Ward SR, Terk MR, Powers CM.
The purpose of this study was to compare the knee extensor mechanics in persons
with and without patella alta. Thirteen subjects with patella alta and 14
subjects with normal patellar position participated in the study. Sagittal and
axial MR images of the knee were acquired at 0 degrees , 20 degrees , 40 degrees
, and 60 degrees of knee flexion. Measurements of actual moment arm, patellar
ligament/quadriceps tendon force ratio, quadriceps effective moment arm, and
joint reaction force/quadriceps force ratio were obtained. There were no
differences between groups in terms of actual moment arm. However, subjects with
patella alta had significantly larger patellar ligament/quadriceps tendon force
ratios (1.04±0.02 vs. 0.92±0.02) and quadriceps effective moment arms
(4.40±0.09 vs. 4.00±0.09 cm) when averaged across the range of knee flexion
angles tested. There was no difference in the joint reaction force/quadriceps
force ratio between groups. The observed differences in knee extensor mechanics
suggest that individuals with patella alta have a more efficient knee extensor
mechanism and would be expected to generate similar joint reaction forces per
unit quadriceps force compared to subjects with normal patellar position.
Therefore, persons with patella alta may experience less patellofemoral joint
reaction force to overcome the same knee flexion moment in the range of 0 degrees
-60 degrees of knee flexion.
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