Comparison of Vastus Medialis Oblique/Vastus Lateralis Electrical Activity Ratio in Active and Reactive Movement Patterns between Patients with Patellofemoral Pain and Normal Subjects

Patellar maltracking is one of the main causes of patellofemoral joint pain. This tracking dysfunction is mainly due to lock of a precise neuromuscular control between two parts of quadriceps muscle vastus medialis oblique (VMO) and vastus lateralis (VL). The ratio between electrical activity VMO/VL muscles is considered as an index for comparison between normal subjects and with those with patellofemoral pain. The purposes of this study are to compare the VMO/VL activity ratio in active and reactive movement patterns.This quasi-experimental study was conducted on a group of 30 healthy men as a control group and 30 patients with patellofemoral pain as an experimental group. These two groups were non-probably assigned, conveniently sampled and randomly asked to perform movement patterns test. During these tests, electromyographic activity of the muscles were normalized and integrated to absolute values. Movement pattern tests include maximum isometric contraction of quadriceps muscle at 60 degree of knee flexion; active movement patterns consist of forward step up (FSU) and lateral step up (LSU), and reactive movement patterns that consist of angular perturbation of ankle and perturbation of waist.in healthy subjects VMO/VL ratio in active and reactive movement patterns was significantly greater than isometric contraction (P<0.05). Also this ratio was significantly greater in upward phase of FSU and LSU compared to downward phase. There was no precise and clear relationship between muscle activity ratios in different movement patterns. Comparison between control and experimental groups revealed the greatest significant difference only in active and isometric movement patterns.results indicate that VMO/VL activity ratio in normal patients has no relationship with the direction and location of perturbation but conversely is task-dependent to direction and location of perturbation in patients with patellofemoral pain.