Dose-response effects of anti-inflammatory steroid injections on mechanical properties of rat tail tendons.

It has been suggested that glucocorticoid drug therapy or usage may be a contributing factor in the occurrence of tendon ruptures among athletes. Our earlier findings (7) did not support this position but may have been dependent on the small quantity of drug injected. We subsequently tested selected biomechanical properties of healthy, non-traumatized tail tendons from sixty 90-day-old Sprague-Dawley rats previously injected weekly for six weeks with 0.1 ml saline (controls) or low (0.03 mg/0.1 ml), medium (0.30 mg/0.1 ml) or high doses (0.60 mg/0.1 ml) of betamethasone. Results indicate the biological effectiveness of the medium and high dose treatments through reductions in body and adrenal weights, but we found no statistically significant change in dry tendon weight, yield load or relative yield load, although there was a suggestive trend toward lessened dry tendon weights and greater relative yield loads. The hypothesis that repeated local injections of an anti-inflammatory steroid deleteriously effects mechanical properties of healthy, non-traumatized rat tendons is not supported by our data, even considering that some dosages were 10 to 20 times greater than recommended therapeutic quantities for humans.