Biofeedback exercise improved the EMG activity ratio of the medial and lateral vasti muscles in subjects with patellofemoral pain syndrome
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.
Section snippets
Method
Twenty-six subjects (16 female and 10 male) aged between 20 and 55 years, diagnosed with PFPS by their attending physicians were recruited for this study. The inclusion criteria were that the subjects had insidious onset of anterior knee pain for at least 6 months without receiving physiotherapy and they experienced pain in at least two of the following activities: ascending stairs, descending stairs, squatting, kneeling, prolonged sitting, hopping or jumping (Cowan et al., 2002a, Dursun et al.,
Results
All subjects completed the study. The ICC (1, 1) for the EMG VMO/VL was higher than 0.9 for both groups, which indicated that the recordings have good reliability (Portney and Watkins, 2000). The initial assessments of the two groups were not different, which indicated that the subjects in both groups were comparable.
Fig. 1 shows the changes in VMO/VL EMG ratio in both groups before and after the physiotherapy exercise program. Improvements over time of VMO/VL EMG ratio were not significant in
Discussion
This study examined the effectiveness of an exercise program on the VMO/VL EMG ratio during functional daily activities in subjects with PFPS and whether the EMG ratio would be improved using the same exercise protocol with the addition of an EMG biofeedback training. Results revealed that the VMO/VL EMG ratios in both groups had improved throughout the study but significant difference was only observed in the ‘EMG biofeedback + exercise’ group. This finding suggested that EMG biofeedback was an
Conclusion
This study showed that there was significant difference in the VMO/VL EMG ratio over time in the subjects performing therapeutic exercise with the assistance of EMG biofeedback. This finding implies that EMG biofeedback is an effective adjunct to physiotherapy exercise for patients with PFPS in facilitating their VMO activity. It has a vital clinical implication in improving the rehabilitation of patients with PFPS.
Acknowledgements
We thank the financial support of The Hong Kong Polytechnic University Internal Competitive Research Grant and Michael Wong of Hong Kong Polytechnic University for technical support in this study.
Gabriel Ng is professor and associate head of Department of Rehabilitation Sciences of The Hong Kong Polytechnic University. He received his physiotherapy educations from the Hong Kong Polytechnic University and the University of Queensland and he obtained his doctor of philosophy from Monash University. His research interests include sports physiotherapy and basic sciences of soft tissue injury/repair, in particular, the therapeutic mechanisms of physical modalities and exercises on tissue
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Gabriel Ng is professor and associate head of Department of Rehabilitation Sciences of The Hong Kong Polytechnic University. He received his physiotherapy educations from the Hong Kong Polytechnic University and the University of Queensland and he obtained his doctor of philosophy from Monash University. His research interests include sports physiotherapy and basic sciences of soft tissue injury/repair, in particular, the therapeutic mechanisms of physical modalities and exercises on tissue repair. Gabriel has received a number of personal awards, including the Young Investigator high commendation certificate from Sports Medicine Australia, the New Investigator Recognition award of the Combined Orthopedic Society of the USA, Canada, Europe and Japan, and the President’s Teaching Award from the Hong Kong Polytechnic University. Gabriel is the associate editor (Asia) of Physical Therapy in Sport.
Zhang Qi received a professional diploma in Physiotherapy and M.Sc. in Physiotherapy from The Hong Kong Polytechnic University in 1990 and 2005, respectively. She is vice director and a senior physiotherapist of the Physiotherapy Department at China Rehabilitation Research Center in Beijing. She also holds a concurrent appointment as lecturer at the Faculty of Rehabilitation at The Capital Medical University in Beijing. Her research is focused on the rehabilitation of patients with stroke, spinal cord injuries and orthopedic problems.
Chi Kwong LI received the B.Sc. (Hons) degree in Instrumentation and Control Engineering (1976), M.Sc. in Cybernetics (1978) and Ph.D. in Control Engineering (1984) from the University of Westminster and London University, respectively.
After being senior lecturer with the University of Westminster, he joined the Hong Kong Polytechnic University as Associate Professor for over 21 years. He is now a Chartered and Registered Professional Engineer, Fellow of the IEE and HKIE, and senior member of the IEEE.