Knee diameters were increased in mBSA-injected wt mice compared to PBS-injected controls (3.21 ± 0.2 vs. 2.98 ± 0.1, p < 0.05, t-test), and this increase was not significant in Fas -/- mice (2.97 ± 0.2 vs. 2.87 ± 0.1). Histology revealed presence of synovial hyperplasia in both mBSA-injected groups, but mBSA-injected wt mice had decreased trabecular bone volume in distal femoral metaphyses (BV/TV) compared to controls (1.08 ± 0.57 vs. 2.55 ± 0.43; p < 0.05, t-test). There was no significant difference between mBSA-injected and control group in Fas -/- mice (2.34 ± 0.62 vs. 2.61 ± 0.65). μCT analysis showed that mBSA-injected wt mice had decreased BV/TV (2.99 ± 0.19 v. 1.96 ± 0.19; p < 0.001, t-test) and trabecular number (TbN) (1.03 ± 0.03 vs. 0.64 ± 0.02), as well as increased trabecular separation (TbSep) (256,89 ± 1395,12 vs. 312.40 ± 1323.91), compared to controls. mBSA injected Fas -/- mice had decreased TbN compared to controls (0.815 ± 0.01 vs. 0.64 ± 0.04; p < 0.05, t-test), with no significant difference in other trabecular parameters. Osteoblast differentiation was increased in both wt and Fas -/- mBSA-injected mice.