ABSTRACT
The pathogenesis leading to symptomatic disease begins with the initial degradation of the intervertebral disc followed by the development of posterior facet arthropathy.4 Fortunately, most patients with DDD respond very well to conservative treatments.5 Numerous modalities, such as physical therapy, massage, and spinal manipulation, have been found to reduce the symptoms associated with DDD.6 Surgical intervention has typically been reserved for patients with intractable pain who have failed all conser-
vative treatment, those with progressive neurologic deterioration or deformity, and patients who develop cauda equina syndrome.3,7,8
Lumbar spine fusion has been considered the benchmark for treating painful degenerative disease in patients requiring surgery. Fritzell et al9 reported that outcomes were better in patients with discogenic pain who had undergone successful spine fusion than in the nonoperative treatment group. Only 60% to 80% of spinal arthrodesis patients have clinical success,10 leading surgeons to examine why patients continue to have pain. One common finding is the development of degeneration at levels adjacent to the arthrodesis, known as adjacent-segment disease (ASD). It occurs in 5.2% to 18.5% of cases over a follow-up period of 45 to 164 months.11 Biomechanical stresses from increased intradiscal pressure, greater facet loading, and hypermobility have been implicated to cause ASD after lumbar arthrodesis.12-17 This led to a paradigm shift in surgical therapy for DDD from absolute stability to the concept of motion preservation, which attempts to restore physiologic motion at the diseased spinal segment. Total disc replacement (TDR) has evolved from this concept.
