Contractures secondary to immobility: Is the restriction articular or muscular? An experimental longitudinal study in the rat knee

Objectives: To measure articular structures' contribution to the limitation of range of motion after joint immobility. Study Design: Experimental, controlled study involving 40 adult rats that had one knee joint immobilized in flexion for durations of 2, 4, 8, 16, and 32 weeks; 20 rats underwent a sham procedure. The angular displacement was measured both in flexion and extension at three different torques. Myotomy of transarticular muscles allowed isolation of the arthrogenic component of the contracture. Results: A contracture developed in all immobilized knees. The articular structures were incrementally responsible For the limitation in range of motion (from 12.6 degrees +/- 6.7 degrees at 2 weeks to 51.4 degrees +/- 5.4 degrees at 32 weeks). The myogenic restriction proportionately decreased over time (from 20.1 degrees +/- 8.4 degrees at 2 weeks to only 0.8 degrees +/- 7.2 degrees at 32 weeks). The increase in the arthrogenic component of contracture was predominant in extension. Conclusion: This study quantified the increasing role of arthrogenic changes in limiting the range of motion of joints after immobility, especially as the period of immobility extended past 2 weeks. These data provide a better understanding of joint contracture development and can be used to guide therapeutic approaches.