Surgical capsular release reduces flexion contracture in a rabbit model of arthrofibrosis

Animal models of joint contracture may be used to elucidate the mechanisms of arthrofibrosis. Patients with joint contracture commonly undergo surgical capsular release. Previous animal models of joint contracture do not simulate this aspect of arthrofibrosis. We hypothesize that a surgical capsular release will decrease the severity of arthrofibrosis in this rabbit model. A capsular contracture was surgically created in 20 skeletally mature rabbits. Eight weeks later, ten rabbits underwent capsular release, which consisted of elevation of the posterior capsule through a lateral incision and manipulation under anesthesia. Ten rabbits had a sham incision, without release (control group). Immediately after release or sham surgery, extension loss (calculated by subtracting the knee extension angle (degrees) of the operative limb from the nonoperative, contralateral limb) was measured using fluoroscopy. All animals were sacrificed following 16 weeks of postoperative free cage activity. At sacrifice, joint contracture was measured using a custom, calibrated device. The histology of the posterior joint capsule was assessed at sacrifice. All animals survived both operations without complications. Immediately after surgical release or sham surgery, the average extension loss was 129.2 ± 10.7° in the control group versus 29.6 ± 8.2° in the capsular release group (p = 0.0002). Following 16 weeks of remobilization, the average extension loss of the control and capsular release animals were 49.0 ± 12.7° and 36.5 ± 14.2°, respectively (p = 0.035). There were no histological differences between the two groups. In this animal model, a surgical capsular release decreased the extension loss (flexion contracture) immediately after surgery, as well as following sixteen weeks of remobilization. There were no histological changes detected in the posterior joint capsule.