A Research Of Risk Factors For Patellofemoral Pain Based On The Lower Extremity Biomechanics

Purpose: Patellofemoral pain is one of the most common overuse injuries in lower extremity,the risk factors of patellofemoral pain are still controversial,the compensatory movement caused by pain may raise the difficult to determine the risk factors through case-control study.This study compared the biomechanics of patients with patellofemoral pain between pain and pain-free situation to determine the effects of pain on lower extremity movement patterns,also comaperd the biomechanics between pain-free patients and non-injured subjects to determine the effects of injury on lower extremity movement patterns.This study aims to providing a new method to investigate the risk factors in sport injuries,and promoting the understanding of risk factors for patellofemoral pain,also this study is a theoretical basis for the prevention and treatment of patellofemoral pain in sports.Methods: 15 male and 10 female amateur runners with patellofemoral pain were recruited as experimental group.According to the information of experimental group,25 non-injuried amateur runners were matched as control group.The experimental group executed biomechanical tests in both pain and pain-free situation,while control group only executed biomechanical test one time.Three-dimentional kinematic and kinetic data,as well as EMG data in the running and drop vertical jump tasks were collected.A two-way analysis of variance with a mixed design was performed to determine the effects of pain and male,or injury and male on the lower extremity biomechanics in running and drop vertical jump tasks.Results: Significant biomechanical differences were observed in patients between pain and pain-free situation.Pain decreased the peak hip external rotation angle,peak knee abduction angle,peak knee external rotation moment and peak horizontal ground reaction force in the running task for male and/or female participants.Also,pain decreased the peak hip external rotation angle,peak knee abduction angle,peak knee extension moment and peak knee external rotation moment,as well as peak patellofemoral joint stress in the drop vertical jump task for male and/or female participants.Significant biomechanical differences were also observed between painfree patients and non-injured subjects.The pain-free male and/or female patients showed greater peak hip adduction angle,peak hip external rotation angle,peak knee flexion angle and peak knee abduction angle,as well as greater peak knee external rotation moment and peak horizontal ground reaction force in the running task.Meanwhile,the pain-free male and/or female patients showed greater peak hip external rotation angle,knee flexion angle at initial contact with ground,peak knee flexion angle and peak knee abduction angle,as well as greater peak knee extension moment,peak knee adduction moment and peak patellofemoral joint stress in the drop vertical jump task.No significant pain or injury effects on EMG data were found in any task for either female or male participants.Conclusions:(1)Pain could compensatory alter the lower extremity kinematics in functional movement.(2)Pain could reduce the knee joint local load through the protection mechanisms,hwoever the pain effects were gender and task specific.(3)The biomechanical risk factors of patellofemoral pain were multi-factors,the greater knee flexion angle,hip adduction and external rotation angle,as well as three-dimensional knee moment and patellofemoral joint stress may result in the development of patellofemoral pain,however these lower extremity biomechanics were gender and task specific.(4)Significant differences in peak knee abduction angle were found in both tasks and genders,the increased knee abduction angle may be the primary biomechanical factors to cause the patellofemoral pain.(5)A gender difference may exist among the biomechanical factors which could cause the patellofemoral pain.