Proximal femoral focal deficiency. Evidence for a defect in proliferation and maturation of chondrocytes.

Proximal femoral focal deficiency is a rare congenital malformation, characterized by a failure of normal development of the proximal part of the femur. To our knowledge, there have been no reports on the histology of fetal growth plates that are affected by this disorder. To characterize this focal developmental anomaly further, we studied the histopathology of the growth plates and epiphyses from a twenty-one-week fetus with unilateral proximal femoral focal deficiency. Although the shape of the cartilaginous anlage of the fetus appeared normal, the growth plate of the proximal part of the involved femur was markedly abnormal. The major findings were: (1) striking failure of the proximal growth plate to migrate proximally, away from the central part of the diaphysis, and failure of formation of a normal growth plate; (2) failure of organization of proliferative and hypertrophic chondrocytes into longitudinal columns; (3) truncation of an immature hypertrophic zone that had abnormal septal architecture; and (4) disorganized vascular invasion with a honeycomb rather than a columnar pattern of primary trabeculae. In contrast, the histological characteristics of the growth plates from the distal part of the femur and from all other long bones were normal.