Patellofemoral Pain Syndrome*

Transcription

1 /84/ $02.00/0 THE JOURNAL OF ORTHOPAEDIC AND SPORTS PHYSICAL THERAPY Copyright O 1984 by The Orthopaedic and Sports Physical Therapy Sections of the American Physical Therapy Association EMG Biofeedback as Treatment for Patellofemoral Pain Syndrome* HOLLY H. WISE, PHD, PT,t IRA M. FIEBERT, PHD, PT,* JONATHAN L. KATES, MDQ Patellofemoral pain syndrome may be classified as a dysfunction of the patella's ability to track in the femoral groove. This study identifies an effective treatment approach for patellofemoral pain syndrome. The approach integrates the concept of improved patellar tracking through selective enhancement of the vastus medialis oblique muscle with conventional exercise regimens for patellofemoral pain syndrome. Six patellofemoral pain syndrome patients were enrolled in a three-phase electromyographic biofeedback and exercise program: 1) biofeedback orientation and instruction in isometric quadriceps contractions, straight leg raises, and a home program; 2) biofeedback training for vastus medialis oblique enhancement with isometric quadriceps contractions, straight leg raises, terminal knee extensions, and progressive resistive exercises; and 3) incorporation of increased vastus medialis oblique activity in functional patterns of movement. All six patients learned to alter their vastus medialis oblique activity through the use of this treatment approach. The alteration of vastus medialis oblique activity resulted in an apparent change in the patellofemoral forces and a concomitant decrease in the patients' complaints of pain. These patients were able to return to pain-free functional activities in only six to nine treatment sessions within a 4- to 6-week period. The use of electromyographic biofeedback coupled with a graded exercise program is an efficient and effective treatment approach for patellofemoral pain syndrome patients. The purpose of this pilot study was to identify an effective, short duration treatment approach for patellofemoral pain syndrome. This treatment approach utilized the concept of improved patellar tracking in an attempt to return patients with patellofemoral pain syndrome to pain-free functional activities. Improved patellar tracking was accomplished in this study through the utilization of integrated EMG biofeedback to selectively enhance the vastus medialis oblique muscle. Patellofemoral pain syndrome may be classified as a dysfunction of the patella's ability to track in the femoral groove. A diagnosis frequently associated with patellofemoral pain syndrome is chondromalacia patellae. The patella is a sesamoid 'This study was conducted at the Physical Therapy Faculty Clinic, University of Miami, 5801 Red Road, Coral Gables, FL t CeOwner. Physical Therapy Associates. P.A., Suite 606, Sunset Professional Building, 6280 Sunset Drive, Miami, FL $Associate Professor and Director, University of Miami, School of Education and Allied Professions, Program in Physical Therapy, Coral Gables, FL Clinical Assistant Professor, University of Miami, School of Medicine, Department of Orthopaedics and Rehabilitation, PO Box (D27), Miami. FL bone within the quadriceps femoris muscle tendon. This bone tracks within the patellofemoral groove, moving cephalically on knee extension and caudally on knee flexion. The ability of the patella to track in this groove is dependent upon passive'and active stabilizers. Passive stabilizers include the lateral femoral condyle, the depth of the patellofemoral groove, and the Q angle. The lateral femoral condyle is more prominent anteriorly than the medial femoral condyle and, therefore, buttresses against lateral patella dislocation. The depth of the patellofemoral groove with its ligamentous attachments maintain the patella. The quadriceps femoris tendon and the patellar tendon hold the patella stable superiorly and anteriorly, respectively. The medial and lateral patellofemoral ligaments maintain medial-lateral stability of the patella in the groove.13 The Q angle is the angle formed between two drawn lines. Line 1 is drawn from the middle of the patella to the center of the tibia1 tubercle. Line 2 is drawn from the center of the patella to the center of the anterior superior iliac spine. The normal measurement for this angle is approxi-

2 WISE ET AL JOSPT Vol. 6, No. 2 mately An angle greater than this increases the valgus angle between the quadriceps femoris muscle and the patella tendon and increases the tendency of the patella to shift lateral/~.~ The vastus medialis oblique is the most frequently cited active stabilizer of the patella.6~8,11-'4 This portion of the vastus medialis muscle originates from the medial aspect of the distal femur and transverses horizontally to insert into the medial aspect of the patella via the medial retinaculum.' The orientation of these fibers counteract lateral shifting of the patella during active knee extension. The patella serves three primary functions. The most important function is to increase the efficiency of the quadriceps femoris muscle throughout knee extension. A second function is to transmit the quadriceps femoris force to the tibia. The third function is one of protection and'cosmesis." It is through this second function that compressive forces are generated on the articular surfaces of both the patella and femur. Alterations in the patella's ability to track may lead to patellofemoral pain syndrome. When the patella tracks in the patellofemoral groove, the contact point of the articular surfaces against the femoral condyles varies with the different positions of the knee. When the knee is functioning normally, the medial and lateral patellar articular facets receive compressive forces when contacting the femoral condyles. When the patellar tracking dysfunctions are diagnosed, it is usually an increase in the lateral movement of the patella. This alters the compressive forces on the articular surfaces of the patella and the femoral condyles. In addition, active resistive knee extension and slowly applied compressive loads, such as prolonged sitting with knees bent and walking down stairs, produce discomfort from the compressive forces.8314 CONVENTIONAL MANAGEMENT Historically, conservative management for this tracking dysfunction has consisted of an exercise regimen. This regimen includes isometric exercises for the hip musculature, isometric quadriceps femoris sets, straight leg raising, terminal knee extension, and minimal impact loading activities. These programs emphasize terminal knee extension as this activity is considered the least compressive to the patellofemoral joint and is an activity in which the role of the vastus medialis oblique is considered the most cru- Cia~~l.4.5.7,9,12-14,18 The major concept behind these exercises is strengthening the quadriceps femoris muscle with emphasis on the vastus medialis oblique. Consistent with this approach was the use of faradic current to stimulate the vastus medialis in order to treat chondromalacia at el la.^ The use of the faradic current to stimulate the vastus medialis separate from the remainder of the quadriceps femoris muscle is an available option as the muscle group receives separate innervations from the femoral nerve.'' LeVeau and Rogers1' believe that exercises to the quadriceps femoris muscles, though aimed at the vastus medialis, will also strengthen the vastus lateralis. Therefore, they studied the ability to selectively enhance vastus medialis contraction while maintaining the vastus lateralis at its baseline level during quadriceps femoris muscle contraction with the assistance of EMG biofeedback. They found that in a period of 3 weeks, activity levels of the vastus medialis and lateralis could be altered in normal subjects. The fact that EMG biofeedback produced these changes in 3 weeks, whereas most exercise regimens for patellofemoral pain syndrome require considerably longer time periods, led the authors to undertake this pilot study. MEDICAL EVALUATION This dysfunction is found equally in males and females with an average occurrence ranging between years of age. In the past, patellofemoral pain syndrome was associated with nonathletic adolescent females with genu valgus. Today, not only may patellofemoral pain syndrome be found in patients with osteoarthritis, but it is also one of the most common complaints seen in sports medicine practices. In runners, patellofemoral pain syndrome is consistent with the pattern of an overuse syndrome with pain commencing during activity. If the individual continues to train, pain persists after the activity ceases and may become constant. A frequent complaint of individuals with this syndrome is aching anterior knee pain which the patient will sometimes describe as being inside the knee. The pain is exacerbated by stair climbing (especially going downstairs), getting up from the sitting position, and sitting for long periods of time ("movie sign"). Associated complaints may

3 JOSPTSeptJOct 1984 EMG BIOFEEDBACK AND PATELLOFEMORAL PAIN 97 be giving way of the knee and a clicking sensation. The episodes of giving way are frequently preceded by sharp pain in the knee. The most common findings on physical examination are pain on medial displacement of the patella and tenderness of the medial and lateral patellar facets. The apprehension test, lateral displacement of the patella, is positive if the patient has had an episode of dislocation of the patella. In more advanced cases effusion may be present. The presence of crepitus is not considered a significant finding with this syndrome. An effort should be made to identify and, if possible, treat predisposing factors. Some of these factors are an increased Q angle, atrophy of the vastus medialis oblique, increased femoral anteversion, external tibia1 torsion, a tight iliotibial band, and pronation of the feet." Roentgenographic examination frequently shows no abnormalities. However, anterior-posterior, lateral, and tangential views should be obtained to document patella alta, lateral tilting of the patella, or irregularity of the patellofemoral surface. METHOD Population This pilot study includes six subjects; two men and four women. All subjects were initially evaluated at the student health service center on campus. They were diagnosed as having patellofemoral pain syndrome. They were then referred to the Physical Therapy Faculty Clinic for treatment. In an effort to decrease physician and physical therapist variability, all the patients included in this study were diagnosed by one physician and treated by only one physical therapist. Instrumentation The Hyperion 312 integrated electromyographic biofeedback unit (Hyperion, Inc., SW 136th St., Miami, FL 33186) was used to produce the EMG biofeedback. The unit allows for both visual and auditory feedback, as well as threshold control. This unit was also equipped with a Hyperion 666 electric printer which provided objective printed evidence of the subjects' electromyographic performance (Fig. 1). The patients were connected to this unit by two sets of silver-chloride surface electrodes. These Fig. 1. Hyperion 312 integrated electromyographic biofeedback unit with Hyperion 666 electric printer. Fig. 2. Placement of electrodes over the vastus rnedialis oblique and vastus lateralis muscles. disposable electrodes consisted of a 4-in strip of tape with three electrodes spaced equidistantly within this tape. The ground electrode always occupied the middle position with the active electrodes on either side to ensure consistency in application. One set of electrodes was placed over the greatest bulk of the vastus medialis oblique muscle. The other set of electrodes was placed over the vastus lateralis muscle (Fig. 2). Trial and error was used to locate the most electrically active portion of these muscles. Once the locations were identified, the same locations were used for each treatment session for each respective patient. The areas of the leg were either marked in ink or the area was shaven to facilitate consistency from treatment session to session.

4 Treatment Program The objective of this treatment program was to selectively enhance the vastus medialis oblique muscle by EMG biofeedback in an effort to decrease patients' pain and return them to their functional activity level. In addition, it was believed that this objective would be attainable within a 3- week interval. To attain this objective, the program was developed with three phases. PHASE I The objective of phase I was to orient the patient to the EMG biofeedback unit. The patient was positioned on a plinth in a semisupine position to allow for comfort and visibility to the EMG biofeedback screen. The therapist located the most electrically active portion of the vastus medialis oblique and vastus lateralis while having the patient perform pain-free isometric quadricep contractions. After the placement of electrodes was confirmed, the therapist explained the visual and auditory parameters of the EMG biofeedback unit. The patient was then asked to perform painfree isometric quadriceps contraction to observe and listen to the electrical activity. Through use of visual observation of the electrical activity on the screen and listening to the changes in amplitude and rate of the sound, the patient was asked to increase, decrease, and alter the relationship of the electrical activity produced by the vastus medialis oblique and vastus lateralis muscles. The patient was instructed to perform these exercises within pain tolerance. This isometric quadriceps contraction was used for the patient's orientation as it is considered the least compressive exercise for the patellofemoral joint. The patient was instructed to hold the isometric contraction for 7l/2 sec, the length of the visual screen sweep, and then relax for 71/2 sec, another visual screen sweep. This was to develop a working relationship between patient and the EMG biofeedback unit, and provide for an optimum learning experience. After practicing and observing visual and auditory parameters of the isometric quadriceps contraction, the patient was requested to perform straight leg raising for 71/2-sec intervals. Printouts of the vastus medialis oblique and vastus lateralis activity during the isometric straight leg raising were taken during each of the sessions. These printouts afforded the documentation of change in vastus medialis oblique and vastus lateralis activity during these exercises. ET AL JOSPT Vol. 6, No. 2 While the patient was in phase I, they were instructed to perform the isometric quadriceps contraction and the straight leg raising exercises at home for 71/2-sec intervals, 10 repetitions each, twice daily, free of pain. It was hypothesized that the patient would have some carryover effect from the EMG biofeedback session and the pain-free home exercises would be enhancing the patient's ability to use the vastus medialis oblique muscle when performing quadriceps activities. Phase I was completed within one to two treatment sessions. Supplemental Devices The use of an infrapatellar strap was employed with one subject during this phase of the program. The rationale for the use of this strap was to alleviate the irritation of the patella during extended periods of stress to the knee.'' However, once the vastus medialis oblique enhancement was demonstrated, the subject was able to discontinue use of this strap. The utilization of ice packs and the prescription of anti-inflammatory medication were utilized as needed for relief of pain.16 PHASE II The objective of phase II was to train the patient to selectively increase the vastus medialis oblique muscle activity in relation to the vastus lateralis muscle. This objective was chosen as LeVeau and Rogers demonstrated the feasibility of this with normal subjects." During this phase, the patient was again instructed to perform isometric quadriceps contractions and straight leg raising for 7lh-sec intervals. However, the patient was instructed to alter the EMG activity during contractions. The primary task was to increase the electrical activity of the vastus medialis oblique muscle while maintaining the electrical activity of the vastus lateralis muscle at its already established baseline. The instructions the patient received from the therapist consisted of: try to increase the beeping sounds (this was to increase the electrical activity of the vastus medialis oblique) and try to keep the amplitude of the electrical activity of the vastus lateralis unchanged from its previous amplitude. When the patient was able to master this skill for the activities of isometric quadriceps contraction and straight leg raising, terminal knee extension was added to the regimen. This exercise,

5 JOSPT Sept/Oct 1984 EMG BIOFEEDBACK AND PATELLOFEMORAL PAIN 99 also known as short arc quadriceps, was an active knee extension contraction in the range of -30 to 0' extension. It is believed that this range of knee extension emphasizes vastus medialis contraction and is not as compressive on the articular surfaces of the patella and femoral condyles as are knee exercises from 90' of flexion to 30' of flexion.18 Following successful mastery of this exercise, resistance in the form of cuff weights was added within the patient's tolerance. Once again, the patient was instructed to carry out these exercises on a home program. Phase II was completed within two to six treatment sessions. PHASE Ill The objective of phase Ill was to incorporate this increased vastus medialis oblique activity into functional patterns of movement. Activities such as bicyling, ambulation, and stairs were monitored by the EMG biofeedback. During these activities, the patient was instructed to increase the amplitude of electrical activity of the vastus medialis oblique muscle while maintaining the vastus lateralis at its baseline. Upon becoming pain free during these exercise,^, the patient was instructed to pursue these activities outside of the clinic. When the patient attained pain-free function of these and other functional activities, the patient was discharged from the program. Phase Ill was accomplished in the last two treatment sessions. Supplemental Devices Foot orthoses were prescribed for one subject to enable a smooth transition to phase Ill. This subject, a jogging enthusiast, demonstrated bilateral pronation of the feet. It was felt that pronation, especially during running, was contributing to the stress of the knee joints. Therefore, the subject was fitted with running shoe orthoses and began a walk-run program without discomfort with eventual return to jogging. RESULTS The demographic variables of age and sex for each of the subjects is presented in Table 1. This table also presents a brief history concerning duration of the problem plus the patient's perception of why the problem had recently exacerbated. The electrical activity of the vastus medialis oblique and the vastus lateralis while performing TABLE 1 Subjects ' profile Subject Age Sex History 1 15 M Six-year history. Fractured tibia 1978; recent episode of pain playing soccer F Six-month history. Injured running F Long history. Recent episode aggravated in dance class and marching band M Five-year history of pain. No known trauma. Pain aggravated by increased sitting in class F Two-year history. No known trauma. Increased episode of pain 2O sitting in class F Three-year history. No known trauma. Recent episode of pain provoked by dance class. TABLE 2 Initial EMG activity during isometric quadriceps contraction (in WV) Subject VMO' VL* VM0:VL ratio - - ' VMO, vastus medialis oblique; VL, vastus lateralis. pain-free isometric quadriceps contraction for 7'/2 sec during.the initial session is presented in Table 2. This table also presents the ratio of electrical activity between the vastus medialis oblique and vastus lateralis muscles. In five of six cases the electrical activity of the vastus medialis oblique muscle increased more than the electrical activity of the vastus lateralis. For subject 6, this was reversed as the vastus lateralis muscle demonstrated less microvolt activity at the start of the program and therefore increased its microvolt activity greater than the vastus medialis oblique (Table 3). Through a comparison of the electrical activity of the vastus medialis oblique (VMO) and vastus lateralis (VL) muscles, the VM0:VL ratio is found. The ratio of microvolt activity during the initial session ranged from 1 :1.26 to 1 :2.60 (Table 2). These ratios were changed when the microvolt activity was measured during the final session.

6 100 WISE ET AL JOSPT Vol. 6, No. 2 The final range of ratios was from 1 :1.0 to 1 :1.55 (Table 3). The alterations in electrical activity changed the VM0:VL ratios (Table 4). The intersubject ratio variance depended upon the magnitude of microvolt activity difference from the commencement of the program to the completion of the program. The larger the ratio at the beginning of the program the greater the potential for a ratio improvement. The ratio differences ranged from 0.15 to 1.05 (Table 4). Table 5 presents the summative report on the six patients in this study. The number of treatments received, the number of weeks over which TABLE 3 Final EMG activity during isometric quadriceps contraction (in PV) Subject VMO' VML:VL ratio : : : :1.OO : :1.10 * VMO, vastus medialis oblique; VL, vastus lateralis. TABLE 4 Change from initial to final EMG activity during isometric quadriceps contraction (in pv) Subject VMO' VL' Ratio differential VMO, vastus medialis oblique; VL, vastus lateralis. t NA, not applicable. these treatments were spread, the patient's activities at discharge, and the supplemental material necessary for functional activities are included in this table. DISCUSSION TABLE 5 Surnmative data of subjects at discharge All subjects in this study had long standing pain associated with patellar tracking dysfunction. However, they initially varied greatly in the average microvolt electrical activity associated with maximal pain-free isometric quadriceps contractions. The subjects' vastus medialis oblique electrical activity spanned a range of pv ( pv). The vastus lateralis muscle electrical activity spanned a range of pv ( pv). For all subjects the magnitude of pain-free electrical activity during maximal isometric quadriceps contractions was altered through the use of EMG biofeedback. The subjects vastus medialis oblique electrical activity, as measured in the final session, spanned a range of pv ( pv). The vastus lateralis muscle electrical activity spanned a range of pv ( pv). This highlights the use of EMG biofeedback with exercise as it does alter electrical activity of the vastus medialis oblique and the vastus lateralis. However, since the range of final electrical activity of the subject's vastus medialis oblique and vastus lateralis is so great for the different subjects, it appears that the magnitude of the quadriceps electrical activity is not of primary importance to patellofemoral pain syndrome. It does appear that the ratio of vastus medialis oblique muscle to the vastus lateralis muscle is relevant. The range initially for these subjects was 1 :1.3 as the smallest VM0:VL ratio to 1 :2.6 as the largest VM0:VL ratio. Subject y:'f Treatment Activities at duration discharge Orthoses rnents 6 3 weeks Pain-free bicycling. Returned to soccer. None 6 4 weeks Pain free. Joined fitness center. Started Running shoe orthoses for pronated feet. walk-run program. 9 4 weeks Relatively pain free. Returned to march- None ing band. 8 6 weeks Pain free. Purchased weights. On home None program. 6 3 weeks Pain free. Swimming, bicycling. On lnfrapatellar strap for use when standing home program. for long periods. 6 2 weeks Pain free. On home program. None

7 JOSPT SeptlOct 1984 EMG BIOFEEDBACK AND PATELLOFEMORAL PAIN 101 For all subjects this ratio was altered with the EMG biofeedback program. The range in ratios shifted to 1:l.O to 1:1.55. For each individual subject the ratio was lowered. It appears that the approximation of a 1:1 ratio relates to pain-free quadriceps function (Figs. 3 and 4). Five of the six subjects were approximately in the conventional age range for this syndrome. The one subject who was considerably older (45 years) commenced this program with the largest ratio (1:2.6). This may imply that the patellofemoral pain syndrome progressively worsens with age. This patient was treated six times over a 4- week period with a final ratio of 1 :1.55. It is possible that an increased number of treatment sessions would have brought the ratio down to approximately 1 :l. The six treatment sessions appear to be the low end of the range. Four of the subjects were able to master the learning process in only six sessions, while two subjects required eight and nine sessions, respectively. Subject 6 presented a most unique profile. In this instance, the electrical activity of the vastus medialis oblique (180.0 pv) was greater than the electrical activity of the vastus lateralis ( pv). This was the complete reciprocal of the electrical activity of the other five subjects and the information related to patellofemoral pain syndrome in the literature. Following therapeutic intervention this 1.43:1 ratio was altered to 1 :1.1 as the electrical activity of the vastus medialis oblique increased to pv, an increase of 45.0 pv and the vastus lateralis was increased to pv, an increase of pv. Though this patient presented an EMG profile opposite to the convention, and was treated to enhance the vastus lateralis muscle rather than the vastus medialis oblique, the post-treatment finding was the approximated 1 :1 ratio and freedom from pain. Subject 3 reported overall relief of pain with the biofeedback protocol but was the only subject with occasional episodes of discomfort reported at discharge. A review of this subject's results demonstrate that this subject initiated treatment with the smallest inequality of VM0:VL ratio, received the most number of biofeedback sessions, and at discharge demonstrated the least amount of increased microvolt activity in the vastus medialis oblique, (33.5 pv). Additionally, this subject demonstrated the smallest ratio difference, a decrease of It appears that the subjects with the greatest inequality of VM0:VL ratios, and thus are able to ISOMETRIC QUADRICEP CONTRACTION TIME (SECONDS) KHANNEL 1 MUSCLE: Vastus Medialis Oblique +CHANNEL 2 MUSCLE: Vastus Lateralis Fig. 3. Initial EMG activity during isometric quadricep contraction.

8 WISE ET AL JOSPT Vol. 6, No. 2 ISOMETRIC QUADRICEP CONTRACTION TIME (SECONDS) *CHANNEL 1 MUSCLE: Vastus Medalis Oblique +CHANNEL 2 MUSCLE: Vastus Lateralis demonstrate a larger improvement in vastus medialis oblique function, receive the most dramatic results. SUMMARY This paper presents an efficient and effective treatment approach for patellofemoral pain syndrome. This approach incorporates the concept of improved patellar tracking through selective vastus medialis oblique enhancement and the conventional exercise regimens in the treatment of patellofemoral pain syndrome. Through the use of EMG biofeedback and conventional exercises for patellofemoral pain syndrome, six patients learned to alter the activity of their vastus medialis oblique and vastus lateralis muscles. This alteration of muscular activity resulted in improved patellar tracking and changes in the compressive forces applied to the patellofemoral joint with a concomitant decrease in the patients' complaints of pain. The authors attempted to alter the muscular activity of the patients' vastus medialis oblique and vastus lateralis muscles within 3 weeks, as previously demonstrated in normal subjects by Fig. 4. Final EMG activity during isometric quadricep contraction. LeVeau and Rogers." In this pilot study, the six subjects required from 3-6 weeks of intermittent training sessions before becoming pain free. However, these subjects received only six to nine treatments interspersed over the training duration. It appears that this motor learning, the alteration of muscular activity of the vastus medialis oblique and vastus lateralis muscles, may be facilitated if the treatment sessions are increased in frequency. The results of this pilot study indicate that a 1 :1 ratio or the approximation of a 1 :1 ratio for the vastus medialis oblique and vastus lateralis is the desired target ratio for patellofemoral pain syndrome patients to become pain free. However, EMG documentation of the normal ratio for these muscles has not been established. Preliminary studies are contradictive. Reynolds and Levine15 studied 20 normal women at -30' knee extension and concluded that there are no differences in vastus medialis oblique and vastus lateralis EMG activity during isometric contractions. However, Fox3 reports that, clinically, 40% of his asymptomatic patient population present with vastus medialis oblique and vastus lateralis inequalities. Fox predicts that these individuals will become symptomatic over time. Accordingly, further clinical in-

9 JOSPT SeptlOct 1984 EMG BIOFEEDBACK AND PATELLOFEMORAL PAIN 103 vestigations of the normal ranges for the VM0:VL ratio need to be undertaken. In conclusion, the authors support the use of EMG biofeedback coupled with conventional patellofemoral pain syndrome exercises as an efficient and successful treatment approach for patients with patellofemoral pain syndrome. REFERENCES 1. Dehaven K. Dolana W. Mayer P: Chondromalacia patella in athletes-clinical presentation and conservative management. Am J Sports Med 7:5-11, Ficat R. Hungerford D: Disorders of the Patello-femoral Joint, pp Baltimore: Williams & Wilkins, Fox T: Dysplasia of the quadriceps mechanism: Hypoplasia of the vastus medialis muscle as related to the hypermobile patella syndrome. Surg Clin North Am 55: Halbach J, Straus D: Comparison of electro-myostimulation to isokinetic training in increasing power of the knee extensor mechanism. J Ortho Sports Phys Ther 2: Hungerford D. Lennox D: Rehabilitation of the knee in disorders of the patellofemoral joint: Relevant biomechanics. Ortho Clin North Am 14: , Johnson D, Thurston P, Ashcroft P: The Russian technique of faradism in the treatment of chondromalacia patellae. Physiother Can 29: Keller E: Patellar malalignment syndrome in runners. The nurse practitioner. Am J Primary Health Care 8(6):27-38, Kessler R. Hertling D: Management of Common Musculoskeletal Disorders Physical Therapy Principles and Methods, pp Philadelphia: Harper & Row Lennington K, Yanchuleff T: The use of isokinetics in the treatment of chondromalacia patellae: A case report. J Ortho Sports Phys Ther 4: , Levine J, Splain S: Use of the infrapatellar strap in the treatment of patellofemoral pain. Clin Orthop 139: , LeVeau B, Rogers C: Selective training of the vastus medialis muscle using EMG biofeedback. Phys Ther 60: , Malek M. Mangine R: Patellofemoral pain syndromes: A comprehensive and conservative approach. J Orthop Sports Phys Ther 2: , Paulos L, Rusche K, Johnson C. Noyes F: Patellar malalignment. Phys Ther 60: , Pevsner D. Johnson J. Blazina M: The patellofemoral joint and its implications in the rehabilitation of the knee. Phys Ther 59: , Reynolds L, Levin T: Electromyographic activity of the vastus medialis oblique and vastus lateralis muscles in their role of patellar alignment (abstract). Phys Ther 62:352, Steadman J: Nonoperative measures for patellofemoral problems. Am J Sports Med 7: , Turek S: Orthopaedics Principles and their Applications, Chap 26, pp Philadelphia: JB Lippincott Co, Wild J, Franklin T, Woods G: Patellar pain and quadriceps rehabilitation-an EMG study. Am J Sports Med 10: