March 2017

Foot posture, orthoses, and patellofemoral pain

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Prescription of foot orthoses for runners with patellofemoral pain (PFP) is often based on the premise that individuals with excessive pronation are among those most likely to have a positive response. However, preliminary analyses indicate this may not be the case.

By Thomas Gus Almonroeder, DPT; and John Willson, PT, PhD

Running is a popular mode of physical activity for a variety of reasons (convenience, relatively low cost, etc). According to recent reports from Running USA, an organization that monitors running trends, there are typically more than 17 million participants in organized running events each year.1 Unfortunately, running-related injuries are common, with the knee joint being most frequently affected.2,3 Of these running-related knee injuries, patellofemoral pain (PFP) is most prevalent.4

Patellofemoral pain has traditionally been considered to be a self-limiting condition with relatively benign long-term consequences.5 However, this premise appears to be misguided, as PFP can often persist if untreated6 and may contribute to the development of patello­femoral joint osteoarthritis.7 As a result, the development of effective prevention/treatment approaches is imperative. Unfortunately, traditional interventions (pain management modalities, foot orthoses, quadriceps strengthening, and general flexibility exercises) have been described as “unsatisfactory” by many patients with PFP.8

Although more research in this area is needed, the effects of foot orthoses on knee mechanics during running appear to be independent of foot posture or mobility.

The pathogenesis of PFP is complex; however, it appears to be related to elevated patellofemoral joint stress.9,10 Patellofemoral joint stress is dictated by the forces acting at the patellofemoral joint and the contact area between the patella and the trochlear groove of the femur. When patellofemoral forces are maintained, patello­femoral stress will increase with a decrease in contact area. In addition to factors local to the knee joint, a variety of proximal and distal factors also have the potential to alter patellofemoral joint contact area.11 Not surprisingly, PFP prevention and treatment approaches often attempt to address these local, proximal, and distal factors either in isolation or in combination.

Pronation and PFP

Excessive foot pronation is a distal factor that has the potential to influence patellofemoral joint contact area. Foot pronation is a triplanar motion involving ankle dorsiflexion, calcaneal eversion, and forefoot abduction. Theoretical models have been used to explain how excessive or prolonged pronation of the foot could influence the mechanics of the knee in a manner that would disrupt the normal function of the patellofemoral joint.12,13 For instance, Tiberio et al in 1987 described a theoretical model in which excessive foot pronation results in a compensatory internal rotation of the leg and femur, which reduces ­patello­femoral contact area.13 Excessive foot pronation may also reduce patellofemoral contact area secondary to increased knee abduction.12

The validity of these theoretical models is supported by reports that individuals with PFP commonly demonstrate a more pro­nated foot posture than individuals without PFP.14,15 However, findings from prospective analyses have been relatively inconsistent, as both increased16 and decreased foot pronation17 have been reported to be risk factors for PFP, while two additional pro­spective studies found no association between foot mobility and PFP risk.18,19 While our understanding of the precise role that foot pronation plays in the etiology of PFP is limited at this time, recent evidence20 does indicate excessive pronation may be a contributing factor for a subgroup of individuals (see “Patello­femoral pain subgroups: A critical first step toward per­­son­alized clinical intervention,” January 2017, page 18).

Foot orthoses and PFP

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Due to the potential link between foot pronation and PFP, foot orthoses are often used in PFP management. The design of these orthoses varies considerably (eg, length, material, custom vs prefabricated), but they typically incorporate varying degrees of wedging along their medial border. It is believed that, by altering the alignment of the foot or changing the location of the center of pressure, an orthosis may influence knee mechanics during dynamic activities such as running, and that this has the potential to alleviate symptoms in individuals with PFP.13

There is evidence that foot orthoses may have clinical benefits in individuals with PFP, such as reduced pain and improved function.21-23 In fact, the consensus statement published following the most recent International Patellofemoral Pain Research Retreat recommended the use of foot orthoses for short-term pain management.24 However, the beneficial effects of foot orthoses appear to be relatively small and inconsistent among individuals, particularly in the long term.21,25 As a result, there is a need to identify the subgroup of individuals with PFP who are likely to respond favorably to foot orthoses.

Two studies have attempted to develop clinical prediction rules for this purpose have identified clinical foot posture and mobility measurements as associated with a greater likelihood that an individual will experience reduced pain with the use of foot orthoses.26,27 However, it is important to note that different clinical measurements were identified in these two studies and that neither rule has been cross-validated. Also, each of these studies utilized a single-arm design instead of developing these clinical prediction rules as part of a randomized controlled trial. As a result, it is impossible to determine if the factors identified are truly associated with foot orthoses’ effectiveness or if the authors had instead identified factors associated with self-limiting PFP (ie, PFP that would have subsided without treatment). Regardless, more work in this area is justified.

Questioning the premise

Based on the theoretical rationale, foot orthoses are typically prescribed for individuals who demonstrate clinical evidence of “excessive” foot prona­­tion.28,29 This premise assumes the mechanical effects of the orthoses will be more pronounced in these individuals. However, two recent studies suggest this may not be the case.30,31

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In the first, investigators classified 40 female runners aged between 18 and 35 years into three groups based on their calcaneal eversion angle during single-leg standing (inverted, neutral, or everted).31 Calcaneal eversion represents the frontal plane component of foot pronation. Each participant performed running trials with and without full-length foot orthoses that included 6° of medial wedging. The mechanics of the knee (joint angles and moments) in the frontal and transverse planes were analyzed during the running trials. The authors of the study hypothesized that the effects of the foot orthoses would differ among the groups, with more prominent effects being demonstrated by the individuals in the ‘everted’ group. However, they found no group (inverted, neutral, everted) by condition (with orthoses, without orthoses) interaction, indicating the effects of the orthoses were not dependent on an individual’s standing calcaneal eversion angle.

Similar results were reported in the second study, which analyzed the effects of foot orthoses with 5° of medial wedging on the frontal plane angle and moment time series in healthy male and female runners.30 The authors reported the effects of the orthoses were not significantly related to an individual’s navicular drop height. Navicular drop height is a commonly used clinical measure to assess foot mobility and pronation.

The results of these two studies indicate the effects of foot orthoses on knee mechanics during running may be independent of clinical foot posture or mobility. This is an important finding, as it challenges the underlying premise that foot orthoses should be prescribed to individuals with a more pronated foot.

However, it is important to note that clinical tests and measures involving static assessment of the foot, such as the standing calcaneal eversion angle and the navicular drop height, are limited in that they appear to be only weakly related to the behavior of the foot during dynamic activities, such as walking and running.30,32,33 As a result, it is difficult to determine if the lack of a relationship between foot posture/mobility and the effect of foot orthoses on knee mechanics is the result of: 1) limitations associated with clinical measures of foot posture/mobility, or 2) a flawed assumption that foot orthoses will have greater mechanical effects in individuals with a more pronated foot. While future research efforts should be directed at developing reliable clinical measures that better reflect the dynamic behavior of the foot, further analysis of the theoretical basis upon which foot orthoses are often prescribed also appears warranted.

A step further

As clinical measures of foot posture/mobility may be poor surrogate measures of foot dynamics, Almonroeder, Benson, and O’Connor recently conducted a follow-up analysis34 of their previous work that did not identify a relationship between the effects of foot orthoses and an individual’s navicular drop height.30 Like the analysis conducted by Boldt et al,31 they categorized participants based on their peak calcaneal eversion. However, instead of a static measure of calcaneal eversion, they used a “dynamic foot motion” metric, which was the peak calcaneal eversion angle during running trials relative to the degree of calcaneal eversion during a relaxed standing position.

The study included 31 male and female recreational athletes aged between 18 and 45 years. Each participant performed running trials with and without medially wedged (5°) foot orthoses. The 10 participants with the greatest dynamic foot motion were identified (everted group), as well as the 10 participants with the least dynamic foot motion (inverted group). The everted group demon­strated approximately 8° more dynamic foot motion during the running trials than the inverted group. Interestingly, the effects of the orthoses on frontal and transverse plane knee mechanics did not differ among the groups. These results are consistent with the earlier findings that relied on a clinical measure of foot mobility, and further question the premise that foot orthoses will have more prominent mechanical effects in individuals with greater foot pronation.

Additional considerations

Despite this preliminary evidence, it is important to note that the results of previous analyses may be heavily influenced by the methods used to characterize foot posture or rearfoot dynamics. Although both the standing calcaneal eversion angle and the navicular drop height are commonly used, there is certainly a plethora of alternative clinical measures with which to classify individuals based on their foot posture or mobility.

There are also important factors to consider when characterizing individuals based on their rearfoot dynamics. The dynamic foot motion measure used by Almonroeder et al34 reflected the motion of the calcaneus during running relative to its position during relaxed standing. It is possible that subtle methodological factors could have influenced participant assignment to the everted versus inverted groups. It is also possible that classifying participants based on dynamic foot behavior requires a more precise analysis than what is possible when the foot is modeled as a single rigid segment. Regardless, at this time it appears there is a further need to explore factors that will influence the mechanical effects of foot orthoses at the knee.

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Despite the findings highlighted in this review, foot orthoses may still promote clinical benefits for individuals with a more pronated foot. In fact, a previous study indicates that individuals with greater calcaneal eversion during walking may be more likely to benefit from foot orthoses.35 The authors of this study conducted a baseline 3D motion analysis of 25 individuals with PFP while they walked at a self-selected pace. Following the baseline testing session, participants were provided with prefabricated foot orthoses that included 4° of medial wedging. After 12 weeks of wearing the orthoses during their normal physical activities, participants were asked to rate their level of improvement. Seven of the participants reported that they were “markedly better.” These individuals demonstrated significantly greater calcaneal eversion than the rest of the cohort during the baseline walking trials.

Although this finding indicates individuals with a more pronated foot may be more likely to benefit from foot orthoses, it is difficult to determine why this is the case in light of the available evidence. It is possible that the greater clinical benefits for individuals with a more pronated foot may be explained by nonmechanical factors (eg, altered lower extremity muscle activity).

There also is some evidence to support the premise that the positive clinical benefits associated with foot orthoses may not have a mechanical origin. For instance, a recent study randomly assigned a cohort of runners with PFP to either receive medially or laterally wedged orthoses.36 Although medially wedged foot orthoses are typically used in the management of PFP, after six weeks both groups reported a significant reduction in their pain during running. Although the study did not involve any type of foot assessment (clinical or dynamic), the findings do highlight the fact that nonmechanical mechanisms deserve consideration when attempting to explain the underlying reasons why some individuals with PFP benefit from foot orthoses.

Conclusion

Prescription of foot orthoses for the management of PFP among runners is often based on the premise that their effect on knee mechanics will be greater in individuals with evidence of excessive pronation. However, preliminary analyses of running mechanics among participants classified according to clinical measures of foot posture or mobility indicate this may not be the case. Similar results were reported when individuals were classified based on their rearfoot dynamics during running. Although this is certainly an area that warrants additional analysis, current evidence suggests it may be necessary to reconsider the theoretical basis upon which foot orthoses are prescribed for individuals with PFP.

Thomas Gus Almonroeder, DPT, is a PhD candidate in the Kinesiology Program at the University of Wisconsin-Milwaukee. John Willson, PT, PhD, is an associate professor in the Department of Physical Therapy and director of the Human Movement Analysis Lab at East Carolina University in Greenville, NC.

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