We include an extensive chapter on this subject in recognition of the fact that back pain is among the most frequent of medical complaints. Up to 80 percent of adults have low back pain at some time in their lives and, according to Kelsey and White, an even larger percentage will be found at autopsy to have degenerative spine disease. One task of the neurologist is to determine whether a disease of the spine has compressed the spinal cord or the spinal roots. To do this effectively, a clear understanding of the structures involved and some knowledge of orthopedics and rheumatology is necessary.
Pains in the lower part of the spine and legs are caused by somewhat different types of disease than those in the neck, shoulder, and arms; therefore, these two categories are considered separately.
The lower parts of the spine and pelvis, with their massive muscular attachments, are relatively inaccessible to palpation and inspection. Although some physical signs and imaging studies are helpful, diagnosis often depends on the patient's description of the pain and his behavior in different positions and during the execution of certain maneuvers. Seasoned clinicians appreciate the need for a systematic inquiry and method of examination, the descriptions of which are preceded here by a brief consideration of the anatomy and physiology of the spine.
Anatomy and Physiology of the Lower Part of the Back
The bony spine is a complex structure, roughly divisible into an anterior and a posterior part. The anterior component consists of the cylindrical vertebral bodies, articulated by the intervertebral discs and held together by the anterior and posterior longitudinal ligaments. The posterior elements are more delicate and extend from the vertebral bodies as pedicles and laminae, which encircle the spinal canal. Large transverse and spinous processes project laterally and posteriorly, respectively, and serve as the origins and insertions of the muscles that support and protect the spinal column. The bony processes are also held together by sturdy ligaments, the most important being the ligamentum flavum, which runs along the ventral surfaces of the laminae. The posterior longitudinal ligament lies opposite it—on the dorsal surfaces of the vertebral bodies. These two ligaments define the posterior and anterior margins of the spinal canal, respectively.
The posterior parts of the vertebrae articulate with one another at the diarthrodial facet joints (also called apophysial or zygapophysial joints), each of which is composed of the inferior facet of the vertebra above and the superior facet of the one below. Figure 11-1 illustrates these anatomic features. The configuration and orientation of the facet joints differs in the cervical, thoracic and lumbosacral parts of the spine. The facet and sacroiliac joints, which are covered by synovia, the compressible intervertebral discs, and the collagenous and elastic ligaments, permit a limited degree of flexion, extension, rotation, and lateral motion of the spine.