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Abstract. BACKGROUND: Knee osteoarthritis (OA) is suggested to be induced by multi-factors, and mechanical environment is regarded as a risky factor. OBJECTIVE: To investigate the effect of isolated mechanical factor on cartilage. METHODS: An active wear test system was designed to perform parameters-controlled in vitro wear tests on rat knee joints with specific load magnitude, flexion-extension angle, and movement frequency. Six hind limbs of 9-month-old male SpragueDawley rats, with an additional spring on the medial side, were worn by using the custom-designed apparatus. Researchers observed both the menisci and tibial cartilages of these hind limbs using multiphoton laser scanning microscopy to analyze the change of the collagen microstructure caused by wear. RESULTS: Collagen microstructure of both the medial and lateral meniscus became disordered under cyclic load. Some tissues on the surface of the medial tibial cartilage were removed and the middle layer of the medial compartment displayed cracks. On the contrary, the lateral tibial cartilage was intact. CONCLUSIONS: The results implied that cyclic load caused menisci microstructure disarrangement prior to tibial cartilage damage and the collagen structure of mid-layer tibial cartilage failed before that of the superficial layer under the kinematics adopted in the study.

respectively. Ten of 18 subjects (56%) were classified as the vitamin D deficiency group, while remaining 8 subjects (44%) were classified as the vitamin D insufficiency or sufficiency group. Mean serum calcium (adjusted for the serum albumin level, if it was 4.0 g/dl or less), phosphorus and bone alkaline phosphatase (BAP) levels of the subjects were within the reference range. No one was diagnosed with osteomalacia. No significant difference of total osteophyte length was observed between vitamin D deficiency and vitamin D insufficiency or sufficiency groups. However, cartilage OS of the vitamin D deficiency group (1.8 mm) was significantly longer than that of the vitamin D insufficiency or sufficiency group (1.0 mm, p¼0.001). s25(OH)D level was correlated with JKOM (r¼-0.55, p¼0.029), LDFA (r¼-0.49, p¼0.037), bone OP length (r¼0.48, p¼0.047) and cartilage OP length (r¼-0.62, p¼0.006). A linear regression analysis indicated that the cartilage OP length was mostly associated with s25(OH)D levels [b¼-8.39, p¼0.015]. Conclusions: The lower s25(OH)D levels, the longer cartilage OP length in patients with knee OA, suggesting the association between vitamin D status and osteophyte mineralization.