Congenital Anomalies of the Lumbar Spine
Anatomic variations of the spine are frequent and, though infrequently themselves the source of pain and functional derangement, they predispose an individual to discogenic and spondylotic complications by virtue of altering the mechanics and alignment of the vertebrae, joints, or size of the spinal canal or by giving rise to traumatic fractures of the pedicles. Congenital scoliosis in particular is a complex matter in relation to secondary spinal disease and entire textbooks have been devoted to the analysis of this subject. It is not therefore discussed here except to point out that there is no obligatory relationship between mild degrees of scoliosis that carries over into adulthood and back derangements, and further that some instances of scoliosis occur in parallel with congenital anomalies of the spine and base of the brain such as Chiari malformation and syringomyelia.
A common anomaly is fusion of the fifth lumbar vertebral body to the sacrum (“sacralization”) or, conversely, separation of the first sacral segment, giving rise to 6, rather than the usual 5 lumbar vertebrae (“lumbarization”). However, neither of these is consistently associated with any type of back derangement. Another less-common finding is a lack of fusion of the laminae of one or several of the lumbar vertebrae or of the sacrum (spina bifida). Occasionally, a subcutaneous mass, hypertrichosis, or hyperpigmentation in the sacral area betrays the condition, but in most patients it remains occult until it is disclosed radiologically. The anomaly may be accompanied by malformation of vertebral joints and usually induces pain only when aggravated by injury. The neurologic aspects of defective fusion of the spine (dysraphism) are discussed in Chap. 37, with other developmental abnormalities of the nervous system.
Many other congenital anomalies affect the lower lumbar vertebrae: asymmetrical facet joints, abnormalities of the transverse processes, are seen occasionally in patients with low back symptoms, but apparently with no greater frequency than in asymptomatic individuals.
Spondylolysis consists of a congenital and probably genetic bony defect in the pars interarticularis (the segment at the junction of pedicle and lamina) of the lower lumbar vertebrae. It is remarkably common, affecting approximately 5 percent of the North American population and mainly a disease of children (peak incidence between 5 and 7 years of age). The defect assumes importance by predisposing to subtle fracture of the pars articularis, sometimes precipitated by slight trauma but often in the absence of an appreciated injury. In some young individuals it is unilateral and may cause unilateral lumbar aching back pain that is accentuated by hyperextension and twisting. In the usual bilateral form, small fractures at the pars interarticularis allow the vertebral body, pedicles and superior articular facets to move anteriorly, leaving the posterior elements behind. This leads to an anterior displacement of one vertebral body in relation to the adjacent one, namely spondylolisthesis. (The main cause of spondylolisthesis in older adults is degenerative arthritic disease of the spine as discussed further on.) Patients with progressive vertebral displacement and neurologic deficits require surgery. Reduction of displaced vertebral bodies before fusion and direct repair of pars defects are possible in special cases and back pain is usually reduced or relieved.
Other Causes of Sciatica and Low Back Pain