Ozawa J1, Sakitani N2, Kaneguchi A1, Minamimoto K1, Matsuba J3, Doumen M4, Yamamoto S5, Sudo Y6, Hatasaka S7
1Hiroshima International University, Rehabilitation, Higashi-Hiroshima, Hiroshima, Japan, 2National Rehabilitation Center for Persons with Disabilities, Rehabilitation for Motor Functions, Tokorozawa, Saitama, Japan, 3Teikyo University of Science, Medical Science, Adachi, Tokyo, Japan, 4Tobata Kyoritsu Hospital, Rehabilitation, Kitakyusyu, Hukuoka, Japan, 5Chikamori Rehabilitation Hospital, Rehabilitation, Nijuudaimachi, Kochi, Japan, 6Kure Orthopedic Clinic, Rehabilitation, Kure, Hiroshima, Japan, 7Kure Medical Association Hospital, Rehabilitation, Kure, Hiroshima, Japan
Background: Muscle weakness in the lower extremity, especially quadriceps muscle, is considered as one of the risk factor of knee osteoarthritis (OA) by leading to increased mechanical stress in the lower limb. Whereas, previous study has reported that a combination of ankle plantar flexor gastrocnemius muscle weakness and running exercise also alters cartilage metabolism in knee joint. However, the effect of gastrocnemius muscle weakness alone on the knee joint integrity is still unclear.
Purpose: The purpose of this study is to elucidate the effects of gastrocnemius muscle weakness on the knee joint cartilage and subchondral bone by morphological analyses using histological, biomechanical, and microstructural techniques in a rat model.
Methods: Fifteen male Wistar rat (4-6 months old) were used in this study. Muscle weakness was induced by injection of botulinum toxin type A (BTX, 2 units/kg body weight each) into the right gastrocnemius muscle totally 3 times 4 weeks apart in BTX group (n = 10). The gastrocnemius muscle weakness was confirmed by 3D motion analysis in kinematic features of the hindlimb during locomotion as an increased maximal dorsiflexion angle during the stance phase. Age-matched untreated animals were used as controls (n = 5). At 12 weeks after the first injection, knee joints from both sides and the gastrocnemius muscle were harvested. Muscle samples were used for histological study. Both knees from 5 animals in BTX group and right knees in control group were used for histological and micro-CT analysis, and both knees from the rest of animals in BTX group and left knees in control group were investigated biomechanical properties of joint cartilage in the medial and lateral tibia plateau.
Results: Intramuscular BTX injection decreased the gastrocnemius muscle wet weight (30% of the control) with severe myofiber atrophy. In locomotion analysis, increased dorsiflexion angle during the stance phase representing gastrocnemius muscle weakness were confirmed from 1 week onward. In the knee joint cartilage, there was no difference between BTX group and control group in the cartilage thickness and the chondrocyte number as well as biomechanical parameters in both plateau of tibia. In the trabecular subchondral bone, however, the ratio of bone volume to tissue volume (P = 0.018), trabecular thickness (P = 0.016), bone mineral content to total bone (P = 0.024) were decreased, and trabecular separation (P = 0.013) were increased in lateral tibia plateau in BTX group compared to the control group. Whereas, there was no difference between both groups in all parameters of subchondral trabecular bone in medial tibia plateau.
Conclusion(s): BTX-induced gastrocnemius muscle weakness leads to alterations in locomotion pattern and decrease in subchondral bone morphologically, but not apparent changes in the knee joint cartilage.
Implications: It is known that subchondral bone changes are closely associated with knee OA. Ankle muscle weakness may alter the mechanical environment of the knee and impair the integrity of knee joint. This study provides the possibility of contribution of ankle muscle dysfunction on the breakdown of knee joint integrity, and subsequent generation and progression of knee OA.
Keywords: Botulinum toxin, gastrocnemius muscle, knee joint
Funding acknowledgements: This work was supported by JPJS KAKENHI Grant number JP17KO1548
Purpose: The purpose of this study is to elucidate the effects of gastrocnemius muscle weakness on the knee joint cartilage and subchondral bone by morphological analyses using histological, biomechanical, and microstructural techniques in a rat model.
Methods: Fifteen male Wistar rat (4-6 months old) were used in this study. Muscle weakness was induced by injection of botulinum toxin type A (BTX, 2 units/kg body weight each) into the right gastrocnemius muscle totally 3 times 4 weeks apart in BTX group (n = 10). The gastrocnemius muscle weakness was confirmed by 3D motion analysis in kinematic features of the hindlimb during locomotion as an increased maximal dorsiflexion angle during the stance phase. Age-matched untreated animals were used as controls (n = 5). At 12 weeks after the first injection, knee joints from both sides and the gastrocnemius muscle were harvested. Muscle samples were used for histological study. Both knees from 5 animals in BTX group and right knees in control group were used for histological and micro-CT analysis, and both knees from the rest of animals in BTX group and left knees in control group were investigated biomechanical properties of joint cartilage in the medial and lateral tibia plateau.
Results: Intramuscular BTX injection decreased the gastrocnemius muscle wet weight (30% of the control) with severe myofiber atrophy. In locomotion analysis, increased dorsiflexion angle during the stance phase representing gastrocnemius muscle weakness were confirmed from 1 week onward. In the knee joint cartilage, there was no difference between BTX group and control group in the cartilage thickness and the chondrocyte number as well as biomechanical parameters in both plateau of tibia. In the trabecular subchondral bone, however, the ratio of bone volume to tissue volume (P = 0.018), trabecular thickness (P = 0.016), bone mineral content to total bone (P = 0.024) were decreased, and trabecular separation (P = 0.013) were increased in lateral tibia plateau in BTX group compared to the control group. Whereas, there was no difference between both groups in all parameters of subchondral trabecular bone in medial tibia plateau.
Conclusion(s): BTX-induced gastrocnemius muscle weakness leads to alterations in locomotion pattern and decrease in subchondral bone morphologically, but not apparent changes in the knee joint cartilage.
Implications: It is known that subchondral bone changes are closely associated with knee OA. Ankle muscle weakness may alter the mechanical environment of the knee and impair the integrity of knee joint. This study provides the possibility of contribution of ankle muscle dysfunction on the breakdown of knee joint integrity, and subsequent generation and progression of knee OA.
Keywords: Botulinum toxin, gastrocnemius muscle, knee joint
Funding acknowledgements: This work was supported by JPJS KAKENHI Grant number JP17KO1548
Topic: Musculoskeletal: lower limb; Rheumatology; Sport & sports injuries
Ethics approval required: Yes
Institution: Hiroshima International University
Ethics committee: Committee of Research Facilities for Laboratory Animal Sciences
Ethics number: AE17-019
All authors, affiliations and abstracts have been published as submitted.
