Background

Degenerative disc disease (DDD) is defined in terms of anatomical, biomechanical, radiological and clinical change in the lumbar or cervical spine. Symptoms include pain exacerbated by activities that increase loads on the intervertebral discs. Patients with severe pain may undergo conservative treatment or surgery. Discectomy usually addresses direct nerve root compression, but is not usually indicated for discogenic pain. (Ray 2002) The traditional surgery option of fusion has been shown to lead to donor site morbidity, pseudoarthrosis, and degeneration at the adjacent intervertebral disc. The newer surgical option of artificial disc replacement is also intended to address pain due to DDD. Sagittal motion data suggests that the disc replacement may preserve motion as well as increase or restore motion. Researchers suggest that maintaining motion may protect against future degeneration at adjacent levels. (Delamarter 2003) Two categories of artificial disc replacement devices are currently in use: intervertebral prostheses and disc nucleus replacements. Nucleus replacement products are designed for moderate degeneration while intervertebral prostheses are indicated for more severe degeneration. In contrast to intervertebral prostheses, nucleus replacement preserves the existing structures, which include the annulus, endplates, and ligaments. (Shim 2003) (MAS 2004) Bertagnoli has suggested the following criteria to determine candidacy for intervertebral disc replacement