The sacroiliac joint: an overview of its anatomy, function and potential clinical implications.

This article focuses on the (functional) anatomy and biomechanics of the pelvic girdle and specifically the sacroiliac joints (SIJs). The SIJs are essential for effective load transfer between the spine and legs. The sacrum, pelvis and spine, and the connections to the arms, legs and head, are functionally interrelated through muscular, fascial and ligamentous interconnections. A historical overview is presented on pelvic and especially SIJ research, followed by a general functional anatomical overview of the pelvis. In specific sections, the development and maturation of the SIJ is discussed, and a description of the bony anatomy and sexual morphism of the pelvis and SIJ is debated. The literature on the SIJ ligaments and innervation is discussed, followed by a section on the pathology of the SIJ. Pelvic movement studies are investigated and biomechanical models for SIJ stability analyzed, including examples of insufficient versus excessive sacroiliac force closure.

Correlative changes during early morphogenesis of the sacroiliac complex in squamate reptiles.

We tested the "limb bud" hypothesis, which explains morphogenetic mechanisms of the formation of the sacroiliac skeletal complex in tetrapods. The hypothesis assumes that: 1) the destruction of the embryonal sacral myomeres and the appearance in their place of a sacral gap filled in with mesenchymal cells favor the development of the sacroiliac complex; and 2) the destruction of myomeres takes place under the influence of limb buds. We studied serial hystological sections of embryos from squamate reptiles with large limb buds (sand lizard, Lacerta agilis L.), small and short-living limb buds (slow worm, Anguis fragilis L.) and without limb buds (adder, Vipera berus (L.)). In embryos of the sand lizard, the hypaxial part of the second sacral myomere degenerated, whereas that of the first one survived in its cranial part. Thus, a large sacral gap was formed where two sacral ribs expanded later. They stretched in a manner similar to the sacral gap across the longitudinal axis of the body, the large ilium lying opposite them. In embryos of the slow worm, the sacral gap was of reduced size and was significantly beveled caudally. The only sacral rib and the upper part of the ilium, which lie within the sacral gap, were beveled in the same manner. In embryos of the adder, myomere destruction was not observed, and sacral ribs and the pelvic girdle did not arise. The obtained results generally agree with the limb bud hypothesis; therefore, it can be said that tetrapods possess a simple and effective morphogenetic mechanism by which the hind limbs create their own support on the axial skeleton.

The pathoanatomy and clinical significance of the sacroiliac joints.

The sacroiliac joint has a unique developmental anatomy which is responsible for an unusual and underdeveloped iliac cartilage surface. This surface tends to undergo premature degenerative change, which might be a factor in the pathogenesis of mechanical low back pain.

[Histopathological study of the aging process in the human sacroiliac joint].

It has not been well defined the morphologic characteristics of the aging process of the sacroiliac joints in man. We have, therefore, studied the sacroiliac joints of human subjects by light and scanning electron microscopy. The joints were collected from 55 Japanese fetuses and adult cadavers. The articular cartilages on both sacral and iliac sides were composed of hyaline cartilage in the fetuses and adults. In fetuses, loose fibrous strands were found in the articular space and appeared to represent a residue of the intermediate layer during formation of the articular space. In adults who were older than 30, the joints showed definite degeneration which was more severe on the cartilage at the iliac side than that of sacral side. Scanning electron microscopic observations supported the light microscopic findings. Fusion of the two articular surfaces was observed in 24% of the adult joints. These findings strongly suggest that the buffering capacity of the sacroiliac joints decreases with aging which appears to relate to the clinical symptom of low back pain.

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.