Magnetic resonance imaging was used to quantify in vivo patellofemoral joint contact area and to determine if contact area is affected by quadriceps muscle contraction. Ten subjects without pain (six women, four men) had their right patellofemoral joint imaged. Cartilage-enhanced, axial plane images were obtained at 0 degrees, 20 degrees, 40 degrees, and 60 degrees knee flexion under quadriceps loaded (contracted) and quadriceps unloaded (relaxed) conditions. Medial and lateral facet contact area measurements were obtained on each image, and then summed across all images in a series to yield facet contact area measurements for each knee angle. Total contact area was computed as the sum of medial and lateral facet contact areas. Consistent with in vitro studies, progressive increases in patellofemoral joint contact area were observed from 0 degrees to 60 degrees knee flexion. The lateral facet comprised a greater percentage of total contact area compared with the medial facet at each knee flexion angle, suggesting increased load-bearing potential. Quadriceps contraction did not affect patellofemoral joint contact area indicating that the addition of a compressive load to the joint did not alter the area of the load-bearing surfaces. In vivo assessment of patellofemoral joint contact area could provide insight into mechanisms of patellofemoral joint disorders.

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