Effect of heat in increasing the range of knee motion after the development of a joint contracture: An experiment with an animal model

Objective: To compare the effects of 2 different heat modalities, infrared and ultrasonic therapy, on a knee flexion contracture. Design: In vivo, experimental, controlled study involving a rat knee joint contracture model that was immobilized using a ligature in flexion for 40 days. Setting: Collegiate research laboratory. Animals: Ninety-three adult male Wistar rats. Interventions: After remobilization, rats were assigned to 3 treatment groups: stretching only (S), stretching with infrared therapy (S+IR), and stretching with ultrasonic therapy (S+US). Six treatment sessions were given in 2 weeks. Main Outcome Measures: The angle of maximum knee extension, wet-weight of triceps surae muscles, phase lag, and dynamic stiffness as mechanical responses were measured, and histologic study was conducted. Results: Compared with the S group, both the S+IR an S+US groups exhibited a significant increase in range of motion (ROM) (P=.021, P=.008, respectively) and a tendency to decrease the phase lag, but there was no significant difference between the 2 heat-combined groups. There were no differences in the weights of the triceps surae muscles and in dynamic stiffness among the groups. Conclusions: Six treatment sessions of stretching with infrared or ultrasound were more effective than stretching without heat at increasing the ROM and decreasing the phase lag of a moderately severe joint contracture. The clinical implementation of heat is advocated to regain a normal ROM and mechanical property when experiencing a joint contracture.