Joint Contracture Resulting From a Two-Hour Daily Joint Immobility: An Experimental Study in Rats.

Background Although joint contracture prevention has mainly focused on exercise time, an effective method has not yet been established. A lack of joint movement is considered to be associated with the development of joint contracture; however, this relationship has not been quantitatively investigated. As repositioning is typically performed every two hours, intensive care unit patients and bedridden older adults may experience at least two consecutive hours of immobility. Objective This study investigated whether joint contractures develop after two hours of joint immobility per day, over two weeks, in a non-weight-bearing state, due to hindlimb suspension. Methods The experimental animals were six eight-week-old male Wistar rats weighing 349-380 g (average: 363.8 ± 13.5 g). In the immobilization group, the right hindlimbs of all six rats were immobilized in a maximum plantar flexion position, in which the toes were directed downward, whereas the left hindlimbs of the same six rats served as the control group, with joint movement not restricted. The measured items included the range of joint motion (ankle dorsiflexion angle), muscle fiber cross-sectional area, and soleus muscle relative weight ratio. Results The range of joint motion differed significantly between these groups after two weeks, and the immobilization group showed significant changes between the start of the experiment and after two weeks. The ankle dorsiflexion angle decreased by 1.7% in the control group and by 9.8% in the immobilization group over two weeks. Conclusions These findings suggest that two hours of daily joint immobility combined with hindlimb suspension was associated with a reduction in ankle dorsiflexion range of motion and may contribute to contracture development. This model provides a new perspective that differs from conventional experimental models using continuous joint immobilization during the experimental period.