Healing of experimental muscle strains and the effects of nonsteroidal antiinflammatory medication.

The healing process of muscle strains and the effect of nonsteroidal antiinflammatory medication were studied using an experimental animal model. A standardized strain of the tibialis anterior muscle in adult male rats was produced by a controlled stretch of the muscle. Groups I and II underwent a unilateral strain of the tibialis anterior muscle and were immobilized in the postinjury period. The rats in Group II were fed piroxicam in the postinjury period. Group III underwent a sham procedure and were also immobilized. At 0, 2, 4, and 11 days postinjury both injured and contralateral control muscles were evaluated by determining tensile strength characteristics and histologic appearance. Group I showed a significant drop in maximum failure load to 25.7% of the control leg at Day 2 with a gradual return to the level of Group III at Days 4 and 11 (40.9% and 50.1%). Group II showed a similar drop but was still stronger than Group I at 2 days with 40.8% of the control leg and continued to drop until 4 days postinjury (33.7%). Histology showed a delay in inflammatory reaction and muscle regeneration in Group II. At 11 days both Groups I and II showed regenerated muscle fibers bridging the entire defect and an increase in endomyseal fibrosis. It is concluded that muscle strains continue to weaken in the early postinjury period. Non-steroidal antiinflammatory medication, such as piroxicam, might delay muscle regeneration.