Body Mass & Muscle Weight Following Volumetric Muscle Loss Injuries

Volumetric muscle loss (VML) is the traumatic or surgical loss of a significant amount of skeletal muscle, resulting in decreased function and regenerative abilities. Despite the decrease in function, when one muscle is injured or removed, there is typically a compensatory response in the surrounding muscles that promote hypertrophic adaptations. PURPOSE: The purpose of this study was to observe how surgery impacts body mass and the weight of certain muscle groups 6 weeks after a VML injury to the tibialis anterior (TA) muscle, with particular interest in determining if a hypertrophy response occurs in surrounding muscle groups. METHODS: 10 adult (3-4 months) male Lewis rats underwent a surgical procedure where a 6mm-full thickness biopsy punch was used to create a VML injury in the middle third of the TA muscle of the left hindlimb. The right leg served as an uninjured intra-animal control. Animals were monitored and weighed for 5 days post-surgery and again 6 weeks after the VML surgery. At the conclusion of the study, the right and left TA, extensor digitorum longus (EDL), soleus (SOL), and gastrocnemius (GAST) muscles were harvested and weighed. RESULTS: At the time of surgery, the average body weight of the rats was 364±34 grams (g), which briefly declined during the initial 4 days after surgery (349±29 g) before stabilizing at day 5 (350±26 g; p=0.185). After which, body weight increased significantly over the remainder of the study, day 42 (404±24 g; p=0.001). No statistically significant differences were detected between right and left TA (0.734±0.06 vs 0.743±0.19 g; p=0.32), EDL (0.182±0.04 vs 0.183±0.03 g; p=0.79), or SOL (0.158±0.032 vs 0.184±0.034 g; p=0.30). However, we did detect a significant difference between the right (1.75±0.22 g) and the left (2.04±0.25 g; p=0.036) GAST. CONCLUSION: We were surprised to find no compensatory hypertrophy in the EDL, as this is the muscle that would most likely have an increased compensatory role based on previous TA ablation studies. Meanwhile, the increased weight of the left GAST is unexpected and may indicate that compensation following VML injury requires an increased role of the GAST muscle. Our data also suggests that despite an initial decline in body mass following VML surgery, body weight is ultimately not impacted 6 weeks after the procedure.