[Landing after jumps--wrong technique promotes spondylolysis].

The double-S-shape of the vertebral column usually is explained to be an adaptation to the functional requirements of axial shock absorption. We investigated the effects of axial impacts on the coupled motions of the pelvic girdle and the vertebral column. In contrast to the predictions of the bending spring model, in the first few miliseconds after impact induction the vertebral column shows a tendency of lumbal straightening. This effect may be one reason for high stresses in the vertebral arches, promoting spondylolysis and spondylolisthesis. In sports, high axial impact loads, especially provoked by wrong landing techniques after jumps, should be avoided.