Muscle does not drive persistent posttraumatic elbow contracture in a rat model

Introduction: Posttraumatic elbow contracture is clinically challenging because injury often disrupts multiple periarticular soft tissues. Tissue specific contribution to contracture, particularly muscle, remains poorly understood. Methods: In this study we used a previously developed animal model of elbow contracture. After surgically inducing a unilateral soft tissue injury, injured limbs were immobilized for 3, 7, 21, and 42 days (IM) or for 42 IM with 42 days of free mobilization (42/42 IM–FM). Biceps brachii active/passive mechanics and morphology were evaluated at 42 IM and 42/42 IM–FM, whereas biceps brachii and brachialis gene expression was evaluated at all time points. Results: Injured limb muscle exhibited significantly altered active/passive mechanics and decreased fiber area at 42 IM but returned to control levels by 42/42 IM–FM. Gene expression suggested muscle growth rather than a fibrotic response at 42/42 IM–FM. Discussion: Muscle is a transient contributor to motion loss in our rat model of posttraumatic elbow contracture. Muscle Nerve 58:843–851, 2018.