Knee osteoarthritis is a common joint disease that causes pain, stiffness, and limitations in daily activities, especially in older adults. Changes in the alignment of the lower limb, called the anatomical axis, can increase the mechanical load on the knee joint and may affect pain and mobility. This study aims to investigate the relationship between the anatomical axis measured on knee X-rays and patients' pain levels, functional status, quality of life, and fear of movement (kinesiophobia).

This is a single-center, observational, cross-sectional study. Adult patients diagnosed with knee osteoarthritis who have a standard knee X-ray taken within the last 6 months and who volunteer to participate will be included. Pain will be measured with the Visual Analog Scale (VAS), functional status with the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), quality of life with the 36-Item Short Form Health Survey (SF-36), and kinesiophobia with the Tampa Scale for Kinesiophobia (TSK). The femoro-tibial angle and joint space width will be measured on X-rays by two independent observers.

By examining the relationship between radiographic alignment and clinical findings, this study may provide new insights into the comprehensive evaluation of knee osteoarthritis and help guide treatment planning for patients.

Knee osteoarthritis (OA) is a prevalent degenerative joint disease that leads to pain, disability, and reduced quality of life, particularly in older adults. Alterations in lower limb alignment, specifically deviations of the anatomical (mechanical) axis such as varus or valgus deformities, play a key role in the development and progression of OA by altering joint load distribution. Varus alignment is commonly associated with medial compartment OA, whereas valgus alignment is related to lateral compartment OA. Previous studies have reported that such malalignment may accelerate structural damage, increase pain, and contribute to functional impairment.

In addition to structural changes, chronic pain in OA patients can lead to fear of movement, known as kinesiophobia, which further limits physical activity and negatively affects functional outcomes. However, there are limited studies that simultaneously evaluate the relationship between radiographic alignment, pain, functional capacity, quality of life, and kinesiophobia.

This single-center, observational, cross-sectional study will be conducted at the outpatient Physical Medicine and Rehabilitation clinics of Istanbul Physical Medicine and Rehabilitation Training and Research Hospital. The target sample size is 100 patients with knee OA, based on a priori power analysis. Eligible participants must have an anteroposterior knee X-ray taken within the last six months. Pain intensity will be assessed with the Visual Analog Scale (VAS), functional status with the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), quality of life with the Short Form-36 (SF-36), and kinesiophobia with the Tampa Scale for Kinesiophobia (TSK). Radiographic measurements, including femoro-tibial angle and joint space width, will be performed by two independent observers using standardized procedures.

Collected data will be analyzed using appropriate statistical methods. The findings are expected to provide a more comprehensive understanding of the relationship between anatomical axis alignment and clinical outcomes in knee OA. This may contribute to more effective treatment planning and patient management.

Inclusion Criteria:

• Diagnosis of knee osteoarthritis (clinical and radiographic)
• Having an anteroposterior knee X-ray taken within the last 6 months
• Voluntary agreement to participate in the study
• Cognitive ability sufficient to understand test instructions

Exclusion Criteria:

• History of knee surgery
• Illiteracy (inability to read/write)
• Refusal to participate
• Presence of orthopedic conditions that prevent walking (e.g., amputation, joint prosthesis)

Adult patients diagnosed with knee osteoarthritis who are admitted to the Physical Medicine and Rehabilitation outpatient clinics of Istanbul Physical Medicine and Rehabilitation Training and Research Hospital. Participants must have a knee X-ray taken within the last 6 months and meet the study's eligibility criteria.

De-identified individual participant data (IPD), including demographic information, pain scores (VAS), functional outcomes (WOMAC), quality of life scores (SF-36), kinesiophobia scores (TSK), and radiographic measurements (femoro-tibial angle, joint space width), will be shared. Data will be made available upon reasonable request from qualified researchers with ethics committee approval and a signed data use agreement.

De-identified individual participant data and supporting documents (protocol, SAP, ICF) will be available beginning 6 months after study completion (September 2026) and will remain available for up to 2 years (until March 2028).

Qualified researchers with approval from an independent ethics committee and a signed data use agreement will be granted access to de-identified individual participant data (IPD) and supporting documents (study protocol, statistical analysis plan, informed consent form). Data will be shared in anonymized format to ensure patient confidentiality. Access requests should be submitted to the principal investigator, and data will be provided electronically after approval.