The in ̄uence of orthotic devices and vastus medialis strength and timing on patellofemoral loads during running

Objective. To use a musculoskeletal model and simulation of running to examine: (1) the in ̄uence of two commonly prescribed treatments for patellofemoral pain (vastus medialis oblique strengthening and orthoses) and (2) the functional signi®cance of timing di€erences between vastus medialis oblique and vastus lateralis on lateral patellofemoral joint loads. Design. A three-dimensional musculoskeletal model of the lower extremity was used to simulate running at 4 m/s. Background. Repetitive and excessive joint loading is often associated with overuse injuries that require clinical treatments to reduce pain and restore function. A€ecting one in four runners, patellofemoral pain is one of the most common injuries in running. Although conservative treatments have been reported to successfully treat patellofemoral pain, the e€ectiveness is often based on subjective or empirical data, which have generated disagreement on the most e€ective treatment. Methods. Nine subject speci®c running simulations were generated and experiments were performed by applying the treatments and timing di€erences to the nominal simulations. Results. Both treatments signi®cantly reduced the average patellofemoral joint load and the vastus medialis strengthening also signi®cantly reduced the peak patellofemoral joint load. In addition, when the vastus medialis oblique timing was delayed and advanced relative to the vastus lateralis timing, a signi®cant increase and decrease in the joint load was observed, respectively, during the loading response. Conclusions. Increasing vastus medialis oblique strength yielded more consistent results across subjects than the orthosis in reducing patellofemoral joint loads during running. The e€ect of orthoses was highly variable and sensitive to the individual subject's running mechanics. Vastus medialis oblique activation timing is an important determinant of lateral patellofemoral joint loading during the impact phase. Relevance These ®ndings indicate that a reduction in patellofemoral pain may be achieved through techniques that selectively increase the vastus medialis oblique strength. Therefore, future studies should be directed towards identifying such techniques. Additionally, the functional signi®cance of timing di€erences between the vastus medialis oblique and vastus lateralis is an important consideration in patellofemoral pain treatment and orthoses may be bene®cial for some patients depending on their running mechanics. Ó 2000 Elsevier Science Ltd. All rights reserved.