Influence of steroid injection on ligament healing in the rat

The effect of a single local injection of long acting corticosteroid on the healing of acute rat medial collateral ligament injuries was studied. The medial collateral ligaments of 81 adult female rats were exposed surgically. In 32 rats, the ligament was transected sharply, the overlying muscle was closed, and a human equivalent dose of dexamethasone 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 closed without ligament transection or injection. The rats were divided into 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 smaller group of 6 rats (2 from each group) for histologic changes 40 days after surgery. No histologic differences were noted between the injected and noninjected ligaments 6, 10, or 20 days after injury. At 40 days, the injected specimens showed a slightly more mature crimp pattern 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 appearance or biomechanical strength of healing rat medial collateral ligaments.