Bone Bridge Formation in Hydroxyapatite Spacers Following Cervical Laminoplasty: A Comparative Study of Spondylotic Myelopathy and Ossification of the Posterior Longitudinal Ligament.

IntroductionCervical laminoplasty using hydroxyapatite spacers is a surgical procedure widely performed for managing spondylotic myelopathy and ossification of the posterior longitudinal ligament (OPLL). Despite the procedure's efficacy, the mechanisms underlying bone formation in OPLL remain poorly understood, and postoperative ectopic ossification may still occur. After laminoplasty, we compared bone bridge formation between adjacent hydroxyapatite spacers in patients with cervical spondylotic myelopathy and OPLL.Materials and methodsA retrospective analysis was conducted on 30 patients who underwent double-door laminoplasty involving two or more consecutive laminae between 2006 and 2020. The median patient age was 62 years (42-87 years), with 21 male and nine female patients. Bone bridge formation over an extended postoperative period was evaluated and compared between spondylotic myelopathy (n=16) and OPLL groups (n=14).ResultsThe median duration from laminoplasty to the last postoperative CT scan was 65 months in the spondylotic myelopathy group and 84 months in the OPLL group. No significant intergroup difference was observed between groups (p=0.45). New bone bridges were identified in five of the 16 patients with spondylotic myelopathy (31%) and nine of the 14 patients with OPLL (64%). The difference was not statistically significant (p=0.079). Throughout the observation period, all but one patient demonstrated stable neurological function.ConclusionsThe incidence of bone bridge formation between adjacent hydroxyapatite spacers did not significantly differ between patients with and without spondylotic myelopathy. Hydroxyapatite spacers in laminoplasty were safe and effective under both conditions.