BACKGROUND: Muscle function deterioration in female patients with severe knee osteoarthritis (KOA) is linked to alterations in muscle morphology, composition, and mechanical properties. This study evaluates thigh muscle features in female patients with severe KOA and explores correlations with knee joint function. METHODS: Ultrasound and shear wave elastography measured physiological cross-sectional area (PCSA), echo intensity (EI), and shear modulus (G) in the rectus femoris (RF), vastus lateralis (VL), vastus medialis (VM), biceps femoris long head (BFL), and semitendinosus (ST) of 24 KOA patients and 24 controls. EI indicates intramuscular fat, while G reflects stiffness. Muscle characteristics were compared between groups, and correlations with knee function scores (WOMAC, KSS, HSS) were analyzed. RESULTS: In patients, the symptomatic side displayed reduced PCSA for RF, VL, VM, BFL, and ST (15.85[Formula: see text], 28.18[Formula: see text], 21.53[Formula: see text], 11.67[Formula: see text], 6.59[Formula: see text] respectively) vs. controls (19[Formula: see text], 36.32[Formula: see text], 23.37[Formula: see text], 14.15[Formula: see text], 7.12[Formula: see text] respectively). EI was elevated (128.95, 121.12, 105.72, 90.52, 93.15) vs. controls (100.39, 93.97, 88.14, 77.69, 78.73), and G values (9.48 kPa, 7.88 kPa, 6.9 kPa, 7.2 kPa, 9.03 kPa) was higher than controls (8.85 kPa, 5.28 kPa, 5.98 kPa, 6.58 kPa, 6.73 kPa). BFL`s G, ST`s G, and VM`s EI, negatively correlated with knee function, whereas BFL`s PCSA positively correlated. The variable importance of BFL's PCSA and G ranked at the top in all scores. CONCLUSIONS: Compared to controls, PCSAs in muscles on both sides of KOA patients were lowered by up to 22%, indicative of muscle loss and diminished strength. The G value is 20.65% higher, suggesting poor flexibility and elevated passive tension. EI in muscles on both sides of KOA patients was greater, reaching up to 23.88%, possibly reducing contractile components and muscle force. G, PCSA, and EI are closely correlated with function scores, and PCSA and G of BFL are the most significant predictors of knee function. These results may help explain muscle dysfunction in KOA patients. CLINICAL TRIAL NUMBER: Not applicable.