Evaluation and treatment of clinical instability associated with pseudoarthrosis after anterior cervical surgery for ossification of the posterior longitudinal ligament.

BACKGROUND: Between 1989 to 1993, clinical instability associated with pseudarthrosis was evaluated in 76 patients with cervical ossification of the posterior longitudinal ligament (OPLL). Average 2.5 level extended anterior diskectomy and fusion and average 3.0 level anterior corpectomy and fusion were performed without anterior plate instrumentation using iliac crest or fibular strut autografts.
METHODS: Fusion versus pseudarthrosis resulting in clinical instability, as defined by White and Panjabi, was assessed using flexion and extension X-rays 3 and 6 months post-operatively. Radiographic instability was defined by > 3.5 mm. of sagittal plane translation (or 20%) and > 20 degrees of sagittal plane rotation on dynamic X-rays. Two and 3 dimensional (D) computed tomography (CT) scans, also obtained 3 months postoperatively, either confirmed fusion or indicated failed bony union. The average clinical follow up period was 3 years (range, 25-52 months).
RESULTS: Three months postoperatively, dynamic X-rays in 20 patients demonstrated radiographic instability consistent with pseudarthrosis, whereas 2 and 3D CT studies indicated a lack of fusion. At 6 months, flexion and extension X-rays revealed that 10 patients were fused and that another 7 were clinically stable despite persistent, irregular, linear lucencies at graft/body interfaces. Three (4%) patients with clinical instability associated with pseudarthrosis required secondary posterior wiring and fusion.
CONCLUSION: Only 4% of patients undergoing average 2.75 level anterior OPLL surgery without anterior plate instrumentation required secondary posterior wiring and fusion for clinical instability associated with pseudarthrosis.