Background: Current treatment for Perthes disease aims at preventing deformation of the femoral head during the active stage of the disease by obtaining containment of the femoral head. To effectively pre-empt femoral head deformation, one needs to know, when during the disease irreparable femoral head deformation occurs. This study was undertaken to attempt to clarify this.

Methods: Records and 2634 pairs of radiographs (AP and lateral) of 610 patients with Perthes’ disease were reviewed. The evolution of the disease was divided into seven stages (Stages Ia, Ib, IIa, IIb, IIIa, IIIb & IV) based on plain radiographic appearances. Intra-observer and inter-observer reproducibility of this new classification system was assessed. The duration of each stage of the disease was noted. The stage at which epiphyseal extrusion and widening of the metaphysis occurred and the stage at which metaphyseal and acetabular changes appeared were identified. The shape and the size of the femoral head, the extent of trochanteric overgrowth and the radius of the acetabulum were assessed in hips that had healed.

Results: The reproducibility of the new classification system of the evolution Of Perthes’ disease was good. The median duration of each stage varied between 95 and 326 days. Epiphyseal extrusion and metaphyseal widening was modest in Stages Ia, Ib and IIa but increased dramatically after Stage IIb. > 20% extrusion occurred in 70% of the hips by Stage IIIa. Metaphyseal changes were most frequently encountered in Stage IIb, while acetabular changes were most prevalent in Stage IIIa. At healing, only 24% of untreated patients had spherical femoral heads, while 52% had irregular femoral heads.

Conclusions: The new classification of the stages of evolution of Perthes’ disease helps to identify when crucial events occur during the course of the disease. The timing of epiphyseal extrusion, metaphyseal widening and the appearance of adverse metaphyseal and acetabular changes suggest that femoral head deformation occurs by Stage IIIa in untreated hips. Hence, if containment were to succeed, it should be achieved before this stage.

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.