Meyer's dysplasia epiphysealis.

Meyer's femoral cephalic dysplasia (FCD) is a rare affection that is often confused with Perthes' disease from which it differs in terms of both treatment and prognosis. A constant feature is the absence of the nucleus of ossification that does not occur until 15-18 months of age; at times there are multiple nuclei of ossification, so that the epiphysis has a "morulated" aspect. Fusion of the various centers of ossification occurs at about 5 years of age. The epiphysis does not collapse and it preserves its density and its structure. Differential diagnosis involves Perthes' disease and other pathologies such as multiple dysplasia epiphysealis, hypothyroidism, dyschondroplasia.