knee osteoarthritis ( oa ) is one of the most common musculoskeletal disorders worldwide , and 
 a leading cause of knee pain and disability in the elderly .
the number of patients ( aged 
 40  years ) in japan with knee oa diagnosed from radiological findings is estimated to be 
 approximately 25.3 million , and approximately 8 million patients are estimated to exhibit oa 
 symptoms but do not have a definitive diagnosis1 .
therefore , there is an urgent need to reduce the progression and 
 incidence of knee oa in japan .
the medial tibiofemoral compartment of the knee is the part most commonly affected by 
 oa2 .
the peak force is higher in the 
 medial compartment of the knee than in the lateral compartment during walking and other 
 weight - bearing activities3 , 4 .
excessive knee load is a significant risk factor for an 
 increased risk of structural progression4 , 5 . a high knee adduction moment ( kam )
reflects 
 increased compressive forces acting on the medial aspect of the knee6 and is widely considered a surrogate measure of medial knee 
 compression7 .
lateral wedge insoles ( lwis ) are one of the treatment options frequently recommended in 
 clinical guidelines8 for the management of 
 medial knee oa .
lwis have been shown to reduce kam7 and pain9 , and to 
 prevent or delay the progression of medial knee oa10 , 
 11 . on the other hand , medial wedge 
 insoles ( mwis ) tend to increase kam7 , 12 .
the efficacy of lwis may be limited 
 because they fail to reduce kam or increase kam in certain persons13 , 14 .
however , no study has evaluated the effects 
 of lwis and mwis , or has identified nonresponders to those types of therapy .
the possible explanations for nonresponders are variations in the foot alignments and gait 
 patterns .
it is recommended that the assessment of patients with knee oa should include foot 
 evaluations because these patients have been shown to exhibit a more pronated foot type 
 compared with controls15 .
in addition , 
 previous studies have reported that patients with knee oa demonstrate changes in gait 
 patterns , such as increased toeing out16 , 17 , reduction in gait speed18 , and leaning of the trunk in the direction 
 of the stance leg19 , to reduce kam during 
 gait .
therefore , to more accurately investigate the effects of a wedged - insole intervention , 
 unilateral weight bearing was analyzed as a movement task that assumed the mid - stance during 
 gait according to a previous study20 .
thus , the primary purpose of this study was to evaluate the immediate effects of lwis and 
 mwis under unilateral weight - bearing conditions in healthy young adults .
the secondary 
 purpose was to examine whether variations in foot alignment influence the changes in kam .
it 
 was hypothesized that kam in subjects who have normal foot alignment would significantly 
 decrease under the lwi condition than under the barefoot ( bf ) and mwi conditions .
the subjects were 30 healthy young adults without disease and/or present illnesses that 
 would affect unilateral standing ( mean age , 21.2  1.9  years ; mean height , 1.62  0.08 m ; 
 mean weight , 55.6  9.5  kg ; and mean body mass index [ bmi ] , 21.1  2.2  kg / m ) . 
 before the experiments ,
the purpose of this study was explained to the participants and 
 informed consent was obtained from them .
this study was approved by the ethics committee of 
 human research , hiroshima international university ( no . 13 - 4 ) . before motion analysis
, foot alignment measurements were performed for all subjects by 
 using the foot posture index ( fpi ) .
the fpi is a six - item foot posture assessment performed 
 with the subject standing and relaxed in the bipedal position21 .
the six items of fpi include talar head palpation , curves above 
 and below the lateral malleoli , calcaneal angle , talonavicular bulge , medial longitudinal 
 arch , and forefoot to rearfoot alignment .
each item was scored on a five - point scale between 
 2 and + 2 , which provided a total sum of all items between 12 ( highly supinated ) and + 12 
 ( highly pronated ) .
all subjects were assessed by using fpi as follows : normal foot ( total 
 score between 0 and + 5 ) , pronated foot ( total score between + 6 and + 12 ) , and supinated foot 
 ( total score between 12 and 1 ) . a three - dimensional motion analysis system that included eight infrared cameras ( vicon mx ; 
 vicon motion systems , oxford , uk ) and two force plates ( amti , watertown , ma , usa ) were used 
 to record the kinematics and kinetic data at the sample frequency of 100  hz . kinematic and 
 kinetic data were low - pass filtered with a fourth - order butterworth filter with cutoff 
 frequency at 6 and 15  hz , respectively .
a total of 40 reflective markers were placed at the 
 following landmarks on both sides of the subjects : the acromion process , olecranon , radial 
 styloid process , anterior superior iliac spine , posterior superior iliac spine , superior 
 aspect of the greater trochanter , medial and lateral femoral condyles , midpoint between the 
 greater trochanter and the lateral femoral condyles , medial and lateral malleoli , midpoint 
 between the lateral knee joint line and the lateral malleolus , posterior distal aspect of 
 the calcaneus , posterior proximal aspect of the calcaneus , lateral calcaneus , sustentaculum 
 tali , and head of the first and fifth metatarsals .
these anatomical markers were used to 
 construct anatomical coordinate systems for the trunk , pelvis , thigh , shank , and foot 
 segments .
in addition , a marker was attached to the right scapula to distinguish the right 
 and left sides .
this study involved a within - subject design where every subject was tested under three 
 conditions .
all subjects were instructed to stand on their left leg under three different 
 conditions .
the lwis had a base 
 height equal to that of the fifth metatarsal and were medially inclined , and the outside was 
 7  mm thicker than the inside .
the mwis had a base size equal to that of the fifth metatarsal 
 and were medially inclined , and the inside was 7  mm thicker than the outside .
the insoles 
 were made of high - intensity silicon rubber ( nakamura brace , ohda , japan ) , with a hardness of 
 durometer type a ( shore a ) 40 . following a previous study22 ,
the subjects were asked to stand on one leg with a toe - out angle 
 of 0 and to flex the contralateral hip to 30 while maintaining the contralateral hip at 
 neutral abduction / adduction and rotation , with their hands on their abdomen . before 
 collecting experimental data , the subjects practiced standing on one leg under each 
 condition several times , to become familiar with the task .
they were then instructed to 
 stand on one leg while looking straight ahead for 10 s. the three conditions were applied in 
 a random order , and measurements were repeated three times for each condition .
data analyses were done by using the bodybuilder software ( vicon motion systems , oxford , 
 uk ) .
the coordinates of each joint center were calculated according to methods described in 
 previous studies23 , 24 .
an eight - link segmental model was developed to calculate the hip , 
 knee , and ankle kinematic and kinetic data by using inverse dynamics according to the 
 techniques described by vaughan et al25 . 

anthropometric parameters for mass , center of mass , and moment of inertia for each segment 
 were obtained from the report by okada et al26 .
a knee joint moment was calculated by using the tibial coordinate 
 system with the origin in the knee joint center . in this study ,
kam was defined as the 
 external knee adduction moment after normalization to the subject s body mass ( nm / kg ) . 

furthermore , a knee - ground reaction force lever arm ( kla ) was calculated , defined as the 
 perpendicular distance between the ground reaction force and the knee joint center in a 
 laboratory frontal plane , based on the report by hinman et al27 . in this study ,
changes in kam and kla between the lwi and mwi 
 conditions were independently examined .
the change as the difference was calculated between 
 each subject s kam and kla when using lwis or mwis , and their kam and kla in the bf 
 condition .
the percentage change was calculated as follows:(kam or kla under 
 the lwi or mwi condition / kam or kla under the bf condition )  100 .
the above equation expresses the change in kam or kla as a percentage of the value under 
 the bf condition .
although data during a 10-s duration was recorded for each condition , the 
 time between 5 and 6  s was used for the analysis to eliminate the initial unstable phase 
 associated with the transition from the initial stance to standing on one leg22 . the mean value during this 1-s duration 
 was calculated for all variables , and the mean value of three trials was determined for each 
 subject .
all statistical analyses were performed with ezr on r commander v1.10 ( easy r , saitama , 
 japan ) .
the normality of data distribution was assessed by using the shapiro - wilk test . to 
 compare the three conditions , repeated - measures one - way analysis of variance with a post hoc 
 tukey s test
was used to evaluate the differences that were normally distributed , or the 
 kruskal - wallis test with a post hoc steel - dwass test for those that were not .
similarly , to 
 compare the changes in kam and kla between the lwi and mwi conditions , the paired t - test or 
 wilcoxon signed - rank test was used to evaluate the differences .
pearson s correlation or 
 spearman s rank correlation was also used to examine the associations between the changes in 
 kam and kla .
concerning the reliability of the fpi , the results showed an intraclass correlation 
 ( icc1,1 ) of 0.87 . therefore
all subjects ( n = 30 ) were classified into three subgroups according 
 to the left foot alignment results of the fpi .
the characteristics of the three groups are 
 summarized in table 1table 1.the characteristics of the three groups based on fpinormal group ( n = 18)pronated group ( n = 6)supinated group ( n = 6)age ( years)21.1  1.321.3  1.021.3  1.2height ( m)1.61  0.081.63 
0.071.61  0.06body weight ( kg)54.8  9.156.0  9.657.7  11.9bmi ( kg / m)20.9  1.821.0  2.822.0
 3.1values are expressed as mean  sd . the subjects age , height , body weight , and bmi were similar between the 
 subgroups .
values are expressed as mean  sd table 2table 2.kam and kla for three conditions ( n = 30)bflwimwikam ( nm / kg)0.43  0.080.42  0.080.45  0.08kla ( mm)127.6  12.6126.7  12.7130.7  12.7bf : bare foot , lwi : lateral wedge insole , mwi : medial wedge insole , kam : knee 
 adduction moment , kla : knee - ground reaction force lever arm .
values are expressed as 
 mean  sd shows the value and standard deviation of kam and kla under the bf , lwi , and 
 mwi conditions .
on 
 the other hand , concerning the changes in kam and kla as a percentage of the value under the 
 bf condition , both of these variables significantly decreased under the lwi condition 
 compared with the mwi condition ( table 
 3table 3.the change in kam and kla under the lwi and mwi conditions ( n = 30)lwimwikam ( % ) 99.6 ( 96.4102.7)104.6 ( 101.7107.0 ) * kla ( % ) 99.9 ( 97.1102.4)102.2 ( 101.0104.6 ) * values are expressed as median ( iqr ) . *
bf : bare foot , lwi : lateral wedge insole , mwi : medial wedge insole , kam : knee 
 adduction moment , kla : knee - ground reaction force lever arm .
values are expressed as 
 mean  sd values are expressed as median ( iqr ) .
* p < 0.05 under the lwi condition , the change in kam positively significantly correlated with the 
 change in kla ( r = 0.356 , p < 0.05 ) . however , under the mwi condition , there was no 
 significant association between the change in kam and kla ( r = 0.307 , p = 0.11 ) .
the changes in kam and kla under the lwi and mwi conditions between the subgroups are 
 presented in table 4table 4.the change in kam and kla under the lwi and mwi conditions between the 
 subgroups 
 lwimwikam ( % ) normal ( n = 18)98.9  4.4104.2  5.7 * pronated (
n = 6)94.4  8.8108.6  6.4 * supinated ( n = 6)101.8  2.6102.7  4.1kla ( % ) normal ( n = 18)99.2  3.0101.3  3.7 * pronated (
n = 6)99.7  5.4104.8  3.8supinated ( n = 6)100.9 ( 98.5103.2)103.6 ( 102.4105.5)values are expressed as mean  sd or median ( iqr ) * p < 0.05 . in the normal and pronated groups ,
the change in kam significantly decreased 
 under the lwi condition compared with the mwi condition ( p < 0.05 ) .
however , it was not 
 significantly different between conditions within the supinated group . in the normal group , 
 the change in kla
also significantly decreased under the lwi condition compared with the mwi 
 condition ( p < 0.05 ) . in contrast , it was not different between conditions within the 
 pronated and supinated groups
. values are expressed as mean  sd or median ( iqr ) * p < 0.05
in this study , we evaluated the immediate effects of lwis and mwis under unilateral weight 
 bearing conditions in healthy young adults .
the findings from our study revealed that both 
 the kam and kla were not significantly different between the three conditions .
however , the 
 change in kam and kla significantly decreased in the lwi condition compared with the mwi 
 condition .
these variables ware normalized to the value in the bw condition , which suggests 
 that the lwi may have effects of decreasing the kam and kla , whereas the mwi may have 
 effects of increasing those variables .
additionally , in the lwi condition , the change in kam 
 was positively correlated with the change in kla .
therefore , this study has demonstrated 
 that the primary mechanism of the biomechanical effects of lateral wedges is related to a 
 reduced kla .
our results showed that kam and kla were not significantly different between the three 
 conditions .
these results did not agree with those of previous kinematic studies that 
 demonstrated that lwis significantly reduced kam in patients with knee oa28 , 29 .
the difference in findings can be assumed to be due to a difference 
 in the measurement tasks .
most of the previous studies analyzed kam during gait , 
 particularly a value of peak during the stance phase .
on the other hand , takacs and 
 hunt20 reported that kam increased 
 significantly with a contralateral pelvic drop during unilateral weight bearing . to 
 eliminate the influence of gait speed and patterns that affect kam in the present study , we 
 also selected unilateral weight bearing for the measurement tasks .
therefore , the lack of a 
 difference between the three conditions may have been caused by variations in individual 
 motor control .
we therefore conclude that the common lwi and mwi conditions could not affect 
 kam and kla during unilateral weight bearing when compared with the bf condition . under the lwi condition ,
a 
 previous study reported that lwis of approximately 5 reduced the peak kam and knee 
 adduction angular impulse27 .
furthermore , 
 a stepwise regression analysis demonstrated that the reduction in the peak kam may have been 
 the result of a decreasing kla27 .
similar 
 to their findings , our results demonstrated that the change in kam mildly correlated with 
 the change in kla under the lwi condition . in brief , the reduction in kla with lwis may be 
 the central mechanism explaining the load - reducing effect , which also led to the reduction 
 in kam with lwis .
however , there was no association between the change in kam and that in 
 kla under the mwi condition .
a previous study demonstrated that there were no significant 
 changes in either the first or second peak kam during the gait stance phase with the 
 addition of medial arch supports in patients with knee oa30 .
moreover , the researchers observed considerable individual 
 variations in response to the arch support across participants . on the other hand
, in the 
 present study , we observed that the changes in both kam and kla significantly increased 
 under the mwi condition compared with the lwi condition .
these results suggest that although 
 mwis may cause an increase in kam and kla , the increase in kam does not necessarily 
 correlate directly with the increase in kla . as a result of the fpi classification , the changes in kam and kla significantly decreased 
 under the lwi condition than under the mwi condition in the normal group .
in contrast , the 
 change in kam significantly decreased under the lwi condition than under the mwi condition 
 in the pronated group ; however , the change in kla was not significantly different under the 
 two conditions .
these results suggest that persons with a pronated or flat foot receive a 
 beneficial effect with a reduction in kam ; however , this could not be closely correlated to 
 the reduction in kla .
a previous study reported that the reduction in the peak kam 
 correlated with a reduction in peak hip adduction during the stance phase27 .
another previous study revealed that 
 healthy subjects could decrease the first peak of kam by 65% compared with a normal gait by 
 walking while leaning their trunks toward the stance limb31 .
therefore , the present study suggests that the mechanism of 
 reducing kam can be potentially explained by not only the decrease in kla but also another 
 kinematic or kinetic change such as a response of the hip , pelvis , or upper trunk . neither the change in kam nor that in kla was significantly different between the lwi and 
 mwi conditions in the supinated group , indicating that lwis or mwis could not change these 
 values in persons with a supinated or hollow foot .
furthermore , this suggests that such 
 persons do not experience positive effects on kam , which is considered a surrogate measure 
 of medial knee compression .
therefore , the present results provide important insights that 
 could help clinicians decide whether lwis will be efficacious for patients with medial knee 
 oa by using a simple clinical examination .
first , because our study did not clarify the 
 influence on gait , the findings need to be interpreted with caution .
second , as our study 
 involved healthy participants , we can only draw conclusions about the effects of lwis 
 without the limitations of diseases .
the purpose of the present study was to evaluate the 
 inherent effect of lwis and mwis on kam without possible confounding parameters such as the 
 severity of knee oa and gait speed .
third , our decision to categorize participants by using 
 the fpi resulted in a decrease in the sample size per group .
the findings from our study 
 suggest that not only changes in kla but also those of another factor may have an influence 
 on the change in kam in some persons with a particularly pronated or flat foot .
therefore , 
 in addition to the assessment of the foot alignment by using the fpi , future research should 
 be performed with a larger number of subjects , and should aim to examine additional 
 kinematic and kinetic factors that indicate decreased kam .
furthermore , longitudinal studies 
 are needed to examine both the immediate and long - term effects of lwis for knee oa patients . 
 despite these limitations
, our findings suggest that the assessment of foot alignment would 
 assist in the identification of persons who may respond positively to lwi treatments .
 [ purpose ] lateral wedge insoles reduce the peak external knee adduction moment and are 
 advocated for patients with knee osteoarthritis . 
 however , some patients demonstrate 
 adverse biomechanical effects with treatment . in this study 
 , we examined the immediate 
 effects of lateral and medial wedge insoles under unilateral weight bearing . 
 [ subjects and 
 methods ] thirty healthy young adults participated in this study . 
 the subjects were 
 assessed by using the foot posture index , and were divided into three groups : normal foot , 
 pronated foot , and supinated foot groups . 
 the knee adduction moment and knee - ground 
 reaction force lever arm under the studied conditions were measured by using a 
 three - dimensional motion capture system and force plates . [ results ] in the normal and 
 pronated groups , the change in knee adduction moment significantly decreased under the 
 lateral wedge insole condition compared with the medial wedge insole condition . in the 
 normal group , 
 the change in the knee - ground reaction force lever arm also significantly 
 decreased under the lateral wedge insole condition than under the medial wedge insole 
 condition . 
 [ conclusion ] lateral wedge insoles significantly reduced the knee adduction 
 moment and knee - ground reaction force lever arm during unilateral weight bearing in 
 subjects with normal feet , and the biomechanical effects varied according to individual 
 foot alignment . 