Mobility in the sacroiliac joints in the elderly: a kinematic and radiological study.

Movement in eight sacroiliac joints was measured in preparations of embalmed elderly humans and compared with radiological findings. For the biomechanical part of the study the connections between sacrum and fifth lumbar vertebra were spared, as were the surrounding ligaments. The pelvis-spine preparation was fixed at the fifth lumbar vertebra. To induce movement, forces were directed at the acetabula. With digital displacement meters rotation was measured between the sacral and iliac part of the sacroiliac joint. In the sagittal plane both ventral rotation (as part of nutation) and dorsal rotation (as part of contranutation) could be demonstrated. Most sacroiliac joints were mobile, allowing a total rotation of up to 4°. Significant intraindividual differences in mobility occurred. One sacroiliac joint without mobility showed radiographically pronounced arthrosis. The impact of the findings on kinematic chain and clinical diagnosis is discussed. In the literature no data are available on the radiographic appearance of biomechanically studied sacroiliac joints. In the present study a biomechanical and radiological approach has been combined. The study emphasizes the clinical importance of intraindividual sacroiliac differences as well as the need for a thorough integration of pelvic and lumbar kinematics.