Relationship of the Anterior Humeral Line to the Capitellar Ossific Nucleus: Variability with Age

Background The anterior humeral line is used to assess displacement and the adequacy of reduction of supracondylar humeral fractures in children. It is said to pass through the middle third of the capitellum in the elbow of a normal child. Few reports in the published literature have discussed this measurement, and the intra-rater and inter-rater reliability of the measurement is not known. The purposes of the present study were to define the position of the anterior humeral line in normal, skeletally immature elbows and to determine the intra-rater and inter-rater reliability of this parameter. Methods On two occasions, three observers (a pediatric orthopaedic surgeon, a senior orthopaedic resident, and a senior medical student) recorded the location of the anterior humeral line as it passed through the capitellum as seen on the lateral radiographs of thirty normal elbows in children ranging in age from four months to three years and eleven months and thirty normal elbows in children ranging in age from four to nine years. For these measurements, the capitellum was divided into three regions: the anterior third, the middle third, and the posterior third. All observers received written instructions, and identical rulers were used to make the measurements. Results Each observer made 120 measurements. Overall, the anterior humeral line passed through the anterior third of the capitellum in 31% of the elbows, the middle third in 52%, and the posterior third in 18%. In children younger than four years of age, the line passed nearly equally through either the anterior or middle third of the capitellum. In older children, the anterior humeral line passed through the middle third in 62% of the elbows. Overall, intra-rater reliability and inter-rater reliability were moderate to substantial. Conclusions The anterior humeral line passes through the middle third of the capitellum in the majority of normal children. In children younger than four years of age, it passes nearly equally through the anterior or middle third of the capitellum, whereas in older children it more consistently passes through the middle third of the capitellum. The surgeon must be aware of the variability of the location of the anterior humeral line with age when utilizing it to assess radiographs of the elbow in children after an injury or after the reduction of a displaced supracondylar fracture.