Background: Patellofemoral pain syndrome (PFPS) is a common functional disorder of knee joint. Its etiology involves biomechanical abnormalities and dynamic stability defects. Most of the existing studies focus on young people, and the biomechanical characteristics and functional compensation mechanism of middle-aged and elderly patients are still unclear. The Y-Balance test is becoming an important tool in PFPS research because of its sensitivity to assess the dynamic balance ability of lower limbs. Objective: To analyze the functional characteristics of lower limbs of PFPS patients aged 40-60 by Y-Balance test, and to explore the differences between PFPS patients and healthy people, so as to provide evidence for clinical rehabilitation. Methods: A cross-sectional observational study was conducted in 49 PFPS patients and 21 healthy controls. Y-Balance test was used to evaluate bilateral forward difference, composite score, lateral and posterior balance, symmetry ratio and bilateral difference. SPSS 25.0 was used for statistical analysis.

Inclusion Criteria:

• Aged between 40 and 60 years
• Clinically diagnosed with patellofemoral pain (PFP) with symptoms lasting ≥3 months
• No other serious lower extremity disorders
• No neurological diseases
• No history of recent lower extremity surgery (<12 months)
• No history of major lower extremity trauma
• Control group: Age- and sex-matched healthy volunteers without knee pain or lower limb dysfunction

Exclusion Criteria:

Acute inflammatory conditions Meniscus injury Knee ligament injury Intra-articular fracture Bone tumor Bone tuberculosis

Neurovascular injury including:

1. Stroke history
2. Parkinson's disease Subjective unwillingness to comply with testing Inability to complete Y-Balance Test

Serious systemic diseases affecting:

Cardiovascular system Hepatic function Renal function Hematological system

People with patellar pain