[Principles of growth in the acetabulum. Consequences for the shelf operations (author's transl)].

Not unlike a Mercedesstar the arms of the Y-growthzone divide the cup of the acetabulum into three equal segments. The three branches of the Y-zone are spheroid. So the socket can expand evenly and conform to the head by feed back. Otherwise the socket would fill up. For the cartilage of the concave acetabulum proliferates by apposition to its uppermost layers, exactly as the hyaline cartilage does in the convex condyles. The trend of the socket during growth goes outwards, forwards and downwards. It moves away from a metal mark, set into the ileum flush with the shelf. It is precisely this increasing distance, that happens to a surgical shelf in a child. Failure will be inevitable. 614 shelf operations checked.