The effects of weight bearing after ACL reconstruction on joint contracture in rats.

PURPOSE: Joint contractures after anterior cruciate ligament (ACL) reconstruction are a serious problem. Given the uncertain effects of weight bearing after ACL reconstruction on contractures, this study was conducted to examine such effects. MATERIALS AND METHODS: To control the amount of weight bearing, ACL-reconstructed rats were reared with either untreated (small weight bearing; weight bearing during locomotion was 54% of pre-surgery at minimum), hindlimb unloading (non-weight bearing), or sustained morphine administration (large weight bearing; weight bearing during locomotion was maintained at 80% or more of pre-surgery) conditions. Untreated rats were used as controls. Knee extension range of motions (ROMs) before (includes myogenic and arthrogenic factors) and after myotomy (includes arthrogenic factor only) and fibrotic reactions in the joint capsule were assessed 7 and 14 days post-surgery. RESULTS: ACL reconstruction significantly reduced ROMs both before and after myotomy and induced fibrosis in the joint capsule accompanying upregulation of fibrosis-related genes (i.e., type I and III collagens and transforming growth factor-ß1) at both time points. Morphine administration increased the ROM before myotomy, but not after myotomy 7 days post-surgery. Unloading after ACL reconstruction improved ROMs both before and after myotomy at both time points. In addition, unloading after ACL reconstruction attenuated fibrotic reactions in the joint capsule. CONCLUSIONS: Our results suggest that morphine administration improves myogenic contractures in parallel with an increase in the amount of weight bearing. Unloading after ACL reconstruction is effective in reducing both myogenic and arthrogenic contractures.

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

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.

The combined effects of treadmill exercise and steroid administration on anterior cruciate ligament reconstruction-induced joint contracture and muscle atrophy in rats.

Rehabilitation protocols to treat joint contracture and muscle atrophy following anterior cruciate ligament (ACL) reconstruction have not been established. In this study, we examined the combined effects of exercise therapy and steroid administration on joint contracture and muscle atrophy following ACL reconstruction. Rats received ACL transection and reconstructive surgery in one knee. After surgery, they were divided into four groups: no intervention, treadmill exercise (started from day three post-surgery, 12 m/min, 60 min/d, 6 d/week), treatment with the steroidal drug dexamethasone (250 µg/kg on days 0-5, 7, and 9 post-surgery), and dexamethasone treatment plus treadmill exercise. Age-matched untreated rats were used as controls. At day 10 or 30 post-surgery, we assessed ACL-reconstruction-induced joint contracture, joint capsule fibrosis, osteophyte formation, and muscle atrophy of the rectus femoris and gastrocnemius. Treadmill exercise after ACL reconstruction improved several indicators of muscle atrophy in both muscles, but it did not have positive effects on joint contracture. Dexamethasone treatment after ACL reconstruction improved joint contracture and joint capsule fibrosis at both timepoints and partially attenuated osteophyte formation at day 10 post-surgery, but delayed recovery from atrophy of the rectus femoris at day 30 post-surgery. The two treatments combined improved both joint contracture and atrophy of the rectus femoris and gastrocnemius. Exercise therapy combined with steroid administration may therefore be a novel therapeutic strategy for joint contracture and muscle atrophy following ACL reconstruction.