Echo intensity (EI) assessment using ultrasonography helps monitoring disease-induced muscle quality changes. However, there are no study investigating the reliability of EI in patients with knee osteoarthritis (OA). The primary aim of the present study was to investigate the inter and intra-rater reliability of EI evaluation by grayscale histogram analysis of quadriceps femoris muscle in patients with knee OA. The second aim was to compare the mean grayscale values obtained using both the Free Hand Tool (FHT) and Rectangular Marquee Tool (RMT) methods in ImageJ. Thirty patients with knee OA were included in this cross-sectional study. The echogenicity measurements of the Rectus Femoris, Vastus Inter-medius, Vastus Lateralis and Vastus Medialis were performed by two different researchers. Reliability analysis of EI measurements were calculated with using intraclass correlation coefficient (ICC), standard error of measurement (SEM) and coefficient of variation (CV) and Bland and Altman plot analysis.

Inclusion Criteria:

• Patients had tibiofemoral joint OA in at least one knee according to the American College of Rheumatology classification criteria with knee pain most days of the past month and osteophytes apparent on knee radiograph were included to the study

Exclusion Criteria:

• Patients were excluded if they had a history of lower limb joint replacement and fracture, rheumatoid arthritis, diabetic neuropathy or polyneuropathy, and cardiovascular and neuromuscular problems.

Patients had tibiofemoral joint OA in at least one knee according to the American College of Rheumatology classification criteria with knee pain most days of the past month, and osteophytes apparent on knee radiograph were included to the study. Patients were excluded if they had a history of lower limb joint replacement and fracture, rheumatoid arthritis, diabetic neuropathy or polyneuropathy, and cardiovascular and neuromuscular problems.