Risk factor analysis of hinge fusion failure after plate-only open-door laminoplasty

Study Design Retrospective study. Objectives To analyze lamina hinge fusion failure after plate-only open-door laminoplasty. Methods Thirty-one patients who underwent plate-only open-door laminoplasty (110 levels) for cervical myelopathy and who had serial computed tomography (CT) scans at 6 and 12 months were analyzed. Risk factors for fusion failure at 12 months were analyzed, including age, sex, smoking, presence of diabetes mellitus and ossification of posterior longitudinal ligament, bone mineral density (T-score), preoperative cervical curvature, operated levels, presence of a ventral cortical bony continuity, and reflection angle of the lamina hinge. Clinical outcomes were assessed with neck pain score using visual analog scale, neck disability index, and Japanese Orthopedic Association score. Results Hinge fusion occurred in 84% (26/31) of patients at 12 months. A significant risk factor for fusion failure was the absence of a ventral cortical bony continuity at 6 months (p < 0.01; 100 versus 48%). No lamina with ventral cortical bony continuity at 6 months showed depression at 12 months, but two lamina without continuity showed depression of 2.5 and 2.1 mm, respectively, at 12 months. Clinical outcomes were not different between patients with and without hinge fusion. Conclusion Absence of a ventral cortical bony continuity at 6 months is a risk factor for fusion failure at 12 months. However, bicortically defective laminae usually heal with minimal displacement, although it may take longer than 12 months.