osteoarthritis ( oa ) is the most prevalent disease associated with significant morbidity , 
 and it is one of the most common causes of functional limitation and dependency .
knee oa is 
 particularly disabling because of symptoms such as pain , stiffness , and muscle weakness1 , 2 .
it 
 causes difficulty in climbing stairs , rising from a seated position , and walking , eventually 
 leading to physical disability and decreased quality of life3 , 4 . in many previous studies ,
associations between the mechanical axis alignment of the lower 
 limb and oa severity were found5,6,7,8,9 .
malalignments of the knee 
 joint make individuals more susceptible to developments of knee oa7 , and valgus or varus alignment increase the risk of knee oa 
 occurrence6 , 10 .
varus alignment , in particular , resulted in the largest stresses 
 at the medial compartment of the knee5 .
the adduction moment at the knee during gait is the primary determinant of the 
 medial - to - lateral distribution11 . 

measurement of the knee joint moments provides an indication of the actual knee joint loads 
 related with the progression of oa12 .
the 
 knee adduction moment is mainly determined by the ground reaction force and its lever arm . 

the line of action of the ground reaction force is directed to the medial side and the 
 center of the knee during gait , and its lever arm is the perpendicular distance from this 
 force vector to the knee joint center .
the knee adduction moment tends to adduct the knee 
 into a varus position , which is significantly correlated with disease severity11 .
an altered kinematic pattern of the ankle joint can also influence lower extremity 
 function13,14,15,16,17,18 , and the foot progression angle is related to the knee adduction 
 moment during gait19,20,21,22 . during the late stance phase in the gait cycle , the ground 
 reaction force passes through the forefoot , and medial to lateral disturbances caused by 
 foot rotation influence knee kinetics23 . 

thus , patients with knee oa tend to rotate their foot in order to reduce their adduction 
 moments24 .
most previous studies on foot position and knee adduction moment have focused on foot 
 progression19 , 22 .
only a few studies have examined the relationship between the foot 
 rotation angle and knee adduction moment .
therefore , the purpose of this study was to 
 investigate the relationships among the foot progression angle , foot rotation angle , lower 
 limb alignment , and knee adduction moments in patients with degenerative knee oa .
we included 48 female patients aged 65  years and older who were diagnosed by radiography 
 with degenerative knee oa ( kellgren - lawrence grades 2 and 3 ) .
we excluded patients who 
 received more than 7 points in a physical therapy evaluation , which included an assessment 
 of sensation , circulation , range of motion , muscle strength of the lower limbs , and problems 
 concerning the feet and balance25 . 

additional exclusion criteria were as follows : cardiovascular disease , diabetes , peripheral 
 nervous disease , history of lower extremity surgery , difficulties with visual or auditory 
 function , and cognitive disorder ( korean mini - mental state examination score 24 ) .
the 
 purpose of the study was explained to the participants , and informed consent was obtained . 

the study protocol was approved by the institutional review board of sahmyook university , 
 seoul , republic of korea . to assess the lower extremity alignment and weight - bearing ratio , a static radiographic 
 measurement system ( shimadzu 500 ma and 35.56  91.44  cm cassette ; shimadzu seisakusho , 
 ltd . , kyoto , japan ) was used . to minimize errors during knee angle assessment ,
the examiner conducted anterior - posterior radiography 
 while subjects stood with their knees straight and their big toe and heel aligned with a 
 marked line .
the foot progression angle , foot rotation angle , and knee adduction moments were measured 
 by using a three - dimensional motion analysis system ( orthostat 6.29 ; motion analysis , inc .
, 
 santa rosa , ca , usa ) composed of two force plates ( piezoelectric force plate , 600  900  mm ; 
 kistler corp . ,
winterthur , switzerland ) , six infrared cameras , and 25  mm reflective markers . 

the reflective markers were attached to the right and left of the center of the sacrum , 
 anterior superior iliac spine , middle point between the greater trochanter and lateral 
 femoral condyle , lateral femoral condyle , middle point between the femoral condyle and 
 lateral malleolus , lateral malleolus , calcaneus , and 2nd metatarsal bone . after a warm - up walk ,
the assessment was conducted five times , and the subjects were asked 
 to walk as usual and had a 2  min rest during the intervals between the assessments .
the foot progression angle and foot rotation angle were measured at the point of the first 
 peak knee adduction moment in the early stance phase and during the second peak knee 
 adduction moment in the late stance phase .
additionally , we measured lower limb alignment 
 and the first and second peak knee adduction moments .
descriptive statistics were used for general features . to determine 
 the relationships among foot position , lower limb alignment , and knee adduction moments in 
 the subjects , we used pearson s correlation coefficient .
the general characteristics and gait analysis results of the subjects are described in 
 table 1table 1.general characteristics of the subjects ( n=48)parametersvalueskellgren - lawrence radiographic criteria 
 ( n)2nd grade(21)3rd grade(27)vas ( scores)6.5  1.6age ( years)70.5  4.7height ( cm)154.2  4.9weight ( kg)64.7  8.4foot length ( cm)22.8  0.9foot breadth ( cm)10.2  0.7cadence ( steps / min)121.8  9.1gait speed ( cm / s)118.9  10.5step length ( cm)117.5  11.7stride length ( cm)8.9  1.8values are means  sd .
vas : visual analogue scale . the foot position , knee adduction moments , and lower limb alignment of the 
 subjects are summarized in table 2table 2.foot position , knee adduction moment , and lower limb alignment of the subjects 
 ( n=48)parametersvaluesfoot progression angle ( )early stance phase8.95  5.81late stance phase10.25
 1.07knee adduction moment ( nm / kg)1st peak value0.55  0.132nd peak value0.47  0.16weight - bearing ratio ( % ) 32.0  12.2tibiofemoral angle ( )3.60  2.22femoral valgus angle ( )medial5.19  1.49lateral4.16  1.90patellofemoral q angle ( )8.79  5.46patellotibial q angle ( )9.23  5.40values are means  sd .
vas : visual analogue scale values are means  sd in the early and late stance phases , the foot progression angle was significantly 
 correlated with the first and second peak values of the knee adduction moments ( p < 0.05 ) 
 ( table 3table 3.relationship between foot position and knee adduction moment ( n=48)foot positionknee adduction moment1st peak value2nd peak valuefoot progression angle ( )early stance phase0.30*0.45*late stance phase0.33*0.48*foot rotation angle ( )early stance phase0.080.31*late stance phase0.140.38*pearson s correlation coefficient . *
the weight - bearing ratio was significantly correlated with the first and 
 second peak knee adduction moments .
the tibiofemoral angle was significantly correlated with 
 the first and second peak knee adduction moments ( p < 0.05 ) ( table 4table 4.relationship between lower limb alignment and knee adduction moment 
 ( n=48)lower limb alignmentknee adduction moment1st peak value2nd peak valueweight - bearing ratio ( % ) 0.58 * 0.62*tibiofemoral angle ( )0.57 * 0.59*femoral valgus angle ( )medial0.390.27lateral0.080.23patellofemoral q angle ( )0.060.22patellotibial q angle ( )0.010.30pearson s correlation coefficient .
the results of the present study indicated that as the foot progression angle and foot 
 lateral rotation angle increased , the knee adduction moment decreased .
in addition , the 
 weight - bearing ratio and tibiofemoral angle assessment with mechanical axis alignment were 
 correlated with the knee adduction moments .
we found that a higher foot progression angle 
 was correlated with a reduction in knee adduction moments .
a study by lin et al . 
 demonstrated a reduced peak knee adduction moment when out - toeing during normal walking22 .
additionally , a study by teichtahl et al . 
 showed that subjects who walked with their feet externally rotated reduced their knee 
 adduction moment during the late stance phase23 .
guo et al . suggested that walking with a toe - out strategy may be 
 beneficial for persons in the early stages of medial knee oa , because the toe - out foot 
 position can transfer ground reaction force to the outside of the foot , resulting in a 
 reduction in knee adduction moment20 .
our results showed that the foot rotation angle was higher in the second knee adduction 
 moment .
similarly , teichtahl et al . described that the foot rotation position was more 
 related to the late stance phase than the early stance phase because of the ground reaction 
 forces distributed to the forward , inside , and outside parts of the foot23 .
anatomical lower limb alignment assessment of the knee measured on standard knee 
 radiographs is widely used to investigate the relationship with the knee adduction 
 moment5 , 10 , 
 26 and to detect the progression of 
 degenerative knee oa23 , 27,28,29,30 .
the anatomical 
 tibiofemoral angle of the knee obtained using a short cassette ( 35.56  43.18  cm ) is more 
 widely used because of its economical and practical benefits .
however , a limitation of this 
 measurement is its wide variation due to exclusion of the hip and ankle joints28 .
thus , we used a measurement method that 
 assessed the mechanical tibiofemoral angle and the weight - bearing ratio using the hip , knee , 
 and ankle angles with full - limb radiographs using a long cassette ( 35.56  91.44  cm )
. the weight - bearing ratio is calculated by measuring the distance from the medial edge of 
 the proximal tibia to the point where the weight - bearing line intersects the proximal tibia 
 and then dividing the measurement by the entire width of the proximal tibia ; the percentage 
 is calculated by multiplying this ratio by 100% . by definition , a weight - bearing line of 

< 50% indicates varus alignment of the lower extremity , and a line > 50% indicates 
 valgus alignment19 . in our results ,
the 
 weight - bearing ratio was significantly correlated with the first knee adduction moment and 
 the second knee adduction moment , meaning that as the knee adduction moment in the early and 
 late stance phase increased , the inside of the knee joint loading increased . in the present study ,
the tibiofemoral angle of the subjects was 3.60  2.22 , which was 
 greater than that of a normal person ( 1.22.2)30 , because the subjects had knee oa with varus alignment . regarding 
 the relationship between the tibiofemoral angle and the knee adduction moment , the first and 
 second knee adduction moments were significantly correlated with the valgus alignment 
 angle .
the femoral valgus angle was 5.19 at the time of measurement of the medial tibiofemoral 
 angle and was 4.16 at the time of measurement of the lateral tibiofemoral angle .
these 
 values were less than that of the normal group ( 6)31 , because the subjects with knee oa had varus alignment .
therefore , 
 there was no relationship between the femoral valgus angle and the knee adduction moment in 
 our subjects .
the normal anatomical q angle is 15  330 , but in our subjects , the patellofemoral q angle was 8.7 , and the 
 patellotibial q angle was 9.2 , both of which were less than the normal range due to the 
 varus deformity of the knee joints .
additionally , there was no significant relationship 
 between the q angle and the knee adduction moment . in conclusion
, we found that as the foot progression angle and foot lateral rotation angle 
 increased , the knee adduction moment decreased .
the weight - bearing ratio and tibiofemoral 
 angle assessment with mechanical axis alignment were correlated with the knee adduction 
 moments . however
, the femoral valgus angle and anatomical q angle may not be relevant to the 
 knee adduction moment .
therefore , the mechanical tibiofemoral angle is more appropriate for 
 assessing patients with knee oa than anatomical lower limb assessment .
these findings may be 
 helpful for selecting therapeutic options for patients with degenerative knee oa .
 [ purpose ] the aim of this study was to determine the relationships among the foot 
 progression angle , foot rotation angle , lower limb alignment , and knee adduction moments 
 in patients with degenerative knee osteoarthritis ( oa ) . [ subjects ] forty - eight patients 
 diagnosed with degenerative knee oa ( kellgren - lawrence grades 2 and 3 ) were included . 
 
 [ methods ] to assess the lower extremity alignment and weight - bearing ratio , static 
 radiographic measurement was used . 
 foot progression angle , foot rotation angle , and knee 
 adduction moments were measured by using a three - dimensional motion analysis system . 
 [ results ] the results of this study were as follows : the foot progression angle in the 
 early and late stance phase was significantly correlated with the first and second peak 
 knee adduction moments ; the weight - bearing ratio was significantly correlated with the 
 first and second peak knee adduction moments ; and the tibiofemoral angle was significantly 
 correlated with the first and second peak knee adduction moments . 
 [ conclusion ] the results 
 of the present study indicated that as the foot progression angle and the foot lateral 
 rotation angle increased , the knee adduction moment decreased . 
 the weight - bearing ratio 
 and tibiofemoral angle assessment with mechanical axis alignment were correlated with the 
 knee adduction moments . 
 these parameters may be helpful for selecting therapeutic options 
 for patients with degenerative knee oa . 
INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION