[Shape transformations of the lumbar spine in relation to passive extension of the lower extremities in the sagittal level].
PROBLEM: The interdependencies between movements of the thighs and the lumbar vertebral shape are of high practical interest. Which are the normals of this phenomenon? METHOD: In an experiment on 107 volunteers without before known spinal disorders and complaints of back pain (47 f, 60 m, 17 a-30 a), the interdependencies between movements of the thighs in the sagittal and the lumbar back profile were analysed. Hip joint movements were provoked by a lift jack, elevating the feet to the volunteers, which sat on a bicycle chair. The hip joint flexion was measured by a Zebris CMS 50. The sagittal profile of the lower back was sensed by a comb of steel needles with low friction support. RESULTS: At 30 degrees of hip flexion, 68% of the volunteers demonstrated a kyphotic, 17% a straight and 15% a lordotic lumbar shape. Starting at 90 degrees of hip flexion, "definitively kyphosating movements" of the lumbar motion segments occur. At the end of the motion, 89% of the volunteers had a kyphotic, 3% a straight and 8% a lordotic lumbar configuration. Each 2 degrees of additional hip joint flexion caudo-cranially one more lumbar motion segment is recruited for the definitive kyphosation of the lumbar spine. CONCLUSIONS: Instead of a "physiological shape of the lumbar spine" its "physiological function" or its "physiological interaction between shape und function" should be in the focus of future discussions. In the sitting, hip joint flexion leads to a coupled motion of the thighs, the pelvic girdle and the lumbar vertebral column with the consequence of a kyphosation of the lumbar back shape.