Impact of Cervical Ossification of the Posterior Longitudinal Ligament Characteristics on Retro-odontoid Soft-tissue Thickness.

Abstract

This was a retrospective study. To retrospectively analyze the impact of different ossification of the posterior longitudinal ligament (OPLL) characteristics-including upper cervical involvement, concurrent ossification of the anterior longitudinal ligament (OALL), OPLL grades, and OPLL types-on retro-odontoid soft-tissue thickness (ROSTT). Abnormal thickening of the retro-odontoid soft tissues can lead to the formation of a retro-odontoid pseudotumor (ROP), which may compress the spinal cord. Increased ROSTT and ROP development are associated with pathologies-such as OPLL-as well as cervical biomechanical imbalance. Notably, OPLL may influence ROSTT by altering cervical curvature and biomechanical properties. A total of 143 patients with cervical OPLL were enrolled in this retrospective analysis. Patients were divided into subgroups based on the following criteria: upper cervical spine involvement by OPLL, presence or absence of OALL, OPLL grades, and OPLL types. In addition, patients were stratified into the high ROSTT group (≥3.8 mm) and low ROSTT group (<3.8 mm). These subgroups were included in comparative analyses to assess differences in ROSTT, cervical sagittal balance parameters, and cervical range of motion (ROM). Patients with OPLL who had upper cervical involvement, concurrent OALL, or higher OPLL grades exhibited significantly greater ROSTT and reduced ROM of C2-C7 (all P<0.05). Both the cervical ossification index (OP-index) and upper cervical ossification index (UOP-index) were significantly correlated with ROSTT (P<0.05). This retrospective study of 143 cervical OPLL patients confirms that increased OPLL extent, upper cervical OPLL involvement, and concurrent OALL are significantly associated with ROSTT thickening. In contrast, OPLL type only affects C2-C7 ROM and exerts no significant impact on ROSTT or cervical sagittal balance. For such patients-specifically those with extensive OPLL, upper cervical involvement, or concurrent OALL-close attention should be paid to the further increase in ROSTT and the potential development of ROP.