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Lateral wedges with and without custom arch support for people with medial knee osteoarthritis and pronated… Hunt, Michael A; Takacs, Judit; Krowchuk, Natasha M; Hatfield, Gillian L; Hinman, Rana S; Chang, Ryan May 2, 2017

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RESEARCH Open AccessLateral wedges with and without customarch support for people with medial kneeosteoarthritis and pronated feet: anexploratory randomized crossover studyMichael A. Hunt1*, Judit Takacs1, Natasha M. Krowchuk1, Gillian L. Hatfield1, Rana S. Hinman2 and Ryan Chang3AbstractBackground: Pronated foot posture is associated with many clinical and biomechanical outcomes unique tomedial compartment knee osteoarthritis (OA). Though shoe-worn insole treatment, including lateral wedges, iscommonly studied in this patient population, their effects on the specific subgroup of people with medial knee OAand concomitant pronated feet are unknown. The purpose of this study was to evaluate whether lateral wedgeinsoles with custom arch support are more beneficial than lateral wedge insoles alone for knee and foot symptomsin people with medial tibiofemoral knee osteoarthritis (OA) and pronated feet.Methods: Twenty-six people with pronated feet and symptomatic medial knee OA participated in a randomizedcrossover study comparing five degree lateral wedge foot insoles with and without custom foot arch support. Eachintervention was worn for two months, separated by a two-month washout period of no insoles wear. Mainoutcomes included the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) pain and physicalfunction subscales, the revised short-form Foot Function Index (FFI-R) pain and stiffness subscales, and the timedstair climb test. Regression modeling was conducted to examine treatment, period, and interaction effects.Results: Twenty-two participants completed the study, and no carryover or interaction effects were observed forany outcome. Significant treatment effects were observed for the timed stair climb, with greater improvementsseen with the lateral wedges with arch support. Within-condition significant improvements were observed forWOMAC pain and physical function, as well as FFI-R pain and stiffness with lateral wedges with arch support use.More adverse effects were reported with the lateral wedges alone, while more people preferred the lateral wedgeswith arch support overall.Conclusions: Addition of custom arch support to a standard lateral wedge insole may improve foot and kneesymptoms in people with knee OA and concomitant pronated feet. These preliminary findings suggest furtherresearch evaluating the role of shoe-worn insoles for treatment of this specific sub-group of people with knee OA iswarranted.Trial registration: Clinicaltrials.gov identifier: NCT02234895.Keywords: Knee, Osteoarthritis, Lateral wedges, Pain, Function* Correspondence: michael.hunt@ubc.ca1Department of Physical Therapy, University of British Columbia, 212-2177Wesbrook Mall, Vancouver, BC V6T 1Z3, CanadaFull list of author information is available at the end of the article© The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, andreproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link tothe Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver(http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.Hunt et al. Journal of Foot and Ankle Research  (2017) 10:20 DOI 10.1186/s13047-017-0201-xBackgroundOsteoarthritis (OA), commonly affecting the knee joint,is one of the most prevalent chronic musculoskeletaldisorders and is a leading cause of long-term physicaldisability affecting adults [1]. While we are unaware ofjoint specific indicators of the economic burden of OA,a recent report indicates that more than 6.9% of theadult population in the Unites States had symptomaticknee OA in 2007-2008 [2] – a number that is expectedto rise dramatically in the coming decades. Further,symptomatic OA (the combination of symptoms andradiographic evidence of OA) is more commonly foundin the knee than in any other joint [3]. Given that thereis no cure for knee OA and the overall economic burdenof OA is high, there has been a recent push towards theidentification of non-surgical, non-pharmacologicaltreatments for knee OA that can be delivered effectively,safely, and with minimal personnel and economic re-sources [4]. Shoe-worn insoles/orthotics are a low-costand low-burden self-management option that has wide-spread appeal for managing knee OA symptoms.Recent research confirms the link between knee andfoot problems in people with knee OA. An examinationof data from the Osteoarthritis Initiative showed that25% of individuals with painful knee OA concurrentlyreport foot pain, and that the presence of foot pain ad-versely affected overall health and function [5]. Individ-uals with knee OA also tend to exhibit more pronatedfeet compared to those without knee OA [6, 7]. Indeed,a recent study involving 164 people with symptomaticmedial tibiofemoral OA reported that 45% had pro-nated or severely pronated feet [8]. Recent researchhas also shown that the presence of foot/ankle symp-toms significantly increases the odds of developingknee OA symptoms and symptomatic radiographicknee OA [9]. Additionally, rearfoot eversion duringwalking has also been shown to be associated withmedial compartment knee joint load, as quantified bythe external knee adduction moment (KAM) [10].Specifically, more rearfoot eversion appears to be as-sociated with lower KAM values. Finally, older adultswith pronated feet are more likely to exhibit kneepain and medial tibiofemoral cartilage damage thanolder adults with other foot types [11]. Taken to-gether, these findings indicate that people withpronated feet form a large, and clinically relevant,sub-group of the population with knee OA. Thus, tar-geted treatment approaches for this subgroup thatconsiders their unique biomechanical needs may bewarranted. However, current methods for the treat-ment of knee OA symptoms and biomechanics hastypically failed to directly address any aspect of footbiomechanics in general, and in those with knee OAand concomitant pronated feet specifically.A commonly studied conservative treatment approachfor knee OA is shoe-worn insoles, in particular insolesthat are built up along the lateral edge (lateral wedges).There have been a number of studies examining the bio-mechanical and clinical changes associated with use oflateral wedges. Although lateral wedges have been shownto provide immediate reductions in KAM magnitudes[12, 13] – consistent with the reported negative correl-ation between increased rearfoot eversion (which wouldoccur with lateral wedging) and the KAM [10] – the ef-fects on knee symptoms are less clear [14]. A primarylimitation of previous lateral wedges for knee OA re-search has been a failure to consider participants’ footmorphology in the study design and delivery of treat-ment. In clinical practice, pronated feet are typically man-aged with some form of medial arch support [15, 16], andwhile some research shows that beneficial changes inankle kinematics [17] and foot pain [18, 19] may be ob-tained with this clinical approach in people with pronatedfeet, the evidence in this area is sparse [20]. However,there is potential that a combination of lateral wedges andarch supports may be beneficial for people with painfulknee OA and pronated feet [21].Given the apparent strong link between pronated foottype and disease characteristics specific to medial com-partment knee OA, and that biomechanical interven-tions such as lateral wedges are advocated in clinicalguidelines for the use of conservative treatments forknee OA in general [22], a better understanding of theclinical effects of shoe-worn insole treatment for in thisspecific subgroup of knee OA is warranted. Therefore,the purpose of the present exploratory randomizedcrossover study was to compare clinical effects (kneeand foot symptoms) of lateral wedges alone to insolesthat combined lateral wedging with customized archsupport in people with medial knee OA and concomi-tant pronated feet. We were also interested in the safetyof these interventions and adherence to treatment. Itwas hypothesized that the combined insole would pro-duce greater improvements in knee pain and physicalfunction, as well as foot pain and stiffness, and would bemore comfortable.MethodsParticipantsCommunity-dwelling individuals with medial tibiofe-moral OA were recruited via advertisements in printmedia. Inclusion criteria included: (i) definitive medialtibiofemoral osteophytes on radiograph; (ii) joint spacenarrowing greater in the medial tibiofemoral compart-ment compared to the lateral compartment; (iii) historyof knee pain longer than six months; (iv) average kneepain of at least 3 out of 10 (using an 11-point numericalrating scale (NRS) with terminal descriptors of 0 = “noHunt et al. Journal of Foot and Ankle Research  (2017) 10:20 Page 2 of 10pain” and 10 = “worst pain imaginable”) over the onemonth prior to initial screening; and (v) pronated feet,defined as +4 or higher on the Foot Posture Index [23],with at least four items rated as +1 (indicating prona-tion). Exclusion criteria included: (i) knee surgery orintra-articular injection for pain within the previous sixmonths; (ii) current or past (within six weeks) oral cor-ticosteroid use; (iii) history of knee joint replacement ortibial osteotomy; (iv) any other condition affecting lowerlimb function; and (v) current, or failed previous (i.e.premature cessation of orthotic treatment due to adverseeffects), wearing of shoe insoles/orthotics. The study wasapproved by the Institution’s Clinical Research EthicsBoard and all participants provided written informedconsent. In contrast to information provided on the tri-als registry (Clinicaltrials.gov identifier: NCT02234895),gait biomechanics data were only collected at the initialbaseline data collection session, rather than at all timepoints, and are presented elsewhere [24].Study designThis was an exploratory, within-subjects cross-overstudy.ProceduresInterested participants were initially screened for inclu-sion and exclusion criteria, and eligible individuals werereferred for a physical screening of foot posture. Individ-uals who passed the foot posture eligibility criteria de-scribed above were referred for radiographic evaluation.Standing, semi-flexed, postero-anterior radiographs wereobtained and graded for disease severity using theKellgren and Lawrence (KL) OA classification system[25]. Individuals who met all study eligibility criteriawere then referred to a Canadian Certified Pedorthist,who obtained foot measurements and made volumetriccasts of both feet to inform manufacture of insoles. Par-ticipants returned to the same Pedorthist followingmanufacture of both sets of the insoles for final modifi-cations and instruction on insoles wear. Insoles weremade for bilateral wear, even in cases where knee OAwas unilateral. Both sets of insoles were then sent dir-ectly to the University laboratory, and participants werescheduled for their first baseline testing session.Following baseline assessment of outcomes (month 0),participants were randomly allocated to either i) lateralwedges alone or; ii) lateral wedges plus custom arch sup-port. Allocated insoles were worn for a two-month periodin their own usual shoes, and then participants were re-assessed (month 2). After a two-month washout period ofno insole wear, participants were re-assessed again (month4) and then underwent a second two-month period ofintervention with the alternate insole condition, afterwhich they were re-assessed for the final time (month 6).The randomization schedule was produced before studycommencement by a researcher not involved with datacollection or analysis. Random permuted blocks of 4 or 6were developed and randomization codes were sealed inconsecutively numbered, opaque envelopes that wereopened after baseline testing for each participant. To pre-vent cross-contamination of insole wear, the unused pair(in the case of active treatment periods), or both pairs (inthe case of the wash-out period) of insoles were kept on-site at the University. Further, the participants were un-aware of the study hypotheses as well as the justificationfor the design of the insoles. Both pairs were provided toparticipants upon study completion.InterventionsFor both types of insoles, polypropylene sheets of 3-4 mm thickness were vacuum formed or milled directlyto produce a sulcus length insole. For both conditions,the lateral wedges consisted of a 5-degree ethyl-vinyl-acetone (EVA) (Shore A hardness of 55) sulcus-lengthposting. For the lateral wedges plus arch support insole,the same lateral wedges were used in combination witha custom arch support across the foot to match thenegative of the volumetric cast. Both insoles (Fig. 1)were finished with the same neoprene cover and modi-fied as necessary to maximize comfort and fit. Partici-pants were instructed to wear the insoles as much aspossible and no other instructions regarding the inter-vention were provided.Outcome measurementOutcome assessments were conducted by the sameblinded assessor. Testing sessions at the University in-cluded completion of self-report questionnaires and ob-jective assessment of physical function.Fig. 1 Intervention insoles. Left: the lateral wedge only conditionconsisted of a sulcus-length 5-degree lateral wedge. Right: the lateralwedge plus custom foot arch support involved the 5-degree sulcus-length lateral wedge built into a negative of the volumetric cast thatprovided the support across the entire footHunt et al. Journal of Foot and Ankle Research  (2017) 10:20 Page 3 of 10Self-reported knee and foot symptoms were the clin-ical outcomes of interest. Participants completed theWestern Ontario and McMaster Universities ArthritisIndex (WOMAC) Likert version, from which the painand physical function subscales were calculated [26].The WOMAC contains 24 items that quantify pain (5items), stiffness (2 items), and physical function (17items) that has been used in numerous knee OA studies.Foot symptoms were assessed using the Foot FunctionIndex (revised - short form) (FFI-R). This self-reportquestionnaire consists of 34 items that provide the abil-ity to quantify aspects of foot pain, disability and activitylimitation [27]. For the purposes of this study, the painand stiffness subscales were used. Each question is ratedfrom 1 (no pain or stiffness) to 4 (severe pain or stiff-ness). Given that “not applicable” is a potential responsefor some questions, questions rated as “not applicable”were removed and the remaining scores within that sub-scale were summed. Subscale scores were then con-verted to a percentage of the maximum potential scorefor that particular subscale with 25% indicating no painor stiffness and 100% indicating severe pain or stiffness.Objective physical function was assessed using thetimed stair climb test, where participants were instructedto ascend 12 stairs “as quickly as possible” and the fast-est time from two attempts was recorded [28]. Adher-ence to each insole intervention was self-reported indaily log books. Participants reported the total numberof hours of shoe wear each day as well as the total num-ber of hours wearing the insole. Wear time was then cal-culated by the research team following the intervention,and expressed as total number of insole wear hours, aswell as a percentage of total shoe wear time. Participantsalso recorded perceived adverse effects of the insoles,and changes in treatment regimens during the activetreatment periods (months 0 to 2 and 4 to 6) in theirdaily log books. At the month 2 and month 6assessments, participants rated comfort during the inter-vention using an 11-point NRS with terminal descriptorsof 0 = “maximum discomfort” and 10 = “maximumcomfort”. Participants also rated their perceived overallchange in symptoms at follow-up (month 2 and 6) com-pared to baseline (month 0 and 4) using a 5-point Likertscale (1 = “much worse”, 2 = “slightly worse”, 3 = “nochange”, 4 = “slightly better”, and 5 = “much better”). Fi-nally, at the month 6 assessment, participants indicatedwhich pair of insoles (“first or second”) they preferred.Statistical analysisAll statistical analyses were conducted using StatisticalAnalysis Software (SAS, v 9.4; SAS Institute Inc.: Cary,NC, USA) and p values <0.05 were considered signifi-cant. For WOMAC, FFI-R and timed stair climb out-comes, change scores were calculated as follow-upminus baseline values for each intervention period. Ascomfort data were only acquired at the follow-up assess-ments, these were treated as raw data rather than changescores. Mixed effects regression models predictingchange variables against fixed effects for interventionperiod and treatment type, and a random subject effectwere developed for each outcome variable. Interactionsbetween intervention period and treatment type wereinitially included as predictors in a second model, thendropped from the models if non-significant (this wastrue for all models).ResultsBetween July 2014 and June 2015, 127 individualsunderwent eligibility screening, of which 26 were en-rolled. Participant demographics are summarized inTable 1. Fourteen individuals were randomized to re-ceive the lateral wedge plus arch support in the firstiteration (months 0-2), while 12 participants receivedthe lateral wedges alone in the first iteration. Twenty-four individuals completed their first allocated treat-ment period, and of those, 22 completed month 6assessment. Of the four participants who did notcomplete the study, three were lost-to-follow-up (oneprior to the month 2 follow-up assessment, one afterthe month 4 baseline assessment, and one prior toTable 1 Participant characteristics at baseline based on order of intervention. Values are mean (sd) unless otherwise notedWedge to Wedge plus arch support (n = 12) Wedge plus arch supportto Wedge (n = 14)All participants(n = 26)Age (years) 66.3 (10.2) 62.1 (5.0) 64.0 (7.6)Sex (F:M) 9:3 13:1 22:4Foot posturea 5 (4,8) 5 (4,9) 5 (4,9)Body mass (kg) 65.3 (9.8) 75.0 (15.3) 70.5 (13.8)BMI (kg/m2) 25.2 (3.0) 28.9 (4.5) 27.2 (4.2)Disease severity (n)KL 2 9 7 16KL 3 3 7 10a As quantified by the foot posture index (FPI). Values are reported as median (minimum, maximum)Hunt et al. Journal of Foot and Ankle Research  (2017) 10:20 Page 4 of 10the month 6 follow-up assessment), while the fourthwithdrew prior to the month 2 follow-up assessmentdue to health issues unrelated to the study. Mean (sd)intervention times were 2.2 (0.2) months for the lat-eral wedges and 2.1 (0.2) months for the lateralwedges plus arch support, with a washout period of2.1 (0.3) months.Table 2 provides results for clinical outcomes across testconditions. The lateral wedges plus arch support resultedin significant improvements in all parameters, whilst thelateral wedges alone did not significantly change any clin-ical outcome. However, these differences generally did nottranslate into significant treatment main effects (betweenconditions), with the exception of timed stair climb, whereimprovements were significantly greater with the use ofthe lateral wedges with arch support compared to lateralwedges alone (p = 0.02). In addition, a significant periodeffect (Figs. 2 and 3) was seen for WOMAC Pain scores(p = 0.04). There were no intervention by periodinteractions.Using a minimal clinically important improvement of17% for WOMAC pain and 12% for WOMAC function[29], use of lateral wedges alone resulted in improvedpain in 13 (54%) participants and improved function in14 (58%) participants. When using the lateral wedgesplus arch support, 14 (64%) participants had improvedpain while 17 (77%) participants had improved physicalfunction.Wear times were similar between the two treatmentperiods, whether expressed as absolute or relative timevalues. The mean (sd) number of hours that participantsself-reported insole wear was 150.7 (86.5) hours for thelateral wedges and 152.5 (121.0) hours for the lateralwedges plus arch support over the two-month interven-tion periods, which equated to 72.5 (19.2)% and 75.8(24.4)% of total shoe wear time, respectively. There wereno differences (p = 0.55) in self-reported comfort be-tween the two conditions (lateral wedges = 6.4 (2.6) outof 10; lateral wedges plus arch support = 6.9 (2.5) out of10). More participants indicated that they preferred their“first insole” (13/22) than their “second” (9/22), whichtranslated into more individuals preferring the lateralwedges plus arch support (17/22; of these 17, 10 partici-pants were randomized to the lateral wedges plus archsupport first, while the other 7 received the lateralwedges plus arch support second). When asked to reportoverall change in symptoms compared to baseline, 15 in-dividuals reported improvement with lateral wedgesalone (7 = “much better”, 8 = “slightly better”) while 18individuals reported improvement with the lateralwedges plus arch support (9 = “much better”, 9 = “slightlybetter”).A total of 16 unique, yet minor, adverse events wereself-reported during the study, 11 of which occurredduring lateral wedges wear and five during lateralwedges plus arch support wear. With lateral wedgesalone, the most common complaint was onset of footpain or discomfort (n = 3), which lasted between oneand three weeks. There were two reports of increasedbunion pain, one lasting two weeks and the other for theduration of the intervention. Other complaints included:five weeks of toe cramping (n = 1), three weeks of lateralankle pain (n = 1), one week of calf tightness (n = 1), gen-eralized lower leg pain lasting three days (n = 1), and onereport each of lower back and knee pain lasting one andten weeks, respectively. During lateral wedges plus archsupport wear, five individuals reported foot pain or dis-comfort ranging from two days to two weeks. Finally,three individuals underwent additional treatment duringlateral wedges use (two instances of topical pain reliefgel and one instance of foot and lower leg massage),while the same two treatments were completed by an-other two individuals during lateral wedges plus archsupport wear.DiscussionFindings from this study indicate that the addition ofcustom foot arch support to 5-degree lateral wedgesTable 2 Outcomes data. Mean (sd) baseline and follow-up outcome data for all variables, as well as model adjusted differences(follow-up minus baseline; difference (95% confidence intervals)) within each condition as well as between conditions. Modelestimate values represent the within- and between-condition least-square mean differences adjusted for period and randomsubject effects from the regression modelingLateral wedges (n = 24) Lateral Wedges plus Arch Support (n = 22) Between-conditionscomparisonVariable Baseline Follow-up Difference Baseline Follow-up Difference DifferenceWOMAC Pain (0-20) 5.9 (3.0) 5.2 (2.9) -0.7 (-1.8, 0.5) 6.3 (3.4) 4.0 (2.5) -1.9 (-3.1, -0.6)* -1.2 (-2.9, 0.5)WOMAC Function (0-68) 20.2 (11.0) 17.6 (8.9) -2.5 (-6.2, 1.1) 21.4 (12.5) 14.0 (8.8) -6.1 (-9.9, -2.3)* -3.6 (-7.9, 0.8)FFI-R Pain (25-100%) 41.0 (17.4) 38.4 (11.9) -2.7 (-8.9, 3.5) 43.6 (16.2) 33.0 (9.3) -7.0 (-13.5, -0.6)* -4.3 (-12.0, 3.4)FFI-R Stiffness (25-100%) 39.2 (15.7) 37.1 (13.7) -2.1 (-7.3, 3.0) 42.8 (19.5) 32.3 (9.4) -6.3 (-11.7, -0.9)* -4.1 (-11.0, 2.7)Stair climb (seconds) 5.32 (1.68) 5.35 (1.54) 0.04 (-0.55, 0.63) 6.57 (4.04) 5.58 (2.29) -0.69 (-1.3, -0.08)* -0.73 (-1.36, -0.11)** p < 0.05Hunt et al. Journal of Foot and Ankle Research  (2017) 10:20 Page 5 of 10may result in clinical improvements in knee and footsymptoms, and timed stair climb, in people with medialknee OA and pronated feet. However these changeswere generally not statistically significantly better thanthose observed with treatment by lateral wedges alone.Further, more participants subjectively preferred thesupported lateral wedges overall, compared to lateralwedges alone. Data from this study provide importantpreliminary clinical information regarding safety and ef-ficacy of combined insoles for the treatment of an im-portant sub-group of patients with knee OA, namelythose with concomitant pronated feet.Although no other research has specifically evaluatedeffects of insoles in a subgroup of people with knee OAand concurrent pronated feet, our findings are consist-ent with the limited research investigating combined lat-eral wedge insoles with arch supports in heterogeneoussamples of people with knee OA. Indeed, a previous un-controlled study investigating a similar insole designshowed improvements in pain and function in 42 indi-viduals with medial knee OA and varus knee alignment.Skou et al showed that an insole that combined acustom-made arch support with an individualizedamount of lateral wedging produced significant improve-ments in pain, function, and quality of life after an aver-age of 7.75 months of wear [30]. Specifically, they foundgreater than 40% improvement, on average, in knee painintensity (measured using a visual analog scale) with thecombined insole. In the present study, a 30% improve-ment in WOMAC pain was observed with our com-bined insole, compared to only 12% with the lateralwedges alone. Similar findings have been reported else-where, with Jones et al showing more immediate im-provement in knee pain with a combined insolecompared to a standard lateral wedge alone in peoplewith knee OA [21]. Taken together, these studies showthe potential for greater improvement in knee pain witha combined insole than with a lateral wedge alone inpeople with knee OA.Although the combined insole resulted in clinical im-provements across all measured parameters, and we ob-served no significant effect on outcomes whenparticipants were treated with lateral wedges alone, therewas generally no statistically significant difference inFirst iteration WashoutFirst iteration Washout Second iterationabFig. 2 Assessment of treatment and period effects for Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) pain a andphysical function subscales b. Lower scores indicate less knee pain and physical dysfunction. Dotted lines indicate mean values for participantsreceiving the lateral wedges alone first, followed by the lateral wedges plus arch support; solid lines indicate mean values for participantsreceiving the lateral wedges plus arch support first, followed by the lateral wedges aloneHunt et al. Journal of Foot and Ankle Research  (2017) 10:20 Page 6 of 10outcomes when comparing between insole conditions. Alarger sample size may have produced statistically signifi-cant differences, and results from this study can now beused to guide sample size calculations for future clinicaltrials. Importantly, though the lateral wedges plus archsupport produced more symptomatic benefits over atwo-month period, biomechanical data from the currentcohort taken at the initial baseline assessment indicatesthat both insoles produced similar KAM reductions (al-beit slightly larger reductions in the lateral wedgesalone) compared to a no insole walking condition [24].Thus, the differences in clinical outcomes in the presentstudy cannot be attributed solely to the biomechanicaleffects of the lateral wedges. Indeed, a direct relationshipbetween changes in KAM magnitudes and pain levelswith foot-based interventions has not been shown in theliterature [31, 32], suggesting that the relationship be-tween measured external loads and knee pain magni-tudes is complex. Rather, it is likely that the addition ofthe custom arch support played a role in reducing self-reported knee pain in the present study. The reasons forthis are unclear, but may include indirect effects of theinsoles, such as psychological factors on overall benefitsbased on insole preference or foot symptoms obtainedwith the combined insoles which then translated intoperceived changes at the knee. Further research isneeded to better elucidate the relationship between footmechanics and knee symptoms in this patientpopulation.It was clear that participants preferred the lateralwedges with arch support. Indeed, 17 of 22 participants(78%) indicated an overall preference of that insole con-dition, and reported that the combined insole wasslightly more comfortable under the feet. Any differencein comfort with the combined insole may partially ex-plain why we observed clinical improvements with thecombined insole but now with the lateral wedges alone.However, as there were no statistical differences whencomparing group mean comfort ratings, any effect ofperceived comfort would have occurred on an individualbasis. Jones et al also reported slightly more perceivedfoot comfort with a combined insole compared to aabFirst iteration Washout Second iterationFirst iteration Washout Second iterationFig. 3 Assessment of treatment and period effects for Foot Function Index (FFI-R) pain a and stiffness subscales b. Values are presented aspercentages of the maximum scores for each subscale, and lower scores indicate less foot pain and foot stiffness. Dotted lines indicate meanvalues for participants receiving the lateral wedges alone first, followed by the lateral wedges plus arch support; solid lines indicate mean valuesfor participants receiving the lateral wedges plus arch support first, followed by the lateral wedges aloneHunt et al. Journal of Foot and Ankle Research  (2017) 10:20 Page 7 of 10lateral wedge alone, though the differences were also notstatistically significant [21]. Given that 19/26 individualsreported at least some foot pain (values >25% on theFFI-R pain subscale) at the initial baseline assessment,assessment of changes in foot symptoms was important.Within-condition assessment of change in these symp-toms from the current study would indicate that the lat-eral wedges plus arch support were able to improve footsymptoms. Finally, while not statistically tested, moreself-reported adverse events were recorded during lateralwedges use (n = 11) than during the combined insoles(n = 5). While these reports were relatively minor andshort-term, this finding provides further justification forthe need to comprehensively assess the feet when pro-viding any insoles treatment to people with knee OA toprimarily target knee symptoms.Our study is novel, and an important contribution tothe literature for a number of reasons. First, this is thefirst study evaluating shoe-worn insoles in people withknee OA that has considered foot type as an inclusionor exclusion criterion. As noted above, given that pro-nated foot posture is common in people with knee OA[6], and is associated with a higher risk of developingknee pain and medial tibiofemoral cartilage damage [11],this subgroup in particular represents an important tar-get for the study of shoe-worn insoles for the treatmentof knee OA. More research with a homogeneous sampleof pronated foot posture is warranted. This is also thefirst study, to our knowledge, to assess the impact of in-soles on foot symptoms in people with knee OA. Sincerecent research has identified a link between foot symp-toms and development of knee OA [9], and the fact thatshoe-worn insoles evoke change directly at the feet,measurement of foot and ankle symptoms with foot-based treatment for knee OA is necessary. Indeed, giventhat more self-reported adverse events (especially lowerleg, ankle, and foot issues) were reported in the presentstudy with the lateral wedges alone, this finding providesimportant information necessary to inform clinical deci-sion making in this particular subgroup. However, giventhe potential cost difference between the two types of in-soles (potentially in excess of $300 per pair dependingon the provider), a cost-effectiveness analysis of anysymptomatic benefits of the combined insole must beconducted to assist in the justification of prescribing thisaddition to a standard lateral wedge.There are some limitations to this study. First, al-though within-condition changes were observed, ourrelatively small sample size for this exploratory studylikely impacted our ability to detect significant between-condition differences. In addition, certain limitations ofa randomized crossover study in general (such as the po-tential for carryover and learning effects) must be con-sidered. However our findings provide justification forlarger studies in this area. Second, the two-month inter-vention was shorter than previous similar studies whichutilized 6- or 12-month (or longer) intervention periods[33–35]. Although we did observe improvements in painand function with the combined insole over thistimeframe, it is unknown if these benefits would bemaintained over the longer-term. Further, we relied onself-report data to examine outcomes such as usage andadverse events. Future research would benefit from moreobjective outcomes of wear time such as instrumentedinsoles that more accurately measure usage and wouldinclude some form of assessment of load during dynamicmovement. Finally, more than half of our sample wascomprised of individuals with mild radiographic diseaseseverity. Recent research suggests that the relationshipbetween biomechanics and knee symptoms in individ-uals with knee OA is stronger in more advanced radio-graphic disease [36], suggesting that shoe-worn insolesthat attempt to evoke biomechanical changes at the kneemay be less effective at improving knee symptoms inpeople with mild disease. Further research in sampleswith more advanced radiographic knee OA and pronatedfeet is required to determine the effectiveness of shoe-based intervention in this cohort.ConclusionsIn conclusion, we found that the addition of customarch support to standard lateral wedge shoe insoles re-sulted in improvements in foot pain and function in agroup of individuals with knee OA and pronated feet.However changes in symptoms were not statistically dif-ferent from those observed when participants weretreated with lateral wedges alone. Given that shoe-worninsoles represent a relatively inexpensive treatment op-tion with little patient burden, findings from the presentstudy suggest further research is required to evaluate therole of combined insoles in managing knee and footsymptoms in these patients.AbbreviationsEVA: Ethyl-vinyl-acetate; FFI-R: Foot function index revised version; FPI: Footposture index; KAM: Knee adduction moment; KL: Kellgren and Lawrence;NRS: Numerical rating scale; OA: Osteoarthritis; WOMAC: Western Ontario andMcMaster Universities Osteoarthritis IndexAcknowledgementsNot applicable.FundingThis study was funded, in part, by a grant from the Pedorthic ResearchFoundation of Canada. The funding body had no role in any aspect of thisstudy. RSH is supported by an Australian research Council Future Fellowship(FT130100175). The funders had no role in any aspect of this study.Availability of data and materialsThe datasets used and/or analysed during the current study available fromthe corresponding author on reasonable request.Hunt et al. Journal of Foot and Ankle Research  (2017) 10:20 Page 8 of 10Authors’ contributionsMH was involved in study design, data analysis, as well as drafting andapproval of the manuscript. JT was involved in study design, data collection,and approval of the manuscript. NK was involved in participant recruitment,data collection, and approval of the manuscript. GH was involved in datacollection and approval of the manuscript. RH was involved in study design,data analysis, and approval of the manuscript. RC was involved in studydesign, data analysis, and approval of the manuscript.Competing interestsR. Hinman has received royalties from sales of an osteoarthritis shoe fromAsics Pty Ltd.Consent for publicationNot applicable.Ethics approval and consent to participateThis study was approved by the University of British Columbia ClinicalResearch Ethics Board (approval number: H14-01313).Publisher’s NoteSpringer Nature remains neutral with regard to jurisdictional claims inpublished maps and institutional affiliations.Author details1Department of Physical Therapy, University of British Columbia, 212-2177Wesbrook Mall, Vancouver, BC V6T 1Z3, Canada. 2Department ofPhysiotherapy, University of Melbourne, Melbourne, VIC, Australia. 3HumanPerformance Engineering Laboratory, Reebok International, Canton, MA, USA.Received: 13 December 2016 Accepted: 22 April 2017References1. Vos T, Flaxman AD, Naghavi M, Lozano R, Michaud C, Ezzati M, et al. 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Osteoarthritis Cartilage. 2017;25:34–41.•  We accept pre-submission inquiries •  Our selector tool helps you to find the most relevant journal•  We provide round the clock customer support •  Convenient online submission•  Thorough peer review•  Inclusion in PubMed and all major indexing services •  Maximum visibility for your researchSubmit your manuscript atwww.biomedcentral.com/submitSubmit your next manuscript to BioMed Central and we will help you at every step:Hunt et al. Journal of Foot and Ankle Research  (2017) 10:20 Page 10 of 10

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