Factors affecting the incidence of symptomatic adjacent-level disease in cervical spine after total disc arthroplasty: 2- to 4-year follow-up of 3 prospective randomized trials.

STUDY DESIGN Prospective randomized clinical trials. OBJECTIVE To compare the outcome data with respect to clinical success rates and incidence of adjacent level disease (ALD) in patients after total disc arthroplasty (TDA) or anterior cervical fusion (ACDF) for 1- and 2-level cervical disc disease. SUMMARY OF BACKGROUND DATA Previously published studies have provided evidence that ACDF procedure for cervical degenerative disc disease (DDD) may increase the stress on the nonoperated adjacent cervical segments, thus possibly increasing the risk of degeneration at these levels. The theoretical assumption that TDA may reduce the incidence of future ALD by preserving motion at the affected segments has, however, never been validated by clinical evidence. METHODS One hundred seventy patients with established symptomatic cervical disc disease at 1 or 2 levels participated in 3 prospective randomized clinical trials at 2 institutions. Participating subjects were randomized to receive TDA (treatment; n = 113) or ACDF (control; n = 57) by 6 independent investigating surgeons. Visual analogue pain scores (0-100), Neck Disability Index, neurological examination, and cervical spine radiographs were collected at enrollment and then 6 weeks and 3, 6, 12, 24, 36, and 48 months after surgery. Patients with persistent symptoms during the follow-up period were investigated for adjacent segment disease (ASD) with computed tomography/magnetic resonance imaging of the cervical spine, neurophysiology, and subsequent active interventions. RESULTS At the median follow-up of 42 months (range: 28-54 months), 9 (14.3%) ACDF and 19 (16.8%) TDA patients developed and were actively treated for ASD. Osteopenia dust energy x-ray absorptiometry T scores of -1.5 to -2.4) (P = 0.04; 95% confidence interval [CI]: 0.007-0.223) and concurrent lumbar degenerative disease (P = 0.02; 95% CI: 0.003-0.196) significantly increased the risk of ASD. CONCLUSION The risk of developing adjacent segment degeneration was equivalent at median 38 months after both ACDF and TDA procedures in cervical DDD. Osteopenia and concurrent lumbar DDD significantly increase the risk of ALD.