The influence of weakness in the vastus medialis oblique muscle on the patellofemoral joint: an in vitro biomechanical study

Objective. Investigation of the influence of weakness in the vastus mediali s oblique muscle on patellar tracking. Design. In vitro biomechanical study. Background. Currently, the influence of weakness in the vastus medialis oblique muscle on patellar tracking has not been well understood. Methods. Seven human cadaveric knees were used. The direction of loading fo rces in the rectus femoris/vastus intermedius, vastus medialis oblique, and the vastus lateralis muscles was decided by the muscle alignment of each c adaver knee measured at the time of dissection. The loads used were 60 N in the rectus femoris, 50 N in the vastus lateralis, and 40 N in the vastus m edialis oblique, according to the ratio calculated from the cross-sectional study. The weakness of vastus medialis oblique was simulated at 30 N (75%) , 20 N (50%), 10 N (25%), and 0 N (0%), and the patellar position was measu red for each condition using a magnetic 3 Space Tracker System. The influen ce of weakness in the vastus medialis oblique muscle on patellar position w as investigated with seven cadaver knees using a magnetic 3 Space Tracker(R ) System. Results. At 0 degrees and 15 degrees of knee flexion, 75%, 50%, 25% and 0% of the normal vastus medialis oblique muscle led to a significant differenc e in lateral patellar shift compared to the normal (P < 0.05). Conclusions. Weakness of the vastus medialis caused the patellar lateral sh ift at 0 degrees and 15 degrees of knee flexion.