Background: Femoral varus osteotomy for Perthes’ disease aims at achieving Containment to prevent femoral head deformation. Theoretically, ontainment is most likely to succeed if it is achieved before the femoral head extrudes and is subjected to deforming stresses. It would follow that the timing of the procedure is an important factor in determining the outcome. This study was undertaken to verify this.

Methods: Records and radiographs of 610 patients with Perthes’ disease were analysed. The data of 302 patients who underwent femoral osteotomy were compared with those of non-operated patients. A new modification of the Elizabthtown classification of the stages of evolution of the disease with seven stages (Stages Ia, Ib, IIa, IIb, IIIa, IIIb & IV) was used to identify the timing of surgery and to monitor the progress of the disease following surgery. The results of treatment were assessed at healing by Mose’s criteria. Multivariate analysis was used to identify variables that influenced the shape and size of the femoral head at healing.

Results: 22 patients among 86 who were operated in Stage Ia or Ib by-passed the stage of fragmentation. The extent of metaphyseal widening was considerably less in operated children. At healing, spherical femoral heads were seen in 72% of operated hips as compared to 24% of non-operated hips. The variables that influenced the shape of the femoral head at healing were, metaphyseal width, sex, age at onset, epiphyseal extrusion and the stage at surgery. Patients who were operated before Stage IIb had significantly better results than those operated later.

Conclusions: The results of the study support the impression that the timing of containment is an important factor that influences the outcome in Perthes’ disease. The best results are obtained if containment is achieved before Stage IIb.