Comparative study of preoperative sagittal alignment between patients with multi-segment cervical ossification of the posterior longitudinal ligament and cervical spondylotic myelopathy

Background: To compare preoperative sagittal alignment between patients with multi-segment cervical ossification of the posterior longitudinal ligament (OPLL) and multi-level cervical spondylotic myelopathy (CSM). Methods: A total of 198 patients (110 men, 78 women; mean age, 58.8 ± 10.4 years) with severe cervical spondylosis underwent surgical treatment from September 2013 to December 2021. In total, 103 patients were diagnosed with multi-segment cervical OPLL, including continuous type (n = 31), segmental type (n = 31), and mixed type (n = 41). The remaining 95 patients had multi-segment CSM. Several clinical variables were assessed preoperatively, including Japanese Orthopaedic Association (JOA) scores, visual analogue scale (VAS) score, number of hand actions in 10 seconds, hand-grip strength, C2–C7 Cobb angle, C2–C5 Cobb angle, C5–C7 Cobb angle, C2–C7 sagittal vertical axis, C7 slope, T1 slope, K-line, K-line tilt, and range of motion (ROM). Results: The JOA scores, number of hand actions in 10 seconds, hand-grip strength, and VAS scores were not significantly different between the two groups (p > 0.05). The C2–C7 and C5–C7 Cobb angles were significantly better in the OPLL group (p < 0.05). The CSM group had a larger ROM (p < 0.001). Within the OPLL group, the ROM was significantly different between the segmental type and continuous type (p < 0.05). Conclusion: The sagittal alignment in patients with multi-segment cervical OPLL is good. However, patients with OPLL have greater loss of ROM than those with CSM. Studying the sagittal alignment could provide a theoretical basis for preoperative decision-making.