Short-term Changes After Corticosteroid Injections Into the Normal Tendons of Rabbits: A Controlled Randomized Study

Background: Corticosteroid injections in or around tendons for the treatment of athletic injuries are a common practice among orthopaedic surgeons and are apparently efficacious in the short term, although controversies persist related to local complications. Purpose: This study evaluated short-term (48 hours) biomechanical, biochemical, and histological alterations after a single injection of betamethasone into the normal tendons of rabbits. Study Design: Controlled laboratory study. Methods: A total of 72 New Zealand White rabbits were randomly divided into 2 groups: the test group—in which 36 animals underwent 1 intratendinous injection of betamethasone (1.4 mg / 0.2 mL) in the right calcaneal tendon; the control group—in which the right calcaneal tendon of 36 animals was injected with saline (placebo control group) and the left calcaneal tendon was left untreated for normal standards (normal control). Forty-eight hours later, animals were euthanized and tendons were harvested. Metalloproteinase (MMP1 and MMP2) and interleukin (IL1 and IL6) expression levels, biomechanical resistance (load × elongation parameters), and histomorphometry (hematoxylin and eosin and picrosirius red stains for collagen fibers, tenocytes, and inflammatory cells) were analyzed in the tendons. Results: The test group had a significant reduction in MMP2 expression as compared with the control groups (P = .027). Regarding the other parameters, there were no additional significant differences between the groups. Conclusion: A single injection of corticosteroid into normal calcaneal tendons did not trigger acute local morphological, structural, or biomechanical injuries at 48 hours, but it did promote a significant decrease in MMP2 levels. Additional studies are needed with increased duration of follow-up, various doses, and multiple injections and in tendinopathic models. Clinical Relevance: Some previous studies demonstrated early structural changes in tendons after a single corticosteroid injection, which was not corroborated by the present study. Metalloproteinase decrease is usually associated with a reduction in collagen degradation, which would be protective for the healing process. More studies are necessary to confirm the possible beneficial effect of these results in the long term and for tendinopathies.