Clinical Importance of Occult Suprapatellar Effusion in Knee Osteoarthritis

Small amounts of fluid in the knee joint may not always be visible during a standard ultrasound examination performed while the leg is relaxed. When the quadriceps muscle contracts, this fluid may move into the area above the kneecap and become visible. This finding is referred to in this study as occult suprapatellar effusion. The aim of this study is to determine whether occult suprapatellar effusion is associated with knee pain and physical function in people with knee osteoarthritis. Participants will undergo ultrasound examination first at rest and then during quadriceps contraction. Based on these findings, they will be classified as having effusion visible at rest, occult effusion visible only during muscle contraction, or no effusion in either condition. Knee pain, self-reported symptoms and function, and chair stand performance will be compared among these groups. The study will also examine whether greater effusion depth is associated with more severe pain, greater functional limitation, and poorer physical performance. No treatment will be assigned as part of the study.

Inclusion Criteria: * Age 40-80 years * Clinical diagnosis of primary knee osteoarthritis and radiographic Kellgren-Lawrence grade 2, 3, or 4 * Pain in the knee to be evaluated * Ability to perform voluntary quadriceps contraction and the 30-second chair stand test * Provision of written informed consent Exclusion Criteria: * Inflammatory rheumatic disease, crystal arthropathy, or active joint infection * Intra-articular injection into the evaluated knee within the previous 3 months * History of major surgery on the evaluated knee * Marked varus or valgus deformity * Knee trauma within the previous 3 months * Inability to perform adequate voluntary quadriceps contraction * Neurological, cardiopulmonary, or other musculoskeletal disease that may substantially affect chair stand performance * Pregnancy