The Influence of Cervical Ossification of the Posterior Longitudinal Ligament on Retro-odontoid Soft Tissue Thickness and Cervical Sagittal Balance

Study Design: This was a retrospective study. Objective: To retrospectively analyze the disparities in retro-odontoid soft-tissue thickness (ROSTT), cervical range of motion (ROM) and sagittal balance among patients with ossification of the posterior longitudinal ligament (OPLL) and cervical spondylotic myelopathy (CSM), while investigating the impact of cervical ROM and sagittal balance on ROSTT in the patients with OPLL. Summary of Background Data: The development of retro-odontoid pseudotumor (ROP) can be caused by various conditions. Several studies have suggested that in the absence of specific pathologic conditions such as increased ROM of C1–C2 and alterations in T1 slope (T1S) magnitude may also contribute to the enlarged of ROSTT, which may lead to the formation of ROP. Materials and Methods: The study retrospectively analyzed 145 patients with CSM and 140 patients with OPLL. The ROSTT was measured using T1-weighted sagittal cervical magnetic resonance imaging (MRI) sequences. The T1S, C1–C2 angle, C2−C7 angle, and C2−C7 sagittal vertical axis (SVA) were measured. The range of motion (ROM) was assessed by measuring the flexion-extension radiographs. Results: The OPLL group exhibited significantly greater ROSTT, C0−C2 angle, C2−C7 angle, T1S, and ROM of C0−C2 compared with the CSM group. In addition, a significantly smaller ROM of C2−C7 was noted in the OPLL group. In the OPLL group, ROSTT showed significant positive correlations with the C2–C7 angle ( r =0.206, P =0.015) and T1S ( r =0.354, P <0.001). There was no significant correlation between ROSTT and age or ROM of C1–C2 ( P >0.05). Conclusions: Compared with patients with CSM, patients with OPLL demonstrate greater lower cervical lordosis, T1S, and ROSTT, as well as reduced ROM of C2–C7. The larger ROSTT is potentially attributed to the larger T1S in patients with OPLL.