Evaluation of the Southwick Angle in Two Hundred Hips of Asymptomatic Children and Adolescents.

To measure the mean value of the Southwick angle using two different methods, the manual (1) and digital (2) methods, and to establish a normality value.  A primarily descriptive study with 100 children and adolescents. Individuals with orthopedic complaints regarding the hips and/or knees or gait alterations were excluded. For each patient, an X-ray was performed on the lateral incidence of Lowenstein, totaling 100 radiographs and 200 hips. The Southwick angle was measured in two different ways by the same researcher: the conventional method (1), tracing the lines with pencils and measuring the angle with the use of a goniometer and negatoscope, and through the GNU Image Manipulation Program (GIMP) image editor (open source), version 2.7.0 (2), in which the lines were plotted and the angles of both hips were gauged on each radiograph. Later, we sought to evaluate the correlation between the two methods and to verify the mean Southwick angle by categorically correlating it by gender, age group and body mass index (BMI) in asymptomatic children and adolescents. All radiographs were authorized by the children and adolescents' parents/legal guardians. The study was approved by the ethics committee of the institutions in which the research was conducted.  The mean of the Southwick angles obtained by the conventional method was of 8.7° (±2.0°), and, by the digital method, it was of 9.9° (±1.8°). The angle obtained by the two methods was statistically significant (  < 0.001). The majority of the studied population (95%) had a body mass index (BMI) > 18.5, and the mean of the angles was within the previously established value (∼ 10°).  For the first time, using a substantial sample size, a normal value for the Southwick angle measured in asymptomatic individuals was demonstrated. In addition, the image editor proved to be a reliable method to measuring the Southwick angle.