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[The significance of mechanical factors in the development of spondylolysis. Experimental studies (author's transl)].

The cause of spondylolysis is a controversial subject. A variety of experiments were conducted at the University Orthopedic Clinic in Frankfurt am Main to determine the significance of mechanical factors. Experiments on dogs whose lumbosacral joints were forced into lordosis by a specially developed instrumentarium did not prove that processes tantamount to fatigue fracture occur in the pars interarticularis. Two series of experiments were carried out on the lumbar vertebral columns of adults, stretch measuring strips being attached to the pars interarticularis. The forces acting on the L5 pars interarticularis are, under all conditions, greater than those acting on the other parts, disproportionately so where there is lordotic stress. Therefore, in the certain instances of intermittent or rhythmic loading without a recovery phase, a fatigue fracture can occur. These results may also be assigned to the series of experiments pointing to spondylolysis as being responsible for a final fatigue fracture.