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By Erik Dalton, Ph.D., Freedom from Pain Institute

Iliosacral upslips occur when joint apposition between the ilium and sacrum is altered. That is, the tissues within the joint have upward shear, resulting in deformation, or creep. In other words , the sacroiliac grooves ain't groovin'. Since these superior ilium-on-sacrum shears are more influenced by gravity than other iliosacral dysfunctions, they have a minimal chance of self correction (Fig. 1). This is where we, as manual therapists, come in.

Ordinarily, when we see cases of upward shearing of the ilium on the sacrum, the client's SI joints are lacking either form or force closure. Form closure is provided to a joint by the skeletal framework. A series of ridges and corresponding depressions produces friction and helps interlock the two bones, providing form closure to the SI joint (Fig. 2).

Synovial joints, however, perform best when there is very little movement between the ilial and sacral articular cartilage surfaces. This tiny movement, termed joint play, not only provides spinal shock absorption, but also enhances lower extremity torque and transverse rotations, which help lift and propel the body forward (Fig. 3).

Musculofascial tissues workto keep the sacroiliac joints in balance and move them back into form closure provided by the skeletal framework. The "binding" force contributed by musculofascial tissues is termed force closure. As interpreted by Andry Vleeming, Ph.D., force closure is Mother Nature's backup system to perpetuate joint stability.

Force closure stability is generated by contractive action of core musculofascial tissues, such as the pelvic diaphragm, transverse abdominis, multifidus, and thoracolumbar fascia (Fig.4). In combination, these deep core stabilizers provide a sophisticated neurologic feedback mechanism that reflexively interacts with the brain to provide coordinated movement and pelvic balance.

When the body is continuously subjected to an unbalanced load, viscoelastic tissues responsible for force closure can become strained. Prolonged cyclical loading can deform SI joint ligaments to the point where an act as innocent as slamming on the brake, tumbling on one hip, or clumsily stepping off a curb can jostle the joint enough to cause the ilium to "jump-a-notch" on the sacrum.

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