Patellofemoral Pain Syndrome
The Use Of Electromyographic Biofeedback For Training The Vastus Medialis Obliquus In Patients With Patellofemoral Pain.
PT, SCS, ATC
Patellofemoral pain is a common ailment affecting one in four of the general population(6). It is caused by a variety of factors including abnormal lower limb mechanics, Vastus Medialis Obliquus (VMO) insufficiency, tight lateral structures and tight anterior and posterior muscles. The condition often develops gradually and is characterized by a diffuse ache in the area of the anterior knee. Pain is a significant factor since it will inhibit muscular activity and alter lower limb function. Anterior knee pain is often diagnosed as chondromalacia patella(2). This diagnosis is only correct when a softened and fissured patellar under-surface is seen during diagnostic imaging or surgery(2). Often, no cartilaginous pathological findings are present in patients who otherwise complain of severe knee pain and functional disability, especially during prolonged sitting, stair climbing or sporting activities.
The VMO muscle is the dynamic medial stabilizer of the patella. Therefore it is important to understand the anatomy and function of the VMO when treating patients with patellofemoral dysfunction. The fibers of the VMO insert into the patella at an angle of 50-55 degrees from the vertical axis(10)(see figure 1). The VMO is active throughout the full range of extension of the knee and is the only dynamic medial stabilizer of the patella(4). Insufficiency of the VMO will contribute to lateral tracking of the patella(3). Training the VMO is important to prevent lateral tracking of the patella and eliminate patellofemoral dysfunction.
Electromyographic(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(7). In knees with patellofemoral pain the VMO:VL ratio is less than 1:1(5,7) and the VMO activity becomes phasic in nature(8). This change in VMO activity may be the result of the asymmetric wasting of the Quadriceps muscle. Spencer et al(9) 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 may result 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. Lower limb mechanics are assessed and the alignment of the patella is evaluated. Patellar alignment is improved with tape and muscles are trained to optimize dynamic control. Taping the patella into correct alignment has been shown to increase EMG activity of the VMO, increase muscle torque and decrease pain (6). Change in the muscle activity of the knee improves patellar tracking and lower limb mechanics and significantly decreases pain.
EMG monitoring is utilized to assist with the assessment of muscle activity and to demonstrate any imbalance to the patient. The patient is then shown how to use EMG while training the VMO and VL. During training, the patient can use a portable EMG device to monitor the firing pattern of the muscles. Such a device can be used in a clinical setting as well as part of a home program. Training may also be specific to a particular part of the range of motion i.e. at 20-30 degrees of knee flexion, as the patella is engaging in the trochlear groove of the femur. As the VMO control improves, training progresses to include functional activities such as climbing stairs, squats, vocational and sporting activities, provided they are pain free ( see figure 2). In many instances, the problem is related to the timing of muscle contractions; when there is an imbalance of muscle activity, lateral tracking of the patella will result. This muscle imbalance can be demonstrated with EMG. Training may require subtle shifts in the timing of activity of the VMO:VL muscles. A portable EMG device provides the patient with instant feedback on the VMO activation (single channel EMG) or a comparison of VMO to VL activity (dual channel EMG). It then becomes easy for the patient to change the timing or the quantity of VMO activity (single channel) or VMO to VL activity (dual channel). The patient can progress to monitor his/her effort in functional or sporting activities. For example a ballet dancer can monitor the firing of the VMO in a pliť, a tennis player can ensure activation of the VMO while hitting through the ball and a basketball player can check the VMO while landing from a jump, etc.
Motivating patients to train the muscles is easier when they understand the underlying mechanism contributing to the problem. Training becomes an integral part of the patient's day to day living as well as sporting and recreational activities. Skill is enhanced and maintained with practice(1).
A 35 year old male complained of right knee pain. He had a history of patellar subluxation and had undergone an arthroscopic medial menisectomy 8 years earlier. X-rays revealed early arthritic changes in the tibiofemoral joint. The patient's occupation as a photographer required him to walk, bend and squat frequently. His primary complaint was pain while at work and with recreational sports including tennis, downhill skiing and softball.
Objective examination showed an increased Q angle, pes planus, decreased VMO bulk and poor timing of the VMO to VL muscle activity. Step downs and partial squats reproduced the patient's pain. Patellar alignment tests revealed an inferior tilt, lateral tilt and external rotation. The lateral structures were tight, demonstrated by decreased patellar medial glide and medial tilt.
The patient's knee was taped to correct the patellar alignment. Patellar taping immediately resolved the patient's knee pain produced by partial squats and step downs. He was instructed in localized stretching for the lateral structures. The EMG sensors were applied to the VMO and VL and a training program was implemented to improve the VMO's timing and endurance. The EMG feedback helped the patient to monitor his VMO activity and change the timing of VMO to VL activity. It provided encouragement 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 was a total of three clinical visits. A one year follow-up call revealed continued absence of symptoms and the patient had returned to full functional activities without pain.
USING THE MYOTRAC EMG MONITOR
The MyoTrac single channel EMG monitor from Thought Technology helps the patient train the VMO by reinforcing the appropriate activity and monitoring fatigue. To accelerate the rate of learning, gain and threshold settings are adjusted to raise the level of difficulty. The visual and/or auditory feedback reward the patient for consistence in training and quality of effort.
TECHNIQUE FOR VMO TREATMENT
With the EMG monitor's gain at X10 and the threshold set to 0.5, if the first yellow light is on when the leg is relaxed, then the threshold dial should be turned counter clockwise (toward the higher numbers), until the green lights come on. If the first yellow light does not turn on with patient effort and the threshold dial is set to 0.5, then the unit should be adjusted to a more sensitive gain setting (i.e. X1). Once the green lights are on, the patient performs a Quadriceps contraction, ensuring that the VMO is recruited before or at the same time as the VL. The first yellow light indicate that the desired contraction is achieved (threshold). 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 lights to the right of the threshold indicator and the sound. However quality of contraction, rather than 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 first yellow light, the scale is switched to X100 and the threshold returned to 0.5.
The patient progresses to using the MyoTrac to monitor the VMO function in all of his/her functional training. The patient also learns to identify VMO fatigue during treatment and is told to stop 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 a dual channel EMG allows for comparison of the timing and contraction and will assist the patient to train the 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 the dual channel MyoTrac 2 can be used to monitor both muscles.
USING MYOTRAC 2 FOR PF PAIN
The MyoTrac 2, also from Thought Technology, is a dual channel EMG monitor similar to the MyoTrac but with a numeric readout in addition to the visual (LED) feedback and audible tone. With the aid of the digital readout (displaying absolute micro-Volt levels), it becomes easy to demonstrate to the patient the initial asymmetry between the VMO and the VL activity. As well, this permits an easier visualization of the effect of training. The MyoTrac 2 also permits the recording of the patient's training sessions, thus allowing to demonstrate progress of training over time. The stored data may be downloaded to a printer for documentation purposes, or downloaded to an IBM compatible computer for further analyses.
(Do this only once, settings are saved automatically for subsequent use)
Note: You can also use ratio feedback to monitor a VMO:VL greater than 1:1 by choosing the 'Ratio' display (see the MyoTrac 2 User's Manual).
TRAINING WITH MYOTRAC 2
Clinical evidence shows that the VM and VL muscles can be trained specifically to align the patella(6). Ongoing and regular training will produce effects that are beneficial and long term, and the patient can remain free of pain even while participating in activities which are demanding on the patellofemoral joint. Using a single or dual channel EMG device to monitor the VMO and evaluate the patient's progress is the key to success.
Copyright, 1997 The Biofeedback Federation of Europe