Reduced Vertebral Hounsfield Unit Values in the Bridging Group of Ossification-Related Segments in Patients with Ossification of the Posterior Longitudinal Ligament of the Cervical Spine.

Background: Increased systemic bone mineral density has been reported in patients with ossification of the posterior longitudinal ligament (OPLL). This study investigated the differences in vertebral Hounsfield unit (HU) values between the bridged and nonbridged groups of patients with OPLL of the cervical spine at the ossification-related segments.

Methods: A total of 436 ossification-related segments from 157 patients were involved in the study. X-ray and computed tomography scans were used to assess the segmental cervical range of motion (ROM), C2-7 Cobb angle, K-line, ossification thickness, maximum canal occupancy, HU values, and presence and type of OPLL.

Results: In terms of imaging parameters, HU values were significantly higher in the OPLL group (P < 0.001), whereas the ROM was greater in the control group (P < 0.05). In the OPLL group, the K-line positive group had a better C2-7 Cobb angle and greater T1 slope. The ossification-related segments were divided into bridging and nonbridging groups, with smaller vertebral HU values, thicker ossification lesions, greater canal occupation, and reduced interbody mobility in the bridging group. However, we found no significant correlation among segmental ROM, ossified material thickness, maximum canal occupancy of the ossified material, and segmental HU values.

Conclusions: We found that the mean HU value of the cervical spine in patients with OPLL was higher than that of the control group, and the ROM was smaller than that of the control group, with the smallest ROM in the continuous type. In the ossification-related segments, the bridging group exhibited lower vertebral HU values, reduced segmental mobility, and thicker ossification thickness.