Mechanics of Single Leg Jumps During Exertion in Females with and without Patellofemoral Pain Syndrome

Abstract

Patellofemoral pain syndrome (PFPS) is often associated with abnormal lower extremity (LE) transverse and frontal plane kinematics, which are known to increase retropatellar contact pressure during weightbearing activities. Recent studies suggest that these LE rotations may be particularly evident during athletic activities when greater demands are placed on hip muscles that resist these rotations. Similarly, these abnormal rotations are likely to be more apparent as the capacity of these muscles to produce force decreases with exertion. PURPOSE: The purpose of this study was to compare hip strength and LE kinematics in females with and without PFPS during single leg jumps as they participated in an exertion protocol. METHODS: As part of an ongoing study, 18 healthy females (age = 24.4yr, weight = 60.8kg, height = 1.64m) and 15 females with PFPS (age = 23.3yr, weight = 60.3kg, height = 1.65m) participated. Hip external rotation (HER) and abduction (HABD)strength was measured at the beginning and conclusion of an exertion protocol. 3D LE kinematics were recorded during repetitive single leg jumps at five stages the protocol. RM mixed ANO VAs (group(2) x protocol stage(5)) were used to compare discrete hip and knee frontal and transverse plane variables believed to increase retropatellar contact pressure during weightbearing. RESULTS: Females with PFPS produced 13% less HABD (p= 0.06) and 12% less HER isometric force (p= 0.06) than healthy female subjects. Following the exertion protocol, females in both groups demonstrated decreased HABD (p< 0.001) and HER (p= 0.04) strength. With respect to the kinematic variables of interest, there were no interactions between factors or effects of exertion protocol stage. However, females with PFPS demonstrated greater hip adduction (p= 0.012), hip adduction excursion (p= 0.036), hip external rotation (p= 0.005), knee external rotation (p= 0.11), and knee external rotation excursion (p= 0.009) during single leg jumps across the stages of the exertion protocol. CONCLUSION: Females with PFPS demonstrate LE kinematics that may increase retropatellar contact pressure during simulated athletic events. However, decreased hip strength at the conclusion of the exertion protocol did not correspond with altered LE kinematics as the exertion protocol advanced.