Failure load and displacement of the human sacroiliac joint under in vitro loading.

The stability of the sacroiliac joint was studied using an in vitro loading system. Forty-nine sacroiliac joints taken from fresh cadavers were examined. The ligamentous structures of the joint disrupted at 3368 +/- 923 N under transverse loading. Higher disruption forces were observed under ventrocranial (4933 +/- 1038 N) and dorsocranial (5150 +/- 947 N) loading. At joint failure the displacement in loading direction ranged from 5.5 +/- 2.3 mm in the transverse to 6.6 +/- 2.3 mm in the dorsocranial direction. In some experiments the interlocking effect between the articular surfaces of the sacrum and ilium were examined. The best interlocking capacity was observed under dorsocranial loading. This capacity is much higher than the friction in other human joints. The study shows that correct anatomical reconstruction without displacement increases the stability of the disrupted sacroiliac joint.