Biomechanical and histological reproducibility and validity of a new post-traumatic model of arthrofibrosis in rats.

Abstract

PURPOSE: Experimental post-traumatic arthrofibrosis studies have been conducted using mostly rabbit models. However, there is great interest in developing and validating models in smaller animals, which would allow for more cost-effective research. The aim is to validate a model in rats recently described by Owen et al. MATERIALS AND METHODS: Twenty 14-weeks old Sprague Dawley female rats were used in the study: 10 rats were used to assess biomechanical contracture, as passive extension angle at different torques (PEA-2, PEA-4, PEA-8) and at capsule disruption, and 10 rats to assess histological fibrosis (area and thickness of posterior capsule). Left knee acted as control. Index surgery was performed on the right knee (operated knee) as described by Owen at al.: intra-articular injury, disruption of posterior capsule, and immobilization with a percutaneous suture in flexion. After a 4-week immobilization period, the suture was removed, followed by another 4-week remobilization period and euthanasia. RESULTS: Operated knees showed lower PEA-4 (-40.6°; P=.011), PEA-8 (-45.6°; P=.044) and PEA at capsule disruption (-66.5°; P=.043) than the control knees. Mean PEA-2, PEA-4 and PEA-8 from our sample were similar to those reported by Owen et al. Operated knees showed a larger posterior capsule area (1.82mm; P=.033) and thickness (.31mm; P=.043) than the control knees. CONCLUSIONS: The post-traumatic arthrofibrosis model described by Owen et al. has the capacity to induce biomechanical contracture and histological fibrosis. Our biomechanical results are comparable to those of Owen, supporting the model's reproducibility.