MECHANICAL-BEHAVIOR OF THE FEMALE SACROILIAC JOINT AND INFLUENCE OF THE ANTERIOR AND POSTERIOR SACROILIAC LIGAMENTS UNDER SAGITTAL LOADS

Objective. The purpose of this study was to examine the mechanical beh aviour of the female sacroiliac joint and the effects of its two major ligaments to joint stability. Design. A cadaveric model was used to s tudy the mechanical behaviour of the sacroiliac joints, and sequential dissection was performed to examine the contribution of the anterior and posterior sacroiliac ligaments in joint stability. Background. Ins tability of the sacroiliac joints have been suspected as a possible ca use of low back pain. Despite several investigations on joint anatomy and joint mobility, its stabilising mechanism is still not dear. Metho ds. Four fresh cadaveric specimens of the female pelvis were tested on an Instron material testing machine. Eccentric compressive force of 6 0% of the subject's body weight was applied to the pelvis through the sacrum. Relative three-dimensional six-degree-of-freedom movement at t he left sacroiliac joints was recorded with a specially designed motio n tracking device. The device has an accuracy of 0.01 mm and is compac t enough to be mounted across the joint. The test was repeated after s equential selective dissection of the bilateral anterior, and then pos terior sacroiliac ligaments. Results. Rotation up to 1.2 degrees and t ranslation up to 0.9 mm were measured from the intact specimens. Later al rotation, which tended to open the top portion of the joint, and sa cral nutation were the primary rotations. On average, the rotation ang les increased 10% when either the anterior or posterior ligaments were cut, and 30% when both ligaments were cut. Conclusions. Lateral rotat ion and nutation rotation of the sacrum were found to be the predomina nt motion, though the values were limited to less than 1.2 degrees. Bo th the anterior and posterior sacroiliac ligaments were found to play an important role in resisting rotations at the joints.