Total disc arthroplasty does not affect the incidence of adjacent segment degeneration in cervical spine: results of 93 patients in three prospective randomized clinical trials

Background context: Advancements in the philosophy of "motion preservation" have led to the use of total disc arthroplasty (TDA) as an alternative to fusion for degenerative disc disease (DDD) in the cervical spine. A commonly proposed theory is that TDA could reduce the incidence of adjacent segment disease. All the published clinical studies for TDA discuss the "equal efficacy" results of different investigational device exemption (IDE) trials between TDA and anterior cervical discectomy and fusion (ACDF) but have not addressed the issue of adjacent segment disease.

Purpose: To present the comparison of outcome data with respect to clinical success rates, symptom-free period, and incidence of adjacent segment disease in 93 patients with one- and two-level cervical DDD treated with TDA or ACDF in three different Food and Drug Administration (FDA) investigational trials.

Study design: Prospective, randomized, FDA IDE trials.

Patient sample: Ninety-three patients with established symptomatic one-or two-level cervical disc disease who failed to respond to conservative treatment were randomized to receive TDA (59) or ACDF (34) as part of clinical trials involving three different artificial discs at our institution. Subjects were blind to the assigned group until after the surgery.

Outcome measures: Visual analog pain score (VAS), Neck Disability Index, and cervical spine radiographs were collected at 6 weeks and at 3, 6, 12, 24, 36, and 48 months after surgery.

Method: Success of the index surgery was assessed based on outcome measures at the seven data points. Success was defined as reduction by more than 30 points in both VAS and Neck Disability Index, absence of neurological deficits, and no further intervention at the index level. Adjacent segment disease was established by radiology, neurophysiology, and subsequent interventions administered to the patients.

Results: At median follow-up of 37 months (range, 24-49 months), 64 (25 ACDF and 39 TDA) patients satisfied the criteria for clinical success. Neck Disability Index was a better predictor of outcome than pain score (p<.05). Sixteen percent of TDA patients and 18% ACDF patients developed adjacent segment degeneration and were treated actively (p=.3). Concurrent lumbar DDD significantly increased the risk of adjacent segment degeneration (p=.01). Age, gender, smoking habits, and number of levels at index surgery had no predictive value.

Conclusion: Total disc arthroplasty is equivalent to ACDF for providing relief from symptoms in the treatment of one- and two-level DDD of cervical spine. The risk of developing adjacent segment degeneration is equivalent after both procedures but is significantly higher in patients with concurrent DDD in lumbar spine.