[A histopathological study on aging process of the acetabulum with special reference to the pathogenesis of the acetabular cyst (author's transl)].

This is to report the aging process of the acetabula studied as an aid to the investigation of the pathogenesis and progression of osteoarthritis of the acetabulum. The material consisted of 45 acetabula obtained from 45 fresh cadavers. Regarding the morphological changes of the labrum-cartilage junction of middle and old age groups, marked degenerative changes such as tear, detachment, fissuring and scar formation were observed in many cases at the loaded part of the acetabulum. Among these, a loose connective tissue had invaded into the subchondral space through a fissure in one case, and infusion of the joint fluid into a fissure was observed in another. All of the 3 acetabular cysts were from the middle and old age groups and at the weight-bearing portions of the acetabula. All cysts were found to have communication with the joint cavities through the fissures. The trabeculae surrounding the cysts showed slight destructive changes apparently due to compression by the cysts. The above findings would suggest that the cyst formation as an aging process at the weight-bearing portions is probably due to infusion of the joint fluid into the subchondral space through the fissure at the labrum-cartilage junction or through the fissure at the junction resulting from subchondral plate fracture, although some additional causative factors might also play a role in the process.