Mechanical disorders of the spine are defined as degenerative spinal conditions, such as disc degeneration and spondylosis, which are frequent causes of radiculopathy and myelopathy, and which are not associated with trauma or neoplasm. These conditions are among the most commonly treated diseases in neurosurgical practice. Lumbar discectomy represents the most common neurosurgical procedure performed in the United States. Lumbar stenosis is the most commonly diagnosed condition in adults, older than 65 years, undergoing lumbar spine surgery (Turner et al. 1992). Similarly, cervical spondylotic myelopathy is said to be ‘the most common spinal cord disorder in persons over 55’ (Rengachary & Redford 1991). The operative treatment of mechanical disorders of the spine has undergone unparalleled technical advancement during the past 10 years. However, the reported outcome of surgery for these conditions is highly variable. The majority of outcome studies are retrospective analyses which are methodologically imperfect. A critical review of the literature reveals several consistent flaws in the study design as well as in the analysis and reporting of outcome data (Turner et al. 1992).

This chapter is divided into four sections. We have reviewed the outcome of surgical treatment of four common mechanical disorders of the spine: cervical spondylotic myelopathy, herniated lumbar disc, lumbar stenosis and degenerative lumbar instability. A critical analysis of the results reported in the literature is undertaken.

Cervical spondylotic myelopathy

Cervical spondylosis is extremely common in the adult population (Rengachary & Redford 1991). Radiographic spondylosis is present in 25–50% of the population by age 50 years and increases to 75–85% by age 65 years (Montgomery & Brower 1992).