Objective：To elucidate factors associated with physical function and clarify the actual condition of functional deterioration in patients with knee osteoarthritis (OA) prior to total knee arthroplasty (TKA)．

Methods：We enrolled 467 patients with severe knee OA and preoperatively assessed the following parameters：background factors (sex, age, BMI, K-L grade, and pain) and physical function (muscle strength of knee extensors and flexors, and knee joint angles). A multiple regression analysis was performed to determine the relationship between the independent background factors and dependent physical functions. The median of preoperative function based on selected factors of physical function was calculated.

Results：Based on the multiple regression analysis, sex, BMI, K-L grade, and pain statistically significantly correlated with muscle strength of knee extensors and flexors. Sex and BMI statistically significantly correlated with knee joint flexion angle. K-L grade statistically significantly correlated with knee joint extension angle. The median of muscle strength for knee extension was 0.98/0.92 Nm/kg (Grade 3/Grade 4) for males and 0.70/0.59 Nm/kg for females. The median of muscle strength for knee flexion was 0.53/0.45 Nm/kg for males, 0.36/0.30 Nm/kg for females. The median for knee joint flexion angle was 130° for males and 120° for females. The median for knee joint extension angle was -5°/-10° (Grade 3/Grade 4)．

Conclusion：We clarified the degree of muscle strength and range of motion before TKA in patients with knee OA. We believe that the findings obtained in this study will contribute to explaining the functional deterioration of patients with knee OA.