Subluxated hip joint (left side of image). Migration index (MI) is calculated by dividing width of uncovered femoral head A by total width of femoral head B. Acetabulum is dysplastic (type 2 sourcil) with lateral corner of acetabulum above weight-bearing dome. Normal hip (left side) with acetabular index (AI) indicated. Acetabulum is normal (type 1 sourcil); lateral corner is sharp and below weight-bearing dome. H, Horizontal axis.