Recovery from muscle atrophy following short-term joint immobilization and non-weight-bearing after anterior cruciate ligament reconstruction in rats.

Previous studies have reported that joint immobilization and non-weight-bearing after anterior cruciate ligament reconstruction (ACLR) exacerbate muscle atrophy. However, it remains unclear whether the combination of these interventions worsens muscle atrophy additively. In addition, it is also unclear whether the muscle atrophy induced by immobilization and non-weight-bearing following ACLR recovers with remobilization and reloading. We investigated the recovery of muscle atrophy following short-term joint immobilization and non-weight-bearing after ACLR. ACLR rats were divided into four groups: no intervention, joint immobilization, non-weight-bearing, and joint immobilization plus non-weight-bearing. Joint immobilization and non-weight-bearing were performed for two weeks after ACLR, and then, all rats were reared without intervention. Age-matched untreated rats were used as controls. At 2, 4, and 12 weeks post-surgery, atrophy in the rectus femoris, semitendinosus, and gastrocnemius was assessed by measuring fiber cross-sectional area. ACLR alone did not induce a significant decrease in muscle fiber cross-sectional area in all examined muscles. Two weeks of immobilization or non-weight-bearing individually induced muscle atrophy in the rectus femoris and/or gastrocnemius, but there were no apparent additive effects with their combined use. Atrophy of the rectus femoris and gastrocnemius induced by immobilization and non-weight-bearing persisted until two weeks after remobilization and reloading, but disappeared within 10 weeks after remobilization and reloading. In conclusion, the combined use of immobilization and non-weight-bearing after ACLR did not have adverse additive effects on muscle atrophy. Muscle atrophy induced by two weeks of immobilization and non-weight-bearing after ACLR recovered within 10 weeks after remobilization and reloading.