163. Post-injury Local Controlled Cooling Significantly Improves Functional Recovery After Volumetric Muscle Loss in Rats

PURPOSE: Volumetric muscle loss (VML) contributes to up to 65% of long-term disability in patients with open fractures associated with traumatic loss of skeletal muscle. The current standard of care for VML is conservative surgical management followed by physical therapy, and therapeutic interventions to induce skeletal muscle regeneration are limited. Studies in murine models of skeletal muscle injury have demonstrated that post-injury local controlled cooling reduces inflammatory and fibrotic processes without impacting regenerative markers. We hypothesize that controlled cooling treatment can limit inflammation and fibrosis while promoting skeletal muscle regeneration, thus improving functional recovery after VML in rats. METHODS: A standardized defect (8mm diameter) was created in the tibialis anterior (TA) muscle of female adult Sprague Dawley rats (200-250 g, n=10 per group). The control group received no treatment post-injury, and the treated group underwent local controlled cooling treatment of the injured muscle. At post-injury days (PID) 14 and 30, functional recovery was assessed by measuring tetanic torque of the TA, and running endurance on a treadmill. Samples of TA muscle were obtained at PID 30 and processed for histological (Masson: fibrosis) and immunohistochemical analysis (CD68: inflammation). RESULTS: At PID 30, the tetanic torque in the treated (cooling) group was significantly higher than in controls (72.2±25.1% of pre-injury baseline vs. 42.1±25.1%, p=0.015). The cooling group recovered a greater treadmill endurance than in controls (103.9±29.7% of pre-injury baseline vs. 37.6±37.4%; p=0.0085). At PID 30, fibrosis was significantly lower in the cooling group than in controls (49.2±6.5% vs 81.4±7.0%, p=0.004), and TA muscle samples from the cooling group demonstrated a significant reduction in CD68 stain uptake when compared to controls (13.8±4.9% vs 69.6±22.2%, p=0.0002). CONCLUSIONS: Controlled cooling promotes functional recovery of VML in rats, including tetanic torque of injured muscle and running endurance. Modulation of fibrosis and inflammation might be biological mechanisms contributing to the observed functional recovery. Validation of these findings in a large animal model may help develop novel, noninvasive treatments for individuals with volumetric muscle loss.