Destruction of hyaline cartilage in the sigmoid notch of the human ulna.

In an ulna from an adolescent a fossa nudata divided the articular surface of the sigmoid notch into olecranon and coronoid areas. In the floor of the fossa a layer of loose avascular pannus covered a thin layer of articular cartilage. The pannus appeared to have been formed by removal of chondroitin from the cartilage, freeing the cells and unmasking the fibres. Probably the change followed loss of contact between the articular cartilages of the sigmoid notch and trochlea during postnatal growth.