Objective: Ossification of posterior longitudinal ligament (OPLL) is a progressive disease that causes spinal canal compromise and serious neurological sequelae in advanced cases. The incidence of OPLL in the Asiatic population is 2%-3%, but the incidence is more in the background of fluorosis. Our aim was to study the association of OPLL with fluorosis by comparing urine fluoride levels and to study the types of OPLL.

Materials and Methods: Thirty consecutive patients with OPLL, observed on cervical skiagram, and confirmed by the computed tomography (CT) of the cervical spine, underwent a 24-h urine fluoride level assessment by the ion-selective electrode method. Due consent of all the patients was obtained and the data was collected. Thirty patients with a normal cervical radiograph were taken as a control group and their 24-h urine fluoride levels were compared with the test group. The 24-h urine fluoride level above 1.6 mg/L was taken as the diagnostic parameter of fluorosis. Imaging analysis of the study group focused on the subtype of OPLL, the mass occupying ratio, the sagittal cervical angle, the signs of dural penetration, and the spinal levels involved. Urinary fluoride levels were correlated with the presence of OPLL and different types of OPLL.

Results: Of the 30 patients with OPLL, 25 were males and 5 were females. The most common presentation was myelopathy. Continuous type of OPLL was seen in 11 (36.6%), segmental in 8 (26.6%), focal in 5 (16.6%), and mixed variant in 6 (20%) patients. 24-h urinary fluoride levels ranged from 0.26 mg/L to 12.2 mg/L. 18 (60%) of the patients in the study group were found to have urinary fluoride levels above 1.6 mg/L and only 1 patient (4%) of the control group had the urine fluoride level >1.6 mg/L. This difference was statistically significant. Patients with continuous and mixed types of OPLL had a higher mean urine fluoride level than those with a segmental and focal type of OPLL. The continuous variant of OPLL had a statistically significant occupancy ratio when compared to the other three variants, and the high mass occupancy ratio of the OPLL was directly associated with the presence of dural penetration.

Conclusion: Fluorosis is associated with a higher incidence of OPLL. Higher urinary fluoride levels correlate with the severe forms of OPLL.