Introduction

Of all the disorders affecting the intervertebral disks, degenerative conditions are by far the most common, to such an extent that conditions of other causes—neoplastic, infectious/inflammatory, and developmental—are of only secondary clinical importance. Degenerative disturbances of the structure and function of the intervertebral disks have attracted a great deal of attention in recent decades, both because of their wide intrinsic variety and because of their widespread effects on other organs. At first, the discovery of the causal relation between disk prolapse and sciatica led physicians interested in the subject to concentrate on the structural, rather than functional, properties of the disks. This almost exclusive focus on pathoanatomical changes led to a situation in which functional disturbances of the spine unaccompanied by objectively detectable structural abnormalities were most often dealt with, not by physicians, but by other types of practitioners. It was soon realized that mere removal of the disk prolapse did not solve all of the patient’s problems. All too often, there was a remarkable discrepancy between the patient’s radiologically defined pathoanatomical condition on the one hand, and the symptoms on the other.

Despite a widely expressed belief to the contrary, structural and functional disturbances of the motion segment do not always appear simultaneously. Morphological abnormalities do not cause symptoms in every patient. Indeed, various types of deformity, such as scoliosis and juvenile kyphosis, are often asymptomatic.

The main determinant of whether symptoms will arise is the length of time over which the structural deformity of the motion segment developed.

Sudden impingement on a nerve root by a fracture or disk prolapse produces very severe symptoms. If a nerve is gradually stretched, however, as in idiopathic scoliosis or spondylolisthesis, the organism is able to adapt so that no neurological symptoms will arise.

Our current functional—dynamic approach is based on recent advances in biochemistry and biomechanics. It is possible for the function of the spine as a whole to be impaired by changes in tissue volume and consistency, deep within the intervertebral disk, that cannot be detected with the usual morphological techniques. Each disk, the vertebrae above and below, and the associated spinal ligaments and muscles make up a functional unit that Junghanns (1951) appropriately named the “motion segment.” A disturbance in any component of this unit inevitably affects all of the other components as well. The mechanical stress of movement is distributed among all components of the motion segment, but the intervertebral disk is more vulnerable to disease than the rest, because of the special nature of its metabolism. Symptoms most commonly arise in the lower motion segments of the cervical and lumbar spine, which are sites of transition between relatively fixed and relatively mobile parts of the trunk. Furthermore, the structures delimiting the intervertebral disks at these levels lie in close proximity to the spinal nerve roots and are thus likely to impinge on them if they become pathologically deformed.

Of necessity, therefore, any monograph on intervertebral disks must concern itself largely with pathological states of the lower cervical and lumbar segments. As the title of this book implies, we have consciously chosen to focus the present discussion on clinical disorders. Other topics such as embryology, histopathology, electron microscopy, and special surgical techniques are discussed here only as far as their practical importance warrants. The common features of all intervertebral disk disorders have been highlighted to facilitate diagnosis and simplify treatment. One such feature is the positional dependence of the pain, i.e., its tendency to vary with the patient’s posture or lying position.

All diagnostic and therapeutic measures must be chosen with care to satisfy four important conditions, as stated by the MIRACLE principle: a good intervention is one that has

Minimal
Invasiveness,
Risks,
And
Cost,
but has a
Lasting
Effect.