The effect of intersegmental knee moments on patellofemoral contact mechanics in cycling.

The aim of this study was to evaluate the effect of bicycle pedal design on the mechanics of the patellofemoral joint. Previous research determined that for certain riders the non-driving varus and internal knee moments could be reduced by switching from fixed to free floating pedals (Ruby and Hull, 1993). It was postulated that the presence of varus and internal knee moments during fixed pedal cycling may adversely affect patellofemoral joint contact mechanics which could lead to the development of anterior knee pain. To investigate the effect of pedal design the hypothesis that varus and internal intersegmental knee moments significantly increase patellofemoral contact pressure, contact area and contact force was tested. To test this hypothesis cycling loads were simulated in vitro using a six-degree-of-freedom load application system (LAS). Using the LAS, varus moments ranging from 0-20 Nm and internal knee moments ranging from 0-10 Nm were applied simultaneously with quadriceps force at knee flexion angles of 60 and 90 degrees. Patellofemoral contact patterns were measured using pressure sensitive film. An applied 10 Nm internal moment significantly increased both contact area by 16% and contact force by 22% at 90 of flexion. The application of a 20 Nm varus moment modestly yet significantly increased contact area by 6% and contact force by 5%. When applied in combination, varus and internal knee moments increased contact area and force by as much as 29% and 28% respectively. The mean contact pressure was not significantly increased by either of the two moments. The results suggest that non-driving intersegmental knee moments subject the patellofemoral joint to loads and contact patterns which may accelerate the development of chondromalacia.