Muscle Oxygenation and Recovery Dynamics in Individuals With Knee Osteoarthritis: A Case-Control Study

Knee osteoarthritis (OA) is a degenerative joint disorder associated with pain, muscle weakness, and functional limitations that negatively affect lower extremity muscle performance. Previous studies have reported structural and physiological alterations in the quadriceps muscle in individuals with knee OA, particularly in the vastus medialis obliquus (VMO). These alterations include reduced muscle cross-sectional area, increased intramuscular fat infiltration, vascular changes, and impaired neuromuscular activation, which may contribute to decreased knee joint stability and progression of the disease.

Muscle oxygenation (SmO₂) is an important physiological parameter reflecting the balance between oxygen delivery and utilization in skeletal muscle and provides objective information about muscle metabolic and circulatory function. Despite the potential relevance of SmO₂ in understanding quadriceps dysfunction in knee OA, studies investigating exercise-induced oxygenation responses and recovery dynamics in this population remain limited.

This observational, comparative cross-sectional study aims to evaluate VMO SmO₂ dynamics in individuals with knee OA and compare these parameters with healthy controls matched for age and sex. The study will also investigate the associations between SmO₂ parameters, muscle strength, functional performance, and pain intensity.

Individuals diagnosed with knee OA by a physical medicine and rehabilitation physician and healthy volunteers meeting the eligibility criteria will be invited to participate. Written informed consent will be obtained from all participants prior to participation. Participants who meet the inclusion criteria will be allocated into two groups: a knee OA group and a healthy control group. All participants will undergo the same assessment procedures during a single evaluation session.

In accordance with the recommendations of Osteoarthritis Research Society International (OARSI), in participants with bilateral knee OA, the target knee for analysis will be determined using a predefined strategy: (1) the knee with greater pain at rest or during activity will be selected; (2) if pain levels are equal, the knee with greater radiographic severity (Kellgren-Lawrence grade) will be selected; (3) if both pain and radiographic severity are equal, the dominant leg (the extremity preferred for kicking a ball) will be designated as the target knee. The target knee will serve as the reference knee for follow-up measurements, including SmO₂ and knee-specific clinical assessments.