Effects of short-term gentle treadmill walking on subchondral bone in a rat model of instability-induced osteoarthritis.
OBJECTIVE
Subchondral bone cyst (SBC) growth, caused by osteoclast activity during early knee osteoarthritis (OA) pathogenesis, should be treated to prevent further progressions of OA. In the present study, we evaluated the effects of gentle treadmill walking on subchondral bone and cartilage changes in an experimental rat model of destabilized medial meniscus (DMM).


METHODS
Twelve-week-old Wistar rats underwent DMM surgery in their right knee and sham surgery in their left knee and were assigned to either the sedentary group or walking group (n = 42/group). Animals in the walking group were subjected to treadmill exercise 2 days after surgery, which included walking for 12 m/min, 30 min/day, 5 days/week for 1, 2, and 4 week(s). Subchondral bone and cartilage changes were evaluated by micro-CT analysis, histological analysis, and biomechanical analysis.


RESULTS
Treadmill walking had a tendency to suppress SBC growth, which was confirmed by micro-CT (P = 0.06) and positive staining for tartrate-resistant acid phosphatase (TRAP) activity for the osteoclast number per bone surface (P = 0.09) 4 weeks after surgery. These changes coincide with the prevention of cartilage degeneration as evaluated by the Osteoarthritis Research Society International (OARSI) score (P < 0.05) and biomechanically softening (P < 0.05). Furthermore, treadmill walking could suppressed increasing osteocyte deaths (P < 0.01), which was positively correlated with the OARSI score (r = 0.77; P < 0.01).


CONCLUSIONS
These results indicate biomechanical and biological links exist between cartilage and subchondral bone; preventive effects of treadmill walking on subchondral bone deterioration might be partly explained by the chondroprotective effects.
Department of Motor Function Analysis, Human Health Sciences, Graduate School of Medicine, Kyoto University, Japan. Electronic address: iijima.hirotaka.75s@st.kyoto-u.ac.jp.
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Iijima
Department of Development and Rehabilitation of Motor Function, Human Health Sciences, Graduate School of Medicine, Kyoto University, Japan. Electronic address: aoyama.tomoki.4e@kyoto-u.ac.jp.
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Aoyama
Department of Motor Function Analysis, Human Health Sciences, Graduate School of Medicine, Kyoto University, Japan. Electronic address: ito.akira.27n@st.kyoto-u.ac.jp.
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Ito
Department of Motor Function Analysis, Human Health Sciences, Graduate School of Medicine, Kyoto University, Japan. Electronic address: yamaguchi.shouki.26n@st.kyoto-u.ac.jp.
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Yamaguchi
Department of Motor Function Analysis, Human Health Sciences, Graduate School of Medicine, Kyoto University, Japan. Electronic address: nagai.momoko.36v@st.kyoto-u.ac.jp.
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Nagai
Department of Motor Function Analysis, Human Health Sciences, Graduate School of Medicine, Kyoto University, Japan. Electronic address: tajino.junichi.57z@st.kyoto-u.ac.jp.
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Tajino
Department of Motor Function Analysis, Human Health Sciences, Graduate School of Medicine, Kyoto University, Japan. Electronic address: zhang.xiangkai.48v@st.kyoto-u.ac.jp.
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Zhang
Department of Motor Function Analysis, Human Health Sciences, Graduate School of Medicine, Kyoto University, Japan. Electronic address: kuroki.hiroshi.6s@kyoto-u.ac.jp.
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Kuroki
D000135:Acid Phosphatase / Q000032:analysis; D000818:Animals; D017209:Apoptosis; D002358:Cartilage, Articular / Q000473:pathology; D016923:Cell Death; D004195:Disease Models, Animal; D005080:Exercise Test; D007150:Immunohistochemistry; D020287:In Situ Nick-End Labeling; D008297:Male; D008592:Menisci, Tibial / Q000503:physiopathology; D010003:Osteoarthritis / Q000473:pathology; D020370:Osteoarthritis, Knee / Q000473:pathology / Q000628:therapy*; D010011:Osteocytes / Q000473:pathology; D054850:Osteophyte / Q000473:pathology; D051381:Rats; D017208:Rats, Wistar; D013977:Tibia / Q000473:pathology; D016138:Walking; D055114:X-Ray Microtomography
D000135:Acid Phosphatase
Bone μCT; Exercise; Osteoarthritis; Osteoclasts; Subchondral bone cyst