Impact of the K-line in patients with ossification of the posterior longitudinal ligament: Analysis of sagittal cervical curvature changes and surgical outcomes

OBJECTIVE: This study aimed to investigate the relationship of the K-line with sagittal cervical curvature changes and surgical outcomes in patients with cervical ossification of the posterior longitudinal ligament (OPLL). METHODS: We retrospectively reviewed 84 patients with OPLL who underwent posterior cervical single-door laminoplasty. The patients were divided into a K-line-positive (+) group and a K-line-negative (−) group. Perioperative data, radiographic parameters, and clinical outcomes were compared between the two groups. RESULTS: Of 84 total patients, 50 patients were in the K (+) group and 29 patients were in the K (–) group. Neurological function improved in both groups after laminoplasty. The C2–7 Cobb angle, T1 slope, and C2–7 sagittal vertical axis were significantly changed in the K(−) group compared with those in the K (+) group before the operation and at the 3-month and final follow-ups. CONCLUSION: Neurological function was recovered in both groups, and the clinical effect on the K (+) group was better than that on the K (−) group. The cervical curvature in patients with OPLL tends to be anteverted and kyphotic after laminoplasty and is an important factor in reducing the clinical effect.