The effects of weight bearing on muscle atrophy early after ACL reconstruction in rats

Abstract

We examined the effects of weight bearing after anterior cruciate ligament (ACL) reconstruction on muscle atrophy in rats. Rats were divided into the following groups: untreated control, ACL reconstruction (amount of weight bearing was small), ACL reconstruction plus hindlimb unloading (nonweight bearing), and ACL reconstruction plus morphine administration (amount of weight bearing was large) groups. At 7 or 14 days after surgery, atrophy of the rectus femoris and gastrocnemius was assessed. ACL reconstruction induced muscle atrophy in the rectus femoris and gastrocnemius. Unloading facilitated atrophy in the gastrocnemius but not in the rectus femoris. Morphine administration partially prevented atrophy in the gastrocnemius but not in the rectus femoris. After ACL reconstruction, the gene expression of insulin-like growth factor-1 (IGF-1), which is involved in protein synthesis, was downregulated in the gastrocnemius. Unloading decreased the gene expression of IGF-1 and increased the gene expression of atrogin-1, which is involved in protein breakdown, in the gastrocnemius. Morphine administration attenuated the downregulation of IGF-1. Atrophy of the gastrocnemius was more severe with a decrease in weight bearing, although the effect of weight bearing on rectus femoris atrophy was limited in rats. Early weight bearing is effective for reducing gastrocnemius muscle atrophy after ACL reconstruction.