Patella alta: association with patellofemoral alignment and changes in contact area during weight-bearing.
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 degrees , 20 degrees , 40 degrees , and 60 degrees of knee flexion with the quadriceps contracted.


RESULTS
With the knee at 0 degrees 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 degrees +/- 1.9 degrees and 15.5 degrees +/- 1.8 degrees ; p = 0.028), and less contact area (157.6 +/- 13.7 mm(2) and 198.8 +/- 14.3 mm(2); 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 degrees 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.
Musculoskeletal Biomechanics Research Laboratory, Department of Biokinesiology and Physical Therapy, University of Southern California, Los Angeles, CA 90089, USA. srward@ucsd.edu
Samuel R
SR
Ward
Michael R
MR
Terk
Christopher M
CM
Powers
D000328:Adult; D001696:Biomechanical Phenomena; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D007593:Joint Instability / Q000503:physiopathology*; D007719:Knee Joint / Q000503:physiopathology*; D008279:Magnetic Resonance Imaging; D010147:Pain Measurement; D010329:Patella / Q000002:abnormalities* / Q000503:physiopathology*; D016474:Weight-Bearing