Detrimental Effect of Repeated and Single Subacromial Corticosteroid Injections on the Intact and Injured Rotator Cuff A Biomechanical and Imaging Study in Rats

Background:The effect of corticosteroids on tendons is poorly understood, and current data are insufficient and conflicting.Purpose:To evaluate the effects of corticosteroid injections on intact and injured rotator cuffs (RCs) through biomechanical and radiographic analyses in a rat model.Study Design:Controlled laboratory study.Methods:A total of 70 rats were assigned to 7 groups. Uninjured rats (no tear) received either a single saline injection, a single methylprednisolone acetate (MTA) injection, or triple MTA injections. Injured rats (unilateral supraspinatus injury) received either a single saline injection, triple saline injections, a single MTA injection, or triple MTA injections (injections were subacromial; repeat injections were administered weekly). Rats were sacrificed 1 week after final injection. Shoulders were harvested and grossly inspected, and the supraspinatus tendon was evaluated biomechanically. Bone density at the tendon insertion site on the greater tuberosity was assessed by micro...