Measurement Variability of the Lateral Head-Shaft Angle in Slipped Capital Femoral Epiphysis

The lateral head-shaft angle as described by Southwick is used to assess the severity of slipped capital femoral epiphysis and to measure progression. Intraobserver variability in measuring the lateral headshaft angle may influence decision making. The purpose of this study was to determine intraobservervariability in the measurement of the lateral head-shaft angle of slipped capital femoral epiphysis. The lateral head-shaft angle of 108 hips was measured twice by three observers. The two-way analysis of variance method of Bland and Altman as outlined by Loder was used to determine the intraobserver variability. For the lateral head-shaft angle in slipped capital femoral epiphysis, the intraobserver variability was +5.9°. To ensure true change, a single observer should document at least a 12° change in the lateral head-shaft angle between two radiographs.