February 2011

Role of foot orthoses for patellofemoral pain

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The key to documenting the effectiveness of foot orthoses for patellofemoral pain syndrome appears to be identifying which specific subgroup of PFPS patients are most likely to benefit. Evidence-based clinical prediction rules offer guidance for optimizing clinical outcomes.

By Christian J. Barton, BPhysio(Hons)

Patellofemoral pain syndrome (PFPS) is defined as retropatellar or peripatellar pain in the absence of other pathologies including patellar tendinopathy, ligament insufficiency and internal derangement. Pain is most commonly aggravated by activities that increase patellofemoral joint (PFJ) loading, such as running, squatting, and stair negotiation. Highlighting the significance of PFPS to sports medicine is that it has been reported to represent around 25% of knee injuries and 5% of all injuries presenting to a sports medicine clinic.1 The importance of improving treatment approaches for PFPS is underscored by reports that between 71% and 91% of individuals with PFPS continue to report recurring pain, up to 20 years after initial diagnosis.1-3

There is a consensus among researchers and clinicians that PFPS develops from elevated or altered lateral PFJ stress.4-7 However, the cause of elevated or altered PFJ stress is highly debated and frequently considered to be multifactorial. As a result, various possible contributing factors must be considered when choosing an appropriate management strategy. Many potentially modifiable extrinsic factors are thought to play a role, including body mass, environment (e.g. surfaces, slopes and stairs), and footwear. Additionally, a number of intrinsic biomechanical factors may need to be assessed and considered. Common considerations include neuromuscular control of the quadriceps;8-12 weakness13-17 and altered function18,19 of hip musculature; and excessive hip adduction/internal rotation,17,20-24 and tibial rotation/subtalar joint pronation.25

First line treatment generally consists of physical therapy and home exercises to strengthen the quadriceps and hip musculature.26,27 In addition to physical therapy, many adjunctive treatments have been proposed to be effective in the management of PFPS. One of these adjunctive interventions is the prescription of foot orthoses designed to control excessive subtalar joint pronation.

Traditionally, foot orthoses have been prescribed to individuals with PFPS to control any excessive foot pronation that may be present. Tiberio25 proposed that excessive foot pronation would lead to greater tibial and femoral internal rotation as a result of joint coupling. In turn, this would lead to greater dynamic knee valgus and greater stress on the lateral patellofemoral joint.25 Foot orthoses designed to control excessive foot pronation are thought to prevent this sequence and thereby reduce pain in individuals with PFPS.

Evidence for foot orthoses prescription

In a recent systematic review, we established level I evidence for foot orthoses prescription when treating individuals with PFPS,28 identifying one high quality randomised controlled trial by Collins et al.26 Specifically, there were significantly more self-reported improvers at six weeks in a group receiving prefabricated foot orthoses compared to a group receiving a control intervention (flat inserts).26 The number needed to treat for one additional improver in the foot orthoses group from this study was calculated to be four. Considering the inexpensive nature of the prefabricated orthoses provided in this study,26 these are promising findings for the efficacy of foot orthoses when treating individuals with PFPS.

Despite the positive clinical outcomes produced by foot orthoses prescription in the Collins et al study,26 it should be noted that these were only seen in the short term (six weeks). Longer term follow up (at 12 and 52 weeks) indicated no significant difference in outcomes between the group receiving prefabricated foot orthoses and the group receiving a placebo (flat inserts).26 However, no attempt was made by Collins et al to recruit those most likely to benefit from foot orthoses. Additionally, only one form of foot orthoses (prefabricated) was used. In reality, this is unlikely to reflect clinical practice, where foot orthoses are prescribed for certain individuals and are frequently customised. Therefore, Collins et al’s findings26 may underestimate the potential benefits of foot orthoses prescription. This possibility requires further research.

Comparison between the efficacy of prescribing prefabricated (“off the shelf”) foot orthoses and cast molded customized foot orthoses was an area of research identified in the review that needs to be addressed.28 This choice requires two major considerations: establishing the need to customize the orthotic device to match the individual’s foot type; and affordability of the device, given that customized devices are substantially more expensive than prefabricated devices. A number of lower quality studies29-34 support both prefabricated and customized foot orthoses.28 However, there is currently a paucity of research comparing the efficacy or cost-effectiveness between these two prescription approaches.28 Until this area of research is addressed, the decision should be made jointly between the patient and the clinician, taking into account both clinical judgement and cost implications.

Those most likely to benefit

One vital consideration regarding foot orthoses prescription to individuals with PFPS is who should and should not receive them. It is clear both anecdotally and in research evidence that not all individuals with PFPS benefit equally from foot orthoses prescription. Previous research from two separate studies26,34 indicates that when individuals with PFPS are prescribed prefabricated foot orthoses, between 25% and 40% will report marked improvement at 12 weeks. Additionally, between 18% and 33% will report no improvement, or worsening of their condition at 12 weeks.26,34 These findings highlight the variability in outcomes following foot orthoses prescription, and the need to identify those most likely to benefit in order to optimize treatment outcomes.

As discussed earlier, foot orthoses have been traditionally prescribed to individuals with PFPS to control any excessive foot pronation that may be present. Three studies have evaluated the ability of clinical measures of foot pronation to predict foot orthoses outcomes in individuals with PFPS,29,35,36 and produced inconsistent results. Specifically, Sutlive et al29 reported that a less pronated foot type (measured using forefoot alignment and navicular drop) was predictive of success, while Vicenzino et al36 reported that greater midfoot mobility (i.e., change in midfoot width from non-weight bearing to weight bearing) was predictive of success. Additionally, we recently found no association between foot posture (Foot Posture Index [FPI]) or mobility (navicular drop) and outcomes 12 weeks following prefabricated foot orthoses prescription.35

A semirigid custom orthosis with a minimum positive arch fill, a 2 mm medial skive, a closed-cell neoprene top cover, and an EVA orthotic arch fill is one option for treating patellofemoral pain syndrome. (Figure reprinted from Recent Advances in Orthotic Therapy by Paul R. Scherer, DPM; published by Lower Extremity Review.)

Inconsistent findings regarding the ability of clinical measures of foot type to predict foot orthoses outcomes in individuals with PFPS29,35,36 suggests that their value in a clinical setting may be limited. However, one vital consideration is that none of these studies evaluated foot pronation dynamically during a functional activity. Considering this, we evaluated the relationship between static foot posture, measured using the FPI, and peak angular motions associated with foot pronation during walking in a group of 26 individuals with PFPS. Unpublished results from this study indicated the FPI was only moderately associated with peak forefoot abduction, predicting about 25% of its variance. Additionally, there were no associations between the FPI and either peak forefoot dorsiflexion or peak rearfoot eversion.

We then evaluated the predictive value of kinematics at the rearfoot and forefoot associated with foot pronation during walking in a group of 26 individuals with PFPS.37 Our findings indicated that greater dynamic peak rearfoot eversion relative to the floor was predictive of marked improvement 12 weeks following prefabricated foot orthoses prescription. Interestingly, the 26 participants from this study were a sub-population of our larger study of 60 participants,35 where measures of foot posture and mobility were unable to predict marked improvement. This would indicate that basing foot orthoses prescription on dynamic evaluation of foot function (i.e. rearfoot eversion relative to the floor) is more appropriate than static clinical measures of foot type. Until validated clinical measures of dynamic foot function are established, the clinician should rely of visual observation and use of video analysis to assist this.

Alternative evaluation

In addition to evaluating dynamic foot function, there are other clinical observations that may assist clinical decisions relating to foot orthoses prescription to individuals with PFPS. In a recent clinical prediction rule study, we identified a cluster of variables that were predictive of outcomes 12 weeks following prefabricated foot orthoses prescription.35 Specifically, the likelihood of marked improvement increased from 25% to 78% if three of the following four criteria were satisfied at baseline: reduced pain with the orthoses during the completion of a single leg squat, use of less supportive footwear (e.g. skate shoes, pumps, etc.), lower baseline pain (< 22/100), and reduced weight-bearing ankle dorsiflexion (< 41º).35

Of the four variables identified in our clinical prediction rule, the prediction test with the greatest accuracy was the immediate change in pain during the completion of a single leg squat. If pain was reduced immediately by the foot orthoses, the likelihood of marked improvement increased from 25% to 45%. This finding highlights an important concept when considering the appropriateness of foot orthoses prescription for individuals with PFPS: immediate improvement in functional performance enhances the likelihood of positive longer term outcomes. Supporting this concept, our group also has unpublished data indicating that two additional functional performance measures are predictive of marked improvement with foot orthoses in individuals with PFPS: improved ease of completing a single leg squat (i.e., they found it easier to balance), and an increase in the number of pain-free step downs from a 20-cm high step at a rate of 48 steps per minute.

Evaluating functional performance measures to guide decisions related to foot orthoses prescription is not a new theoretical concept. Vicenzino38 proposed the use of the “treatment direction test” (TDT) to identify individuals most likely to benefit from foot orthoses prescription. The basis of the TDT is to use an external control (e.g., adhesive strapping tape or temporary orthoses) to facilitate the desired motion control (e.g., reduce foot pronation in individuals with PFPS). Pain and quality of movement are assessed with and without this external control. If the external control produces a significant improvement, both patient and clinician can be confident that prescribing foot orthoses is likely to be effective.38 This same approach may be particularly useful in PFPS patients where symptoms often cannot be reproduced in a clinical setting using tests such as a single leg squat. For example, a runner demonstrating signs of excessive foot pronation may report pain onset after 5 km but is otherwise symptom-free. In this case, external control such as applying adhesive tape to control foot pronation (i.e. mimic foot orthoses control) may be implemented, and distance to pain onset re-evaluated. If it is significantly improved (e.g., 10 km or no pain at all), then foot orthoses would be prescribed. Considering our recent findings, and its clinical applicability, use of the TDT concept is recommended when considering foot orthoses prescription for individuals with PFPS.

Footwear considerations

Footwear is one potential extrinsic risk factor for the development of PFPS. Interestingly, our clinical prediction rule indicated that footwear with reduced motion control properties (i.e., less supportive) was predictive of marked improvement 12 weeks following foot orthoses prescription. As well as providing a potential predictor, this is an interesting finding for two reasons: (i) poor footwear may have led to the development of PFPS in these individuals since improving support resulted in symptom reduction; and (ii) encouraging an individual to wear more supportive footwear may also lead to therapeutic benefits similar to that provided by the foot orthoses. Although both points require further research to establish their validity, these results still highlight the importance of considering footwear when treating individuals with PFPS, and in particular when considering foot orthoses prescription.

Recently established Level I evidence for foot orthoses prescription in individuals with PFPS indicates they are a valuable treatment option in the short term. However, due to the multifactorial nature of PFPS, foot orthoses prescription represents only one of many possible interventions for treating PFPS. The inclusion of mild pain (i.e. usual pain < 22.0 mm) in our clinical prediction rule highlights that foot orthoses as a stand-alone treatment may not be appropriate for the majority of PFPS cases, where pain is more severe. Therefore, it is recommended that foot orthoses be considered as an adjunct to other conservative interventions with established evidence, such as physical therapy and home exercises to strengthen the quadriceps and hip musculature.26,27

Conclusion

Current evidence indicates foot orthoses may be an effective intervention for individuals with PFPS in the short term. With a lack of current evidence to support the superiority of either prefabricated or custom prescription, choice should be made on an individual basis, considering the potential benefit of customization versus the greater affordability of a prefabricated device. The presence of excessive rearfoot eversion during dynamic function, and immediate improvements in functional performance with a temporary device will increase the likelihood of improvement in individuals with PFPS.

Christian J. Barton, BPhysio(Hons), is a PhD candidate at the Musculoskeletal Research Centre at La Trobe University in Bundoora, Australia, and research supervisor at the Centre for Sports and Exercise Medicine at Queen Mary University of London, UK.

Acknowledgement: Thank you for the assistance and guidance provided by a number of individuals with research reported in this paper, including A/Prof Hylton Menz, Dr. Kay Crossley, Dr. Pazit Levinger, and Dr. Kate Webster.

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One Response to Role of foot orthoses for patellofemoral pain

  1. Tom Michaud says:

    Beautiful paper. I was surprised to see excessive calcaneal eversion predicted success with orthotic intervention as it correlates so poorly with three-dimensional movement. Would have been nice if the authors used William and McClay’s arch height ratio, as it more accurately predicts three dimensional movement patterns. I’d love to see some of the unpublished research they referred to in print soon.
    Thanks,
    Tom

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