Influence of Hinge Position on the Effectiveness of Expansive Open-door Laminoplasty for Cervical Spondylotic Myelopathy

Study Design: A prospective study. Objective: To assess the influence of different hinge positions on the clinical results of expansive open-door laminoplasty (EOLP) for cervical spondylotic myelopathy (CSM). Summary of Background Data: EOLP is currently the most widely adopted surgical treatment for CSM, although many long-term clinical follow-up studies have reported that most patients recover satisfactorily after EOLP, there have been numerous reports regarding postoperative complications, such as stubborn axial symptoms and segmental motor paralysis. The hinge position in EOLP plays a decisive role in determining the openness of the door so that affect clinical outcomes, whereas no thorough studies on the hinge positions have been published. Methods: A total of 102 consecutive CSM patients who underwent EOLP from February 2006 to February 2007 were enrolled in this randomized controlled trial and assigned alternatively to 1 of 2 treatment groups. Using a random digits table, 57 patients with the hinge located at the inner margin of the lateral mass were classified as wide-open group, whereas 45 patients with the hinge positioned at the lamina margin served as narrow-open group. All patients were followed up over 24 months, clinical results including operation duration, intraoperative bleeding volume, Japanese Orthopaedic Association scores, axial symptoms assessment, and C5 palsy, and radiologic examinations like C2-C7 angle, cervical curvature index, and range of motion were analyzed statistically. Results: In this study, there were no significant differences in terms of operation duration, intraoperative bleeding volume, neural function recovery rate, curvature index, and range of motion. The neural functions were satisfactorily improved after EOLP in both groups (Japanese Orthopaedic Association score developed from 7.2 +/- 1.1 to 14.3 +/- 1.2 and 8.1 +/- 0.9 to 15.1 +/- 1.6 with P = 0.01 and 0.02, respectively), whereas the severity of axial symptoms was significantly lower in narrow-open group than in wide-open group (P < 0.01). The incidence of C5 palsy in wide-open group was higher than that in narrow-open group (5.3% vs. 0%), even though the difference did not reach statistical significance (1-tailed Fisher exact test, P = 0.17). Conclusions: Our results indicate that proper inward shift of the hinge can ensure effectiveness of surgical decompression, avoid an excessive backward shift of the spinal cord, reduce the incidence of C5 palsy, and alleviate the severity of axial symptoms. In addition, an inward shift should be cautious and contraindicated in patients with fluorosis cervical stenosis, ossification of posterior longitudinal ligament, and ossification of ligament flavum.