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Supplemental digital content is available in the text. Objective: The aim of the study was to determine whether tibiofemoral contact stress predicts risk for worsening knee pain over 84 ms in adults aged 50–79 yrs with or at elevated risk for knee osteoarthritis. Design: Baseline tibiofemoral contact stress was estimated using discrete element analysis. Other baseline measures included weight, height, hip-knee-ankle alignment, Kellgren-Lawrence grade, and Western Ontario and McMaster Universities Osteoarthritis Index pain subscale. Logistic regression models assessed the association between baseline contact stress and 84-mo worsening of Western Ontario and McMaster Universities Osteoarthritis Index pain subscale. Results: Data from the dominant knee (72.6% Kellgren-Lawrence grade 0/1 and 27.4% Kellgren-Lawrence grade ≥ 2) of 208 participants (64.4% female, mean ± SD body mass index = 29.6 ± 5.1 kg/m2) were analyzed. Baseline mean and peak contact stress were 3.3 ± 0.9 and 9.4 ± 4.3 MPa, respectively. Forty-seven knees met the criterion for worsening pain. The highest tertiles in comparison with the lowest tertiles of mean (odds ratio [95% confidence interval] = 2.47 [1.03–5.95], P = 0.04) and peak (2.49 [1.03–5.98], P = 0.04) contact stress were associated with worsening pain at 84 mos, after adjustment for age, sex, race, clinic site, and baseline pain. Post hoc sensitivity analyses including adjustment for body mass index and hip-knee-ankle alignment attenuated the effect. Conclusions: These findings suggest that elevated tibiofemoral contact stress can predict the development of worsening of knee pain. [ABSTRACT FROM AUTHOR]

Supplemental digital content is available in the text. Objective: The aim of the study was to assess the effectiveness of a hybrid training system with walking that simultaneously applies electrical stimulation to the knee extensors/flexors during walking in obese women with knee pain. Design: This is a randomized, single-blind (assessor), controlled trial. Twenty-eight obese women with knee pain were randomized to 12 weeks of biweekly walking with either hybrid training system with walking or with transcutaneous electrical nerve stimulation (control). Primary outcomes (maximum isokinetic knee extensor torque and maximum isokinetic knee flexor torque) and secondary outcomes (20-m walk time, chair-stand time, stair-climb time, knee pain, and knee-related quality life) were evaluated. Change-point regression analyses were used to model the interaction for the primary outcomes. Two-sample t tests were used on pre-post change scores in secondary outcomes. Results: Knee extensor torque increased significantly more in the hybrid training system with walking group than the control group when baseline knee extensor torque was greater than 57.2 Nm (P = 0.0033). When baseline knee flexor torque was at 30 or 50 Nm, there was a trend toward greater increase in the hybrid training system with walking group than the control group (P = 0.0566, P = 0.0737, respectively). There were no significant differences between groups in secondary outcomes. Conclusions: These results suggest that hybrid training system with walking is effective for improving knee extensor torque in obese women with knee pain. However, the superiority of hybrid training system with walking may vary depending on baseline knee muscle strength. [ABSTRACT FROM AUTHOR]