Critical Analysis of the Functional Dynamics of the Sacroiliac Joints as they Pertain to Normal Gait

Abstract

The purpose of this paper is to describe the basic structure of the sacroiliac joint, the loading sequence of the primary ligaments, its function during normal gait and the supportive muscle functions. The goal of treatment of low back and pelvic pain should be the restoration of normal function and so it is important to understand just how the low back and the pelvis normally function.The sacroiliac joint has been assumed to be structurally so strong as to be immune to injury through minor trauma. Motion in the joint is minimal and its function has been obscure. There is essentially no motion in the sacroiliac joint on a transverse axis when the sacrum is loaded with the superincumbent weight and the pelvis is symmetrical as in relaxed standing. During normal gait, however, when the pelvis moves into asymmetry, the sacrum flexes laterally and rotates toward the side of loading to drive rotation and counter rotation of the trunk during normal gait to decrease the loading impulse. Primary loading of the superincumbent weight on the sacrum is on the posterior interosseous ligaments with a secondary loading on the sacrotuberous and sacrospinous ligaments. It is the secondary loading that draws these joints together in a critical balance of loading forces. The result of this loading is to create a force couple. The sacroiliac joints function as self-compensating, interdependent force couples with force-dependent transverse and oblique axes of rotation to absorb, modify and redirect forces such as linear and angular momentum, linear and angular acceleration and deceleration, loading and unloading and others.