Extent and direction of joint motion limitation after prolonged immobility: An experimental study in the rat

Objectives: To test the hypotheses that contractures progress at different rates in relation to the time after immobilization, that immobilization in flexion leads to loss of extension range of motion, and that joints of sham -operated animals are better controls than the contralateral joint of exper imental animals. Study Design: Experimental, controlled study in which 40 adult rats had one knee joint immobilized at 135 degrees of flexion for up to 32 weeks and 20 animals underwent a sham procedure. At intervals of 2, 4, 8, 16, and 32 we eks, 8 experimental and 4 sham-operated animals were killed and their knee motion measured in flexion and extension. Results: In the experimental group, the range of motion decreased in the fi rst 16 weeks of immobility at an average rate of 3.8 degrees per week (p < .0001) to reach 61.1 degrees of restriction. A plateau was then observed fr om which the contracture did not progress further. The loss in range of mot ion occurred in extension, not in flexion. Conclusion: This study defined an acute stage of contractures starting at t he onset of immobility and lasting 16 weeks during which the range of motio n was progressively restricted, and a chronic stage during which no additio nal limitation was detected. The loss in motion was attributed to posterior knee structures not under tension during immobilization in flexion. Contra ry to the hypothesis, the contralateral joint was validated as a control ch oice for range-of-motion experiments. (C) 1999 by the American Congress of Rehabilitation Medicine and the Americ an Academy of Physical Medicine and Rehabilitation.