Effects of interleukin-6 ablation on fracture healing in mice

This study examined the impact of an interleukin-6 (IL-6) knockout on fracture healing in terms of histological and biomechanical responses. Following IACUC approval, tibial fractures were produced in 4- to 6-week-old IL-6 knockouts (n = 35) and wild-type mice (n = 36) and harvested along with contralateral limbs at 2 and 6 weeks postsurgery. Histology quantified stage of healing, lymphocyte infiltration, TRAP+ cells, and osteocalcin deposition. Bend testing established maximum load and stiffness. Based on normality assessments, Mann-Whitney U or independent t-tests were used for data analysis using a p-value threshold of 0.05. Stage of healing, lymphocyte infiltration, and osteocalcin deposition were similar for all time points (p ≥ 0.243). TRAP+ cell counts were reduced approximately 10-fold in the knockout at 2 weeks (p = 0.015) but were similar at 6 weeks (p = 0.689). Force-to-failure in knockouts was approximately 40% that of wild-type mice at 2 weeks (p = 0.040) but similar at 6 weeks (p = 0.735). Knockout bone was about 25% less stiff at 2 weeks but approximately 60% stiffer at 6 weeks (p ≥ 0.110). The absence of IL-6 during early fracture healing significantly reduced osteoclastogenesis and impaired callus strength. By 6 weeks, most histological and biomechanical parameters were similar to fractures in wild-type bone.