Eccentric Rule Of The Radiocapitellar Lines From X-rays Of Normal Elbows In Young Children

ObjectiveThe radiocapitellar line(RCL) has long been recommended for the radiographic evaluation of elbow injuries in children. However, the RCL doesn’ t always intersect the ossified capitellum centrically on X-rays of normal elbows so that the utility of the RCL is limited. For confirming the diagnosis of radiocapitellar joint’s malalignment by using the RCL, this study sought to draw up the reference values of the RCL’s eccentric distance in accordance with the different age groups.MethodsOn radiographs of 1022 normal elbows (age range,1 to 10 years), lines were drawn along the radial neck on anteroposterior(AP) and lateral projections. When the RCL intersects the ossified capitellum, the widest perpendicular distances from the edges of the ossified capitellum to the RCL were measured on both sides of RCL. A formula was designed for calculation of the eccentrical distance (ED) to the center point of the ossified capitellum. The collodiaphyseal angle of proximal radius and the humeroradial angle were also measured on each X-rays film. Linear correlation analysis was performed to assess the impacts of patient sex, age, forearm and elbow position, X-rays projection on eccentrical distance.ResultsOf the 1022 series of eccentric distance, patient sex uncorrelated with ED among any age groups (P>0.05) except the group aged 3 years on lateral view (P=0.009). The eccentrical rule of the RCL includes average 0.17～0.31 cm’s radial offsets on AP views and average 0.10～0.23 cm’s posterior offsets on lateral views, except the group aged 3 years on lateral view. Among children aged 3 to 8 years, the RCLs of older children tended to slope more radially(r=0.212, P<0.001) and less posteriorly(r=0. 111, P=0.002) than those of younger children. On AP X-rays, the measured collodiaphyseal angle of proximal radius correlated positively with ED(r=0.496, P<0.001); on lateral X-rays, the measured collodiaphyseal angle of proximal radius uncorrelated with ED(P=Q.273), and the measured humeroradial angle correlated inversely with ED(r=-0.210, P<0.001).GonelusionResulted from the eccentric ossification pattern of capitellum in the cartilaginous capitellum, the eccentrical rule of the RCL includes the radial offsets on AP views and the posterior offsets on lateral views. It should be taken into consideration when dealing with radiocapitellar joint injuries among young children. For diagnosis and treatments of radiocapitellar injuries, our result of RCL’s eccentrical distance may provide referrals.