The labrum acetabulare in infants.

The knowledge of embryology and early development of the hip joint (and especially the "Anlage" of the acetabular labrum) is necessary to correctly understand further growth disturbances and developmental dysplasias and dislocations of the hip joint. "Teratologic" luxations - based on damages of the fetal "Anlage"- should be distinguished from "developing deformations" of originally normal-shaped hip joints. By using modern imaging techniques, especially sonography and MRI, the morphologic relationships of the acetabular labrum in centered and decentered hip joints could be clarified. The tip and the basis of the labrum and their relations with the hyalin-preformed growth zone cartilage of the acetabular roof are changing during the process of decentering and can be clearly visualized by sonographic means. To understand the morphologic changes in decentered hip joints, a clear and consistent terminology should be used: The term "limbus" is misleading and should be avoided; one should use the terms "acetabular labrum" and "hyalin-preformed cartilaginous acetabular roof" for the two histologic subdivisions of the acetabular roof cartilage. We do not know much about size and shape, about nutrition and vascularity of the acetabular labrum, and only few facts about the junction zone of the labral attachment to the hyalin cartilage acetabular roof, and so on. We also do not have any clear evidence about possible micro-damages of the labral-capsular-complex during successful closed reduction and their sequelae in childhood and adolescence, possibly being one cause of labral lesions in adults. Further basic research in this field seems useful and necessary.