Sacroiliac Joint ( SI Joint ) Anatomy & Biomechanics

The SI Joint is the connection between the spine and the pelvis. The SI Joint is a true diarthrodial joint. The articular surfaces are ear shaped, containing irregular ridges and depressions. Its concave sacral surface is covered with thick hyaline cartilage and its convex iliac surface lined with thin fibrocartilage.

Biomechanically, the SI Joint’s movement is induced by motion occurring at other locations in the body.
This movement is very small, with less than 4 degrees of rotation and less than 1.6 mm of translation.

While the SI Joint is vulnerable to shear during rotation or translation, compression of the joint allows it to resist shear.

Learn more about the sacroiliac joint at

1 comment

  • Aya 2 years ago

    I’m guessing you’re new (or at least rntnreiug from hiatus) to exercising (because I had the same problem). Stiffness is normal and it will decrease and eventually disappear the more you exercise. Joint pain is a little different. You may want to consider not overextending yourself in your workout and avoiding exercises that are hard on joints. Running is obviously good for you, but your running surface makes a huge difference if you have sensitive joints. Try to keep on softer surfaces like grass. It absorbs the impact better than concrete. A good pair of shoes is also key. A light well-padded, well-fit pair is ideal. Any of the major brands make good shoes. Try going to a specialty shoe store and have your foot fitted. They will measure it and fit you with a perfect shoe. As far as joint pain and stiffness now. Try some icy-hot on the affected areas. That stuff does wonders. Stretching before and after workouts is also imperative to reducing those problems. As far as diet, avoid junk food such as fried chips, soda, candy . . . You don’t have to completely eliminate them, but keep it to small amounts. A well-balanced diet with meat, fruits and vegetables, and grains is very important. And being well-hydrated is key. That can contribute to cramping and your stiffness.


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