The aim of this study is to examine in detail the ultrasonographic characteristics of the vastus medialis obliquus and vastus medialis longus muscles in individuals with patellofemoral pain syndrome and to compare these findings with those of healthy individuals. It is anticipated that the results obtained will contribute to a better understanding of the muscle-based mechanisms of PFAS and provide a scientific basis for the development of muscle-specific assessment and intervention strategies in physical therapy and rehabilitation practices.

Patellofemoral pain syndrome (PFAS) is a musculoskeletal problem characterized by pain in the front of the knee joint, commonly seen in young and physically active individuals. The etiology of PFAS is multifactorial and is associated with abnormal loading of the patella within the femoral trochlear groove, alterations in joint biomechanics, and functional deficiencies of the surrounding soft tissues. These mechanical irregularities in the patellofemoral joint can lead to pain, loss of function, and activity limitations over time. The quadriceps femoris muscle group plays a fundamental role in providing dynamic stability to the patella. The vastus medialis obliquus (VMO) and vastus medialis longus (VML) muscles within this muscle group are critical for controlling the patella medially and maintaining its proper alignment within the femoral groove. It is known that the oblique fiber structure of the VMO muscle provides medial stabilizing force to the patella, while the VML muscle contributes to force production during knee extension and overall patellar guidance with its longer fibers. In individuals with PFAS, delayed activation patterns, decreased muscle strength, and morphological changes in the vastus medialis muscle have been reported. However, it is observed in the literature that the VMO and VML muscles are treated as a single structure in most studies, and the separate morphological characteristics of these two muscles and their relationship with patellofemoral pain have not been sufficiently investigated. However, the different anatomical, biomechanical, and functional characteristics of these muscles necessitate that their roles in PFAS pathophysiology be evaluated separately. Ultrasonography is a non-invasive, reliable, and reproducible imaging method for evaluating the morphological characteristics of muscle tissue and is increasingly used in clinical research. Ultrasonographic evaluation allows for the objective examination of muscle thickness, cross-sectional area, and architectural features, thereby providing important information about structural changes in muscle function. The aim of this study is to examine in detail the ultrasonographic characteristics of the vastus medialis obliquus and vastus medialis longus muscles in individuals with patellofemoral pain syndrome and to compare these findings with healthy individuals. It is anticipated that the results will contribute to the understanding of the muscle-based mechanisms of PFAS and provide a scientific basis for the development of muscle-specific assessment and intervention strategies in physical therapy and rehabilitation practices.

Inclusion Criteria:

• Between the ages of 18 and 65
• Have had localized pain in the front of the knee for at least the past 3 months
• Experience pain during activities that require stair climbing, squatting, prolonged sitting, or knee flexion
• Have been diagnosed with patellofemoral pain syndrome based on clinical evaluation
• Volunteer to participate in the study and sign the informed consent form

Exclusion Criteria:

• History of previous surgery on the knee joint
• History of significant trauma to the knee region within the last 6 months
• Diagnosis of meniscus, ligament injuries, knee osteoarthritis, or inflammatory rheumatic disease
• Neurological diseases or systemic diseases affecting the musculoskeletal system
• Presence of other lower extremity pathologies causing pain at a level that could affect measurements

The study will include individuals aged 18-65 who have been diagnosed with patellofemoral pain syndrome, as well as healthy volunteers with similar characteristics in terms of age and gender. The study group will consist of individuals who have applied to a physical therapy and rehabilitation clinic or who have been referred to relevant units. The control group will be selected from healthy volunteers who do not have any knee pain or lower extremity musculoskeletal problems.