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L i s te n to T h e A B M P Po d c a s t a t a b m p.co m /p o d c a s t s o r w h e reve r yo u a cce s s yo u r favo r i te p o d c a s t s 23 years with the explorations of fascial anatomy. There are important fascial connections between muscles that span across the sacroiliac joint. For example, there is fascial continuity between the gluteus maximus on one side and the latissimus dorsi on the other. There is also a connection between the sacrotuberous ligament and the gluteus maximus on the same side. These fascial connections seem to have an important role in force transmission across the sacroiliac joint. We are still discovering to what extent we can infl uence force transmission across this joint with the manual therapy we apply to the soft tissues in the region. These myofascial connections across the sacroiliac joint are one of the main reasons why encouraging movement and strengthening of torso and lower extremity muscles play a crucial role in treatment of SI joint problems. Pain in the lumbar, pelvic, or lower extremity regions is often attributed to problems of the SI joint. In most of these instances, there is some alignment or movement disorder that is considered the root of the problem. However, the more we learn about the biomechanics of the sacroiliac joint, the more some of these theories are called into question. Let's take a deeper dive into some of the mechanics around the SI joint to better understand this. ANATOMY OF THE SI JOINT There is a slight degree of upward and downward sliding motion at the SI joint called translation. There is only about 1–2 millimeters worth of translation available at the SI joint. This amount of movement will decrease if the person is older because of the increasingly complex contours between the sacrum and ilium. This amount of motion of the SI joint is almost inconsequential in most cases. The majority of movement at the SI joint is a forward and backward tipping of the sacrum in relation to the ilium. This movement occurs around an imaginary horizontal axis going through the center of the sacrum. The forward movement of the sacrum in relation to the ilium is called nutation (Image 4). Keep in mind that the movement of nutation can occur when the sacrum tips forward or when the ilium tips backward. The opposite of nutation is counternutation. In the counternutation movement, the top edge of the sacrum tips backward in relation to the ilium (Image 4). This can also occur if the ilium tips forward in relation to the sacrum. There is only about 1–4 degrees of movement capability in either nutation or counternutation. That limited degree of movement at the SI joint has led to some common misunderstandings about SI joint mechanics. For example, as noted above, if the ilium rotates anteriorly Posterior sacroiliac ligaments Sacrospinous ligament Iliolumbar ligament Sacrotuberous ligament Posterior sacroiliac ligaments. Sacrotuberous, sacrospinous, and iliolumbar ligaments. 2 3