Biofeedback exercise improved the EMG activity ratio of the medial and lateral vasti muscles in subjects with patellofemoral pain syndrome

Abstract

Patellofemoral pain syndrome (PFPS) is usually due to weakness of vastus medialis obliquus (VMO) resulting in abnormal patellar tracking. One of the objectives of rehabilitation is to strengthen the VMO so as to counterbalance the vastus lateralis (VL) action during normal activities. This study compared the effects of an 8-week exercise program with and without EMG biofeedback on the relative activations of VMO and VL. Twenty-six subjects with PFPS were randomly allocated into an “exercise” group (Group 1) and a “biofeedback + exercise” group (Group 2). Both groups performed the same exercise program but subjects in Group 2 received real time EMG biofeedback information on the relative activations of VMO and VL during the exercises. After 8 weeks of training, Group 1 had insignificant changes in their VMO/VL EMG ratio (p = 0.355), whereas Group 2 had significantly greater VMO/VL EMG ratio (p = 0.017) when performing normal activities throughout a 6-h assessment period. The present result reveals that the incorporation of an EMG biofeedback into a physiotherapy exercise program could facilitate the activation of VMO muscle such that the muscle could be preferentially recruited during daily activities.

Introduction

Patellofemoral pain syndrome (PFPS) is a common condition presented with diffused pain in the anterior compartment of the knee with causes other than intra-articular pathologies, peripatellar tendonitis or bursitis (Thomee et al., 1999). The incidence of PFPS ranges from 10% to 28% in the general population and people with high physical activity levels (Almeida et al., 1999, Witvrouw et al., 2000). It often affects people between 10 and 35 years of age and it occurs 2–3 times more frequently in women than in men (Lichota, 2003).

Stability of the patellofemoral joint (PFJ) is largely maintained by soft tissues, in particular, the dynamic balance of the medial and lateral quadriceps muscle. The resultant vector of the knee extensors acting on the patella is normally directed laterally because of the tibiofemoral angle (Huberti and Hayes, 1984). Previous studies (Bose et al., 1980, Goh et al., 1995) had reported that the vastus medialis obliquus (VMO) played an important role in controlling the contact area and pressure distribution in the PFJ. Atrophy of VMO is often associated with PFPS, possibly as a result of the interaction between mechanical and neuromuscular factors (Flynn and Soutas-Little, 1995).

The normal VMO/VL EMG ratio was reported to be about 1:1 (Souza and Gross, 1991) but there were controversies surrounding this ratio in subjects with PFPS. In a study with intramuscular EMG, Powers (2000) reported that the VMO/VL EMG ratio was 0.54 and 0.85 for subjects with and without PFPS, respectively. The lowering of VMO/VL EMG ratio would result in less medial pull on the patella (Davlin et al., 1999) leading to an imbalance of shearing and compressive forces on the PFJ during normal activities (Sikorski et al., 1979).

EMG biofeedback is a device that detects the neuromuscular contractions and provides feedback signals to the subject (Dursun et al., 2001). Because an EMG biofeedback system can provide immediate information on the muscle activation pattern, Ingersoll and Knight (1991) stated that the use of EMG biofeedback training to selectively strengthen the VMO as being essential for correcting excessive lateral tracking of the patella for patients with PFPS.

Wise et al. (1984) explored the use of EMG biofeedback coupled with a graded exercise programme and found that with 4–6 weeks of training, there was a change in the PFJ force and a concomitant decrease in pain. Therefore, they concluded that EMG biofeedback was effective for treating patients with PFPS.

It was reported that patients with PFPS had a lower VMO/VL EMG ratio than healthy subjects (Powers, 2000, Souza and Gross, 1991), and such a change in EMG ratio was a predisposing factor for the development of PFPS. An increase in the ratio of VMO/VL EMG implies that there is an increase in medial pull on the patella. Therefore, the EMG ratio of VMO/VL appears to be an important parameter in these patients.

Controversies exist in the literature regarding the altered VMO/VL EMG ratios in patients with PFPS. It is not known whether this alteration can be changed after a physiotherapy exercise program. Furthermore, the effect of exercise on the VMO/VL EMG before and after the training program in subjects with PFPS has not been well studied. Therefore this study was conducted to investigate if subjects with PFPS had differences in VMO/VL EMG ratios before and after a physiotherapy exercise program, and whether the addition of an EMG biofeedback to exercise would alter the VMO/VL EMG ratio during functional daily activities.