This observational cohort study aimed to comprehensively assess the muscle quality of gluteus, quadriceps femoris, and calf muscles. Seventy-seven patients with knee osteoarthritis scheduled for total knee arthroplasty participated in this retrospective cohort study. The cross-sectional area (CSA) of the lower limb muscles was assessed using computed tomography images, and muscular attenuation was evaluated in Hounsfield Units (HU). Muscle quality was categorized into four groups based on HU values:​ intramuscular fat tissue, very low-density muscle (VLDM), low-density muscle (LDM), and normal-density muscle. The ratio of the four tissue CSAs was calculated and compared between surgical scheduled side (affected side) and contralateral side or among gluteus, quadriceps femoris, and calf muscles. The results revealed affected side had a lower ratio of normal-density muscle in all muscle groups compared to contralateral side. In addition, gluteus had the highest intramuscular fat tissue CSA ratio, followed by the calf muscles and quadriceps femoris. Gluteus also had significantly higher ratios of VLDM and LDM than quadriceps femoris and calf muscles. The ratio of normal-density muscle CSA was the lowest in the gluteus, followed by the calf muscles and quadriceps femoris. This study provides a detailed characterization of lower limb muscle quality in patients with knee osteoarthritis, demonstrating that gluteus have higher fat infiltration and lower normal-density muscle compared to the quadriceps femoris and calf muscles. These findings highlight the importance of assessing muscle quality in gluteus, quadriceps femoris, and calf muscles for optimal rehabilitation planning in patients with knee osteoarthritis.