In vivo kinetic evaluation of an adhesive capsulitis model in rats.

Background and Hypothesis We hypothesized that extra-articular, internal fixation of the shoulder in rats would result in a subsequent decrease in rotational range of motion (ROM) and an increase in joint stiffness. We further hypothesized that residual kinematic changes would still be present at 8 weeks after immobilization. Extra-articular, internal fixation of the shoulder has been used to induce adhesive capsulitis in rats; however, the effects on in vivo kinematics have not been assessed. Methods Baseline measurements of rotational torque and ROM were acquired (n = 10 rats), and the left forelimb of each animal was immobilized with sutures passed between the scapula and the humeral shaft. After 8 weeks, the sutures were removed, and changes in kinematics and kinetics were longitudinally quantified in the follow-up period. Changes in stiffness, defined as the area under the angle-torque curve, were also quantified. Results Immediately after suture removal, there was a 63% decrease in total ROM compared with baseline (51° ± 10° vs. 136° ± 0°; P P  = .002). Residual total ROM restrictions and an increased torque in internal rotation were still evident at 8 weeks of follow-up (113° ± 8° vs. 137° ± 0°, P P  = .036). Stiffness also increased after suture removal and at 8 weeks of follow-up compared with baseline. Conclusion This animal model of adhesive capsulitis rendered lasting effects on in vivo kinematics of the shoulder.