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In Vivo Noninvasive Evaluation of Abnormal Patellar Tracking During Squatting in Patients with Patellofemoral Pain
Nicole A. Wilson, PhD1; Joel M. Press, MD1; Jason L. Koh, MD2; Ronald W. Hendrix, MD2; Li-Qun Zhang, PhD1
1 Rehabilitation Institute of Chicago, 345 East Superior Street, Room 1406, Chicago, IL 60611. Email address for L.-Q. Zhang: l-zhang@northwestern.edu
2 Department of Biomedical Engineering, Northwestern Memorial Hospital, 251 East Huron Street, Chicago, IL 60611
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Disclosure: In support of their research for or preparation of this work, one or more of the authors received, in any one year, outside funding or grants in excess of $10,000 from the National Institutes of Health. Neither they nor a member of their immediate families received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, division, center, clinical practice, or other charitable or nonprofit organization with which the authors, or a member of their immediate families, are affiliated or associated.
Investigation performed at the Sensory Motor Performance Program, Rehabilitation Institute of Chicago, Chicago, Illinois

The Journal of Bone and Joint Surgery, Inc.
J Bone Joint Surg Am, 2009 Mar 01;91(3):558-566. doi: 10.2106/JBJS.G.00572
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Background: Patellofemoral pain syndrome is one of the most common knee problems and may be related to abnormal patellar tracking. Our purpose was to compare, in vivo and noninvasively, the patellar tracking patterns in symptomatic patients with patellofemoral pain and those in healthy subjects during squatting. We tested the hypothesis that patients with patellofemoral pain exhibit characteristic patterns of patellar tracking that are different from those of healthy subjects.

Methods: Three-dimensional patellar kinematics were recorded in vivo with use of a custom-molded patellar clamp and an optoelectronic motion capture system in ten healthy subjects and nine subjects with patellofemoral pain. The position of osseous knee landmarks was digitized while subjects stood upright, and then patellofemoral kinematics were recorded during squatting. The tracking technique was validated with use of both in vitro and in vivo methodologies, and the average absolute error was <1.2° and <1.1 mm.

Results: At 90° of knee flexion, the patella showed lateral spin (the distal pole of the patella rotated laterally) in subjects with patellofemoral pain (mean and standard deviation, -10.13° ± 2.24°) and medial spin in healthy subjects (mean, 4.71° ± 1.17°) (p < 0.001). At 90° of knee flexion, the patella demonstrated significantly more lateral translation in subjects with patellofemoral pain (mean, 5.05 ± 3.73 mm) than in healthy subjects (mean, -4.93 ± 3.93 mm) (p < 0.001).

Conclusions: Kinematic differences between healthy subjects and subjects with patellofemoral pain were demonstrated through a large, dynamic range of knee flexion angles. Increased lateral patellar translation and lateral patellar spin in subjects with patellofemoral pain suggest that the patella is not adequately balanced during functional activities in this group. Prospective studies are needed to identify when patellofemoral pain-related changes begin to occur and to determine the risk for the development of patellofemoral pain in individuals with abnormal kinematics.

Clinical Relevance: This study presents a simple extension of standard motion analysis tools, which allows for accurate assessment of three-dimensional patellofemoral kinematics in the clinical setting. The identification of kinematic differences associated with patellofemoral pain suggests that the dynamic tracking technique is a potential diagnostic tool for this syndrome.

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    These activities have been planned and implemented in accordance with the Essential Areas and policies of the Accreditation Council for Continuing Medical Education (ACCME) through the joint sponsorship of the American Academy of Orthopaedic Surgeons and The Journal of Bone and Joint Surgery, Inc. The American Academy of Orthopaedic Surgeons is accredited by the ACCME to provide continuing medical education for physicians.
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