The Comparison of Hip Abductors with Hip External Rotator Muscles Fatigue on Static Standing Balance in Subjects with and without Patellofemoral Pain Syndrome

Purpose: The patellofemoral pain syndrome (PFPS) is one of the most common musculoskeletal disorders of the knee joint. Hip muscles’ weakness is one of the reasons for PFPS occurrence. The aim of this study was to recognize the effective muscle group in prevention and treatment of patients with PFPS. Methods: This is a prospective and quasi-experimental study in which 30 participants (15 healthy/15 patients) who were aged between 18 and 38 years were recruited through nonprobability simple sampling. Exhaustion process of hip abductors and hip external rotator muscles was performed using Delorme method in separate sessions with a rest interval of at least 48 hours. Then, the parameters of pressure center were measured on the anterior, internalexternal plates using Force Plate System. Results: Before the exhaustion process, parameters of the displacement length of the pressure center on the internal-external plate (P = 0.002) and the sum of the pressure center displacement length on the internal-external plate (P=0.052) were higher in the patients group. After the occurrence of fatigue in the abductor muscles of the control group, the sum of the pressure center displacement length on the internal-external plate (P = 00.1) and the velocity of the pressure center displacement length on the anterior plate (P = 0.001) and the internal-external plate (P = 0.016) were significantly increased. But in the patients group, all of the above mentioned parameters were decreased after fatigue in both the rotator muscles (P = 0.005, P = 0.054, P = 0.038) and the abductor muscles (P = 0.045, P = 0.005, P = 0.004). Conclusion: Before the induction of fatigue, patients had more postural swing than the control group. As the fatigue increased in the abductor and the external rotator muscles, the postural swing increased in the control group but decreased in the patients group. In healthy subjects, the fatigue of abductor muscles has a greater role in postural disturbance but there was no significant difference between the fatigue in abductor and rotator muscles in patients with PFPS.