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 degrees +/- 10 degrees vs. 136 degrees +/- 0 degrees; P < .001). Similarly, total torque was found to increase 13.4 N. mm compared with baseline (22.6 +/- 5.9 N. mm vs. 9.2 +/- 2.6 N. mm; P = .002). Residual total ROM restrictions and an increased torque in internal rotation were still evident at 8 weeks of follow-up (113 degrees +/- 8 degrees vs. 137 degrees +/- 0 degrees, P <. 001 and 3.5 +/- 0.4 N. mm vs. 2.7 +/- 0.7 N. mm, 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. (C) 2015 Journal of Shoulder and Elbow Surgery Board of Trustees.