Participants were asked to wear their Fitbit TM daily during waking hours (removing for water-based activities), and sync the device at least every three days during the study period of 90 days. We downloaded step count data from each participant's Fitbit TM using the product interface (www. fitbit.com). For each day of the 90-day period, a minimum of 1500 steps was needed to be recorded by the device for that day to be considered a valid day. Average daily step count was presented as mean (±SD). Participants were classified as physically inactive (5000-7499 steps/day), moderately active (7500-9999 steps/day), physical active (10,000 steps/day), and very active (12,500 steps/day) (Tudor-Locke & Basset, Sports Med, 2004). The associations between step count and health-and knee-related quality of life were evaluated with Pearson correlation coefficients (r). Results: Thirty-two participants with PF OA were included (Table 1). Participants reported moderate to severe knee-related symptoms, with the greatest limitations reported on the pain and function in activities of daily living subscales of KOOS. The mean (±SD) daily step count was 9660±3455 (range 5148 to 17380), and the average number of valid days was 87±6 (range, 67 to 90). 34% of participants were classified as physically inactive, 25% were moderately active, 22% were physically active, and Values represent median (range). g¼grams, IU¼international units, kcal¼kilocalories, mg¼milligrams, n¼number of participants, mg¼micrograms Abstracts / Osteoarthritis and Cartilage 28 (2020) S86eS527 S391

Peculiarities of the morphology of some phenotypes of experimental osteoarthrosis was studied in experiments on rats. Reorganization of the knee articular cartilage of Wistar rats during aging (age-associated phenotype), obesity (metabolic phenotype), circulatory disturbances (e.g., chronic heart failure), and their combinations (polymorbidity) was studied by hematoxylin and eosin staining, immunohistochemical staining for collagen II and caspase 3, and morphometry. High sensitivity of the cartilage to non-traumatic influence of different anthropomorphic factors was demonstrated; morphological changes in osteoarthrosis of different genesis. The most pronounced pathological changes were observed in polymorbid animals, which allowed developing a new pathogenetically substantiated model of nontraumatic osteoarthrosis.

Structural-and-functional reorganization of the synovial membrane and articular cartilage in the knee joint was studied in rats with experimental chronic heart failure. Separation of fibers, decrease in the relative volume density of microcirculatory vessels, and increase in the expression of MMP-9 and caspase 3 were found in the synovial membrane. A decrease in the thickness of the surface layer (tendency to erosion), vacuolization and necrosis of chondrocytes, and increase in their readiness to programmed cell death were observed in the articular cartilage. Changes in the content of type II collagen and metachromasia were revealed in the cartilage matrix. These changes illustrate the development of degenerative arthropathy in cartilage components.