THE ARTICULAR SURFACES OF THE SACRO-ILIAC JOINT AND THEIR RELATION TO THE MOVEMENTS OF THE SACRUM

Abstract

Using cartographic methods the articular surfaces of 62 sacro-iliac joints were examined. The surfaces are proportionately longer and narrower on the sacra than on the ilia. The shape of the ventral border is related to the sacral curvature and to the ala. The concavity of the dorsal border is more marked in females and changes with age. The sacral surface consists of two main elevations, a cranial, on some part of the lateral aspect of the first sacral vertebra, and a caudal, which is less prominent. These two elevations are separated by a saddle-shaped depression in young subjects. The sacral articular surfaces are hollowed out dorsal to both the cranial and caudal elevations. The iliac surfaces are reciprocally shaped but the two surfaces are not exact mirror images. Aging leads to an increase in the size of the elevations and depressions on the articular surface and the formation of a large elevation near the dorsal border and several smaller ones on the ventral margin. The relation of movement and structure in the sacro-iliac joint is discussed. The present account of the articular surfaces is compatible with the movements of the sacrum seen in the living.