Midline Splitting Cervical Laminoplasty Using Allogeneic Bone Spacers: Comparison of Fusion Rates between Cervical Spondylotic Myelopathy and Ossification of Posterior Longitudinal Ligament

OBJECTIVE: To analyze factors associated with fusion using allogeneic bone spacers for midline splitting cervical laminoplasty (MSCL). METHODS: During April 2012 and September 2013, seventeen patients with cervical spondylotic myelopathy (CSM) or ossification of posterior longitudinal ligament (OPLL) underwent MSCL with allogeneic bone spacers by a single surgeon. Mean follow up periods was 11.3 months (range, 6-19 months). Clinical outcomes were evaluated by the Japanese Orthopedic Association (JOA) scores at preoperative and postoperative 6 months. Simple cervical X-rays were taken preoperatively, immediate postoperatively, 3, and 6 months after operation. Computed tomography (CT) scans were performed preoperatively, immediate postoperatively and 6 months postoperatively. The differences between two diseases were analyzed on cervical lordosis, canal dimension, anteroposterior (AP) distance, fusion between lamina and allogeneic bone spacer and affecting factors of fusion. RESULTS: All surgeries were performed on 59 levels. There were no significant differences on the changes of lordosis (p=0.602), canal dimension (p=0.554), and AP distance (p=0.924) as well as JOA scores (p=0.257) between CSM and OPLL groups. Overall fusion rate was 51%. Multivariate analysis on the factor for the fusion rates between lamina and spacers showed that the immediate postoperative contact status between lamina and spacers in CT as significant factor of fusion (p=0.024). CONCLUSION: The present study suggests that CSM and OPLL did not show difference of surgical outcome in MSCL using allogeneic bone spacer. In addition, we should consider the contact status between lamina and bone spacer for the better fusion rates for this surgery.