Teardrop-femoral head distance after shelf acetabuloplasty for Perthes' disease.

Shelf acetabuloplasty is an accepted treatment for Perthes' disease. Favourable outcomes have been reported. This study aimed at determining whether changes in femoral head subluxation after shelf acetabuloplasty occur and whether they predict outcome. We assumed that reduction of subluxation after shelf acetabuloplasty would improve the long-term outcome. During follow-up, growth presented as a source of error when comparing the amount of absolute subluxation. Correction for growth was achieved by calculating a subluxation index. This index showed a significant reduction during follow-up. There was no correlation between clinical and radiological outcome, but the fact that the subluxation index showed a decreasing trend could be promising regarding outcome. This might be one of the reasons why shelf acetabuloplasty produces its effect. Following shelf acetabuloplasty the enlarged acetabulum could possibly direct the growth of the femoral head to a better-contained joint. This could result in better joint congruity and lesser tendency to degenerative arthritis.