INFLUENCE OF STEROID INJECTION ON LIGAMENT HEALING IN THE RAT

The effect of a single local injection of long acting corticosteroid o n the healing of acute rat medial collateral Ligament injuries was stu died. The medial collateral ligaments of 81 adult female rats were exp osed surgically. In 32 rats, the ligament was transected sharply, the overlying muscle was closed, and a human equivalent dose of dexamethas one was injected under the muscle layer, bathing the injured ligament. The identical operation with no corticosteroid injection was done in 32 additional rats: in the remaining 17 animals, the incision was clos ed without ligament transection or injection. The rats were divided in to 3 groups of 25. Each group consisted of 10 rats that were injected, 10 that were not injected, and 5 that underwent sham operations. One group was euthanized 6 days after surgery, 1 group after 10 days, and 1 group after 20 days. Histologic evaluation and biomechanical testing were performed for each subgroup. A cellular pathologist examined a s maller group of 6 rats (2 from each group) for histologic changes 40 d ays after surgery No histologic differences were noted between the inj ected and noninjected ligaments 6, 10, or 20 days after injury. At 40 days, the injected specimens showed a slightly more mature crimp patte rn than the noninjected specimens. Mechanical testing demonstrated no significant difference in ultimate load or ultimate stress between the injected and noninjected groups, There were no detrimental effects of a single dose administration of dexamethasone on the histologic appea rance or biomechanical strength of healing rat medial collateral ligam ents.