[Stress analysis and movement in sacroiliac joints].

Biomechanical experiments were performed on sacroiliac joints of the cadaver pelvis in three different positions to determine changes in stress pattern. The infrared stress analyzing method was used. In the neutral position, principal stress was observed in the middle to upper part of the sacrum, adjacent to the sacroiliac joints, in the central area of the ilium, and in the acetabular region. In the anterior tilting position, the stress on the sacroiliac joints was smaller than in the posterior tilting position, while it was greater in the symphysis pubis area. Further experiments with dial gauges were performed to measure load-displacement value in four cadaver pelves. Vertical loads of up to 100 kg were applied to the fourth lumbar vertebra. At the maximum test loads, displacement of the anterior surface of the first sacral vertebra ranged from 0.18 mm to 0.73 mm in the anterior direction. In conclusion, it is clear that the range of movement in the sacroiliac joints is very small and that this joint plays a significant role in the maintenance of stability in the pelvic girdle.