VIM and ossification of the posterior longitudinal ligament of the spine: As expected, vimentin was generally expressed in the cytoplasm of the cells derived from both OPLL and non-OPLL ligament fibroblasts, and keratin was not detected in these ligament fibroblasts (Fig. 2b), which indicated that cells derived from patients with OPLL and non-OPLL patients showed similar fibroblast-like morphological characters in size, nucleus, and shape (Fig. 2c).