although benign and self - limiting in most cases , these deformities sometimes cause a great concern to the parents and the relatives ( 1 - 6 ) , and such anxieties frequently lead physicians to conduct physical or radiological examinations ( 4 , 7 - 9 ) . however , even after these examinations have been conducted , misunderstandings of physiologic ranges and changes in knee alignment might initiate costly and time - consuming therapeutic measures , such as , bracing , which may be entirely unnecessary and in certain instances may prove harmful ( 8) . it has been well established by previous studies involving radiological analysis and clinical measurements that children undergo sequential physiologic changes in axial alignment , i.e. , genu varum , neutral , and genu valgum , during normal development ( 4 , 5 , 7 , 8 , 10 ) . moreover , the physiologic changes in knee angle have been investigated with respect to gait , joint range of motion , and torsional deformities ( 4 , 5 ) , and have been found to correct spontaneously in time ( 3 , 4 , 10 ) . however , the absence of values defining normal ranges in different ethnic groups limits the application of this information . the purposes of the present study were to provide normative data on the axial alignment or the anatomical tibiofemoral angle ( atfa ) of the lower extremity in normal korean children , and to compare its trend with those reported by previous studies . we retrospectively reviewed the teleradiographs of the lower limbs taken in children younger than 16 yr old from july 2001 to march 2004 . in total 818 limbs ( 433 boys and 385 girls ) in 452 children ( 243 boys and 209 girls ) were enrolled in this study . ninety - seven patients underwent repeat radiographic examinations by at least at one - year intervals , and were considered independent cases . the chronological age of the subjects was rounded off to the nearest integer , and the ones from 2-yr-7-month to 3-yr-6 month old were grouped into age 3 group ( table 1 ) . to prevent any selection bias in a retrospective design study , strict inclusion and exclusion criteria were implemented , all the more because the radiographs had probably been taken owing to any discomfort of the leg . the children who were brought to orthopedic clinic for the parents ' concern of malalignment , and only to get negative result constituted most of the subjects . those with growing pain or osgood - schlatter disease were included , and so does the children who had been admitted to pediatric or urological department owing to diseases unrelated to the musculoskeletal system , and happened to have a leg discomfort . those with skeletal or extra - skeletal disorders that might have affected the alignment of the lower extremity were excluded from the study including orthopaedic disorders such as developmental dislocations of the hip , various skeletal dysplasias , cerebral palsy , neuromuscular disorders , foot deformities , and metabolic diseases influencing the musculoskeletal system . those with a leg length discrepancy over 2 cm , angular deformity of a lower limb over 10 , or those with a height deviated more than 2 standard deviation from the age and gender matched norm were also left out . weight - bearing anteroposterior radiographs of the entire lower extremities , or teleradiographs , were taken in a standing position when the subject was compliant , or in a supine position , if not . extreme caution was needed to ensure that the patella was positioned facing forward , indicating a neutral rotational position of the lower extremity , and inadequate films for measurement were abandoned . both of the legs were not included in all the subjects , and only available radiographs were included . the radiographs were taken with radiography beams centered at the knee , and projected from 101.6 cm onto a 35.6  43.2 cm cassette and from 182.9 cm onto a 35.6  91.4 cm cassette . the acquisition and storage of the digitalized images were conducted using a picture archiving and communication system ( pacs ) ( marosys , marotec , seoul ; or impax , agfa , antwerp , belgium ) . the atfa was defined as the angle between the anatomical axes of femur and tibia , being given a positive value for varus and a negative value for valgus ( fig . the means , standard deviations , and 95% confidence intervals were calculated for each age and gender group . the mean atfa gender differences were tested using the t - test , and the significance level was set at p<0.05 . in order to assess the reliability of the measurement , 2 orthopedic surgeons performed the measurement twice at an interval of 1 week in 5 randomly selected limbs of each age group . the reliability of the measurement was attested by the intraclass correlation ( icc ) ( 11 ) . a typical interpretation of an icc value is as follows : 0.00 - 0.20 , poor ; 0.21 - 0.40 , fair ; 0.41 - 0.60 , moderate ; 0.61 - 0.80 , substantial ; 0.81 - 1.00 , perfect agreement . these findings led the authors to rely on the validity of the measurement , and the measurement of a single investigator was utilized in the following analysis . knee alignment or atfa was in varus alignment in infancy , and became neutral at an average age of 1.5 yr . development into valgus alignment continued until age 4 yr when it peaked at 7.8. it then decreased slowly to plateau at 5 - 6 at age 7 to 8 yr , and remained at this level thereafter ( table 2 , fig . this pattern of knee alignment change is similar to that found previously in other ethnic groups , except that the valgus peak occurred later . chronological atfa changes can be divided into 3 phases : phase i ( 0 - 4 yr ) , during which knee alignment changes from an infantile physiologic varus to maximum valgus ; phase ii ( 5 - 8 yr ) when valgus knee alignment decreases in amount ; and phase iii ( 9 - 15 yr ) during which knee alignment remains stationary , i.e. , the adult pattern of genu valgum . females showed a larger peak valgus alignment at age 4 yr , but this did not differ significantly from that of males . in addition , a significant difference was observed between males and females at age 12 yr , but knee alignment change trends seemed similar in both sexes at this time of age . the establishment of a normal range of the knee alignment in children is of paramount clinical importance , as such knowledge would allow physicians to determine whether the knee alignment in a specific patient represents physiologic development or not . moreover , a relevant and correct understanding of the development of the knee angle and limb alignment would prevent unreasonable apprehension by parents and relatives , and unnecessary diagnostic measurements , such as repeated exposure to radiation , and the inappropriate application of orthotics or bracing , which are not often cost - effective and might even hinder natural development ( 6 - 8 ) . in addition , this understanding would help diagnose , evaluate , and treat pathologic conditions , such as , infantile tibia vara or blount 's disease ( 1 , 3 , 6 ) . several authors , based upon clinical measurements and radiological analysis , have reported on the development of knee angle in children . engel and staheli ( 4 ) investigated lower extremity axial alignment with respect to the mid - longitudinal axis of the thigh and lower leg in 160 normal caucasian elementary school children , in pre - school children , and in infants and neonates . it was found that children of less than one year displayed genu varum , and that this spontaneously corrects during the second year of life , and further that the greatest mean values of genu valgum occurred in 2 or 3 yr of age . ( 8) studied 2,630 chinese children attending nurseries , kindergartens , and schools , and heath and staheli ( 7 ) studied 392 limbs of 196 caucasian children from daycare centers , day camps , and local elementary schools . these three studies were based upon clinical or photographic measurements . however , we consider that radiological analysis is more suitable for determining axial alignment of the lower extremity because the clinical or photography - based measurements can not exclude the soft tissue over bone , which hinders accurate measurement . salenius and vankka ( 10 ) were the first to investigate the development of the knee angle in children radiologically . they conducted a study on 1,480 patients in a hospital for a variety of reasons and whose knees and legs were radiographically examined for the reasons unrelated to their illnesses . they found that the knee angles underwent serial changes , i.e. , genu varum before 1 yr , neutral at 1 yr and 6 month , increasing genu valgum at 2 - 3 yr , reaching a maximum value at 3 yr 6 months , and followed by a subsequent slight decrease to adopt the adult knee angle pattern at 5 - 6 yr . one should be cautious when describing what is ' normal ' , because of the possibilities of individual and ethnic variations . ( 8) concluded that trends in the chinese were nearly identical to those shown by other races in this context . ( 8) concluded that soon after 3 yr of age the tibiofemoral angel of chinese children approaches 0 , which indicates that normal chinese children aged between 3 and 11 yr exhibit a significant amount of varus , heath et al . ( 7 ) observed preservation of valgus with a mean of 2.8 at 11 yr , and normal limits of these ages did not include any amount of varus , hence more varus in chinese children than in white children ( fig . korean children in our study showed patterns of sequential physiologic knee angle changes that are similar to those reported in other races ( 4 , 5 , 7 , 8 , 10 ) , although the valgus peak occurred later and the overall development of alignment more prolonged . a cohort study would have been more meaningful and reliable , but it would have required unnecessary repeated radiation exposure in growing children . moreover , if emphasis is placed on the representation of knee angle in different age groups rather than on sequential changes in a specific cohort group , then the current study design has a seat at the table . second , the wide range of data and the large standard deviation encountered hinders the establishment of a ' cut - off ' value . although general trends in knee angle changes were detected by the study , the determination as to whether a specific limb is mal - aligned or not is difficult . the authors recommend that alignment testing , including the determination of mechanical axis deviation , is clinically more appropriate in children over 10 yr . third , as with most of the study depending on measuring of radiographs , the reproducibility and reliability of the measurement deserve attention . the characteristics of the children 's bone including wide metaphysis , short diaphysis , and occasional bowing hinder exact measurements . the acceptable reliability of the measurement of the current study probably arose in that all the rater shared the basic notion and measurement tips through discussion . although exact reproducibility might be doubted , the general trends of the development of the tibiofemoral angle might well be represented nonetheless . in summary , we provided the data of the chronological changes of the lower limb alignment for the korean children by radiographic measurement . the overall pattern of chronological changes in the knee angle or the anatomical tibiofemoral angle was similar to those found in other ethnic groups , but the development of the knee angle was slightly delayed , i.e. , genu varum before 1 yr , neutral at 1.5 yr , increasing genu valgum with a maximum value of 7.8 by 4 yr followed by a gradual decrease to 5 - 6 of genu valgum to the adult pattern at 7 to 8 yr of age . these normative data should be taken into consideration when evaluating lower limb alignment in children .
this study was performed to identify the chronological changes of the knee angle or the tibiofemoral angles in normal healthy korean children . 
 full - length anteroposterior view standing radiographs of 818 limbs of 452 korean children were analyzed . 
 the overall patterns of the chronological changes in the knee angle were similar to those described previously in western or asian children , but the knee angle development was delayed , i.e. , genu varum before 1 yr , neutral at 1.5 yr , increasing genu valgum with maximum a value of 7.8 at 4 yr , followed by a gradual decrease to approximately 5 - 6 of genu valgum of the adult level at 7 to 8 yr of age . 
 these normative data on chronological changes of knee angles should be taken into consideration when evaluating lower limb alignment in children .