Yes, It Moves! Let’s Demystify the S.I. Joint.

By Dan Hellman

The sacroiliac joint (S.I. joint) is widely misunderstood, particularly its movement, so let’s unravel the mystery a bit. In fact, most allopathic, or traditional, practitioners don’t believe the joint moves at all. This myth is understandable, because it is based mostly on “dead people anatomy,” the study of cadavers. And we all know that cadavers don’t move.

We practitioners in the rehabilitation fields of physical therapy, chiropractic, osteopathy, massage therapy and personal training know better. We know without a doubt that the S.I. joint moves and performs many functions. The only real questions we have are where is the axis of movement and how do we name the movements. According to the pioneering early 20th century chiropractic researcher Dr. Fred Illi, humans are the only vertebrate on the planet with a movable S.I. joint, and that simple advantage has allowed us to navigate the earth on just two legs.

Micro movements manage macro.

The S.I. joint moves anywhere from 2 to 18 degrees, or 2 to 4 mm. This doesn’t sound like much, but it makes a big difference in the human body. That is because the micro (tiny) movements of the body actually manage the macro (big) movements. Without the minute movement at the S.I. joint, which cannot be seen by the naked eye, our gait pattern would be clumsy and uneven. We would all walk like the Frankenstein monster. The S.I. joint also acts like a large shock absorber, dissipating ground reaction forces before they can jolt the spine and the ever-so-important spinal cord.

The S.I. joint is really a complex structure.

The right and left S.I. joints and the pubic symphysis, which is in the front, are the three joints of the pelvis, so the pelvis is really a three-joint complex. One might think that would make the pelvis easy to treat, but the structure of the pelvis presents therapists with a significant challenge. The S.I. joint looks something like an uneven boomerang. The top arm, called the lesser arm, is shorter and more vertical than the bottom arm, which is called the greater arm.  They are separated by a bony area called the isthmus, and they both have an apex and a base (see diagram below).  A lesion can occur in any of these areas, and S.I. joint experts say there are 22 possible axes of motion. Despite all this complexity, most chiropractors and therapists know only one adjustment for this joint.

The pelvis is the body’s foundation.

You wouldn’t build your dream home on an unstable foundation, and you shouldn’t ignore or overlook pelvic pain or dysfunction. The pelvis is much like the foundation of a house, and the S.I. joints and the pubic symphysis are the movable joints that keep the foundation in order. They work like the joints of a building that move with settlement or shaking of the earth and prevent the structure from collapsing. S.I. joint problems are a major untreated pathology today.  They are common in both men and women and can stem from inactivity, trauma, sports and even the things we do as we go about our day.

Because the lower back and pelvis are joined, S.I. joint problems also go hand-in-hand with lower-back discomfort and dysfunction. It is impossible to have one without the other. The area where the back and pelvis meet, called the lumbo-pelvic-hip complex, needs to be treated as a whole. And there’s more: No matter the complaint—back or neck pain, hip pain, shoulder pain, ear infection, hernia, pelvic pain, headache, etc.—a  good therapist will always clear the pelvis first. That is, the therapist will check the pelvis for problems first and treat them if they exist. The pelvis is the foundation, after all, and it is not wise to build house on a weak foundation. 

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