Does vastus medialis weakness really predispose to patellofemoral syndrome?
Traditionally, one of the major causes of patellofemoral pain cited in the literature is dysplasia/insufficiency of the vastus medialis obliquus muscle. Lieb & Perry found there was a different orientation of the proximal and distal fibers of the vastus medialis muscle, with the more obliquely oriented distal vastus medialis obliquus causing a medial rather than an extension moment on the patellofemoral joint. Although the early literature suggested there was a significant imbalance of vastus medialis and vastus lateralis activity, but recent studies have not supported this contention.
There have been many investigations of whether relative timing of vastus medialis obliquus and vastus lateralis contraction contributes to patellofemoral pain. This issue also remains controversial. Some studies have found that vastus medialis obliquus had a faster reflex response time than the vastus lateralis in pain-free subjects, whereas the reverse was the case in subjects with patellofemoral pain. This has also been shown in dynamic situations isokinetically and in a stepping task.
The above findings are at odds, however, with the findings of other investigators who found that the vastus medialis obliquus did not fire earlier than the vastus lateralis in the asymptomatic group and that the vastus medialis obliquus was not delayed in the symptomatic group. Because of this lack of change in the firing pattern, some of the investigators have concluded that general quadriceps strengthening only is required in the rehabilitation of patellofemoral pain. However, it has been found that taping the patella of patellofemoral pain sufferers causes an earlier activation of the vastus medialis obliquus and a delayed activation of the vastus lateralis particularly on stair descent. It could be surmised that the vastus medialis obliquus of the patellofemoral pain sufferers needs to fire earlier to overcome the abnormal tracking forces. Perhaps the ability to selectively fire the vastus medialis obliquus is a learned skill rather than an innate ability, much like one would train the abductor hallucis to abduct the great toe or isolate one frontalis to elevate one eyebrow and not the other.
Another predisposing factor for patellofemoral pain is the type and amount of training. Increased training (e.g. increased volume and intensity, hills, steps or squats) increases the load on the patellofemoral joint and this often contributes to the knee pain along with other predisposing factors. The interrelationship of the predisposing factors in patellofemoral syndrome is shown in Figure 24.4.
Fig. 24.4 Factors that can contribute to the patellofemoral syndrome
Assessment of patellar position
As a major component of the treatment of the patellofemoral syndrome is correction of patellofemoral biomechanics, it is essential to assess the relationships between the patella and the femur and the patella and its surrounding soft tissues. The practitioner should carefully assess passive movement of the patella in all directions (medial, lateral, superior, inferior). Also assess the position of the patella in relation to the femur for tilt, rotation and glide. Unfortunately, the tests for patellar position may not be reliable. However, rather than abandon the examination of patellar position, the clinician should use the tests when deciding how to tape the patella, remembering that the tape should decrease the symptoms by at least 50%.
The aim of patellar taping is to site the bone in an ideal position. The patella should sit approximately midway between the two condyles. The most common abnormality is a laterally sited patella which is described as having restricted medial glide. The medial and the lateral patellar borders should be of equal height. A common abnormality is a lower lateral border, a reflection of tight deep retinacular fibers. This is called a lateral tilt. The long axis of the patella should be parallel with the long axis of the femur and deviation is described as a rotational abnormality. The superior and inferior poles of the patella should lie in the same plane. The abnormality seen most commonly in this axis is called posterior tilt and clinically results in the inferior pole being difficult to palpate as it is embedded in the infrapatellar fat pad.
Assessment of muscle function
The clinician must assess the state of the vastus medialis obliquus. In severe cases, there may be frank muscle wasting. This may be bilateral if the condition is congenital, or unilateral if it is acquired as a result of surgery, disuse or injury. It is important also to assess the timing of the vastus medialis obliquus contractions to ensure it is synchronous with the rest of the quadriceps mechanism. On occasions, the vastus medialis obliquus may be strong and bulky but rendered ineffective due to its incoordinate action. It is important to assess the vastus medialis obliquus in weightbearing. Often a patient is able to contract the vastus medialis obliquus correctly while sitting but not while standing.
Examination of the hip is also an important component of the clinical assessment of patellofemoral pain. Internally rotated femurs cause tightness of anterior hip structures. This must be assessed in prone in a figure of four position to determine the flexibility of the hip in extension and external rotation. Restricted hip range of motion decreases strength and impairs control of the posterior fibers of gluteus medius. Any weakness or incoordination requires treatment.
Assessment of foot position
While the patient is in prone, the intrinsic foot mechanics can be examined to determine if there is a component of the patellofemoral problem that may be affected by abnormal foot mechanics.
Treatment
The management of a patient with patellofemoral syndrome requires an integrated approach which may involve:
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reduction of pain and inflammation
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taping to correct abnormal patellar position
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vastus medialis obliquus strengthening
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stretching
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massage therapy
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bracing
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correction of abnormal biomechanics
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correction of other possible causative factors
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acupuncture
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surgery
Reduction of pain and inflammation
The first priority of treatment is to reduce any acute inflammation that may be present. This is achieved with a combination of rest from aggravating activities, ice, NSAIDs and electrotherapeutic modalities (e.g. ultrasound, laser, electrical stimulation). Taping should have an immediate pain-relieving effect.
Taping
The aim of taping in the management of patellofemoral pain is to correct the abnormal position of the patella in relation to the femur. Taping the patella relieves pain but the mechanism of the effect is still being investigated. Taping the patella of symptomatic individuals that decreased pain by 50%, resulted in an earlier activation of the vastus medialis obliquus relative to the vastus lateralis on both step up and step down. For example, when subjects stepped down, vastus medialis was activated for the first 8.3o of knee flexion before vastus lateralis contracted. This occurred because the vastus medialis activated earlier in the step-down than in the pre-taped condition, and because vastus lateralis activation was significantly in the taped condition. Patellar taping has been associated with increases in loading response knee flexion, as well as increases in quadriceps muscle torque. Taping is an effective interim measure to relieve patellofemoral pain while other biomechanical abnormalities (e.g. vastus medialis obliquus weakness, excessive pronation) are being corrected.
It is important that the clinician recognizes a posteriorly displaced inferior pole of the patella, as taping the patella too low will increase the patient's symptoms. A commonly used technique involves taping the patella with a medial glide (Fig. 24.5a). It may also require correction of abnormal lateral tilt (Fig. 24.5b), rotation (Fig.24.5c) or anterior tilt (Fig. 24.5d). The taping is performed with rigid strapping tape.
24.5 Patellar taping techniques
The effect of taping should always be assessed immediately. A pain provoking activity such as a single or double leg squat should be performed immediately prior to taping and repeated afterwards. If the tape has been applied correctly, the post-taping squat will be painless. If pain persists, the tape should be altered, possibly including a component for tilt or rotation or both. If patients are able to perform strengthening exercises pain-free without tape, then exercises alone will usually correct the abnormality. Most people, however, require tape to perform the exercises and, initially, to continue their sporting activities. Acute cases of patellofemoral pain may initially need tape applied 24 hours per day until the condition settles. The tape time is then gradually reduced.
Adverse skin reactions can occur beneath the rigid tape. Therefore, the area to be taped should be shaved and a protective barrier applied beneath the rigid strapping tape to reduce both the reaction to the zinc oxide in the tape adhesive and the reaction to shearing stresses on the skin. This can be achieved with adhesive gauze tape (Hypafix or Fixomull) applied to the area to be taped. A protective barrier or plastic skin can also be used in patients with extremely sensitive skin. If skin irritation still occurs, the patient must be advised to remove the tape. Treatment with a hydrocortisone cream may be necessary. Patients with fair skin seem to have particularly sensitive skin and need to be monitored closely.
Muscle training
The patient needs to improve the loading of the lower extremity, so the forces can be spread more evenly though the patellofemoral joint. This usually involves training the vastus medialis obliquus and the gluteus medius muscles.
The first step in a vastus medialis obliquus strengthening program is for the patient to learn to isolate the muscle as much as possible. The patient should palpate the vastus medialis obliquus while contracting in various degrees of knee flexion to determine which position gives maximum contraction. A dual channel biofeedback machine may also be used (Fig. 24.6). The patient needs to be free of patellofemoral pain before these exercises can become effective, otherwise muscle action may be inhibited. Therefore, taping may be required to relieve the pain and allow contractions to occur. The patient should attempt to recruit the vastus medialis obliquus to contract before the rest of the quadriceps. Note that electrical stimulation of the vastus medialis obliquus and EMG biofeedback training improve congruency of the patella within the trochlea on X-ray.
What types of exercises are most appropriate in training? Current evidence suggests that closed chain exercise, i.e. when the foot is on the ground, is the preferred method of training, as closed kinetic training has been shown to improve patellar congruence. Also, effective muscle training is specific to limb position, as synergistic movement patterns need to be trained.
Initially if the patient is in severe pain or is suffering from 'movie-goer's knee', vastus medialis obliquus exercises can commence in sitting with the knee at 90o, the foot on the floor and the patient palpating the vastus medialis obliquus to facilitate muscle activation. A dual channel biofeedback or in some cases, a muscle stimulator may assist the process. As soon as possible, the patient should begin training in a weightbearing position and perform functional exercises with steadily increasing load and difficulty. The aim is to achieve a carry over from functional exercises to functional activities. As the wasted vastus medialis obliquus may suffer fatigue easily, the patient should perform small numbers of exercises frequently throughout the day. Isometric adduction may be useful in facilitating vastus medialis obliquus activity during weight bearing as well as in sitting with the knee flexed, but has no effect on the quadriceps contraction in nonweightbearing and supine lying. A series of graded vastus medialis obliquus exercises is demonstrated in Figure 24.6.
24.6 Vastus medialis obliquus strengthening exercises
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(a) Lunge
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(b) Step-down with biofeedback machine in place |
(c) Hip stability exercise |
Pelvic control may need to be addressed as poor anterior, lateral or rotational control of the pelvis during activity may load the patellofemoral joint excessively. Strengthening of the gluteus medius helps to stabilize the lateral pelvis and to control external hip rotation. This may be performed in weight-bearing positions (Fig. 24.7) and incorporated into functional exercises. In patients with unilateral poor pelvic control, comparison with the other side is beneficial as it helps the patient to understand the relevance and function of the exercises.
Fig. 24.7
There are various strengthening exercises for gluteus medius. In the method illustrated, the patient stands on one leg and raises and lowers the other leg. This strengthens the gluteus medius on the weightbearing side
Stretching
Stretching of tight lateral structures such as the lateral retinaculum is beneficial. This is best done in a side-lying position with the knee flexed. The patella is glided medially using the heel of the hand for a sustained stretch (Fig.24.8a). Other simple stretching techniques can be performed by the patient as shown in Figure 24.8b. Attention must also be paid to stretching the quadricep, hamstring and calf muscles as well as the iliotibial band.
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Fig 24.8 Stretching of lateral structures
(a) Mobilizing the patella. With the patient in a side-lying position, the patella is mobilized in a medial direction. This can be combined with massage therapy to the lateral structures (e.g., transverse gliding, friction)
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(b) Self-mobilizing of the patella. This may be combined with self-massage while stabilizing the patella. |
Massage therapy
Massage therapy may be performed to release tight structures (e.g. iliotibial band, hamstrings). Attention should be given to restoring normal muscle and fascial length. Transverse friction and transverse gliding should be applied to focal regions of thickening. Sustained myofascial tension (myofascial release) is the technique of choice to correct fascial thickening and shortening (Fig. 24.9).
Fig. 24.9
Soft tissue therapy--sustained myofascial tension of the distal iliotibial band
Braces
Some commercially available braces are available to maintain medial glide. In North America, the GII Patellar stabilizing Fx brace has been specifically designed to treat this condition. Although braces are less specific than taping and are unable to affect tilt or rotation, they may play a role in those patients who suffer recurrent patellar subluxation or dislocation and in those who are unable to wear tape (Figure 24.10).
Fig 24.10
Patellar stabilizing brace.
Orthotics
Excessive subtalar pronation causes increased internal rotation of the lower limb and this changes the alignment of the patella in the femoral groove. Orthotics may be required to correct this.
Correction of other precipitating factors
The history and examination may have shown other possible causative factors (e.g. training, shoes, surfaces) that require correction.
Surgery
The need for surgery in patellofemoral syndrome has been almost eliminated due to the improved understanding of its etiology and the introduction of the vastus medialis obliquus strengthening and taping program. The only indication for surgery in this condition is failure of an appropriate conservative management program.
In the presence of clinical and arthroscopically demonstrable chondromalacia patellae, chondroplasty may be performed. The previously popular procedure known as lateral retinacular release is now rarely necessary but, if performed, requires appropriate post-operative rehabilitation with an emphasis on vastus medialis obliquus control. |
Patellofemoral syndrome II
