TRANSFER OF LUMBOSACRAL LOAD TO ILIAC BONES AND LEGS .2. LOADING OF THE SACROILIAC JOINTS WHEN LIFTING IN A STOOPED POSTURE

We developed a biomechanical model of load transfer by the sacroiliac joints in relation to posture. A description is given of two ways in w hich the transfer of lumbar load to the pelvis in a stooped posture ca n take place. One way concerns ligament and muscle forces that act on the sacrum, raising the tendency of the sacrum to flex in relation to the hip bones. The other refers to ligament and muscle forces acting o n the iliac crests, raising the tendency of the sacrum to shift in cau dal direction in relation to the hip bones. Both loading modes deal wi th the self-bracing mechanism that comes into action to prevent shear in the sacroiliac joints. When a person is lifting a load while in a s tooped posture, the force raised by gravity acting in a plane perpendi cular to the spine and the sacrum becomes of interest. In this situati on a belt such as used by weight lifters may contribute to the stabili ty of the sacroiliac joints. Verification of the biomechanical model i s based on anatomical studies and on load application to human specime ns. Magnetic resonance imaging pictures have been taken to verify geom etry in vivo.