Each innominate bone (ilium) joins the femur (thigh bone) to form the hip joint; thus the sacroiliac joint moves with walking and movement of the torso.In this joint, hyaline cartilage on the sacral side moves against fibrocartilage on the iliac side. The sacroiliac joint contains numerous ridges and depressions that function in stability. Studies have documented that motion does occur at the joint; therefore, slightly subluxed and even locked positions can occur.Muscles and ligaments surround and attach to the SI joint in the front and back, primarily on the ilial or sacral surfaces. These can all be a source of pain and inflammation if the SI joint is dysfunctional. The sacroiliac joint is highly dependent on its strong ligamentous structure for support and stability. The most commonly disrupted and/or torn ligaments are the iliolumbar ligament and the posterior sacroiliac ligament. The ligamentous structures offer resistance to shear and loading. The deep anterior, posterior, and interosseous ligaments resist the load of the sacrum relative to the ilium. More superficial ligaments (e.g., the sacrotuberous ligament) react to dynamic motions (such as straight-leg raising during physical motion). The long dorsal sacroiliac ligament can become stretched in periods of increased lumbar lordosis (e.g., during pregnancy). Affected muscle groups
Many large and small muscles have relationships with the ligaments of the sacroiliac joint including the piriformis (see "piriformis syndrome", a condition often related with sacroiliac joint dysfunction), rectus femoris, gluteus maximus and minimus, erector spinae, latissimus dorsi, thoracolumbar fascia, and iliacus.
In the acute phase (first 1–2 weeks) for a mild sprain of the sacroiliac, it is typical for the patient to be prescribed rest, ice/heat, spinal manipulation, and physical therapy; anti-inflammatory medicine can also be helpful.If the pain does not resolve in the first 1–2 weeks, then the patient may benefit from a steroid and anesthetic mixture fluoroscopically injected into the joint (this also serves in confirming diagnosis), as well as manipulative or manual therapy. For the most severe and chronic forms of sacroiliac dysfunction, treatment should proceed with the support of a sacroiliac belt, injection therapy, and finally, surgery. The anti-inflammatory effect of injection therapy is not permanent, and the injections do not offer an opportunity to stabilize an incompetent joint. Surgery is often considered a last resort, but for some patients, it is the only method of effectively stabilizing the loose joint. A fixation of the joint (screws or similar hardware only, without the use of bone grafting) is more common than a spinal fusion, as it is much less invasive, surgically straightforward, and results in a quicker recovery time for the patient. Some experts in the field believe that it is important to make sure the sacroiliac joint is in an anatomically correct position prior to fixation or fusion, but published research contradicts this belief.Platelet-rich plasma (PRP) injections have shown positive results as a treatment for Sacroiliac Joint Dysfunction, with randomized trials & case reports showing them to be more effective over periods of 3 months than steroid injections.