Plain radiographs and arthrograms on 46 patients with Legg-Calvé-Perthes were evaluated. Measurements of containment including epiphyseal extrusion, caput index, femoral subluxation, percentage acetabular coverage, were determined. Only with arthrography are measurements of acetabular coverage, subluxation and epiphyseal extrusion consistent and reliable. The concept of eccentricity was developed to assist in the understanding of femoral containment.