Radiographic Features and Correlation Analysis of Location of Ossification in Patients with Cervical Ossification of the Posterior Longitudinal Ligament Combined with Ossification of the Nuchal Ligament

OBJECTIVE: To investigate the incidence, distribution characteristics, and radiographic features of the ossification of the posterior longitudinal ligament (OPLL) combined with ossification of the nuchal ligament (ONL) and to analyze the correlation between the location of ONL and degree of ossification in patients with cervical OPLL. METHODS: From January 2010 to December 2016, the clinical data of 217 patients with cervical OPLL were reviewed retrospectively. Type and location of OPLL and ONL were determined on computed tomography images and lateral radiograph films. For patients with the local type of ONL, the segment with the largest spinal canal occupation ratio (COR) of OPLL was determined on cross-sectional computed tomography slices. The correlation between the location of ONL and segment with the largest COR of OPLL was evaluated. RESULTS: Of the 217 patients with cervical OPLL, 118 patients (54.4%) had OPLL combined with ONL (92 male and 26 female patients). The incidence of ONL was almost 1.4 times greater in males than in female patients (P = 0.03). C5-C6 (49.5%) was the segment at which ONL occurred most. Of 60 patients with the local type of ONL, 34 patients' ONL was located at the segment with largest COR of OPLL. The matching ratio was the largest (77.8%) when the type of OPLL was locally circumscribed (P = 0.003). CONCLUSIONS: The incidence of ONL was 54.4% in patients with cervical OPLL, and male patients were affected more than female patients. ONL occurred most in segment C5-C6. The location of local-type ONL commonly corresponded to the segment with the largest COR of OPLL when type of OPLL was circumscribed.