|dc.description.abstract||In this study, the gross, microscopic, ultrastructural,
and comparative anatomy and development of the sacroiliac
joint are presented. Sacroiliac joints were obtained from
108 human, 43 bovine, 24 equine, 21 porcine, and 21 canine
autopsies, spanning a full range of ages. The specimens were
photographed and examined under the light microscope. The
human specimens were also examined under the transmission and
scanning electron microscopes. The sacroiliac joint angle
and the relative lengths of the caudal and cephalad limbs of
the joint were compared between species.
On gross inspection, the sacral surface has the smooth,
shiny, creamy-white appearance of normal articular cartilage.
The iliac surface has the rough, dull, bluish appearance of
a thin layer of fibrocartilage. Histological and
ultrastructural examination confirms the presence of hyaline
cartilage on the sacral side and fibrocartilage on the iliac
side in all species. The equine joint has a greater angle
and a relatively shorter caudal limb than the other species.
The unique juxtaposition of hyaline and fibrocartilage
in the sacroiliac joint is explained by the developmental
anatomy of the joint. The sacral articular cartilage
develops directly from the primary hyaline cartilage anlage.
Enchondral ossification progresses from the primary centre of
ossification toward the articular surface. At maturity, a
hyaline cartilage cap is left as the articular cartilage. On
the iliac side, ossification of the cartilage anlage precedes
cavitation of the joint space. Therefore, the iliac
articular cartilage is derived from other progenitor cells
and not directly from the primary cartilage anlage. As a
result, it contains undifferentiated spindle cells and
secondary cartilage that matures into a thin layer of
fibrocartilage. The same situation is observed in the young
Premature degenerative changes develop in the iliac
cartilage in all species. In the human, ultrastructural
signs of degenerative change can be observed in specimens
from the second decade of life onward. Similar changes are
observed on the sacral side by the third decade of life. A
similar chronology of events occurs in the animal specimens.
The iliac cartilage is affected at a very young age, followed
soon after by the sacral cartilage.||en_US