Strain on the interarticular stress distribution. Measurements regarding the development of spondylolysis.

In discussion the aetiology of spondylolysis, attention has been increasingly directed to the biomechanics of the lumbar vertebral column and the lumbo-sacral transition. The theory of a traumatic induction of spondylolysis was tested with stress distribution measurements on the vertebral column of cadavers. Using stretch measuring strips it was possible to investigate, the strain exerted upon the interarticular portion of the intact lumbar vertebral column preparation. A particular strain upon the pars interarticularis occurs through hyperextension, axial stress and torsion of the lumbar vertebral column. It is worth to be mentioned that force transmission within the vertebral arch structures is influenced by the positioning of the vertebral arch joints. Sagittaly positioned vertebral arch joints lead to a greater strain exerted upon the interarticular portion. Our results have to be compared with those of others, who are of the opinion that spondylolysis is a condition resulting from a fatique fracture.