Abstract
Introduction: A prospective, randomized, controlled study has been conducted to compare the clinical outcomes of patients treated with an artificial cervical disc to patients who receive fusion after cervical discectomy for the treatment of primary cervical disc disease. It is hypothesized that maintenance of motion after anterior cervical discectomy will prevent the high rate of adjacent level premature degeneration. The primary purpose of the study is to prove equivalence (non inferiority) of outcome of the disc prosthesis in the short term compared with fusion. Enrolment has closed and this is a report of the data with 50 cases with 6 month follow-up and 9 cases having reached 24 month final follow-up.
Methods: In four centres, 52 patients with primary, single level cervical disc disease producing radiculopathy and/or myelopathy were randomised prospectively to receive anterior cervical discectomy with either fusion or artificial cervical disc replacement. The patients were evaluated with pre- and post-operative serial flexion-extension cervical x-rays at 6 weeks, 3, 6, 12, and 24 months. At the same intervals, the patients had pre and postoperative neck disability indexes, visual pain analogue scales, European myelopathy scores, SF-36 general health scores, and neurological status examinations assessing the patient’s reflex, motor and sensory function.
Results: At 6 weeks the neck disability index reduced by 34.1 for the investigational group compared to 35.2 for the fusion group. The pain score had reduced by 7.7 for the investigational group and by 9.7 for the control group. This improvement appeared to be maintained until the 12 month follow-up. The mean pain scores at 24 months were similar (4.3 and 5.6 respectively) In general there appeared to be a slightly better outcome for the investigational group, though the investigational group showed slightly less preoperative pain (p=0.091) and disability (p=0.055) than the fusion group. Both pain score and disability scores improved statistically significantly compared to the pre op scores (p< 0.001 all comparisons). Analysis of non-inferiority of outcome for the investigational group using ANCOVA with the preoperative score as the covariate and a non-inferiority margin of 5 points (5%) showed statistical significance at 12 weeks for Neck Disability Index.
Discussion: Anterior cervical discectomy and fusion has a good short-term outcome though there is a high incidence of failure at adjacent levels over time. It is hypothesized that the maintenance of motion of a segment will prevent adjacent premature degeneration. It will take long term follow-up studies however to prove this. In the mean time, the justification to insert artificial cervical prostheses rests on being able to prove equivalence of outcome between fusion and prosthesis in the short term. This paper shows that the outcomes appear to be equivalent. Though there is insufficient power to prove equivalence with a clinical margin of 5%.
The abstracts were prepared by I. B. McPhee. Correspondence should be addressed to the Spine Society of Australia Secretariat, The Adelaide Centre for Spinal Research, Institute of Medical and Veterinary Science, PO Box 14, Rundle Mall, Adelaide SA 5000, Australia.
