3.1 | LF thickness and fibrosis score
As is shown in Fig. 1A, the LF thickness is measured on axial T2-weighted images of MRI through the level of facet joint. In the imaging analysis, the LF has a dominating role for the load induced narrowing of LSCS. Specifically, the LF is 4 to 8 mm-thick in patients with LSCS, contrary to the 4 mm or less thickness of normal LF (Sakai et al., 2017; Lafian & Torralba et al., 2018). Consistent with these results, The thickness of LF was more than 4 mm in LSCS group. Consequently, the hypertrophic LF compressed the dural sac and nerve root and caused LSCS (Fig. 1A). In LDH group, the LF thickness was less than 4 mm without compression (Fig. 1A). Briefly, the mean LF thickness in the LSCS group was 4.75±0.39 mm, which was significantly higher than 2.57±0.69 mm in the LDH group (Table 1 and Fig. 1B). Moreover, based on the Masson’s trichrome (MT) staining, the fibrosis score of the dorsal side of LF in the LSCS group was 3.14±0.85, while that of LDH group was 0.95±0.92 (P< 0.05). Furthermore, correlation analysis demonstrated that fibrosis score was positively correlated with the the LF thickness (r = 0.272, P<0.05) (Fig. 1D ), indicating that fibrosis was the main pathological feature of LF hypertrophy.