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 head-shaft angle may influence decision making. The purpose of this study was to determine intraobserver variability 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 degrees . To ensure true change, a single observer should document at least a 12 degrees change in the lateral head-shaft angle between two radiographs.