Akinori Kaneguchi1, Junya Ozawa2, Kengo Minamimoto3, Kaoru Yamaoka1. 1. Department of Rehabilitation, Faculty of Rehabilitation, Hiroshima International University, Kurose-Gakuendai 555-36, Higashi-Hiroshima, Hiroshima, Japan. 2. Department of Rehabilitation, Faculty of Rehabilitation, Hiroshima International University, Kurose-Gakuendai 555-36, Higashi-Hiroshima, Hiroshima, Japan. Electronic address: j-ozawa@hirokoku-u.ac.jp. 3. Major in Medical Engineering and Technology, Graduate School of Medical Technology and Health Welfare Sciences, Hiroshima International University, Kurose-Gakuendai 555-36, Higashi-Hiroshima, Hiroshima, Japan.
Abstract
BACKGROUND: Range of motion restriction following immobilization is spontaneously recovered at least in part by remobilization. However, the mechanisms underlying how muscles change with range of motion recovery are poorly understood. This study aimed to reveal morphological and biomechanical changes in the knee flexor semitendinosus muscle that contribute to knee joint contracture following the relief of immobilization. METHODS: To induce flexion contracture, we immobilized rat right knees by an external fixator at a flexed position for three weeks. After removal of the fixator, the joints were allowed to move freely (remobilization) for up to 14 days. We obtained muscle length and passive stiffness of the isolated semitendinosus muscles after measuring passive knee extension range of motion. FINDINGS: Three weeks of immobilization induced range of motion reduction, as well as changes in morphological and biomechanical properties of the semitendinosus muscle, such as reduced muscle length and increment of passive stiffness leading to myogenic contracture. Joint immobilization-induced reduction of range of motion, representing flexion contracture, was partially reduced by 14 days of remobilization. Concomitantly, both muscle length and muscle stiffness returned to levels not significantly different from those in the contralateral side during this period. INTERPRETATION: These results suggest that improvement of myogenic contracture during the early phase of remobilization occurs via both morphological and biomechanical adaptations.
BACKGROUND: Range of motion restriction following immobilization is spontaneously recovered at least in part by remobilization. However, the mechanisms underlying how muscles change with range of motion recovery are poorly understood. This study aimed to reveal morphological and biomechanical changes in the knee flexor semitendinosus muscle that contribute to knee joint contracture following the relief of immobilization. METHODS: To induce flexion contracture, we immobilized rat right knees by an external fixator at a flexed position for three weeks. After removal of the fixator, the joints were allowed to move freely (remobilization) for up to 14 days. We obtained muscle length and passive stiffness of the isolated semitendinosus muscles after measuring passive knee extension range of motion. FINDINGS: Three weeks of immobilization induced range of motion reduction, as well as changes in morphological and biomechanical properties of the semitendinosus muscle, such as reduced muscle length and increment of passive stiffness leading to myogenic contracture. Joint immobilization-induced reduction of range of motion, representing flexion contracture, was partially reduced by 14 days of remobilization. Concomitantly, both muscle length and muscle stiffness returned to levels not significantly different from those in the contralateral side during this period. INTERPRETATION: These results suggest that improvement of myogenic contracture during the early phase of remobilization occurs via both morphological and biomechanical adaptations.