The Journal of Bone and Joint Surgery (American). 2007;89:1749-1755.
doi:10.2106/JBJS.F.00508
© 2007 The Journal of Bone and Joint Surgery, Inc.
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Patella Alta: Association with Patellofemoral Alignment and Changes in Contact Area During Weight-Bearing

Samuel R. Ward, PhD, PT1, Michael R. Terk, MD2 and Christopher M. Powers, PhD, PT2

1 Muscle Physiology Laboratory, Department of Radiology, University of California and VA Medical Center San Diego, 9500 Gilman Drive (mail code 9151), San Diego, CA 90293. E-mail address: srward{at}ucsd.edu
2 Musculoskeletal Biomechanics Research Laboratory, Department of Biokinesiology and Physical Therapy, University of Southern California, 1540 Alcazar Street, CHP 155, Los Angeles, CA 90089

Investigation performed at the Musculoskeletal Biomechanics Research Laboratory, Department of Biokinesiology and Physical Therapy, University of Southern California, Los Angeles, California

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 Foundation for Physical Therapy. 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.

Background: Patella alta is a condition which may predispose individuals to patellofemoral joint dysfunction. We compared patellofemoral joint alignment and contact area in subjects who had patella alta with subjects who had normal patellar position, to determine the effect of high vertical patellar positions on knee extensor mechanics.

Methods: Twelve subjects with patella alta and thirteen control subjects participated in the study. Lateral patellar displacement (subluxation), lateral tilt, and patellofemoral joint contact area were quantified from axial magnetic resonance images of the patellofemoral joint acquired at 0°, 20°, 40°, and 60° of knee flexion with the quadriceps contracted.

Results: With the knee at 0° of flexion, the subjects with patella alta demonstrated significant differences compared with the control group, with greater lateral displacement (mean [and standard error], 85.4% ± 3.6% and 71.3% ± 3.0%, respectively, of patellar width lateral to the deepest point in the trochlear groove; p = 0.007), greater lateral tilt (mean, 21.6° ± 1.9° and 15.5° ± 1.8°; p = 0.028), and less contact area (157.6 ± 13.7 mm2 and 198.8 ± 14.3 mm2; p = 0.040). Differences in displacement and tilt were not observed at greater knee flexion angles; however, contact area differences were observed at all angles evaluated. When data from both groups were combined, the vertical position of the patella was positively associated with lateral displacement and lateral tilt at 0° of flexion and was negatively associated with contact area at all knee flexion angles.

Conclusions: These data indicate that the vertical position of the patella is an important structural variable that is associated with patellofemoral malalignment and reduced contact area in patients with patella alta.


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Letters to the Editor:

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Patella Alta: Association with Patellofemoral Alignment and Changes in Contact Area
Benedict A. Rogers, MA, MSc, MRCS
JBJS Online, 16 Aug 2007 [Full text]
Dr. Ward and Dr. Powers respond to Dr. Rogers
Samuel R. Ward, PhD, PT, et al.
JBJS Online, 20 Sep 2007 [Full text]