Natural evolution of Perthes disease: a study of 610 children under 12 years of age at disease onset.

Records and 2,634 pairs of radiographs (anteroposterior 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, and IV) based on plain radiographic appearances. Intraobserver and interobserver reproducibility of this new classification system was assessed. The duration of each stage of the disease was noted. The stages at which epiphyseal extrusion and widening of the metaphysis occurred and the stages 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. The new classification system of the evolution of Perthes disease was reproducible and helped to identify when crucial events occur during the course of the disease. The median duration of each stage varied between 95 and 335 days. Epiphyseal extrusion and metaphyseal widening was modest in stages Ia, Ib, and IIa but increased dramatically after stage IIb. More than 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. 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.