that trauma is more likely to fracture a vertebra than to rupture a disk, i.e., that all disk disease is a matter of biological destiny and attributable to degenerative change. Other assessors will attribute the entire disability in disk disease to one or more traumatic events, resulting in the official recognition of the problem as a traumatic injury.

Basic research, above all the studies of Krag (1987), Andersson (1991), Pope (1992), and Waddell (2004), has shown that external factors are part of the multifactorial causation of disk-related diseases and play a role in their etiology and pathogenesis, particularly with respect to the consequences of disk herniation. Individual traumatic events also have a degree of significance as part of this process.

In medicolegal assessment, the main issue is in many cases a displacement of disk tissue—intradiscal displacement, protrusion, or prolapse—that may have been provoked or exacerbated by an accident. The assessment is complicated by the possibility that the changes seen in the plain radiographs, CT scans, and MRI scans obtained at the time of the accident might already have been present before the accident without causing any symptoms: 20% of all protrusions and prolapses are asymptomatic.

Because it can never be assumed that an adult patient had entirely healthy disks before an accident, the demand commonly made by insurance providers for proof of full bodily integrity before the event loses its relevance. No one over 30 years of age has a spine without degenerative changes rendering them more susceptible to external traumatic injury.

Normal work activities can, however, be disturbed by external influences. If, in the course of a work activity, the individual must suddenly exert him/herself more than usual, with a sudden, involuntary (reflex) muscle contraction, or when an unusual type of movement is necessitated by an external influence, then this would satisfy the condition of a sudden, unpredictable external event required by the definition of an accident for the purposes of both private and statutory accident insurance.

The effects of such events on the mechanically labile intervertebral disk are much more marked than those of movements that are consciously executed as planned. Such situations arise, for example, when a worker stumbles while lifting and carrying, or when a carrying strap tears and the weight suddenly shifts. A traumatic event is also within the scope of accident insurance protection when, for example, several workers lift up a heavy object simultaneously and then, because the load tilts or one worker drops out, the entire load must suddenly be borne by a single individual. The high intradiscal pressures that come about during such an event, combined with torsion and undue stress on the lateral edge of the intervertebral disk, are produced before the individual has a chance to protect the disk with voluntary contraction of the truncal and proximal appendicular muscles.

Table 17.1 Requirements for a disk herniation or acute disk syndrome to be legally recognized as the result of an accident

There must be a sufficiently severe trauma, with high intradiscal pressure caused by a violent force originating outside the body and/or an unanticipated exertion that is unforeseen, unpredictable, and unavoidable.
The typical symptoms must arise immediately.
The patient must have been free of symptoms immediately before the event.

Criteria for Recognition

Statutory accident insurance. In Germany the principle of contributory causation applies, with all-or-nothing compensation. If the traumatic component predominates, then the overall compensable injury—i.e., the clinical syndrome of post-traumatic low back pain or sciatica—is to be viewed as being entirely the consequence of the accident, for a certain period of time. Only if the disease manifestations caused by the accident subside over time, to be replaced by other manifestations, can the latter be fully ascribed to pre-existing degenerative damage independent of the accident.

The medical experience of the spontaneous course of acute disk syndromes implies that permanent damage is not to be expected, unless the disk herniation provoked by the accident has caused a demonstrable, permanent neurologic deficit or has been treated by surgery with consequent adverse sequelae.

The loss or significant functional impairment of an upper limb induces an asymmetrical posture, particularly in the lower cervical motion segments. The healthy, functional limb is used preferentially; the cervical spine is laterally bent with the convexity on the side of the functional limb (so-called “idemscoliosis”). This abnormal posture, in time, leads to a fixed abnormal curvature of the spine with structural scoliosis. Symptoms arise through the overloading or abnormal loading of the shoulder and neck muscles and through the over-stretching or sprain of the intervertebral joint capsules of the cervical motion segments. On the concave side of the cervical spine, narrowing of the intervertebral foramina can produce signs of nerve root irritation.

When an uncompensated leg-length discrepancy has been present for a long time, as after an amputation or severe knee injury (including fusion of the knee joint), a pelvic tilt develops, with a consequent lateral curve in the spine. The convexity usually points to the shorter, or damaged, side. The lateral curvature can be compensated for at first, but over time a structural scoliosis develops. Leg prostheses for amputees are usually fitted so as to be 1–2 cm shorter than the intact leg, to allow easier swinging of the prosthetic limb during walking, which is particularly useful if the ground is uneven.

Besides this static deviation in the frontal plane, prostheses with a containment socket for the ischial tuberosity also cause a change in the sagittal plane: the pelvis is tilted forward, with consequent hyperlordosis of the lumbar spine. Both of these static abnormalities, lateral curvature and hyperlordosis, are normally well compensated in younger patients, particularly those who actively participate in sports and gymnastics. When these compensatory mechanisms are no longer adequate, because of constitutional or age-related muscle insufficiency, the lumbar motion segments are put under excessive mechanical stress, particularly in the intervertebral joints. Decompensation is illustrated by a fixed lateral curvature of the lumbar spine on an AP plain radiograph, which should be supplemented by functional views in lateral bending to the left and the right. Such changes can also occur after long-standing unilateral functional impairment of a lower limb, resulting, e.g., from fusion of a knee, flexion contractures at the hip and knee joints, or deformities of the foot. The resulting limp places an asymmetrical stress on the spine, particularly the lower lumbar motion segments and the sacroiliac joints. The patient complains of spinal symptoms that arise mainly in the muscles and intervertebral joints. Back pain is most severe when the patient stands or walks. The symptoms are usually those of a local lumbar syndrome. Signs of nerve root irritation resulting from narrowing of the intervertebral foramina are relatively rare.

Unlike idiopathic constitutional scoliosis, lateral curvatures associated with amputation or severe damage to a limb are free of torsion, i.e., the spinous processes and the oval shadows of the roots of the laminae are projected normally (symmetrically) on plain radiographs. An exception to this rule is seen in permanent unilateral damage to a limb beginning in childhood; in such cases, the scoliosis induced by the injury always has a torsional component as well.

Degenerative changes of the cervical or lumbar spine that would have arisen even without any arm or leg injury must be taken into account as a contributory factor in assessments for private accident insurance and as a contributory cause of symptoms in assessments for statutory accident insurance. The more important changes of this type are loss of disk height in the lower segments of the cervical and lumbar spine and the accompanying local, sometimes radicular manifestations.

Summary

The extent of a unilateral upper or lower limb injury should be assessed. Measurements should be made of any tilting of the pelvis or lateral curvature of the spine, as seen in functional plain radiographs with maximal lateral bending to the right and left. The radiographs should also be inspected for signs of torsion.

If an injury-related lateral curvature of the cervical or lumbar spine is documented, the corresponding injury-related loss of loss of earning capacity should be no more than 10%.