Macroscopic and microscopic anatomy of the sacroiliac joint from embryonic life until the eighth decade.

The macroscopic and microscopic anatomy of the sacroiliac joint from embryonic life until the eighth decade is presented to establish a baseline of normal anatomy for this joint. The literature concerning the anatomy of the joint was reviewed and found to be fragmentary and conflicting, particularly concerning the diarthroidial characteristics of the joint. From fetal life onward, the iliac cartilage surface is fibrocartilaginous, while the sacral surface is hyaline cartilage. Degenerative arthrosis of the joint commences at an early age, affecting the iliac cartilage to a greater extent than its sacral counterpart. These early degenerative changes in the sacroiliac joint may very well be a more common cause of low-back pain than previously thought.