Comparison of Imaging Features and Clinical Outcomes between Cervical Ossification of Posterior Longitudinal Ligament Patients with Cervical Diffuse Idiopathic Skeletal Hyperostosis and those without: A Retrospective Study

Background Both ossification of the posterior longitudinal ligament (OPLL) and diffuse idiopathic skeletal hyperostosis (DISH) are characterized by abnormal calcification of the ligaments surrounding the spine and can be observed simultaneously in one patient. However, the association between cervical DISH and cevical OPLL has not been comprehensively investigated. This study aimed to investigate the influence of c-DISH on the progression of c-OPLL and to evaluate the clinical outcomes in patients with both c-DISH and c-OPLL. Methods A total of 192 patients with c-OPLL were enrolled and divided into DISH(-) (n = 152) and DISH(+) (n = 40) groups on the basis of the presence or absence of c-DISH. C-OPLL severity was evaluated via the ossification index (OP index) and canal narrowing ratio (CNR) on CT images. The distribution characteristics were analyzed by c-OPLL type and ossification range, with a focus on the most affected segment. Radiographic measurements included the C2–7 lordosis angle (CL angle), C7 slope, and C2–7 sagittal vertical axis (CSVA). Clinical outcome was assessed via both JOA and VAS scores. Results Both the OP index and the CNR were significantly greater in the DISH(+) group than in the DISH(-) group (P < 0.01). Patients in the DISH(+) group had a greater proportion of continuous-type OPLL but lower segmental and local types than those in the DISH(-) group. Patients in the DISH(+) group also had a greater incidence of OPLL at the C2, C3, and C4 levels (P < 0.05). Maximal ossification most frequently affects the C3 level in DISH(+) patients, whereas it affects the C5 level in DISH(-) patients. Compared with DISH(-) patients, DISH(+) patients had significantly poorer clinical outcomes both preoperatively and at the last follow-up. A significant negative correlation was observed between the CNR and both preoperative JOA scores. Conclusion C-OPLL in patients with c-DISH tend to have a proximal cervical distribution, more extensive lesions, and more severe spinal canal occupation, leading to poor neurological function recovery.