Principles of Manual Medicine
Illiosacral Motion
The sacroiliac mechanism can be viewed from the perspective of each innominate articulating with the sacrum. The motion can be described as one innominate moving on one side of the sacrum (iliosacral movement). Each innominate in the walking cycle rotates anteriorly and posteriorly around the anterior axis at the symphysis pubis and anteriorly and posteriorly with each side of the sacrum in a posterior axis.
In anterior innominate rotation, the innominate rotates forward in relation to the sacrum with the anterior superior iliac spine being carried anterior and inferior, the posterior superior iliac spine being carried posterior and superior, and the ischial tuberosity being carried posterior and superior.
In posterior innominate rotation, the anterior superior iliac spine is carried superior and posterior, the posterior superior iliac spine is carried anterior and inferior, and the ischial tuberosity is carried anterior and inferior. Anterior and posterior innominate rotation occurs in the presence of normal sacroiliac joint contour.
If the opposing surfaces of the sacrum and ilium at the sacroiliac joint are altered, atypical movements appear clinically.
- A superior-inferior translatory shearing movement occurs when the opposing joint surfaces are flatter and more parallel.
- If the sacral side of the joint surface is convex and the ilial concave, internal and external rotation around a vertical axis appears possible. These movements are termed in-flare and out-flare, describing the medial and lateral rotation observed clinically.
Somatic dysfunction can occur with any of these motions within the pelvic girdle. Each of these motions is quite small, but when lost, each has a significant clinical effect. In dysfunctions within the pelvic girdle, it is not uncommon to find restriction of several movements within the mechanism.
Click here to join Dr. Philip E. Greenman, D.O., F.A.A.O., as he presents an overview of illiosacral motion.
