rehabilitation of patellofemoral joint disorders: a critical review

Rehabilitation of Patellofemoral Joint Disorders: A Critical Review Christopher M. Powers, A D , PT'

Christopher M. Powers

atellofemoral pain is the most prevalent disorder involving the knee ( 1 5, 46). Over a $year period, Devereaux and Lachmann

( 1 1') demonstrated that 25% of all knees evaluated in a sports injun clinic were diagnosed with patellofemoral pain, while McConnell (50) reports that patellofemoral pain affects one in four of the general population. In addition, a study of 100 painful knees conducted by Outerbridge and Dunlop (56) reported patellofemoral joint pathology in 40 of 50 women and in 15 of 50 men. While patellofemoral-related problems occur with an incidence of two to one in females w. males, men outnumber women when athletes are studied (41 ).

The symptoms of patellofemoral pain are multiple (16,41,68). Pain is generally characterized as being dif- fuse and arising from the anterior aspect of the knee (68). Pain along the medial aspect of the patella is the most common complaint; however, retropatellar pain and pain along the lateral border is often reported ( 1 7). Generally, onset is insidious and progression is slow. Patellofemoral pain

Patellofemoral pain is one of the most common knee disorders seen in orthopaedic practice. Despite its high incidence, treatment of this disorder remains controversial. Traditionallv, nonoperative management of patellofemoral pain has focused on restoring normal patellar tracking by improving dynamic stability. Of particular interest to clinicians has been the vastus medialis oblique, which has been implicated as being the primary medial stabilizer of the patella. Although emphasis on the vastus medialis oblique continues to be the mainstay of conservative care of patellofemoral pain, there exists considerable disagreement between research outcomes and clinical practice. This article criticallv reviews the current literature concerning the treatment of patellofemoral pain with respect to the vastus medialis oblique, taping, and bracing, as well as various forms of therapeutic exercise, and relates these findings to the prevailing views regarding the management of this disorder.

Key Words: patellofemoral pain, rehabilitation, vastus medialis oblique ' Assistant Professor and Director, Musculoskeletal Biomechanics Research Laboratory, Department of Biokinesiology and Physical Therapv, University of Southern California, 1540 E. Alcazar St., CHP-155. Los Angeles, CA 90033

is typically activity-induced and aggra- vated with functions that increase patellofemoral compressive forces. such as ascending and descending stairs, inclined walking, squatting, and prolonged sitting (13,41). Ortho- paedic assessment is usually positive for a patellar grind test and discom- fort with palpation of the medial and lateral borders of the patella (41,58). Swelling, loss of motion, and a sensa- tion of giving way o r instability may also be present (6).

Despite the high incidence of patellofemoral pain in the general population, the pathophysiology of this disorder is not clearly under- stood. The most commonly accepted hypothesis is related to abnormal patellar tracking which increases patellofemoral joint stress and subsequent articular cartilage wear (18,27,30,34, 53,55). Although articular cartilage is aneural and has been dismissed as a possible source of symptoms, it has been proposed that the subadjacent

endplate is exposed to pressure variations that would normally be a b sorbed by healthy cartilage (22). This mechanical stress is believed to stimulate pain receptors in the subchon- dral bone (22).

Historically, conservative treatment of patellofemoral pain has focused on restoring normal patellar tracking by improving dynamic stability (29,40,49). Of particular interest to clinicians has been the vastus medialis oblique (VMO), which has been implicated as being the primary medial stabilizer of the patella (42). In their classic work, Lieb and Pen). (42) identified the distal fibers of the vastus medialis to be angled at a p proximately 55" from the longitudi- nal axis of the femur, making this portion of the muscle best suited to prevent lateral subluxation of the patella (Figure 1 ) . As a result of this mechanical advantage, it has been proposed that the VMO is capable of counterbalancing the lateral pull of

JOSPT Volume 28 Number 5 November 1 9 8

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L I T E R A T U R E R E V I E W

FIGURE 1. F ik r orientation of the quadriceps musculature in relation to the iemur (VL = Vastus lateralis, VI = Vastus intermedius, RF = Rectus [emoris, VML = Vastus medialis longus, VMO = Vastus medialis oblique).

the larger vastus lateralis to ensure patellar stability within the trochlear groove (42).

A lack of equilibrium between the VMO and vastus lateralis is widely accepted as contributing to lateral patellar subluxation (48,76,86). Most authors and clinical protocols at- tribute this dynamic imbalance to W O insuffkiency, which has been associated with atrophy, hypoplasia, inhibition, and impaired motor control (2,15,49). k s a result of these assertions, there has been a strong clinical focus on selective rehabilitation of the VMO in the treatment of patellofemoral pain. The goal of such treatment is to restore dynamic bal- ance of the patella to correct patellar tracking (49,56,59,79). In addition, external suppor~5 such as taping and bracing are commonly used as adjuncts to supplement specific VMO strengthening techniques (26,33,49,57).

Although emphasis on restoring patella stability continues to be the

mainstay of consewative care of patellofemoral pain, there exists considerable controversy between research outcomes and clinical practice. For example, despite the commonly accepted clinical practice of focusing on the VMO in the treatment of patellofemoral pain, recent studies in this area are not entirelv supportive (8,25,36,37,62). The apparent dis- crepancv between research findings and clinical practice may lie in the interpretation of the available research and its subsequent application clinically. Therefore, the purpose of this paper was to 1) compare and contrast the current literature relat- ing specifically to the treatment of patellofemoral pain and 2) relate these findings to the prevailing views regarding the clinical management of this disorder.

Does VMO Insufficiency Exist in the Patellofemoral Pain Population?

The apparent need to focus on the VMO in the treatment of patellofemoral pain is related to the belief that the W O is selectively atrophied or more readily inhibited by pain and/or effusion compared with the other vasti. The only support of this hypothesis, however, was presented by Gerber et al (1 9), who reported that in patients with anterior-cruciate- deficient knees, the vastus medialis was found to demonstrate greater atrophy than the rest of the quadriceps. Although this study did not look at the \'MO specificallv, the relative difference was only 2.7%.

In contrast, the notion of selective \'MO inhibition has been refuted by Spencer et al (77), who reported that through assessment of the H reflex, joint effusion resulted in inhibition of the quadriceps as a whole. Although it appeared that the vastus medialis was affected to a greater ex- tent (the VMO was not isolated), there was no statisticallv significant . .

difference to support this observa- tion. These authors concluded that

reflex inhibition of the quadriceps was not selective as to the various components it affects. This conclu- sion was recently supported by the work of Powers et al (62). who found that subjects with patellofemoral pain demonstrated reduced recruitment of the entire quadriceps muscle group during gait activities. These authors reported that this reduced recruitment was similar for all the vasti and that there were no differences that would suggest a preferential inhibition of the VMO.

Since assessment of isolated VMO and vastus lateralis strength in v i m is not possible, electromvographv (EMG) has been used to compare the relative recruitment of these muscles with the rationale that decreased activity of the \'MO relative to the vastus lateralis is indicative of compromised medial patellar stabilih. Although several investigators have studied the EMG activity of the dynamic patellar stabilizers in subjects with patellofemoral pain, the results of these studies are equivocal. M'hile some authors have found significant differences in VMO and vastus lateralis activity in patients with patellofemoral pain (48,76,86), others have not (6,45,52,85). Direct comparisons of these studies are difficult be- cause of differences in experimental technique and methods of assessing EMG data.

One likelv reason for the incon- sistent results in these investigations may be related to the inherent variability within the patellofemoral pain population. Since etiology of patellofemoral pain has been considered a dynamic entity, it is logical that a deficiency of the medial stabilizers should result in lateral displacement of the patella. It has been documented through radiological examination, however, that less than 50% of patients with patellofemoral pain demonstrate isolated lateral subluxation (70.71 ). This would suggest that lateral patellar tracking is not a uni- versal finding in this disorder and,

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therefore, such an inference cannot be generalized to all patients.

If medial quadriceps deficiency is responsible for patellar malalignment, then it stands to reason that subjects with documented lateral s u h luxation may exhibit imbalances between the dynamic patellar stabilizers, while patients that demonstrate relatively normal alignment may not. To date, only two studies have at- tempted to control for this potential variation within the patellofemoral pain population. Moller et al (52) classified patients into two categories: those with a histoy and clinical findings of patellar instability and those without evidence of patellar instabil- ip. Results showed no differences in VMO and vastus lateralis EMG activity within groups or between groups. indicating that EMG could not be used to identifi subjects with patellar subluxation. This finding is somewhat understandable, considering EMG is not an indicator of muscular strength and, therefore, may not be an appropriate measure to estimate the dynamic forces acting on the patella.

In contrast, Powers et al (65) have provided evidence suggesting that individuals with greater amounts of lateral subluxation demonstrate increased recniitment of the vastus medialis. Using kinematic magnetic resonance imaging techniques and dynamic EMG, these authors found an inverse relationship between lateral subluxation and vastus medialis activity, suggesting that increased recruitment of the vastus medialis relative to the vastiis lateralis is in response to abnormal patellar alignment, and that diminished vastus medialis activity is not necessarily a cause of abnormal patellar tracking.

Although it is not clear from a research standpoint whether VMO insufficiency exists in the patellofemoral pain population (as assessed through EMG) , decreased VMO activity relative to the \astiis lateralis is commonlv reported clinically with the use of EMG biofeedback units. Rased on information o b

RAW EMG (knee extension)

VMO

FIGURE 2. Raw electromvographic (EMGJ signals obtained irom the vastus medialis oblique (VMOI and vastus lateralis (VL) during knee extension. The unnormalized VL:VMO EMG ratio during this activity would be 2: I , suggesting greater recruitment of the VL relative to the VMO. mv = Millivolts.

tained from these devices, clinicians routinely make statements regarding the status of W O recruitment relative to the vastus lateralis and use this information to infer abnormal joint mechanics. There is, however, a fun- damental problem with direct comparison of raw EMG signals between muscles that render such interpreta- tions invalid. To compare EMG signals between muscles, EMG data need to be "normalized" or related to a common standard (87). This proce- dure is necessay to account for ex- traneous factors unrelated to motor unit recruitment, such as potential differences in electrode placement, variable subcutaneous fat layers, and degrees of skin impedance (60). As

Max knee ext.

shown in Figure 2, analysis of the raw EMG signal would suggest that the vastus lateralis (VL) is being recruited twice that of the VMO (a 2:l VL:VMO EMG ratio). However, when that activity is compared with a refer- ence level of EMG (ie., normalized to the EMG obtained diiring a maximal isometric contraction and reported as a percentage of maximum), the VL: VMO EMG ratio becomes 1 :1 (Figure 3). Interpretation of the normalized EMG in Figure 3 would not indicate VMO insufficiency and suggests that the EMG difference in Figure 2 was the result of some other variable unrelated to neuromuscular recniitment (ie., electrode placement). Given the fact that comparisons of EMG between muscles can only be made after some type of normalizing proce- dure, care must be taken in using unnormalized EMG as a basis for guiding treatment and formulating hypotheses regarding the etiology of patellofemoral pain. The failure to normalize EMG data may account for the observed differences in the p ~ i h lished literature and the clinical setting.

It is apparent that there is some disagreement as to whether VMO insufficiency exists in the patellofemoral pain population. Even if compromised VMO function (relative to the vastus lateralis) could be documented on a consistent basis, there is

Knee ext.

VMO = 10Yo Max.

VL = 10% Max.

FIGURE 3. Raw electromvographic fEMGJ signals obtained from the vastus medialis oblique (VMOI and vastus laterah (VL) during both a maximal (max) isometric knee extension maneuver and submaximal knee extension. When the EMG obtained from the submaximal knee extension contraction is expressed as a percentage of the EMG obtained during the maximal isometric knee extension, the normalized VL:VMO ratio becomes l : l , suggesting qua1 relative recruitment of the VL and VMO.

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evidence suggesting that decreased VMO recruitment may not translate to patellar instability and altered patellofemoral joint function. Further research is necessary to correlate EMG patterns with patellar tracking to clearly define the role of the vasti in contributing to patellar kinematics. Until this evidence is available, however, the role of the VMO in contributing to patellar malalignment will remain somewhat speculative.

Neuromuscular Timing of VMO Relative to the Other Vasti

In addition to the magnitude of motor unit activity, asynchronous timing of vasti muscle contraction also has been implicated as contributing to patellar instability. In this model, it is hypothesized that the vastus lateralis contracts earlier than the VMO, therefore, contributing to a laterally directed force on the patella (82). Evidence in support of a timing difference with respect to the onset of VMO activity relative to the vastus lateralis was first presented by Voight and Wieder (82) who reported that activation of the VMO was delayed compared to the vastus lateralis in patients with patellofemoral pain during a monosynaptic reflex (patellar tendon tap), and that this trend was reversed in control subjects. Despite statistical significance, the magnitude of these differences was not reported. and, therefore, the clinical rele\ance of the results could not be assessed.

Voight and Wieder (82) also postulated that a feedforward mechanism may exist, in which the VMO normally contracts prior to the vastus lateralis. Such a temporal advantage would theoretically facilitate the ability of the VMO to maintain patellar stability against the laterally directed forces of the much larger vastus lateralis. The concept of a feedforward mechanism is supported by the findings of Grabiner et al (24) who also reported that activity of the VMO preceded that of the vastus lateralis

in normal subjects. The magnitude of this timing difference, however, was only 5.6 milliseconds, thus, casting doubt as to the clinical significance of this finding.

In contrast, recent investigations have failed to find significant timing differences between the different vasti in subjects with patellofemoral pain (21,37,54,62). These studies var- ied from those of Voight and Wieder (82) and Grabiner et al (24). in that timing was assessed during tasks that typically reproduce patellofemoral pain. In addition, neither of the latter studies reported any evidence of a possible feedforward mechanism with respect to the onset of vasti activity. However, the study by Gilleard et al (21) found that when the patellofemoral joint was taped the VMO was recnlited earlier than the vastus lateralis during both stepup and stepdown tasks.

Based on the results of the above studies, it would appear that the ar- gument for a neuromuscular timing is somewhat tenuous. Vasti timing differences that have been identified in the patellofemoral pain population are of the magnitude of a couple of milliseconds, well below the temporal resolution of most EMG biofeedback units. Although there remains a strong clinical focus on altering the timing of the VMO relative to the vastus lateralis through the use of muscle reeducation techniques (49), further research is necessary to vali- date these treatment approaches.

Can the VMO Be Selectively Recruited or Strengthened?

As mentioned previously, the treatment of patellofemoral pain has focused on restoring dynamic patella stability through strengthening of the VMO. Such clinical practice is based on the assumption that the VMO is disproportionately weak relative to the vastus lateralis, despite the fact that assessment of VMO strength in vivo cannot be quantified. Although

isolated strengthening of the VMO would appear to be desirable from a biomechanical standpoint, there is little evidence suggesting that this is possible. The concept of VMO strengthening is prefaced on the belief that the VMO can be selectively recruited independently of the vastus lateralis through various exercises (29,31,50). The most common activities which have been postulated to facilitate VMO strengthening include various quadriceps exercises (ie., straight leg raises, isometric quadriceps sets, terminal knee extension), hip adduction, and internal tibia1 rotation.

Quadric+ ~xmri.ws For many years, short arc knee extension exercises were thought to selectively strengthen the VMO, as this portion of the vastus medialis was implicated as being responsible for terminal knee extension (1 1,75). A mechanical study by Lieb and Perry (42) demonstrated, however, that the VMO was not capable of independent terminal knee extension and that this range of motion was the result of all vasti working in concert to achieve knee extension. Subsequent to this investigation, there have been many studies supporting the concept that there is no selective function attributable to the VMO with respect to knee extension (1,28,35,43,61,67, 69).

Recent investigations have evaluated whether the VMO can be preferentially recruited with various types of activities in both normal and patellofemoral pain subjects. Cerny (8) examined 22 variations of quadriceps exercises (ie., quadriceps sets, isometric holds with knee flexion, knee extension, wall slides, etc.) and found that neither resulted in greater VMO activity relative to the vastus lateralis. Likewise, studies by Laprade et al (39) and Vaatainen et al (80) found no differences in VMO and vastus lateralis activity during isometric knee extension in both patellofemoral pain and control subjects.

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Hip n0hrt ion Various types of hip adduction exercises (either independently or in conjunction with knee extension) have been advocated as means by which the VMO can be preferentially recruited (29.31 ). The foundation for this hypothesis is based on the anatomical work of Bose et al (5), who observed that the VMO originates from the adductor magnus tendon and, to a lesser ex- tent, from the adductor longus tendon. From a clinical standpoint, i t is thought that contraction of the hip adductors may transfer a physiologi- cal stretch to VMO, which could possibly alter the length-tension proper- ties of these fibers, thus, promoting enhanced force of contraction (31 ). Additionally, it has been proposed that contraction of the hip adductors may provide a more stable proximal attachment and, therefore, facilitate preferential activation of the VMO (36,5O).

There have been many investigations looking at whether the VMO can be preferentially recruited with various hip adduction exercises. Hanten and Schulthies (29) reported greater VMO activity compared with the vastus lateralis during hip adduction, while Hodges and Richardson (31) found that simultaneous hip adduction and knee extension during weight bearing increased VMO EMG activity relative to the vastus lateralis. The latter study did not use normalized EMG, however, and, therefore, the validity of the results must be questioned.

In contrast to the findings of the above studies, other authors have reported no differences in relative recruitment of the VMO compared with the vastus lateralis during various exercises incorporating hip adduction. Kxst and Jewett (36) found that the concurrent use of the hip adductors during knee extension did not increase VMO activitv. Subsequent studies by Grabiner et al (25). Cernv (8). and Laprade et al (39) have also reported that hip adduction has no effect on W O recruitment.

As mentioned previously, differences in experimental technique (ie., surface vs. fine wire electrodes), methods of quantif\ing EMG (normalized vs. nonnormalized) data, and the inherent variability of EMG mea- surements may partially explain these conflicting findings. Additional stnd- ies utilizing larger sample sizes and appropriate experimental techniques are necessan to further explore whether or not hip adduction influences \&I0 activation.

J n t m n l tihinl rotntion As a result of the fascia1 attachment of the VMO to the anteromedial aspect of the tihia through the medial extensor aponeurosis, it has been proposed that the VMO can resist tibial external rotation and be preferentially ac- tivated through internal rotation of the tihia (29.39). Although the VMO would appear to have a role in limit- ing tibial rotation, Hanten and Schul- thies (29) found no etidence of preferential activation of the VMO with resisted internal tihial rotation in normal subjects. This finding is s u p ported by recent work of Cernv (8). who reported no selective recruitment of the W O when subjects performed an isometric quadriceps contraction with the tibia held in internal rotation. In contrast, La- prade et al (39) found that the WO:VL EMG ratio was significantly greater when the motion of internal tibial rotation was resisted simulta- neously with knee extension when compared with isolated internal tihial rotation and hip adduction exercises. It should be noted, however, that the \%IO:C'L EMG ratio during the com- bined internal tibial rotation and knee extension exercise was no dif- fcrent from the EMG ratio obtained during knee extension alone.

S u m m t r ~ Although there is considerable controversy as to whether the \WO can be preferentially recruited relative to the vastus lateralis, one fact remains consistent: the VMO was never functioning independent of the vastus lateralis in any of the

studies cited. This indicates that isolated recruitment of the VMO does not occur with exercises that are commonly prescribed for the treatment of patellofemoral pain, and that selective strengthening is un- likely. Even if greater VMO EMG activity could be elicited relative to the vastus lateralis, the magnitude of VMO contraction would have to be at least 60% of maximum to stimulate hypertrophy (24,44). Given as such, it would appear that isolated recruitment or strengthening of the VMO through selected exercises may not be a realistic goal, and any emphasis on selective strengthening of the VMO would most likely translate into a general quadriceps strengthening effect.

Strengthening of the Extensor Mechanism and Its Role in the Treatment of Patellofemoral Pain

Physical therapy treatment of patellofemoral pain typically includes one or more of the following: lower e x t r e m i ~ strengthening (especially the quadriceps), stretching of tight musculature and the patellar retinac- ulum, anti-inflammatory agents (ie., ice), the use of patellofemoral bracing or taping, foot orthotics, and re- striction of aggravating activities (41, 50,57-59,74,79,85,84). Treatment approaches for patellofemoral pain v a n however, one component that is regularly recommended and commonly incorporated into most pro- grams is strengthening of the extensor mechanism with emphasis on the vastus medialis or the VMO.

Although it can be debated whether exercises used to isolate the VMO actually increase VMO strength or pro\ide a generalized quadriceps strengthening effect, it is apparent from the literature that this form of treatment has produced successful clinical results (10,50,84). A recent study by Powers et al (64) has suggested that locomotor function in persons with patellofemoral pain is

JOSPT Yolume 28 Number 5 Novcmber 1998 349

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;~ssociated with incrc;~sed qriadriceps femoris ~nuscle torque, thus. lending slipport to the concept of strengthening ;IS a usrfd treatment option. De- spite thcsc findings, however, the mcch;~nism by which strcngthcning improves patellofi~~~ol-al pain symp toms and functional ability has not heen established.

As mentioned ahovc, the fact that only 50% of patients with patellofemoral pain demonstrate tracking ;thnormalitics, but still appear to respond f;~vol-;~bly to qriadriceps strengthening, suggests that this form of treatment may have a more subtle efkct on the patellofemol-al joint. For example, i t is possible that gross quadriceps strengthening may alter the contact location and pressure distribution, possibly relieving ;I sensi- tive area. Further resc;\rch in this arca is needed to identify this niccha- nisrn.

\\'hatcver the means by which qu;~driccps strengthening improves patcllokrnoraI p i n symptoms, such a program should he b;~scd on sound biomech;mic;d foundations and sensi- ble cxercisc pl-ogrcssion. Two com- ~nonly employed mcthods for strengthening the extensor mechanism, open ; ~ n d closed chain excr- cises, will now be discussed fi-om a biomcch;~nic;~l standpoint, with impli- cation for their use in the trcatrnent of patclIofemol-;d pain.

Patellofemoral Joint Biomechanics During Open and Closed Chain Exercises

Sincc p;ttcllofc.niol-;~l pain is ?pi- c;~lly I-rproduccd with acti\ities th;~t are associated with high patcllokmtr ral joint I-eaction forces (ie., stair climbing and sqi~atting) (13.41 ), it would appear that an exercise prw gram shotild be designed to enhance qt~;~driceps strengtlicning while k e e p ing.joint stress to a minimum. This is p;wticularly important during the i~cutc phase of p;~tellofemoral pain when symptoms can hc reatlil!. exac-

FIGURE 4. Compressive iorces on the patelloiemoral joint are determined hv the resultant o i M , (quadriceps tendon iorce vector) and M, patellar ligament iorce vector). from Fulkerson jP, Hungehrd DS: Disorders o i the Patelloiemoral joint (2nd €dl, Baltimore: MM- liams & Mlilkins, 1990, 0 john P. Fulkerson, MD, reprinted with perminionJ.

e r k ~ t e d . To ;~ccomplish this task, klio\vlcdge of the biomcchanics of the patcllofelnoral joint is ncccssal?.

The patellofhol-;~I joint reaction fi~rce is the n1c;lsrircrncnt of compression of the patella against the femur and is dependent upon the angle of knec flexion as well as muscle tension (3,47,81). Thc rcsi~ltant of the qmdriccps forcc vector and patellar tendon fiwce vector is cqrial mid o p posite to the patellofemor;d joint reaction force (7 , which evokes com- pressivc stresses on the patellofi.niol-;d articular c;~rtilage (Figure 4). Another important \;~ri;~hle to consider regarding the biomechanics of the patellofernoral joint is the arca of contact bc twcn the patella and fc- mur. As repor-tcd h!. Good fellow ct ;11 (23), the patellofcmol-;d contact area increases with kncc flexion, with the total areit ;it 90" being ;~ppro>ti~nately twice that at 30' (Figure .5). i2'hen considering the forccs tl-ansmittcd

FIGURE 5. Contact areas on the patella as a iunction oiknee ilevion at 20, 45, 90, and 135: ((A-B = Path of medial margin o i contact zone, I = Inierior, S = Superior, 1 = Lateral, M = Medial). f r o m Goodiellow 1, Hungerford DS, Zindel M: Patelloiemoral joint mechanics and patholqqv. / Bone joint Surg 58B13):287- 290. 1976, reprinted with permission/.

through the patellofemoral joint, an assumption is made that the joint reaction force is equally distributed across the entire contact area. The fact that the q~~adr iceps forcc and the contact area changes with vaying knee flexion angles has significant implications for prescribing different hpes of theraprutic exercise.

During an open chain exercise (ic., knec extension with resistance applied at the ankle), the amount of quadriceps force required to extend thc knee steadil! increases as the knce movcs from 90" to frill knee cxtcnsion. r l study performed by Lieb and Per17 (42) demonstrated that ;I

60% increase in quadriceps forcc was necessary to complete the last 1.5" of

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knee extension. This increase in force was attributed to a decrease in mechanical advantage of the extensor mechanism. In addition to the increase in quadriceps force as the knee extends, the patellofemoral contact area steadily decreases. This com- bination of increased quadriceps force and decreased contact area during terminal knee extension results in greater patellofemoral joint contact stress/pressure compared with greater knee flexion angles where the quadriceps force is not as great and the contact area is larger (32).

Conversely, during closed chain exercise (ie., squatting), the quadriceps force is relatively minimal as the knee is extended and steadily increases as the knee flexes (32). This increase in force is distributed over a greater surface area as the contact area also is increasing as the knee flexes. The greater contact area pre- vents excessive patellofemoral joint pressure during flexed knee activities (32).

An analysis of patellofemoral joint stress during open and closed chain exercises was undertaken by Steinkamp et al (78). The results of this studv found that compared with knee extension against resistance, the patellofemoral joint stress while per- forming a leg press maneuver was less at knee flexion angles from 0 to 48". Revond 48" of knee flexion, however, the patellofemoral joint stress for the closed chain exercise was greater than the open chain exercise (Figure 6) . The results of Steinkamp et al (78) are similar to that reported by Hungerford and Bar? (32). who also estimated patellofemoral contact stress during both open and closed chain exercise. These studies suggest that quadriceps strengthening can be safely performed throughout the 0-90" knee flexion range by varying the mode of exercise. Since both forms of exercise can be used to pro- mote qi~adriceps hypertrophy, it a p pears that a comprehensive strengthening program woiild incorporate both open and closed chain exercise

so that strengthening can be performed throughout a large arc of motion.

The Role of Taping and Bracing in the Treatment of Patellofemoral Pain

External patellar supports are commonly employed in the management of patellofemoral pain and are typically used as an adjunct to other treatment methods (ie., strengthening) (50,5i,i4,79,83). The primary goal of patellofemoral joint bracing is to centralize the patella within the trochlear groove, thus improving patellar tracking (33,57). The patellar taping technique as described by Mc- Connell (49) has gained widespread clinical acceptance as an effective treatment option. In this protocol, rigid strapping tape is applied to the patella to correct malalignment (as determined by clinical evaluation) and is followed bv functional strengthening of the quadriceps. Likewise, the various patellofemoral braces on the market have employed a number of methods to improve patellar tracking, including the use of patellar cut-outs, lateral buttresses, air bladders, and various VelcrodU and Neoprene straps.

The therapeutic success associated with use of external patellar s u p ports in conjunction with other treatment methods is supported by various clinical trials. Utilizing patellar taping, McConnell (50) reported that 92% of patients were pain free after eight treatment sessions, which was comparable with the 96% success rate reported by Gerrard (20) after only five treatments involving taping. Similar success rates have been reported for various patellofemoral braces ( 1 4 5 1.57).

The fact that the various forms of external patellar supports have been shown to be effective in reducing svmptoms immediately after application (4.26.63) indicates that such or- thoses have a mechanical effect on the patellofemoral joint. For exam-

0 30 48.4 60 90

Knee flexion (Degrees)

FIGURE 6. Comparison of patellofemoral joint stress in millipascals (MPa/ during open and closed chain exercise at four knee flexion angles. Error bars repre- sent one standard deviation. f r om Steinkamp LA, Dillingham MF, Markel MD, Hill )A, Kauiman KR: Biomechanical considerations in patellofemoral joint rehabilitation. Am) Sports Med2 1(3):438-444, 1993, reprinted with permission).

ple, Powers et al (63) reported that patellar taping resulted in small but significant increases in loading response knee flexion, which suggested more willingness by patellofemoral pain subjects to load the knee joint during gait. The mechanism by which taping or bracing affects the patellofemoral joint, however, is not entirely clear.

Although i t is assumed that bracing and taping improve patellar tracking, various radiological studies have reported mixed results. Rockrath et al (4) reported that despite a significant reduction in pain patellar taping was not effective in changing patella position. Larsen et al (38) found that patellar taping was effective in moving the patella medi- ally; however, this change was not maintained after exercise. In contrast, Shellock et al (73) reported that 76% of patients demonstrated a qualitative correction in patellar subluxation while wearing the Rauer- feind Genutrdn P3 brace. The study by Shellock et al (73) differed from those described above in that patellar

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tracking was assessed dynamically against resistance using kinematic magnetic resonance imaging instead of through passive positioning techniques. The advantage of the kinematic magnetic resonance imaging approach is that the contribution of the quadriceps to patellar tracking can be assessed (66,71,72). Al- though the results of Shellock et a1 (73) appear promising, care must be taken in interpreting these findings as no objective measures were taken.

Whether or not external patellar supports can change patellar tracking patterns can be debated at this point. It is possible, however, that the use of external supports may cause a change in the contact area between the patella and the trochlea. For example, an elastic sleeve brace can induce

I t is apparent from the literature that external patellar supports can

offer pain relief.

patellofemoral joint compression which could increase patellofemoral joint contact area by seating the patella deeper within the trochlear groove. This could potentially reduce contact stress as the joint reaction force would be distributed over a greater surface area. As shown in Fig- ure 7, the silicon inserts which are designed to center the patella within the trochlear groove are positioned anteriorly to the patella, therebv gen- erating joint compression.

Another proposed mechanism by which taping or bracing influences the patellofemoral joint is that such external supports may change the recruitment patterns of the vasti. As mentioned above, Gilleard et al (21) reported earlier activation of the W O following taping during both step-up and step-down tasks. On the

FIGURE 7. Avial v~ew oi the p~ te l l o f~ rno r~ l joint ioh- tained at 18' o i knee ilexionr usin,? kinematic mg- netic resonance imaging techniques irom a patient wearing the Bauedeind Genutrain P3 elastic sleeve brace. The silicon inserts which are designed to center the patella within the trochlear groove can be visual- ized anterior to the patella, therebv potentiallv inducing patellofemoral joint compression.

other hand, Cernv (8) found that taping had no effect on the VM0:VL EMG ratio. Further research is needed to document the effect of patellar taping and bracing on patellofemoral joint biomechanics and neuromuscular recruitment.

It is apparent from the literature that external patellar supports can offer pain relief. This is significant from a clinical standpoint, as pain may have an influence on quadriceps inhibition (9). If the goal of conservative treatment of patellofemoral pain is strengthening of the extensor mechanism, then it would appear that pain reduction would facilitate recruitment of the quadriceps. Such a decrease in pain would allow for adequate exercise progression and subsequent muscle hypertrophy.

SUMMARY

Rased on the review of the current literature, emphasis on the VMO in the rehabilitation of individuals

with patellofemoral pain mav not be indicated. This premise is supported by the fact that VMO insufficiency has not been consistently documented in this population, and that there is no evidence suggesting that the VMO can be recruited or selectively strengthened independent of the other vasti. Exercises attempting to isolate the VMO most likely result in a general quadriceps strengthening effect; however, the mechanism by which quadriceps strengthening reduces symptoms is not known. Therefore, exercises utilized for the treatment of patellofemoral pain should be aimed at an overall quadriceps strengthening effect, keeping in mind the biomechanics of the patellofemoral joint and the type of exercise prescribed. The use of external patellar supports (ie., taping and bracing) appears to be beneficial in reducing symptoms and may be a useful acljunct to a therapeutic exercise program.

FUTURE RESEARCH

It is evident from this review that continued research is necessary to flirther our knowledge of patellofemoral joint mechanics and how this disorder may be treated most effectively. Of utmost importance are the following: 1) to clearly establish the role of the VMO in contributing to patellar kinematics and patellofemoral pain, 2) to identify the mechanisms by which treatment procedures, such as taping and quadriceps strengthening, influence patellofemcl ral joint biomechanics, and 3) clinical trials aimed at determining which treatment procedures are most effective in reducing the symptoms asociated with patellofemoral pain. 1 0 ~ 1 ~

ACKNOWLEDGMENTS

The author would like to ac- knowledge Jacklyn Heino, MS, PT; H. James Phillips, MS, PT, OCS; and Jaquelin Perry, MD, for their critical reviews of this manuscript.

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7. Cynthia J. Watson, Micah Propps, Jennifer Ratner, David L. Zeigler, Patricia Horton, Susan S. Smith. 2005. Reliability andResponsiveness of the Lower Extremity Functional Scale and the Anterior Knee Pain Scale in Patients With Anterior Knee Pain.Journal of Orthopaedic & Sports Physical Therapy 35:3, 136-146. [Abstract] [PDF] [PDF Plus]

8. Martin Whittingham, Shea Palmer, Fiona Macmillan. 2004. Effects of Taping on Pain and Function in Patellofemoral PainSyndrome: A Randomized Controlled Trial. Journal of Orthopaedic & Sports Physical Therapy 34:9, 504-510. [Abstract] [PDF][PDF Plus]

9. Christopher M. Powers. 2003. The Influence of Altered Lower-Extremity Kinematics on Patellofemoral Joint Dysfunction: ATheoretical Perspective. Journal of Orthopaedic & Sports Physical Therapy 33:11, 639-646. [Abstract] [PDF] [PDF Plus]

10. Catherine L. Mascal, Robert Landel, Christopher Powers. 2003. Management of Patellofemoral Pain Targeting Hip, Pelvis, andTrunk Muscle Function: 2 Case Reports. Journal of Orthopaedic & Sports Physical Therapy 33:11, 647-660. [Abstract] [PDF][PDF Plus]

11. Tony Wilson, Nicholas Carter, Gareth Thomas. 2003. A Multicenter, Single-Masked Study of Medial, Neutral, and LateralPatellar Taping in Individuals With Patellofemoral Pain Syndrome. Journal of Orthopaedic & Sports Physical Therapy 33:8, 437-448.[Abstract] [PDF] [PDF Plus]

12. Mario Bizzini, Capt. John D. Childs, Sara R. Piva, Anthony Delitto. 2003. Systematic Review of the Quality of RandomizedControlled Trials for Patellofemoral Pain Syndrome. Journal of Orthopaedic & Sports Physical Therapy 33:1, 4-20. [Abstract][PDF] [PDF Plus]

13. David A. Wallace, George J. Salem, Ruben Salinas, Christopher M. Powers. 2002. Patellofemoral Joint Kinetics While Squattingwith and without an External Load. Journal of Orthopaedic & Sports Physical Therapy 32:4, 141-148. [Abstract] [PDF] [PDF Plus]

14. Cynthia J. Watson, Hollis M. Leddy, Tine D. Dynjan, Jennifer L. Parham. 2001. Reliability of the Lateral Pull Test and TiltTest to Assess Patellar Alignment in Subjects With Symptomatic Knees: Student Raters. Journal of Orthopaedic & Sports PhysicalTherapy 31:7, 368-374. [Abstract] [PDF] [PDF Plus]

15. Laura H. Lathinghouse, Mark H. Trimble. 2000. Effects of Isometric Quadriceps Activation on the Q-angle in Women Beforeand After Quadriceps Exercise. Journal of Orthopaedic & Sports Physical Therapy 30:4, 211-216. [Abstract] [PDF] [PDF Plus]

16. Cynthia J. Watson, Micah Propps, Wendy Galt, Amy Redding, Debra Dobbs, Scott F. Dye, Jenny McConnell, Christopher M.Powers, Cynthia J. Watson, Micah Propps, Wendy Galt. 1999. Reliability of McConnell's Classification of Patellar Orientationin Symptomatic and Asymptomatic Subjects. Journal of Orthopaedic & Sports Physical Therapy 29:7, 378-393. [Abstract] [PDF][PDF Plus]

17. Christopher M. Powers, Susie Mortenson, Dawn Nishimoto, Debra Simon. 1999. Criterion-Related Validity of a ClinicalMeasurement To Determine the Medial/Lateral Component of Patellar Orientation. Journal of Orthopaedic & Sports PhysicalTherapy 29:7, 372-377. [Abstract] [PDF] [PDF Plus]

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http://dx.doi.org/10.2519/jospt.2009.2873

http://www.jospt.org/doi/pdf/10.2519/jospt.2009.2873

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http://dx.doi.org/10.2519/jospt.2005.35.3.136

http://www.jospt.org/doi/pdf/10.2519/jospt.2005.35.3.136

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rehabilitation of patellofemoral joint disorders: a critical review

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