Assessment of Cervical Myelopathy Risk in Ossification of the Posterior Longitudinal Ligament Patients With Spinal Cord Compression Based on Segmental Dynamic Versus Static Factors

OBJECTIVE: Using segmental dynamic and static factors, we aimed to elucidate the pathogenesis and relationship between ossification of the posterior longitudinal ligament (OPLL) and the severity of cervical myelopathy. METHODS: Retrospective analysis of 163 OPLL patients' 815 segments. Imaging was used to evaluate each segmental space available for the spinal cord (SAC), OPLL diameter, type, bone space, K-line, the C2–7 Cobb angle, each segmental range of motion (ROM), and total ROM. Magnetic resonance imaging was used to evaluate spinal cord signal intensity. Patients were divided into the myelopathy group (M group) and the without myelopathy group (WM group). RESULTS: Minimal SAC (p = 0.043), (C2–7) Cobb angle (p = 0.004), total ROM (p = 0.013), and local ROM (p = 0.022) were evaluated as an independent predictor of myelopathy in OPLL. Different from the previous report, the M group had a straighter whole cervical spine (p < 0.001) and poorer cervical mobility (p < 0.001) compared to the WM group. Total ROM was not always a risk factor for myelopathy, as its impact depended on SAC, when SAC > 5 mm, the incidence rate of myelopathy decreased with the increase of total ROM. Lower cervical spine (C5–6, C6–7) showing increased “Bridge-Formation,” along with spinal canal stenosis and segmental instability (C2–3, C3–4) in the upper cervical spine, could cause myelopathy in M group (p < 0.05). CONCLUSION: Cervical myelopathy is linked to the OPLL’s narrowest segment and its segmental motion. The hypermobility of the C2–3 and C3–4, contributes significantly to the development of myelopathy in OPLL.