The quantitative measurement of normal passive medial and lateral patellar motion limits

To quantify normal motion, medial and lateral passive patellar motion limits were measured in 67 high school athletes randomly selected from a group of 1340 athletes undergoing preseason physical examinations. Patellar displacement was measured at knee flexion angles of 0 degree and 35 degrees, using both a Patella Pusher (a hand-held force gauge) and a manual technique, and the results were compared. Demographic data and physical examination of the deceleration mechanism (Q angle, vastus medialis obliquus dysplasia, patella alta and baja, and valgus and varus alignment) were correlated with patellar motion limits. With the knee in extension, passive displacement of the patella averaged 9.6 mm medially and 5.4 mm laterally. In flexion, medial displacement averaged 9.4 mm and lateral displacement averaged 10.0 mm. No positive correlations were found between demographic data or deceleration mechanism examination parameters and patellar motion limits, suggesting that motion produced by the displacement force was limited by ligamentous restraints only. The clinical assessment of the passive limits of patellar motion should include examination at knee flexion angles of 0 degree and 35 degrees. The manually produced displacement was found to be more reproducible than displacement by the Patella Pusher (P < 0.05).