The ANG, OPN, and OPG were found to be significantly higher in the OPLL group (3.0 vs. 1.94, 1.81 vs. 1.27, and 1.35 vs. 0.75, p < 0.01 and p < 0.001, respectively, Table 2). Here, ANG is linked to ossification of the posterior longitudinal ligament of the spine.