The Anatomy of the Sacroiliac Joint
If you’ve been an athlete in a contact sport or physically demanding sport that requires your body to support heavy loads, chances are you’ve probably had Sacroiliac (SI) pain before. Today’s article will detail the anatomy of the SI joint to give you a better idea of the structures that act on it and what its responsibilities are in movement so you can better determine how to go about your pain.
The SI joints are extremely strong weight-bearing joints that have two articular surfaces on the anterior and posterior portions of the bone. The SI joints are comprised of the sacrum and the ilium and together they help make up a portion of the pelvic girdle. The SI joints are synovial joints, but the differ from other synovial joints in the body because there is not much movement available at the joint. The main responsibility of the SI joints is transmitting weight during weight-bearing to the hip bones. When standing, the SI joints transmit weight to both femurs via the sacro-iliac ligaments. When sitting, the SI joints transmit weight to the ischial tuberosities, again via the sacro-iliac ligaments. For a point of reference, the ischial tuberosities are where the medial and lateral hamstring muscles have a common attachment point, some other people simply refer to them as the “butt bones.” The very cool thing to keep in mind with the SI joints is, they are actually suspended in between the ilium because of the pull and orientation of the posterior and interosseous sacro-iliac ligaments. The posterior sacro-iliac ligaments end up connecting to fibers that make up the sacrotuberous ligament, which ends up forming a large foramen for nerve and vascular supply. Finally the sacrospinous ligament, which spans from the sacrum to the ischial spine, helps separate the greater and lesser sciatic foramen.
Although like I said, there is not much movement at the SI joint because of the articulation between the sacrum and ilium, slight gliding and some rotational movement does occur. This is important because during jumping, weightlifting or other high impact movements, these structures, with the help of the ligaments and musculature around them, absorb the force and transmit it throughout the axial skeleton accordingly. There are over 35 muscles that have either distal or proximal attachments to the sacrum, two of which are the gluteus maximus and piriformis. We will expand on SI pain and management for that in the future, but again this goal of this article is to give you a guide to knowing your body much better and as always, to #HealByMoving.