juvenile idiopathic arthritis ( jia ) is a chronic and progressive inflammatory arthritis of childhood which often results in persistent and disabling foot impairments [ 13 ] .
synovitis , has a predilection for the lower limb joints and results in well - recognised clinical features including joint pain , swelling , limited joint range - of - motion and development of deformity [ 35 ] .
inflammatory pathology is not limited to joints and studies employing musculoskeletal ultrasonography have also detected tenosynovitis , enthesitis , and bursitis in the periarticular ankle region .
unsurprisingly disruption to global gait patterns has been frequently reported as an early and common consequence of jia .
the impact of jia on global function has been studied extensively with the use of patient reported outcome measures ( proms ) such as the childhood health assessment questionnaire ( chaq ) , a widely used 30 item measure of childhood disability .
studies employing proms have demonstrated strong associations between clinical symptoms such as pain or radiographically detected joint destruction , with poor long - term functional outcomes . at a local level , the impact of active disease and related impairments remain unclear .
the development of juvenile arthritis foot disability index questionnaire ( jafi ) , a 27 item measure organised by three dimensions related to impairment , activity limitation , and participation restriction , has allowed researchers to quantify levels of disease - related foot impairments and disability .
recent studies of foot function have improved our understanding of foot impairments in adults with rheumatoid arthritis ( ra ) .
in particular , studies employing three - dimensional ( 3d ) multi - segmented foot models have demonstrated an ability to quantify subtle but functionally important changes to foot segment kinematics and kinetics at an early disease stage .
in contrast , little is known about the functional consequences of active foot disease and/or residual impairments such as foot deformity in patients with jia .
patients with jia who have lower limb involvement tend to walk slower , as a result of a reduced step length , reduced cadence and an increased period of double limb support . reduced peak pressures have been recorded in those with forefoot pain , metatarso - phalangeal ( mtp ) joint and lesser toe deformity . while elevated focal pressures in the forefoot have previously been associated with pes cavus foot types .
abnormal ankle - joint - complex motion has been described where the foot has been modelled as a single segment .
however this approach provides limited information concerning other foot joint function compared to the multi - segment approach .
accordingly , the aim of this study was to compare disease activity , impairments , disability , foot function and gait characteristics between a well described cohort of jia patients and normal healthy controls using a 7-segment foot model and 3d gait analysis .
fourteen patients with a definitive diagnosis of jia , based on the international league of associations for rheumatology ( ilar ) criteria   were consecutively recruited from a phase ii randomised controlled trial of a multi - disciplinary foot - care programme .
participants had a documented history of active inflammatory foot disease affecting the joints and/or soft tissues .
ten community dwelling healthy children and adolescents matched as closely as possible by age and gender , with no history of trauma , neuromuscular or musculoskeletal diseases were recruited for comparison .
this study was approved by the glasgow west local research ethics committee on the 18th march 2008 ( reference number 08/s0709/36 ) .
all participants and parents / guardians provided their informed consent to participate in this study .
age , gender , body mass index , disease subtype , disease duration , and current pharmacological therapy were recorded for each patient .
localised disease activity was estimated by a podiatrist [ gh ] who recorded tender and swollen joint scores in the foot for the ankle , subtalar , calcaneocuboid , talonavicular , mtp , interphalangeal joint of the hallux and proximal interphalangeal joints of the lesser toes ( range 014 ) .
tender and swollen soft tissue sites in the foot were also recorded for the tibialis posterior , flexor digitorum longus , flexor hallucis longus , peroneus longus and peroneus brevis tendons , the retro - calcaneal bursa ( rcb ) , and the calcaneal tendo - achilles ( ta ) and calcaneal plantar fascia entheses ( pf ) ( range 08 ) .
the si summates hallux valgus , 5th mtp exostosis , lesser toe deformities and mtp subluxation for the forefoot ( range 012 ) and calcaneal valgus / varus , ankle range of motion and pes planus / cavus deformities of the rearfoot ( range 07 ) .
the weight - bearing varus / valgus alignment of the heel was measured using a standard hand - held goniometer .
a fully trained paediatric musculoskeletal ultra - sonographer [ det ] independently assessed localised disease activity in the foot .
those joints from the clinical examination were assessed for effusion , synovial hypertrophy ( sh ) , and power doppler signal ( pds ) .
tendons were assessed for grey - scale features of fluid within the tendon sheath and pds ; the ta and pf for abnormal thickening , and rcb for bursal effusion ( bursitis ) .
standardised definitions for ultrasound ( us ) -derived pathology ( defined by the outcome measures in rheumatology 7 consensus statement )   were employed throughout .
us imaging was conducted using an esaote mylab 25 gold ( genova , italy ) with la435 ( 1018  mhz ) probe ( footprint size 40  mm    10  mm ) .
an 8 camera 120  hz motion analysis system ( qualysis oqus , gothenburg , sweden ) was used to track the motion of 25 surface - mounted , spherical , and retro - reflective markers ( 5  mm and 10  mm diameter ) placed on the shank and foot which were positioned in order to represent the underlying skeletal structure .
this model was adapted from the original model proposed by hyslop et al .   previously to measure foot function in adults with psoriatic arthritis ( see supplementary online material for full model description ) , and was selected for use on the basis that jia is an inflammatory arthropathy with similar disease features .
rockville , md , usa ) was used to build segmented foot models which comprised the shank , a single foot segment , rearfoot , midfoot , lateral forefoot , 1st metatarsal and hallux , based on the surface marker coordinates
. ground reaction forces ( 120  hz ) and plantar pressure distributions were measured separately using force ( kistler , winterthur , switzerland ) and pressure ( emed - x , novel gmbh , munich , germany ) platforms .
an instrumented walkway ( gaitrite , cir systems , clifton , nj , usa ) was used to measure spatial and temporal gait parameters . a pre - determined core
set of foot biomechanical variables were selected a priori for analysis based on previous survey and gait analysis data in ra , psoriatic arthritis and jia [ 2,1315,23 ] .
these included walking velocity , cadence , step length , double support time and cycle time as objective measures of global function .
intersegment kinematics , kinetics and plantar pressure distribution parameters were selected to best capture the functional changes associated with joint and soft - tissue damage in jia .
initial foot contact angle , rearfoot terminal stance range - of - motion in the sagittal plane , peak vertical ground reaction forces , ankle joint moment and ankle joint power were selected to describe the three rocker functions of the foot .
peak rearfoot eversion , peak lateral forefoot abduction , peak 1st metatarsal dorsiflexion , peak hallux dorsiflexion , minimum navicular height , midfoot and lesser toe contact areas , and peak pressures in the rear- and forefoot were selected to describe localised functional impairments , compensations and deformities .
the average velocity and duration of the centre - of - pressure ( cop ) throughout the foot , heel , midfoot , forefoot and toe regions was recorded to quantify compensatory foot - loading strategies associated with degraded and adapted ( antalgic ) gait .
peak midfoot dorsiflexion was selected for exploratory analysis as both high- and low - arched midfoot posture is a frequent clinical finding in jia . a relaxed standing ( static ) trial
was collected for the foot from each participant in order to define 0 ( neutral ) for the kinematic data .
kinematic and kinetic and parameters were collected from 5 barefoot walking trials in each patient .
spatial and temporal parameters were recorded from 5 barefoot self - selected walking speed trials over the walkway .
plantar pressure distribution parameters were collected separately from 5 barefoot trials using a two - step protocol .
kinematic , kinetic and plantar pressure measurements were estimated from 5 trials of the right limb for all participants .
automated software routines ( novel gmbh , munich , germany ) were used to define the rearfoot , midfoot , forefoot , lesser toe and hallux regions of the foot for plantar pressure distribution .
clinical and biomechanical variables were summarised as mean and standard deviation ( sd ) or median ( range ) .
the small sample size did not permit formal inferential hypothesis testing , therefore mean differences between groups and associated 95% confidence intervals ( ci ) were calculated using the t distribution .
mean motion patterns of intersegment kinematics were normalised to 101 time points ( 0100% stance ) and both groups ensemble averages ( 1sd ) were superimposed and displayed graphically .
discrete gait variables were normalised where appropriate to dimensionless quantities using the formulae described by hof .
fourteen patients with a definitive diagnosis of jia , based on the international league of associations for rheumatology ( ilar ) criteria   were consecutively recruited from a phase ii randomised controlled trial of a multi - disciplinary foot - care programme .
participants had a documented history of active inflammatory foot disease affecting the joints and/or soft tissues .
ten community dwelling healthy children and adolescents matched as closely as possible by age and gender , with no history of trauma , neuromuscular or musculoskeletal diseases were recruited for comparison .
this study was approved by the glasgow west local research ethics committee on the 18th march 2008 ( reference number 08/s0709/36 ) .
all participants and parents / guardians provided their informed consent to participate in this study .
age , gender , body mass index , disease subtype , disease duration , and current pharmacological therapy were recorded for each patient .
localised disease activity was estimated by a podiatrist [ gh ] who recorded tender and swollen joint scores in the foot for the ankle , subtalar , calcaneocuboid , talonavicular , mtp , interphalangeal joint of the hallux and proximal interphalangeal joints of the lesser toes ( range 014 ) .
tender and swollen soft tissue sites in the foot were also recorded for the tibialis posterior , flexor digitorum longus , flexor hallucis longus , peroneus longus and peroneus brevis tendons , the retro - calcaneal bursa ( rcb ) , and the calcaneal tendo - achilles ( ta ) and calcaneal plantar fascia entheses ( pf ) ( range 08 ) .
the si summates hallux valgus , 5th mtp exostosis , lesser toe deformities and mtp subluxation for the forefoot ( range 012 ) and calcaneal valgus / varus , ankle range of motion and pes planus / cavus deformities of the rearfoot ( range 07 ) .
the weight - bearing varus / valgus alignment of the heel was measured using a standard hand - held goniometer .
a fully trained paediatric musculoskeletal ultra - sonographer [ det ] independently assessed localised disease activity in the foot .
those joints from the clinical examination were assessed for effusion , synovial hypertrophy ( sh ) , and power doppler signal ( pds ) .
tendons were assessed for grey - scale features of fluid within the tendon sheath and pds ; the ta and pf for abnormal thickening , and rcb for bursal effusion ( bursitis ) .
standardised definitions for ultrasound ( us ) -derived pathology ( defined by the outcome measures in rheumatology 7 consensus statement )   were employed throughout .
us imaging was conducted using an esaote mylab 25 gold ( genova , italy ) with la435 ( 1018  mhz ) probe ( footprint size 40  mm    10  mm ) .
an 8 camera 120  hz motion analysis system ( qualysis oqus , gothenburg , sweden ) was used to track the motion of 25 surface - mounted , spherical , and retro - reflective markers ( 5  mm and 10  mm diameter ) placed on the shank and foot which were positioned in order to represent the underlying skeletal structure .
this model was adapted from the original model proposed by hyslop et al .   previously to measure foot function in adults with psoriatic arthritis ( see supplementary online material for full model description ) , and was selected for use on the basis that jia is an inflammatory arthropathy with similar disease features .
rockville , md , usa ) was used to build segmented foot models which comprised the shank , a single foot segment , rearfoot , midfoot , lateral forefoot , 1st metatarsal and hallux , based on the surface marker coordinates .
ground reaction forces ( 120  hz ) and plantar pressure distributions were measured separately using force ( kistler , winterthur , switzerland ) and pressure ( emed - x , novel gmbh , munich , germany ) platforms .
an instrumented walkway ( gaitrite , cir systems , clifton , nj , usa ) was used to measure spatial and temporal gait parameters . a pre - determined core
set of foot biomechanical variables were selected a priori for analysis based on previous survey and gait analysis data in ra , psoriatic arthritis and jia [ 2,1315,23 ] .
these included walking velocity , cadence , step length , double support time and cycle time as objective measures of global function .
intersegment kinematics , kinetics and plantar pressure distribution parameters were selected to best capture the functional changes associated with joint and soft - tissue damage in jia .
initial foot contact angle , rearfoot terminal stance range - of - motion in the sagittal plane , peak vertical ground reaction forces , ankle joint moment and ankle joint power were selected to describe the three rocker functions of the foot .
peak rearfoot eversion , peak lateral forefoot abduction , peak 1st metatarsal dorsiflexion , peak hallux dorsiflexion , minimum navicular height , midfoot and lesser toe contact areas , and peak pressures in the rear- and forefoot were selected to describe localised functional impairments , compensations and deformities .
the average velocity and duration of the centre - of - pressure ( cop ) throughout the foot , heel , midfoot , forefoot and toe regions was recorded to quantify compensatory foot - loading strategies associated with degraded and adapted ( antalgic ) gait .
peak midfoot dorsiflexion was selected for exploratory analysis as both high- and low - arched midfoot posture is a frequent clinical finding in jia . a relaxed standing ( static ) trial
was collected for the foot from each participant in order to define 0 ( neutral ) for the kinematic data .
kinematic and kinetic and parameters were collected from 5 barefoot walking trials in each patient .
spatial and temporal parameters were recorded from 5 barefoot self - selected walking speed trials over the walkway .
plantar pressure distribution parameters were collected separately from 5 barefoot trials using a two - step protocol .
kinematic , kinetic and plantar pressure measurements were estimated from 5 trials of the right limb for all participants
. automated software routines ( novel gmbh , munich , germany ) were used to define the rearfoot , midfoot , forefoot , lesser toe and hallux regions of the foot for plantar pressure distribution .
clinical and biomechanical variables were summarised as mean and standard deviation ( sd ) or median ( range ) .
the small sample size did not permit formal inferential hypothesis testing , therefore mean differences between groups and associated 95% confidence intervals ( ci ) were calculated using the t distribution .
mean motion patterns of intersegment kinematics were normalised to 101 time points ( 0100% stance ) and both groups ensemble averages ( 1sd ) were superimposed and displayed graphically .
discrete gait variables were normalised where appropriate to dimensionless quantities using the formulae described by hof .
fourteen jia patients ( 10 female , 4 male ) with a mean age of 12.4 years ( sd 3.2 ) were studied .
this was a heterogeneous sample including patients with variable jia disease subtype , disease duration and medication .
all patients were in receipt of disease - modifying anti - rheumatic drugs ( dmards ) and/or biologic therapies .
ten control subjects ( 6 female , 4 male ) with a mean age of 12.5 years ( sd 3.4 ) were studied for comparison .
control subjects were closely matched to jia case subjects by age and bmi , but had a greater proportion of m : f than the jia subjects .
functional impairment scores ( chaq ) were typically in the mild - to - moderate category ( > 0.13 to < 0.63 ) for jia patients , although these ranged from no impairment to moderate impairment .
jafi scores for localised foot impairments and disability were in the mild - to moderate category ( 1 to 2 ) but were variable between jia subjects .
median ( range ) scores for each domain were 1 ( 03 ) ( impairment and activity limitation ) and 1.5 ( 03 ) ( participation restriction ) .
there were low levels of clinically detected disease activity in the joints and soft tissues as indicated by tender and swollen joint and soft tissue counts .
foot joint effusions detected using us were a typical finding in patients with jia , suggesting that subclinical disease was present in several patients .
mild forefoot and moderate rearfoot deformities were recorded in patients with jia , who typically exhibited a marginally more valgus foot posture than controls .
ensemble average kinematic - time and kinetic - time variables are summarised in fig . 1 and core biomechanical variables in table 3 .
the magnitude and timing of the kinematic and kinetic variables during the stance phase of gait were similar for both groups .
the average patterns for the jia patients did not deviate outside normal limits ( fig .
trends were observed for reduced peak ankle joint plantarflexor moment , joint power , and the peak vertical ground reaction force at initial contact and terminal stance in the children with jia , however 95% cis of the mean differences for each variable crossed zero ( table 3 ) .
no difference could be detected for in the initial and terminal stance contact angles for the foot relative to the ground .
medial longitudinal arch posture , as indicated by the navicular height , was not different between the two groups .
the rearfoot rom and peak eversion and 1st metatarsal dorsiflexion were the same in both groups .
the jia group showed trends towards slight increases in midfoot dorsiflexion ( 95% ci of mean differences did not cross zero ) , reductions in lateral forefoot abduction and decreases in peak hallux dorsiflexion ( 95% cis of mean differences crossed zero ) .
the distribution of plantar pressure was not different between the two groups in terms of midfoot and lesser toe contact areas ( table 3 ) .
pressure in the rearfoot , 1st metatarsal and lateral forefoot regions were on average 35  kpa and 43  kpa lower respectively , and 1  kpa respectively higher in the children with jia .
the jia children walked with a reduced step length , reduced walking velocity , and increased cadence , in comparison with control subjects although double - support time was unaffected ( table 3 ) .
the average velocity of the cop through the foot regions was similar for both groups ( table 4 ) .
the duration of the cop was slightly increased in the midfoot and slightly decreased in the forefoot regions in the jia patients in comparison with control subjects .
fourteen jia patients ( 10 female , 4 male ) with a mean age of 12.4 years ( sd 3.2 ) were studied .
this was a heterogeneous sample including patients with variable jia disease subtype , disease duration and medication .
all patients were in receipt of disease - modifying anti - rheumatic drugs ( dmards ) and/or biologic therapies .
ten control subjects ( 6 female , 4 male ) with a mean age of 12.5 years ( sd 3.4 ) were studied for comparison .
control subjects were closely matched to jia case subjects by age and bmi , but had a greater proportion of m : f than the jia subjects .
functional impairment scores ( chaq ) were typically in the mild - to - moderate category ( > 0.13 to < 0.63 ) for jia patients , although these ranged from no impairment to moderate impairment .
jafi scores for localised foot impairments and disability were in the mild - to moderate category ( 1 to 2 ) but were variable between jia subjects .
median ( range ) scores for each domain were 1 ( 03 ) ( impairment and activity limitation ) and 1.5 ( 03 ) ( participation restriction ) .
there were low levels of clinically detected disease activity in the joints and soft tissues as indicated by tender and swollen joint and soft tissue counts .
foot joint effusions detected using us were a typical finding in patients with jia , suggesting that subclinical disease was present in several patients .
mild forefoot and moderate rearfoot deformities were recorded in patients with jia , who typically exhibited a marginally more valgus foot posture than controls .
ensemble average kinematic - time and kinetic - time variables are summarised in fig . 1 and core biomechanical variables in table 3 .
the magnitude and timing of the kinematic and kinetic variables during the stance phase of gait were similar for both groups .
the average patterns for the jia patients did not deviate outside normal limits ( fig .
trends were observed for reduced peak ankle joint plantarflexor moment , joint power , and the peak vertical ground reaction force at initial contact and terminal stance in the children with jia , however 95% cis of the mean differences for each variable crossed zero ( table 3 ) .
no difference could be detected for in the initial and terminal stance contact angles for the foot relative to the ground .
medial longitudinal arch posture , as indicated by the navicular height , was not different between the two groups .
the rearfoot rom and peak eversion and 1st metatarsal dorsiflexion were the same in both groups .
the jia group showed trends towards slight increases in midfoot dorsiflexion ( 95% ci of mean differences did not cross zero ) , reductions in lateral forefoot abduction and decreases in peak hallux dorsiflexion ( 95% cis of mean differences crossed zero ) .
the distribution of plantar pressure was not different between the two groups in terms of midfoot and lesser toe contact areas ( table 3 ) .
pressure in the rearfoot , 1st metatarsal and lateral forefoot regions were on average 35  kpa and 43  kpa lower respectively , and 1  kpa respectively higher in the children with jia .
the jia children walked with a reduced step length , reduced walking velocity , and increased cadence , in comparison with control subjects although double - support time was unaffected ( table 3 ) .
the average velocity of the cop through the foot regions was similar for both groups ( table 4 ) .
the duration of the cop was slightly increased in the midfoot and slightly decreased in the forefoot regions in the jia patients in comparison with control subjects .
this is the first study to report selected 3d kinematics and kinetics , spatio - temporal parameters , and plantar pressure distribution in a group of jia children and adolescents in receipt of optimised medical management .
these findings are in contrast to past studies which have shown marked changes in foot function . in an era of optimal medical management exploiting dmard and biological therapies
, the findings may indicate that suppression and tight control of active foot disease prevents or reduces the frequency and severity of joint destruction and the associated structural and functional impairments .
the patients with jia described in this study were heterogeneous for age , disease subtype and disease duration . with established disease
this optimised medical approach appears to have lessened the overall foot disease burden as indicated by low levels of self / parent - reported pain , functional loss and disability .
ultrasound examination indicated on - going active disease in approximately one - third of children .
however , it is acknowledged that significant discrepancies still exist between clinical and us examinations of foot disease in jia . despite this detailed analysis of foot function revealed only subtle changes some indicative of degraded and some of adapted gait . by contrast , studies reported in the pre - biological and tight control era , often where disease factors and treatment regimes are not reported , demonstrate marked degenerative and adapted gait disturbances .
these include changes to overall gait pattern characterised by reduced walking velocity and shortened step and stride length   altered load and pressure distribution characteristic of both high - arch and flat - foot posture ; disturbance of the normal sagittal rocker function ; and muscle imbalance and reduced muscle strength . in terms of joint kinematics , reduced ankle plantarflexion in terminal stance has been demonstrated where the foot was modelled as a single segment . in many of these studies
there is little or no information provided on disease subtype , disease activity , active joint disease , morbid foot state , or medical and non - pharmacological interventions making direct comparisons difficult .
.   demonstrated strong relationships between disease activity and foot - related impairments and disability using the jafi questionnaire .
the jafi scoring system may be vulnerable to a moderate floor effect , resulting in insensitivity for detecting impairments .
nevertheless in the present study active disease was low and this was associated with low levels of self - reported foot impairment and functional disability measured using the jafi .
this study adds additional evidence suggesting the articular function in the foot can be well preserved when disease activity is suppressed using optimised medical care . in other inflammatory joint diseases , in particular rheumatoid arthritis , marked changes in foot function has been demonstrated in a number of studies in both early and established disease [ 1315 ] .
the failure to detect important functional changes in the jia group in comparison can be explained by the cumulative effects of destructive joint disease in the ra patients who , in most studies , have longer disease duration and sub - optimal drug management .
however , even in jia patients the lag time in which to gain optimised case with disease remission or low disease state can take time and in that time joint and soft - tissue damage can occur .
subtle changes were observed in the present study including reduced walking speed and some changes to mid - foot arch posture . at the individual patient level
some children did have marked impairments and this would indicate that on - going studies , in particular inception cohort designs from onset of symptoms / diagnosis are warranted to understand disease progression across all subtypes .
firstly the sample size is small and the inclusion of all disease subtypes precludes wider generalisation of the findings .
secondly , the foot model was developed and tested in adults with inflammatory joint disease .
landmark identification around the rearfoot , in particular , the peroneal tubercle , the dorso - lateral apex of the cuboid , and the dorsal aspect of the intermediate cuneiform was challenging .
as such the rear- and mid - foot segment rotation data may have been vulnerable to errors different from those reported for the original model .
we attempted to limit this by using one experienced paediatric clinician with experience in multi - segment foot model use in disease populations . utilising a similar protocol with adult subjects with and without psoriatic arthritis hyslop et al
.   demonstrated excellent within - day and between - day reliability characteristics for spatio - temporal , plantar pressure , kinematic and kinetic variables .
however peak rearfoot eversion performed poorly   with within - group variance exceeding between group variance .
therefore comparison between cases and controls for peak rearfoot eversion in the present study may be vulnerable to error , particularly since this is the first application of the model to measure children and adolescents with and without jia . furthermore , the shortage of control subjects due to time constraints resulted in an imbalance when matching cases ( n  =  14 ) to controls ( n  =  10 ) . as a result
, group means from heterogeneous groups were compared via an independent t test as opposed to the preferred paired t test , which may have reduced the validity of the comparative analysis .
lastly it is acknowledged that the plantar pressure region identification software is not operator independent and may be vulnerable to variability .
in conclusion , in this optimally medically managed sample of children with jia , foot function as determined by a multi - segment foot model , did not differ from that of normal age- and sex - matched subjects .
this was in spite of many patients reporting mild - to - moderate levels of foot - related impairments and disability via the jafi .
further work is necessary to extend and confirm these observations in specific subtypes linked with close assessment of underlying joint and soft - tissue pathology and foot - related impairment and disability .
gj hendry , r barn and de turner were supported through funding from arthritis research uk ( ref gjh ; 18076 , rb;187381 , det ; 17832 ) .
 highlights foot kinematics were compared between children with and without juvenile idiopathic arthritis . 
  gait measurements and ultrasound features were explored as measures of structure and function . 
  magnitude and timing parameters for foot kinetics and pressure distribution were similar . 
  foot function did not differ despite moderate foot impairments and disability levels . 
Introduction
Methods
Patient selection
Demographic, disease and clinical examination
Biomechanical foot function
Statistical analysis
Results
Demographic and clinical characteristics
Gait analysis
Discussion
Conclusion
Conflicts of interest
Support
Supplementary data