Minamimoto K1, Ozawa J2, Kaneguchi A2, Yamaoka K2
1Hiroshima International University, Major in Medical Engineering and Technology, Graduate School of Medical Technology and Health Welfare Sciences, Kurose-Gakuendai, Higashi-Hiroshima, Hiroshima, Japan, 2Hiroshima International University, Department of Rehabilitation, Faculty of Rehabilitation, Kurose-Gakuendai, Higashi-Hiroshima, Hiroshima, Japan
Background: Although previous studies have reported the mechanical properties of immobilized muscles, there are discrepancies between studies. In addition, these studies were not considered whether the muscle length at stretched position to measure muscle mechanical properties was within the normal joint range of motion (ROM).
Purpose: This study aimed to clarify the contribution of increased passive stiffness in immobilized muscle to joint contracture in a rat model.
Methods: Seven rats (14 hindlimbs) were used to elucidate the physiological limit of semitendinosus muscle length. Rat knee flexor muscles were removed except the semitendinosus muscle. Then, knee flexion-extension movement was recorded by digital cameras, and the relationship between the semitendinosus muscle length and knee joint ROM were automatically calculated using 3-D motion analysis system KinemaTracer. Next, passive force in the semitendinosus muscle after immobilization was measured as an index of muscle stiffness. Unilateral knee joints were fixed for 3 days (n = 9), 7 days (n = 9), and 21 days (n = 15) by external fixators at 140° flexed position. After the measurement of muscle lengths at 0.05 N of the passive force (slack length; Ls), passive extension tests were performed in both sides of the muscles using universal testing machine Autograph. A ramp extension test was applied to muscles immobilized for 21 days (n= 5) and stretched to rupture at a speed of 10 mm/min. The rest of rats were used for incremental stepwise test. Muscles were extended from Ls to 102.5, 105, 107.5, 110, 115, and 120% Ls at a speed of 100 mm/min, and kept for 120 sec to each length to separately access the viscoelastic parameters (dynamic, elastic, and viscous stiffness). Collagen content, which is one of the candidate factors of viscoelastic changes, was also measured.
Results: The semitendinosus muscle length at maximally extended knee joints was approximately 110% Ls. Knee joint ROMs were significantly decreased after 7 and 21 days of immobilization (Immobilized side vs. Contralateral side: 111 ± 6° vs. 135 ± 10° and 93 ± 7° vs. 134 ± 9°, respectively). In a ramp extension test, the semitendinosus muscles passive stiffness increased at 110% Ls. In a stepwise test, dynamic, elastic, and viscous stiffness also increased at 105-110% Ls after 7 and 21 days of immobilization. All viscoelastic parameters in muscle immobilized for 7 and 21 days were decreased to the contralateral side level at strains over 115% Ls. Unexpectedly, the semitendinosus muscle lengths showed slight decrease (98% of contralateral side) only at 21 days. Collagen content also increased only a few (115% of contralateral side) at 21 days.
Conclusion(s): Knee joint immobilization at flexed position increased passive stiffness in the semitendinosus muscle within the physiological range of muscle length.
Implications: Our results indicate that increased passive stiffness in immobilized semitendinosus muscle is involved in knee joint flexion contracture. Reduction of the semitendinosus muscle length may be not a main causative factor of contracture.
Keywords: Immobilization, Joint contracture, Passive stiffness
Funding acknowledgements: The authors have no conflicts of interest to declare.
Purpose: This study aimed to clarify the contribution of increased passive stiffness in immobilized muscle to joint contracture in a rat model.
Methods: Seven rats (14 hindlimbs) were used to elucidate the physiological limit of semitendinosus muscle length. Rat knee flexor muscles were removed except the semitendinosus muscle. Then, knee flexion-extension movement was recorded by digital cameras, and the relationship between the semitendinosus muscle length and knee joint ROM were automatically calculated using 3-D motion analysis system KinemaTracer. Next, passive force in the semitendinosus muscle after immobilization was measured as an index of muscle stiffness. Unilateral knee joints were fixed for 3 days (n = 9), 7 days (n = 9), and 21 days (n = 15) by external fixators at 140° flexed position. After the measurement of muscle lengths at 0.05 N of the passive force (slack length; Ls), passive extension tests were performed in both sides of the muscles using universal testing machine Autograph. A ramp extension test was applied to muscles immobilized for 21 days (n= 5) and stretched to rupture at a speed of 10 mm/min. The rest of rats were used for incremental stepwise test. Muscles were extended from Ls to 102.5, 105, 107.5, 110, 115, and 120% Ls at a speed of 100 mm/min, and kept for 120 sec to each length to separately access the viscoelastic parameters (dynamic, elastic, and viscous stiffness). Collagen content, which is one of the candidate factors of viscoelastic changes, was also measured.
Results: The semitendinosus muscle length at maximally extended knee joints was approximately 110% Ls. Knee joint ROMs were significantly decreased after 7 and 21 days of immobilization (Immobilized side vs. Contralateral side: 111 ± 6° vs. 135 ± 10° and 93 ± 7° vs. 134 ± 9°, respectively). In a ramp extension test, the semitendinosus muscles passive stiffness increased at 110% Ls. In a stepwise test, dynamic, elastic, and viscous stiffness also increased at 105-110% Ls after 7 and 21 days of immobilization. All viscoelastic parameters in muscle immobilized for 7 and 21 days were decreased to the contralateral side level at strains over 115% Ls. Unexpectedly, the semitendinosus muscle lengths showed slight decrease (98% of contralateral side) only at 21 days. Collagen content also increased only a few (115% of contralateral side) at 21 days.
Conclusion(s): Knee joint immobilization at flexed position increased passive stiffness in the semitendinosus muscle within the physiological range of muscle length.
Implications: Our results indicate that increased passive stiffness in immobilized semitendinosus muscle is involved in knee joint flexion contracture. Reduction of the semitendinosus muscle length may be not a main causative factor of contracture.
Keywords: Immobilization, Joint contracture, Passive stiffness
Funding acknowledgements: The authors have no conflicts of interest to declare.
Topic: Musculoskeletal: lower limb; Musculoskeletal: lower limb; Musculoskeletal: peripheral
Ethics approval required: Yes
Institution: Hiroshima International University
Ethics committee: Committee of Research Facilities for Laboratory Animal Sciences
Ethics number: AE16-016
All authors, affiliations and abstracts have been published as submitted.
