Many diseases affecting the peripheral nervous system or the spinal canal may be associated with pathology in the nerve roots, but the most common sources of radiculopathy are conditions that cause direct compression of nerve roots, including prolapsed intervertebral disks, disk degeneration, and osteoarthrosis of the apophyseal joints. The risk for prolapsed lumbar disk is highest in the group 20 to 39 years of age, and it is probably increased by the driving of motor vehicles, full-term pregnancies, and sedentary occupations. Cervical disk prolapses tend to occur in a slightly older age group, but very little is known of specific etiologic agents. Both lumbar and cervical prolapses usually occur in a posterior-lateral direction, and thus they are generally associated with nerve root impingement. Both osteoarthrosis of the apophyseal joints and disk degeneration sometimes progress to nerve root involvement. Although the shape and position of the involved structures undoubtedly influence the likelihood of radiculopathy, it is unclear what other factors cause some individuals to progress to the stage of nerve root involvement and not others. Prevalence rates for osteoarthrosis of the lumbar and cervical spines increase markedly with age, and both are sometimes associated with generalized osteoarthrosis. Mechanical stresses from heavy occupations such as mining and from certain structural abnormalities of the spine such as spondylolisthesis predispose to osteoarthrosis of the lumbar spine. However, little is known about factors associated with osteoarthrosis of the cervical spine. The nature of the stress related to development of osteoarthrosis in the lumbar spine is not known. Disk degeneration is also strongly related to age, with preliminary degenerative changes occurring as early as 20 to 29 years of age and osteophyte formation tending to occur from the fifth decade on. Mechanical stress from heavy occupations is associated with lumbar disk degeneration, but, again, little is known about etiologic factors in cervical disk degeneration. It is apparent that much remains to be learned about the etiology and natural history of these conditions, and it is clear that the gaps in knowledge are even greater for the cervical region than for the lumbar spine. In view of the relatively high frequency of occurrence of these conditions and the amount of pain and disability they cause, epidemiologic studies of etiology and natural history are urgently needed.
