Sacroiliac joint is a synovial joint between sacrum and ilium of the pelvis. The articulating surfaces are kept together by strong ligaments. In humans, the sacrum supports the vertebral column and is in turn supported by an ilium on each side.
Articular surfaces of sacroiliac joint:
The articulating surfaces are flat in infants and irregular in adults. The irregulatities contribute to the strength of the joint in transmitting weight from the spine to the lower limbs. Both sacral and iliac surfaces are covered by hyaline cartilage.
Ligaments of sacroiliac joint:
Sacroiliac joint contains the following important ligaments.
- Anterior sacroiliac ligament: It is in fact a thickening of the capsule and is particularly well-developed near the arcuate line and the posterior inferior iliac spine.
- Interosseous sacroiliac ligament: It is the major bond between the two articulating bones. It fills the irregular space posterior to the joint and is covered superficially by the posterior sacroiliac ligament.
- Posterior sacroiliac ligament: It lies over the interosseous ligament and consists of several weak fasciculi connecting the intermediate and lateral sacral crests to the posterior superior iliac spine and the end of iliac crest.
- Sacrotuberous ligament: It is attached by its base to the posterior superior iliac spine and is partly blended with the posterior ligament.
- Sacrospinous ligament: It is thin and triangular and extends from the spine of ischium to lateral margins of sacrum.
Blood supply of sacroiliac joint:
The blood supply of this joint is derived from the following arteries:
- Iliolumbar arteries
- Superior gluteal arteries
- Lateral sacral arteries
Lymphatic drainage of sacroiliac joint:
The lymphatic drainage of this joint follows the arteries, reaching the iliac and lumbar nodes.
Nerve supply to sacroiliac joint:
The nerve supply of this joint is not very conspicuous. There is not a general agreement on it. The most probable explanation is that it receives branches from the anterior and posterior primary rami of the first two sacral spinal nerves, and from the superior gluteal nerve.
Stability of sacroiliac joint:
It is one of the most stable joints of human body. It supports the entire weight of the body and transmits it through the lower limbs to the ground.