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| ARTICLES - Electromyography (EMG) | ||||||||||||||||||||||
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Patello-Femoral Pain Syndrome The Use of Electromyographic Biofeedback for Training The Vastus Medialis Obliquus In Patients With Patellofemoral Pain. Charles R. Felder, PT, SCS, ATC Maureen A. Leeson, B.App.Sc. (Phty) Introduction Patellofemoral pain is a common ailment affecting one in four of the general population (11). It is caused by a variety of factors including abnormal lower limb mechanics, Vastus Medialis Obliquus (VMO) insufficiency, tight lateral structures and inappropriate physical activity. The condition develops gradually and is characterized by a diffuse ache in the area of the patella. Pain is a significant factor since it will alter function and inhibit muscular activity. Anterior knee pain is often diagnosed as chondromalacia patella (7,9,12). This diagnosis is only correct in the case of a softened and fissured patellar undersurface which is seen during arthrotomy, arthroscopy or with an arthrogram (5,3). Often no pathological findings are present in patients who otherwise complain of severe pain and functional disability (1), especially during sporting activities, stair climbing and prolonged sitting. Patellofemoral pain can be a difficult condition to treat. The fibers of the VMO insert into the patella at an angle of 50-55' from the sagittal plane (17). The VMO is active throughout the full range of extension of the knee and is the only dynamic medial stabilizer of the patella (8). Insufficiency of the VMO will contribute to lateral tracking of the patella (4,6). Training the VMO is important to prevent lateral tracking of the patella and eliminate patellofemoral dysfunction. Electromyogram (EMG) studies of non-painful knees show that the ratio of VMO to Vastus Lateralis (VL) activity is 1:1 and that the VMO activity is tonic in nature (13). In knees with patellofemoral pain the VMO:VL ratio is less than 1:1 (10,13) and the VMO activity becomes phasic in nature (14). This change in VMO activity may be the result of an asymmetric wasting of the Quadriceps muscle. Spencer et al (16) reported that it takes 20-30 ml of fluid to inhibit the VMO, whereas 50-60 ml of fluid is necessary to inhibit the VL activity. This asymmetry results in lateral tracking of the patella, which is a common cause of patellofemoral pain. Management of Patellofemoral Pain The management of patellofemoral pain involves first, a thorough analysis of the problem to identify the contributory factors; and second, correcting these problems. The McConnell Patellofemoral Treatment Plan (11) addresses each component that contributes to patellofemoral pain. Lower limb mechanics are assessed, patellar orientation is corrected by taping and specific muscles are trained to optimize dynamic control. Taping the patella into correct alignment contributes to increased EMG activity of the VMO, increased torque development and decreased pain (11). The EMG is used to demonstrate the muscle imbalance to the patient. The emphasis in treatment is on improving the timing of the VMO contraction. Muscle training has been found to be specific to limb position; joint angle; and velocity, type and force of contraction (15). The aim of training is to acquire a new motor skill which will be incorporated into functional activities (11). Specific training enables a change in the length-tension relationship of the agonist (VMO) and antagonist (VL). During training the patient can use the portable EMG to help monitor the firing patterns of the VMO and VL. It is used in either the clinical situation or as part of the home program encouraged in the McConnell Patellofemoral Treatment Plan. As the VMO control improves, training progresses to include functional activities such as stairs, squats, vocational and sporting activities, provided they are painfree. The goal of treatment is to provide an optimal position of the patella passively by tape until training of the muscles is achieved. The taping procedure is discontinued when the patient regains muscular control of the patella. In many instances the problem is related to the timing of the muscles and this is often only demonstrated by using the EMG. The portable EMG provides the patient with instant feedback of the VMO activation. For example, the ballet dancer can monitor the firing of the VMO in a pli6, the tennis player can ensure activation of the VMO while hitting through the ball and the basketball player can bring in the VMO while practicing jumps, etc. Motivating the patient is easy if the patient understands the underlying mechanisms causing the problem. Training becomes an integral part of the patient's day to day living. Skill is enhanced and maintained with practice (2). Case History A 35 year old male complained of right patellofemoral pain symptoms. He had a history of patellar subluxation and he had undergone an arthroscopic medial menisectomy 8 years earlier. X-rays revealed early arthritic changes. The patient's occupation as a photographer required him to walk, bend and squat frequently. His primary complaint was pain with squatting while at work and with recreational sports including tennis, downhill skiing and softball. Objective examination showed an increased Q angle, pes planus, poor VMO bulk and poor timing of the VMO to VL. Stepdowns and partials squats were painful. Patellar orientation revealed an anteroposterior tilt, lateral tilt and external rotation. The lateral structures were tight demonstrated by decreased patellar glide and tilt. The patient's knee was taped to correct the patellar orientation. The taping immediately resolved the pain produced by stepdowns and partial squats. He was instructed in localized stretching for the lateral structures. The EMG was applied to the VMO and a training program was implemented to improve initially, the VMO timing and later, the VMO endurance. The EMG feedback helped the patient change the firing pattern of his VMO. This feedback encouraged him to activate an earlier, stronger and longer VMO contraction. He trained at home frequently for short periods and eliminated his symptoms within six weeks. There were a total of three clinical visits. A one month follow-up call revealed continued compliance and the absence of symptoms. The patient had returned to full functional activities. Using the MyoTrac EMG Biofeedback The MyoTrac EMG biofeedback monitor helps the patient train the VMO by reinforcing the appropriate VMO activity and monitoring fatigue. To accelerate the rate of learning, the scale reading and threshold settings are increased to raise the level of difficulty. The red lights or sound reward the patient for consistency and quality of effort. Internal Setting
External Setting
Electrode Placement
Technique for VMO Training Set the EMG monitor at "X 10" and turn the threshold dial to "0.5". If the red lights are on when the leg is relaxed then the threshold dial is turned counter clockwise, toward the higher numbers, until the green lights come on. If the red lights do not turn on with patient effort and the threshold dial set to "0.5", then the unit is opened and adjusted to a more sensitive setting (i.e., "X 1"). Once the green lights are on, the patient performs a Quadriceps contraction, activating the VMO before the VL. The red lights indicate that the desired contraction is achieved. Ensure that the patient is achieving a quality contraction of the VMO with minimal activity of the VL. To achieve maximum benefit from the exercise, effort is required to activate the LED and the sound. However, quality of contraction, rather than the quantity of contraction, is of utmost importance. If the threshold dial is turned to "10" and the patient still finds it easy to perform a VMO contraction and activate the red lights, the internal scale reading is switched to "X100" and the threshold to “0. 5”. The patient progresses to using the MyoTrac to monitor the VMO function in all of his or her functional training. The patient learns to identify VMO fatigue during treatment and discontinues when fatigue occurs so that training does not continue in an inappropriate pattern. After a brief rest training is resumed, ensuring that the VMO is recruited before or at the same time as the VL. Simultaneous monitoring of the VMO and VL with dual channel EMG allows for comparison of the timing of contraction and will assist training the patient's timing component. The firing pattern can be monitored by two MyoTrac units used simultaneously; one to monitor the VMO and one to monitor the VL. Alternatively a dual channel MyoDac can be used to monitor both muscles. The MyoDac is a dual channel EMG monitoring system similar to the MyoTrac but with computer interfacing capabilities. With the aid of an IBM compatible computer it may be used to demonstrate to the patient the initial asymmetry between the VMO and the VL, as well as permit an easier graphical visualization of the effect of training. The MyoComp software, included with the instrument, also permits the recording of the patient's initial muscular activity and the progress of training over time. The record may be printed out for documentation purposes. Conclusion Clinical evidence shows that the muscles can be trained specifically to align the patella (11). Ongoing and regular training will produce effects that are beneficial and long-term, and the patient can remain free of pain even when participating in activities which are demanding on the patellofemoral joint. Using the EMG MyoTrac(s) to monitor the VMO and evaluate the patient's progress is the key to success. References
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