Anterior cruciate ligament reconstruction affects the development of muscle atrophy depending on its timing in rats

After anterior cruciate ligament (ACL) reconstruction, muscle atrophy is frequently observed. No conclusions have been reached on the effects of timing of surgery on muscle atrophy. We aimed to determine the best timing of ACL reconstruction surgery to minimize muscle atrophy. Eight-week-old male Wistar rats were used. After 1, 14, or 28 days of ACL transection, rats underwent ligament reconstruction. Some ACL-transected rats were reared without ligament reconstruction. Untreated rats served as controls. At 56 days after ACL transection, muscle atrophy in the rectus femoris and gastrocnemius were assessed. There were no significant differences in any of the parameters relevant to muscle atrophy between the control and ACL-transected rats. ACL reconstruction did not significantly change the parameters relevant to muscle atrophy in the rectus femoris, regardless of timing. In the gastrocnemius, ACL reconstruction resulted in a reduction in slow fiber cross-sectional area (CSA) and an increase in the proportion of fast fiber in the deep region, but not in the superficial region, regardless of timing. When reconstruction was performed at 28 days, a reduction in fast fiber CSA in the deep region was also detected. In conclusion, ACL reconstruction did not alter atrophic parameters in the rectus femoris, while it caused slow fiber atrophy and an increase in the proportion of fast fiber in the deep region of the gastrocnemius, regardless of timing. However, delayed reconstruction surgery developed fast fiber atrophy as well in the deep region of the gastrocnemius. Thus, reconstruction surgery should be performed as soon as possible.