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Abstract
Objective There is growing evidence for the provision of foot orthoses when treating individuals with patellofemoral pain syndrome (PFPS), and prescription is frequently based on the assessment of foot posture/function. However, evaluation of the link between abnormal foot posture/function and foot orthoses outcomes has previously been limited to static alignment measures and has produced inconsistent findings. In this study, the ability of baseline foot kinematics associated with pronation to predict marked improvement 12 weeks following foot orthoses prescription in individuals with PFPS was evaluated.
Methods 26 individuals with PFPS were issued with prefabricated foot orthoses, and patient-reported level of improvement was documented at 12 weeks. Potential predictors of marked improvement at 12 weeks were measured during walking at baseline and included forefoot dorsiflexion and abduction, and rearfoot eversion.
Results Of the 25 participants who completed the study, seven (28%) reported marked improvement with the foot orthoses after 12 weeks. Discriminant function analysis revealed a greater peak rearfoot eversion to be the only significant independent predictor of marked improvement.
Conclusion These findings provide preliminary evidence that greater peak rearfoot eversion is predictive of marked improvement 12 weeks following prefabricated foot orthoses prescription in individuals with PFPS. Therefore, foot orthoses may be most effective in the subgroup of people with PFPS and increased dynamic foot pronation.
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There is growing evidence for the efficacy of foot orthoses prescription when treating individuals with patellofemoral pain syndrome (PFPS).1,–,7 Traditionally, foot orthoses have been advocated for PFPS based on the premise that they are needed to control excessive foot pronation.8 9 Tiberio10 provided a theoretical mechanism underpinning therapeutic foot orthoses effects in individual with PFPS, by describing how altered foot function during gait may detrimentally affect the patellofemoral joint (PFJ). It was proposed that excessive or prolonged foot pronation (rearfoot eversion) during the stance phase of gait would result in greater tibial internal rotation. This would in turn delay or reduce the tibial external rotation relative to the femur required to allow knee extension through midstance. To compensate, the hip (femur) would need to rotate internally to a greater degree, thereby also increasing hip adduction and dynamic Q angle.10 These tibial and femoral kinematic variations are thought to be detrimental to the PFJ owing to the associated reduced contact area and increased lateral PFJ compression.11
What is already known on this topic
There is growing evidence for the prescription of foot orthoses for individuals with patellofemoral pain syndrome (PFPS). However, not all individuals with PFPS benefit equally from foot orthoses prescription.
What this study adds
This study has identified that individuals with PFPS demonstrating signs of excessive rearfoot eversion magnitude during walking are most likely to benefit from prefabricated foot orthoses prescription.
Although the majority of previous studies evaluating foot orthoses for individuals with PFPS have used observations of excessive foot pronation as part of their inclusion criteria,2,–,5 7 evidence linking foot structure or function to clinical success in PFPS populations is limited. Previous clinical prediction studies have been limited to static assessment of posture and reported conflicting findings relating to the association of foot posture with foot orthoses efficacy in individuals with PFPS. Vicenzino et al12 reported that greater foot mobility (change in arch height from non-weight-bearing to weight-bearing) was associated with marked improvement at 12 weeks. Contrary to this, Sutlive et al6 reported a less pronated foot type as measured by navicular drop and calcaneal angle was associated with greater than 50% pain reduction at 3 weeks. Additionally, we recently found that static foot posture as measured by the foot posture index and normalised navicular drop were unable to predict marked improvement in a group of 60 individuals with PFPS following 12 weeks of wearing foot orthoses.13 Inconsistent findings relating to the association between foot posture and foot orthoses efficacy in individuals with PFPS need to be considered in the context of one significant methodological limitation—static posture assessments may not accurately represent dynamic foot function. To date, no previous study has evaluated the association between dynamic foot function and foot orthoses efficacy in individuals with PFPS.
The aim of this study was to identify kinematic predictors of foot orthoses efficacy in individuals with PFPS during walking. Specifically, the predictive value of kinematics associated with foot pronation (rearfoot eversion, forefoot dorsiflexion and forefoot abduction) measured at baseline was evaluated for marked improvement 12 weeks following foot orthoses prescription. It was hypothesised that a subpopulation of PFPS individuals with signs of excessive foot pronation during walking would be the most likely to benefit from foot orthoses prescription.
Methods
Participants
Twenty-six individuals with PFPS (five males and 21 females) were recruited via advertisements placed at La Trobe University, the University of Melbourne, and in the greater Melbourne area. This group of PFPS individuals form a subpopulation (without additional inclusion/exclusion criteria) of a larger clinical prediction rule study. The mean (SD) age, height, weight and usual weekly sport or recreational physical activity time were 25 (5) years, 1.69 (0.09) m, 67 (14) kg and 320 (210) min respectively. The study was approved by La Trobe University's Faculty of Health Sciences Human Ethics Committee, and each participant gave written informed consent prior to participation. Diagnosis of PFPS was based on definitions used in previous high-quality randomised controlled trials (RCTs).1 14 Inclusion criteria were: aged 18–35 years old; insidious onset of peripatellar or retropatellar knee pain of at least 6 weeks' duration; worst pain in the previous week of at least 30 mm on a 100 mm visual analogue scale; pain provoked by at least two activities from running, walking, hoping, squatting, stair negotiation, kneeling or prolonged sitting; pain elicited by patellar palpation, PFJ compression or resisted isometric quadriceps contraction. Exclusion criteria were: use of foot orthoses in the previous 5 years, physiotherapy treatment in the previous 6 months, current use of anti-inflammatory medications, concomitant injury or pain arising from the lumbar spine or hip, knee internal derangement, knee ligament insufficiency, previous knee surgery, PFJ instability or patellar tendinopathy.
Intervention
Participants attended a single treatment (15 min) and data-collection (60 min) session. During this session, all baseline data were collected prior to issuing each participant with a pair of prefabricated foot orthoses. The orthoses were commercially available three-quarter-length devices with lateral cut-outs (Vasyli Pro, Vasyli International), made of ethelene-vinyl acetate of medium (Shore A 55) density, containing built-in arch supports and 4° rearfoot varus wedging (see figure 1). No customisation of the orthoses was performed, as the aim was to provide the same level of support for all participants in the absence of a scientifically validated customisation approach for PFPS. Additionally, these foot orthoses were chosen, as they could be fitted into most participants' footwear without discomfort.
Prefabricated foot orthoses (Vasyli Pro, Vasyli International) issued to each participant.
Participants were then instructed to wear the orthoses for a period of 12 weeks. To assist with compliance, participants were asked to wear suitable footwear to accommodate the orthoses whenever possible. Additionally, a diary was completed, describing when the orthoses were and were not worn during physical activity.
Primary outcome measure
At 12 weeks following foot orthoses prescription, each participant rated the perceived improvement in symptoms using a five-point Likert scale, consistent with previous PFPS RCTs.1 14 The five responses included markedly better, moderately better, same, moderately worse and markedly worse. The association of each kinematic variable with those who reported marked improvement was evaluated.
Kinematic analysis
Data collection included lower-limb kinematic evaluation of each participant's symptomatic limb (those with unilateral symptoms) or most symptomatic limb (in those with bilateral symptoms) during walking. Motion analysis was collected using a three-dimensional motion-analysis system (Vicon MX system; Oxford Metrics, Oxford) combined with 10 cameras (eight MX3 and two MX40) operating at a sampling frequency of 100 Hz. Thirty-six retroreflective markers were placed on specific anatomical landmarks (outlined below) to form forefoot, rearfoot, tibial, femoral and pelvic segments. Ground reaction forces were collected using two force plates (type 9865B; Kistler, Winterthur, Switzerland; and AMTI, OR6, Watertown, MA, USA) at a sampling frequency of 1000 Hz.
The Oxford Foot Model (OFM)15 was used to perform kinematic evaluation of each participant during walking. For the purpose of static calibration, plug-in gait (PIG) was added to the model,15 and each participant's height, weight, inter anterior–superior–iliac–spine (ASIS) distance, ASIS to greater trochanter distance, knee width and ankle width were recorded. Retroreflective markers were placed over the following anatomical landmarks by the same investigator for each participant: midpoint of the sacrum between the posterior–superior–iliac–spines, and bilaterally on the ASIS, lateral aspect of the femur (5 cm wand), head of the fibula, tibial tuberosity, anterior border of tibia, lateral aspect of tibia (5 cm wand), medial and lateral malleoli, three markers bisecting the heel (distal, wand and proximal), lateral calcaneus, sustentaculum tali, base of first metatarsal, head of first metatarsal, proximal first phalanx, head of fifth metatarsal and base of fifth metatarsal (see figure 2). A relaxed standing calibration trial was then captured with knee-alignment devices (KADs) in situ. Prior to the walking trials, the KADs were removed and replaced with lateral femoral condyle markers, and the anatomical markers used to define segment axes were removed (medial malleoli, proximal heels and first metatarsal heads).
Anterior view of Oxford foot model and plug-in-gait marker placements including the knee alignment devices (KADs) (A) and posterior view of Oxford foot model marker placements for the static trial (B).
Participants performed practice walking trials to allow familiarisation with the instrumentation and environment. Once participants felt they were comfortable, and the investigator deemed they were walking with consistent velocity, kinematic data collection commenced. Each participant was asked to walk at their natural comfortable speed across a 12 m walkway. Five successful trials were collected for each participant. A trial was deemed successful when the participant's instrumented foot landed within the borders of the first force plate they traversed, which was used to identify the commencement of the gait cycle. To ensure a natural walking pattern, participants were not made aware of the force plates which were hidden within the floor. Only the investigator knew of their existence and position. Starting positions prior to each trial were adjusted to optimise the likelihood of a successful trial.
Data analysis
Each trial was reconstructed, and the retroreflective markers identified and labelled within the Vicon Nexus software. Gait events (heel strike and toe off) were identified to allow gait-velocity measurement using force plate data, and the OFM model was applied to the captured markers. Data were then exported to a purposely developed Excel template for analysis. Variables of interest included magnitude and timing of peak angles and ranges of motion during stance for:
(i) forefoot relative to rearfoot: dorsiflexion (sagittal plane) and abduction (transverse plane) defined by the OFM;15
(ii) rearfoot relative to the laboratory: eversion (frontal plane) defined by the OFM;15
(iii) rearfoot relative to tibia: eversion (frontal plane) defined by the OFM.15
Additionally, gait velocity was compared between those with marked improvement and those with moderate improvement, no change, moderate worsening or marked worsening.
Statistical analysis
Statistical analysis was performed using SPSS Version 17.0. Prior to statistical analysis, all variables were assessed for normality and found to be normally distributed based on graphical observation and a skewness statistic of between –1.0 and +1.0. Gait velocity and each kinematic variable were evaluated for their association with marked improvements following 12 weeks of wearing the foot orthoses. First, each variable was tested for its univariate relationship using independent-samples t tests comparing those reporting marked improvement with those reporting moderate improvement, same, moderate worsening or marked worsening. All variables with a significance level of p<0.20 were retained for further discriminant analysis. Discriminant analysis with significance set at p<0.05 was then completed entering each retained variable to determine which were predictive of marked improvement at 12 weeks.
Results
Twenty-five of the 26 participants enrolled completed the study at 12 weeks. The one drop-out was unable to be contacted at 12 weeks. Participants who completed the study wore their foot orthoses for 81%±17 of their physical activity performed during the study period. A total of seven (28%) participants reported that they were markedly better after 12 weeks of wearing the foot orthoses. There was no difference (p=0.998) in gait velocity between those with marked improvement (1.36±0.13 m/s) and those with moderate improvement, no change, moderate worsening and marked worsening (1.36±0.14 m/s).
Univariate analysis comparing those with marked improvement with those with moderate improvement, no change, moderate worsening and marked worsening for peak angles, timing of peak angles and ranges of motion for each kinematic variable evaluated can be found in table 1. Greater peak rearfoot eversion relative to the laboratory (p=0.045) was the only variable retained for discriminant analyses (p<0.20). No univariate associations were found for either timing of peak angles or ranges of motion for any of the kinematic variables evaluated. Discriminant analysis revealed that greater rearfoot eversion relative to the laboratory was independently predictive of marked improvement at 12 weeks (p=0.045), producing a standardised canonical discriminant function coefficient of 0.975.
Univariate comparisons for magnitude (°) and timing (percentage gait of cycle) of peak angles and ranges of motion (°) during stance, defining clinical improvement as markedly better.
Discussion
Despite growing evidence that foot orthoses are an effective intervention for PFPS,1,–,7 their longstanding theoretical biomechanical rationale10 lacks validation from empirical evidence. Foot orthoses are often recommended for individuals with PFPS possessing excessive foot pronation.10 However, previous clinical prediction rule studies6 12 have reported inconsistent links between static foot posture measures and clinical outcomes following foot orthoses prescription. The current study is the first to evaluate the association between baseline dynamic foot function during walking and clinical outcomes following foot orthoses prescription in individuals with PFPS. Importantly, findings show that a subpopulation with greater peak rearfoot eversion is likely to benefit from the provision of prefabricated foot orthoses, while those with normal foot function may not.
We previously found that static foot posture was unable to predict clinical outcomes following 12 weeks of wearing prefabricated foot orthoses in 60 individuals with PFPS.13 However, in the current study, which used a subpopulation of the same 60 individuals, we found that greater baseline peak rearfoot eversion was able to predict marked improvement following 12 weeks. In doing so, this study's findings support the traditional theoretical rationale behind foot orthoses prescription for individuals with PFPS.10 Additionally, this finding implies that evaluating foot function dynamically may be more valid than using static foot posture measures when considering foot orthoses prescription for individuals with PFPS.
Previous studies evaluating rearfoot eversion in individuals with PFPS have consistently measured rearfoot motion relative to the tibia.16,–,18 The current study evaluated rearfoot motion relative to both the tibia and laboratory (floor). Interestingly, only rearfoot eversion relative to the laboratory was able to predict a marked improvement at 12 weeks. A likely explanation for the discrepancy between the two methods of rearfoot motion evaluation may be the presence of joint coupling between the rearfoot and tibia, where the tibia is forced into adduction by the everting rearfoot. In the presence of such a coupling relationship, differences in rearfoot eversion relative to the tibia may not be detected despite the presence of greater rearfoot eversion relative to the laboratory. Therefore, measuring rearfoot eversion motion relative to the laboratory (floor) may be more appropriate than measuring relative to the tibia in future research and clinical practice if the goal is to predict outcomes following foot orthoses prescription.
Baseline forefoot kinematics were not found to be associated with marked improvement following prefabricated foot orthoses prescription in the current study. This could imply that evaluating baseline forefoot motion may not assist in determining the likelihood of improvement when prescribing prefabricated foot orthoses prescription to individuals with PFPS. However, it must be considered that the foot orthoses used in this study were not individualised, and while they contained rearfoot varus wedging (4°), they did not contain any intrinsic forefoot wedging. Therefore, they may not have been appropriate to correct the presence of any abnormal forefoot motion which might contribute to PFPS development. Additional research is needed to determine if baseline lower-limb kinematics including forefoot motion are predictive of clinical outcomes when using different foot orthoses prescription approaches such as forefoot posting.
Limitations
The findings of this study need to be considered in the context of several limitations. First, kinematics were only measured at baseline. Therefore, to better understand mechanistic factors behind efficacy, additional evaluation of the association between kinematic changes produced by foot orthoses and clinical outcomes in the future may be of value. Second, owing to the relatively small sample size (n=26), only seven participants reported a marked improvement at 12 weeks. Therefore, it is possible that a larger number of predictors may be identified using a larger sample size. Third, this study did not contain a control group. Therefore, further validation of baseline peak rearfoot eversion as a predictor of foot orthoses outcomes in individuals with PFPS requires confirmation in a larger RCT. Finally, the subpopulation with marked improvement in this study was identified using a three-dimensional marker based analysis. Therefore, directly applying findings to a clinical setting may not be possible. Clinical application may be improved by the development of valid and reliable clinical foot function tests able to identify individuals with excessive rearfoot eversion. Until this is completed, sports medicine practitioners may choose to rely on clinical observation to determine the presence of excessive rearfoot eversion before prescribing prefabricated foot orthoses.
Conclusion
This study is the first to evaluate the association between foot or lower-limb kinematic assessment and clinical outcomes with foot orthoses in individuals with PFPS. Results provide preliminary evidence that measuring dynamic foot function (peak rearfoot eversion) predicted prefabricated foot orthoses efficacy in individuals with PFPS. Therefore, foot orthoses may be most effective in the subgroup of people with PFPS and increased dynamic foot pronation.
Acknowledgments
The authors would like to acknowledge Vasyli International for providing the prefabricated foot orthoses used in this study. HBM is currently an NHMRC research fellow (Clinical Career Development Award, ID: 433049).
References
Footnotes
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Competing interests None.
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Ethics approval Ethics approval was provided by La Trobe University's Faculty of Health Sciences Human Ethics Committee.
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Provenance and peer review Not commissioned; externally peer reviewed.
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Patient consent Obtained.