Knee osteoarthritis is a chronic disease common in middle-aged and older adults, characterized by functional impairment and reduced quality of life due to pain. While physical examination and radiographic Kellgren-Lawrence grading are frequently used in clinical evaluation, the severity of pain does not always correlate with the degree of structural degeneration. Ultrasonography is gaining prominence in osteoarthritis research due to its advantage of simultaneously evaluating both inflammatory and structural components, such as synovial hypertrophy, effusion, power Doppler signal, and osteophytes. The Outcome Measures in Rheumatology (OMERACT) working group has developed a standardized, multidimensional ultrasound scoring system for knee osteoarthritis, and this method is frequently used in the literature. This method consists of a diagnostic ultrasound examination lasting approximately 8-10 minutes. The examination evaluates the anatomical structures of the knee and also includes soft tissue examinations such as synovial hypertrophy. With this method, a diagnostic ultrasound examination lasting approximately 8-10 minutes is performed. The examination evaluates the anatomical structures of the knee and also includes soft tissue examinations such as synovial hypertrophy. Considering the differences between societies in cultural, genetic, biomechanical, body mass index distribution, and healthcare system practices, direct validity, clinical interpretability, and inter-study comparability are of significant importance. The validity, reliability, and applicability of the OMERACT osteoarthritis ultrasound scoring system have been reported in a study conducted on the Egyptian population. However, there is no data on the validity and reliability of OMERACT ultrasound scoring in the Turkish population. This study is the first prospective validation study aimed at establishing standardization for use in clinical practice in Turkey.

Inclusion Criteria:

• Adults aged 45 years and older
• Patients diagnosed with knee osteoarthritis clinically or radiographically
• Being in a clinical condition that allows tolerance of ultrasound evaluation of both knees
• Being able to provide written informed consent for participation in the study
• Having sufficient cognitive ability to understand Turkish forms and scales

Exclusion Criteria:

• Diagnosis of inflammatory arthritis (rheumatoid arthritis, psoriatic arthritis, gout, CPPD, etc.)
• Intra-articular injection into the knee joint within the last 6 months (corticosteroid, hyaluronic acid, PRP, etc.)
• Previous major knee surgery (total knee replacement, major ligament reconstruction, etc.)
• Acute pathology that has developed within the last 6 weeks, such as acute trauma/fracture/ligament injury
• Severe deformity or severe movement restriction that technically prevents ultrasound examination
• Active infection/systemic febrile condition
• Neurological disease causing motor or sensory deficit in the lower extremities
• Use of Gabapentinoid/SNRI/SSRI due to fibromyalgia or psychiatric illness
• Severe cognitive impairment or communication problems that would prevent participation in the study
• Pregnancy
• Subjects who have been informed about the study and refuse to participate

This study will include patients aged 45 years and older who have been diagnosed with knee osteoarthritis based on clinical and radiological evaluation and who have applied to the Physical Medicine and Rehabilitation Outpatient Clinic at İzmir Democracy University Buca Seyfi Demirsoy Education and Research Hospital.

Individual participant data (IPD) will not be shared because the data contain potentially identifiable sensitive clinical information, and sharing was not covered in the original informed consent provided to participants. Additionally, institutional and national data protection regulations limit the transfer of raw, de-identified individual-level data outside the research team.