flexible flatfoot is a common disease in lower limb deformities1 that is characterized by the low medial longitudinal 
 arch2 . it is the deformed structure of 
 the foot bones3 that would cause calcaneal 
 eversion , talar adduction with plantarflexion and dorsolateral forefoot subluxation . the 
 plantar pressure distribution and the gait will be changed by the deformity of foot 
 structure over the time4 , potentially 
 influencing the life of the patients . regarding the former , the arch of the foot was always 
 missing either in the weight - bearing position or non - weight - bearing position6 and it needs operation to restore the 
 missing arch7 . as far as concerned the 
 latter , the arch was missing only in the weight - bearing position , while in 
 non - weight - bearing position , the arch is as the same as that of normal foot8 . due to the arch s flexibility , the methods 
 of the treatment and whether the flexible flatfoot needs the treatment , have always been 
 controversial9 . flexible flatfoot can be further divided into mild flexible flatfoot and severe flexible 
 flatfoot10 . so far , previous studies 
 did not observe the plantar pressure of both kinds respectively and they had only focused on 
 the plantar pressure of walking on the level surface11 , 12 . however , the 
 differences between mild flexible flatfoot and severe flexible flatfoot , and how the plantar 
 pressure changes while walking upstairs or downstairs has not been studied . in this study , we examined the plantar pressure of mid flexible flatfoot , severe flexible 
 flatfoot and normal foot while walking on a level surface , walking up and down 10  cm and 
 20  cm stairs to estimate how plantar pressure changed and further to find out if flexible 
 flatfoot needs the treatment . the study protocol was approved by the institutional review board of the first affiliate 
 hospital of xian jiaotong university . fifteen college students with mild flexible flatfoot , fifteen college students with severe 
 flexible flatfoot and fifteen college students with normal foot were subjected to collecting 
 the footprints by rsscan force plate . all the subjects were female students and there was no 
 significant difference between flatfoot and normal foot in age , height , weight and foot 
 length . none of the participants had suffered from any lower limb diseases in the past 6 
 months . for the normal foot , the arch was always present either in weight - bearing position 
 or non - weight - bearing position . the footprint ratio of solid and hollow area is 1/2 . for the 
 flatfoot , the arch was present only in non - weight - bearing position and it was flattened in 
 weight - bearing position . for mild flexible flatfoot , the footprint ratio of solid and hollow 
 area is more than1/1 and less than 2/1 , for severe flexible flatfoot , the ratio is more than 
 2/1 . before the measurement , all the subjects need to take off their shoes , wear the unified 
 socks and do the walking exercises at the speed of one step per second . then the subjects 
 were firstly told to walk on the level rsscan force plate ; then , they were instructed to 
 walk up or walk down 10  cm or 20  cm stairs on the instrument respectively . the max force and 
 arch index of the foot were recorded by the rsscan system on those walking conditions . to 
 ensure the accuracy , at last , the 
 repeated measures anova with a level of significance of p<0.05 was performed using spss 
 13.0 . the 95% confidence intervals ( cis ) ( p<0.05 ) was considered statistically 
 significant . an rsscan force plate ( rs - footscan 7 usb2 gait ) with an area of 40  50  cm , including 4 
 sensors in each square centimeter , was used to measure the dynamic data of max force and 
 arch index on different walking conditions . when the subject was walking on the force plate , 
 the foot was divided into 10 parts automatically including toe 1 , toe 25 , first metatarsal , 
 second metatarsal , third metatarsal , forth metatarsal , fifth metatarsal , mid foot , medial 
 heel and lateral heel . in addition , there is a main difference of plantar pressure in midfoot region between a 
 normal foot and a flatfoot . for the normal foot , the main load - bearing regions include the 
 metatarsal area and the heel area , but for the flatfoot , it not only includes the metatarsal 
 and heel areas , but also includes the midfoot13 . in other words , it is the pressure of midfoot that differs the 
 flatfoot from normal foot . this study measured two kinds of dynamic data , max force and arch index . with the 
 progression of the disease , the arch will become flat further result in an increase of max 
 force14 and arch index15 . max force , with the unit of newton , is 
 defined as the maximum of plantar pressure of one part of the foot16 . arch index , a proportion of the midfoot area and the 
 whole foot area , is useful in determining the prevalence of flatfoot and possibly predicting 
 pathologic foot conditions17 . all the data were divided into 
 3 groups : mild flexible flatfoot , severe flexible flatfoot and normal foot . each group was 
 further divided into 5 conditions : walking on a level surface , walking up 10  cm stairs , 
 walking up 20  cm stairs , walking down 10  cm stairs , walking down 20  cm stairs . the significant differences were found in max force and arch index between severe flexible 
 flatfoot and normal foot ( p<0.01 ) , and between severe flexible flatfoot and mild flexible 
 flatfoot ( p<0.01 ) . while there was no significant difference between mild flexible 
 flatfoot and normal foot in both data ( p>0.05 ) ( tables 1table 1.max force 
 of 3 groupsleft footgroupgroupmean difference std.errorsig.(a)95% confidence interval for 
 difference(2)lower bound upper boundmildmildsevere90.5(*)10.50.0111.669.3normal 7.710.50.513.528.8severemild90.5(*)10.50.069.3111.6severenormal 
 98.1(*)10.50.077.0119.3normalmild7.710.50.528.813.5severe98.1(*)10.50.0119.377.0normal right 
 footgroupgroupmean difference std.errorsig.(a)95% confidence interval for difference(2)lower bound upper 
 boundmildmildsevere97.2(*)9.30.0115.978.5normal 10.49.30.38.429.1severemild97.2(*)9.30.078.5115.9severenormal 107.6(*)9.30.088.8126.3normalmild10.49.30.329.18.4severe107.6(*)9.30.0126.388.8normal based on estimated marginal 
 means.*the mean difference is significant at the 0.05 level.mild : mild 
 flexible flatfoot ; severe : severe flexible flatfoot ; normal : normal 
 foot and 
 2table 2.arch index of 3 
 groupsleft footgroupgroupmean difference std.errorsig.(a)95% confidence interval for 
 difference(2)lower bound upper boundmildmildsevere3.93(*)0.390.004.733.14normal 0.790.390.050.001.59severemild3.93(*)0.390.003.144.73severenormal 
 4.73(*)0.390.003.935.52normalmild0.790.390.051.590.00severe4.73(*)0.390.005.523.93normal right 
 footgroupgroupmean difference std.errorsig.(a)95% confidence interval for difference(2)lower bound upper 
 boundmildmildsevere4.46(*)0.280.005.023.91normal 0.390.280.170.170.95severemild4.46(*)0.280.003.915.02severenormal 4.85(*)0.280.004.295.41normalmild0.390.280.170.950.17severe4.85(*)0.280.005.414.29normal based on estimated marginal 
 means.*the mean difference is significant at the 0.05 level.mild : mild 
 flexible flatfoot ; severe : severe flexible flatfoot ; normal : normal 
 foot ) . mild : mild 
 flexible flatfoot ; severe : severe flexible flatfoot ; normal : normal 
 foot based on estimated marginal 
 means . * mild : mild 
 flexible flatfoot ; severe : severe flexible flatfoot ; normal : normal 
 foot in addition , there was no intersection of the 95% cis of both data between severe flexible 
 flatfoot and normal foot on 5 different walking conditions . furthermore , no intersection of 
 arch index could be found between mild flexible flatfoot and normal foot when walking 
 downstairs . however , there was an intersection between mild flexible flatfoot and normal 
 foot in both data when walking on the level surface and walking upstairs ( tables 3table 
 3.max force of 5 walking conditionsleft footgroupconditionsmean difference std.error95% confidence interval for 
 difference(2)lower bound upper boundmildlevel191.95.7179.6202.4up 10  cm stairs182.66.2170.2195.0up 20  cm stairs182.76.0170.5194.9down 10  cm 
 stairs236.69.5217.4255.8down 
 20  cm stairs285.912.7260.3311.5severelevel285.25.7273.8296.7up 10  cm 
 stairs274.06.2261.6286.4up 
 20  cm stairs268.76.0256.5280.9down 10  cm stairs330.09.5310.8349.2down 20  cm stairs373.212.7347.6398.8normal level188.75.7177.2200.1up 10  cm stairs176.86.2164.4189.2up 20  cm stairs178.46.0166.2190.6down 10  cm 
 stairs230.89.5211.6250.0down 
 20  cm stairs265.912.7240.3291.5right footgroupconditionsmean difference std.error95% confidence interval for 
 difference(2)lower bound upper boundmildlevel192.45.6181.1203.8up 10  cm stairs184.85.8173.1196.6up 20  cm stairs183.05.7171.5194.5down 10  cm 
 stairs242.08.1225.6258.3down 
 20  cm stairs293.610.5272.3314.8severelevel291.75.6280.4303.1up 10  cm 
 stairs282.85.8271.1294.6up 
 20  cm stairs280.35.7268.8291.9down 10  cm stairs337.18.1320.7353.4down 20  cm stairs389.710.5368.5411.0normal level187.75.6176.3199.0up 10  cm stairs177.95.8166.2189.7up 20  cm stairs179.55.7168.0191.0down 10  cm 
 stairs232.78.1216.4249.1down 
 20  cm stairs266.110.5244.8287.3mild : mild flexible flatfoot ; 
 severe : severe flexible flatfoot ; normal : normal 
 foot and 
 4table 4.arch index of 5 
 walking conditionsleft footgroupconditionsmean 
 difference std.error95% confidence interval for difference(2)lower bound upper boundmildlevel27.00.326.527.6up 
 10  cm stairs27.00.326.327.6up 20  cm stairs26.80.326.227.5down 10  cm stairs30.40.329.831.0down 20  cm stairs32.10.431.332.8severelevel31.50.330.932.1up 10  cm stairs31.20.330.531.8up 20  cm 
 stairs31.20.330.531.9down 
 10  cm stairs33.30.332.733.9down 20  cm stairs35.80.435.036.5normal level26.80.326.227.4up 
 10  cm stairs26.50.325.827.1up 20  cm stairs26.40.325.827.1down 10  cm stairs29.20.328.629.7down 20  cm stairs30.50.429.731.2right 
 footgroupconditionsmean difference std.error95% confidence 
 interval for difference(2)lower bound upper boundmildlevel26.70.226.227.2up 10  cm stairs26.60.326.127.1up 20  cm 
 stairs26.50.326.027.0down 
 10  cm stairs30.90.230.531.5down 20  cm stairs32.00.231.632.5severelevel31.90.231.532.4up 
 10  cm stairs31.30.330.831.8up 20  cm stairs31.20.330.731.7down 10  cm stairs34.50.234.134.9down 20  cm stairs36.20.235.736.6normal 
 level26.70.226.227.2up 10  cm stairs26.40.325.926.9up 20  cm 
 stairs26.40.325.926.9down 
 10  cm stairs29.90.229.530.4down 20  cm stairs31.30.230.931.8mild : mild flexible flatfoot ; 
 severe : severe flexible flatfoot ; normal : normal 
 foot ) . mild : mild flexible flatfoot ; 
 severe : severe flexible flatfoot ; normal : normal 
 foot mild : mild flexible flatfoot ; 
 severe : severe flexible flatfoot ; normal : normal 
 foot furthermore , the 95% cis of downstairs of both data did not intersect with any other 
 walking conditions not only in flatfoot but also in normal foot ( tables 3 and 4 ) . the results implied that the plantar pressure of severe flexible flatfoot were 
 significantly larger than that of normal foot . although there was no difference between mild 
 flexible flatfoot and normal foot when walking on the level surface and walking upstairs , 
 the arch index of mild flexible flatfoot did differ from the normal foot when walking 
 downstairs . additionally , the arches of both normal foot and flatfoot were obviously 
 deformed when walking down 10  cm and 20  cm stairs . the results showed that the max force and arch index of severe flexible flatfoot were 
 significantly increased , which was in accordance with previous studies18,19,20,21 . as the foot arch of severe flexible flatfoot was not steady enough , the height of the foot 
 arch would be lower in load - bearing - position22 and the structure of the foot bones was deformed23 , which increased the max force and arch 
 index . previous study had already estimated the plantar pressure of flatfoot when walking on a 
 level surface18,19,20,21 . however , it has not been examined how the plantar pressure changes 
 when walking upstairs and downstairs . in this study , the max force and arch index of severe 
 flexible flatfoot were significantly larger than that of normal foot not only when walking 
 on a level surface , but also when walking upstairs and downstairs . this result indicated 
 that the structure of severe flexible flatfoot was deformed badly24 due to the instability of its foot arch25 . the largest values of max force and arch index were in walking down 20  cm stairs , the 
 second largest ones were in walking down 10  cm stairs , which may be due to the fact that the 
 plantar pressure will be influenced not only by the body weight but also by the acceleration 
 of gravity when a person walks downstairs26 . therefore , with the increase of the gravity , the plantar pressure 
 would increase as well . according to this study , the data of both normal foot and flexible flatfoot were obviously 
 larger when walking downstairs , illustrating that the arches of both normal foot and 
 flatfoot were apparently deformed whenever walking down 10  cm stairs or 20  cm stairs . as the 
 arch of normal foot needs certain elasticity to protect plantar vessels and nerves from 
 compression27 , the arch could be 
 influenced by the impact of downstairs . in other words , 
 it is harmful to the foot arch when walking downstairs . this is important because people 
 prefer to taking a lift when walking upstairs , as for downstairs , as long as the floor is 
 not much high , they would rather walk downstairs than wait for the lift . the plantar pressure of severe flexible flatfoot were significantly larger than that of 
 normal foot not only when walking on a level surface but also when walking upstairs and 
 downstairs . additionally , the arch of both normal foot and flexible flatfoot were deformed 
 whenever walking down 10  cm or 20  cm stairs . therefore , adults with severe flexible flatfoot 
 may need treatment to prevent further deformation . however , further studies are necessary to 
 analyze the plantar pressure of adults with flatfoot in other areas in the future .
[ purpose ] this study observed the plantar pressure between flexible flatfoot and normal 
 foot on different walking conditions to find out if flexible flatfoot needs the treatment 
 and how the plantar pressure change while walking upstairs and downstairs . [ subjects and 
 methods ] fifteen adults with mild flexible flatfoot , fifteen adults with severe flexible 
 flatfoot and fifteen adults with normal foot were examined while walking on a level 
 surface , walking up and down 10  cm and 20  cm stairs . the max force and the arch index 
 were 
 acquired using the rsscan system . 
 the repeated measures anova was performed to analyze the 
 data . [ results ] compared with normal foot , both max force and arch index of severe 
 flatfoot were significantly increased on different walking conditions . when walking down 
 10  cm and 20  cm stairs 
 , the plantar data of both normal foot and flatfoot were 
 significantly increased . 
 [ conclusion ] the plantar pressure of severe flexible flatfoot 
 were significantly larger than that of normal foot on different walking conditions . in 
 addition , the arches of both normal foot and flatfoot were obviously deformed when walking 
 downstairs . 
 it is therefore necessary to be treated for severe flexible flatfoot to 
 prevent further deformation .