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Yu-Jen Chen and Christopher M. Powers

The purpose of this study was to determine if persons with patellofemoral pain (PFP) exhibit differences in patellofemoral joint reaction forces (PFJRFs) during functional activities. Forty females (20 PFP, 20 controls) underwent two phases of data collection: (1) magnetic resonance imaging (MRI) and (2) biomechanical analysis during walking, running, stair ascent, and stair descent. A previously described three-dimensional model was used to estimate PFJRFs. Resultant PFJRFs and the orthogonal components were reported. The PFP group demonstrated lower peak resultant PFJRFs and posterior component and superior component of the PFJRFs compared with the control group across all conditions. However, the PFP group had a higher peak lateral component of the PFJRF in three out of the four conditions evaluated. The lower resultant PFJRFs suggested that individuals with PFP may employ strategies to minimize patellofemoral joint loading, but it did not result in diminished lateral forces acting on the patella.

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Thomas G. Almonroeder, Emily Watkins, and Tricia Widenhoefer

Patellofemoral pain is relatively common in young, active females. 1 , 2 Unfortunately, the presence of patellofemoral pain during adolescence and/or early adulthood can limit participation in physical activity 3 and appears to be associated with the development of future patellofemoral joint

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Abbigail Ristow, Matthew Besch, Drew Rutherford, and Thomas W. Kernozek

running, jumping, or climbing stairs, and symptoms commonly increase with continued participation. 2 Multiple studies have indicated a relationship between increased patellofemoral joint stress (PFJS) and PFP, 3 , 4 patellofemoral joint reaction force (PFJRF), 5 reduced patellofemoral joint contact area

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Thomas W. Kernozek, Naghmeh Gheidi, Matthew Zellmer, Jordan Hove, Becky L. Heinert, and Michael R. Torry

where there are increased patellofemoral joint (PFJ) compressive loads. 6 Most studies theorize that PFPS is related to symptoms due to excessive patellofemoral joint stress (PFJS). 1 , 7 , 8 Athletes with PFPS often limit their activity, and PFPS has been reported to be a precursor to knee

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Seong-won Han, Andrew Sawatsky, Azim Jinha, and Walter Herzog

spectrum of the population, including a general, nonspecific group, 7 , 8 physically active people, 4 , 9 young/adolescents, 8 , 10 , 11 and older adults. 12 It has been suggested that patellofemoral pain may potentially lead to osteoarthritis in the patellofemoral joint (PFJ). 13 – 15 Despite the

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Michael A. Samaan, Valentina Pedoia, Matthew S. Tanaka, Richard B. Souza, C. Benjamin Ma, and Xiaojuan Li

. 9 These altered kinematic patterns may induce abnormal knee joint loading during activities of daily living, such as walking, 5 , 10 which leads to the high incidence (25%–50%) of radiographic patellofemoral joint osteoarthritis observed at 7 to 15 years after ACLR. 11 – 14 Quantitative magnetic

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Christina Olbrantz, Jamie Bergelin, Jill Asmus, Thomas Kernozek, Drew Rutherford, and Naghmeh Gheidi

predominance of PFP in young, active adults, estimating a 2-fold higher incidence in women. 1 There is currently a lack of consensus concerning the etiology of PFP due to the multifactorial nature of the disorder. 1 – 3 However, recent studies indicate increased patellofemoral joint stress to be an

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Yu-Jen Chen, Irving Scher, and Christopher M. Powers

The purpose of this study was to describe an imaging based, subject specific model that was developed to quantify patellofemoral joint reaction forces (PFJRF’s). The secondary purpose was to test the model in a group of healthy individuals while performing various functional tasks. Twenty healthy subjects (10 males, 10 females) were recruited. All participants underwent two phases of data collection: 1) magnetic resonance imaging of the knee, patellofemoral joint, and thigh, and 2) kinematic, kinetic and EMG analysis during walking, running, stair ascent, and stair descent. Using data obtained from MRI, a subject specific representation of the extensor mechanism was created. Individual gait data were used to drive the model (via an optimization routine) and three-dimensional vasti muscle forces and subsequent three-dimensional PFJRF’s were computed. The average peak PFJRF was found to be highest during running (58.2 N/kg-bwt), followed by stair ascent (33.9 N/kg-bwt), stair descent (27.9 N/kg-bwt), and walking (10.1 N/kg-bwt). No differences were found between males and females. For all conditions, the direction of the PFJRF was always in the posterior, superior, and lateral directions. The posterior component of the PFJRF always had the greatest magnitude, followed by superior and lateral components. Our results indicate that estimates of the magnitude and direction of the PFJRF during functional tasks can be obtained using a 3D-imaging based model.

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John Faltus

Edited by R. Barry Dale

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Steven K. Boyd and Janet L. Ronsky

Abnormal joinl coniact mechanics in the knee joint due to loss of anterior cruciate ligament (ACL) are often speculated to play an important role in the development of osteoarthritis. In this study, a technique was developed so that contact of the patellofemoral (PF) joint could be estimated in situ using a mathematical contact model. The model inputs were PF joint kinematics measured in situ and the PF joint surface topology. Due to the small size of the joint, techniques for measuring joinl kinematics and surface topology with sufficient precision were paramount so that reasonable estimates of joint contact could be obtained. The sensitivity of the model to measurement errors was examined. Differences in joint contact between ACL-intacl and ACL-deficient conditions were analyzed. Statistically significant differences in contact areas were detected between the intact and ACL-deficient knee joint, and different coniact areas and locations as a function of joint angle and quadriceps muscular stimulation.