Effects of Joint Immobilization and Treadmill Exercise on Muscle Atrophy after Anterior Cruciate Ligament Reconstruction in Rats

Objective. Muscle atrophy is frequently observed after anterior cruciate ligament (ACL) reconstruction. The effects of different rehabilitation protocols after ACL reconstruction on muscle atrophy are not well studied. We aimed to examine the effects of joint immobilization and treadmill exercise after ACL reconstruction on muscle atrophy. Methods. After ACL reconstruction, rats were divided into no intervention, joint immobilization, or treadmill exercise (60 min/day, six days/week) groups. Untreated rats were used as controls. At two- or four-weeks post-surgery, muscle atrophy in the rectus femoris and semitendinosus as well as ankle plantar flexors was assessed. Results. ACL reconstruction induced muscle atrophy at two weeks in the rectus femo- ris, semitendinosus, and plantar flexors. Muscle atrophy in the rectus femoris and plantar flexors spontaneously recovered to levels not significantly different from those in the control group at four weeks, while that in the semitendinosus persisted at four weeks. Four weeks of joint immobilization after ACL reconstruction did not affect the muscle atrophy progression until two weeks, but it hindered the recovery of muscle atrophy in the rectus femoris and plantar flexors during the remaining two weeks. Treadmill exercise did not affect muscle atrophy in all examined muscles. Conclusions. Our results suggest that immobilization after ACL reconstruction should be limited to two weeks to avoid inhibition of recovery from muscle atrophy. Exer- cise may not be effective to alleviate muscle atrophy early after ACL reconstruction. However, since the exercise protocol differs from that used in humans, caution is need- ed when interpreting the results.