gms | German Medical Science

Introduction: Cervical fusion is associated with increased incidence of osteophyte formation in the adjacent levels. The purpose of our study was to evaluate the impact of the type of fusion (anterior or posterior) on adjacent levels.

Methods: One hundred and twelve patients were operated on for unstable cervical spine injuries over a 16-year period (1989-2005) according to the instability criteria of White and Panjabi. Seventy-seven patients underwent anterior instrumented fusion, 32 patients had posterior instrumented fusion, while 3 patients were instrumented both anteriorly and posteriorly. The age of the patients was 41.2 years (17-78 years) on average and the mean follow-up was 8.1 years (2-16 years). Retrospective review of the patients’ radiographs was done by an independent examiner. The presence of adjacent level ossification was identified and graded as Grade 0 (none), Grade 1 (mild) if the ossification extended across <50% of the disc space, Grade 2 (moderate) if the ossification extended across 50% of the disc space, or Grade 3 (severe) if there was complete bridging of the adjacent disc space. Two patients had radiographic evidence of preexisting osteophytes and were subsequently excluded from the study. The plate-to-disc distance was measured in anterior fusions (<5mm vs ≥5mm) and evaluated for possible correlation with the ossification both cranially and caudally. Therapeutic Level of evidence III (retrospective comparative study).

Results: Seventy-four patients (96%) with anterior fusion and twenty-eight patients (87.5%) from the posterior fusion group were eligible for the study. Eight patients (10.8%) from the anterior fusion group developed adjacent level ossification, while no one from the posterior fusion group. One patient had signs of ossification from the 3rd postoperative month, while the remainders developed it after the 1st postoperative year. A plate-to disc distance <5mm was recorded in 5 patients cranially and in 7 patients caudally. Severe ossification (grade 3) was observed in 6 out of 8 patients cranially, while 4 patients had moderate and severe ossification (grades 2 & 3) caudally.

Conclusion: Adjacent level ossification does not occur after posterior cervical fusion. On the contrary, ossification following anterior instrumented fusion is associated with a short distance of the plate to the vertebral endplate, especially cranially. Development of ossification early in the postoperative period, or when the plate-to-disc distance is >5mm can be attributed to tissue injury when placing the plate (anterior longitudinal ligament, anterior annulus) and deserves further investigation.