1. The sacro-iliac articulations are true diarthrodial joints. The joint surfaces are covered with hyaline articular cartilage; there is a joint space, synovial membrane, synovial fluid, and slight motion.
2. Mobility is only slight at best. It was present in all the sacro-iliac joints of this group, and was uniformly increased during pregnancy.
3. Relaxation of the ligamentous structures surrounding the joints was a common feature of parturition.
4. Subluxation or slight displacement of the sacro-iliac joints was seen in two cases, and both followed severe sudden trauma.
5. Early degenerative changes in the articular cartilage of the sacroiliac joints were noted microscopically in two cases. In none of the macerated cases were any evidences of osteophyte formation or osteo-arthritis noted.
1. Pathologic changes of the articular cartilages were found in the gross in ninety-one per cent. of the male joints, and in seventy-seven per cent. of the female joints. Microscopically, pathologic changes of varying degrees were noted in all the sections. In two cases a purulent exudate was found in the joints.
2. In males, mobility was present to a slight degree up to the fourth decade and imperceptible in most cases thereafter. In the female, slight motion was obtainable in most of the specimens up to the fifth decade, and in some slight movement could be elicited up to the sixth decade.
3. Osteo-arthritic changes were found in ninety-one per cent. of the male and in fifty-three per cent. of the female joints.
4. Bony ankylosis was found in fifty-one per cent. of the male joints and in five and eight-tenths per cent. of the female joints.
1. Degenerative changes of the articular cartilages in the fresh specimens were found in all of the sacro-iliac joints.
2. Osteo-arthritic changes as seen in the macerated specimens were also present in all the cases. These changes were definitely more marked in men than in women.
3. Bony ankylosis was present in eighty-two per cent. of the male joints and in thirty per cent. of the female joints.