Long-Term Outcomes of Spinous Process Splitting Laminoplasty Using Coralline Hydroxyapatite (SLAC) for Multilevel Degenerative Cervical Myelopathy: A Comparative Study of CSM and OPLL

Study Design Retrospective study. Objective To evaluate the long-term clinical and radiographic outcomes of SLAC for multilevel DCM and to determine whether outcomes differ between patients with cervical spondylotic myelopathy (CSM) and ossification of the posterior longitudinal ligament (OPLL). Methods A total of 146 patients were reviewed, including 99 patients with CSM and 47 with OPLL. Clinical outcomes were assessed using the Japanese Orthopaedic Association (JOA) score, JOA recovery rate, Neck Disability Index (NDI), modified MacNab, bone fusion rate and postoperative complications. Radiographic parameters included C2-C7 Cobb angle and cervical range of motion (ROM). The mean follow-up was 156.5 ± 23.2 months. Results Both groups showed significant postoperative improvement in JOA and NDI scores. In the CSM group, the JOA score improved from 11.4 ± 2.8 preoperatively to 15.0 ± 1.8 at the best postoperative follow-up and remained 14.1 ± 2.5 at final follow-up. In the OPLL group, the JOA score improved from 11.0 ± 3.4 to 14.7 ± 2.2 and remained 14.0 ± 2.0 at final follow-up. No significant intergroup differences were observed in JOA score, NDI, modified MacNab grade distribution, or postoperative complications. However, both groups showed a mild but significant decline in neurological function from the best postoperative status to final follow-up. Radiographically, cervical lordosis decreased significantly only in the CSM group. Preoperative ROM was smaller in the OPLL group, and ROM decreased significantly in both groups. Conclusion SLAC provides durable decompression and sustained functional improvement for multilevel DCM, with comparable long-term outcomes between CSM and OPLL patients.