Abstract
The authors have been studying lumbar disturbances among top class atheletes in Japan and it was proved that the incidence of spondylolysis was surprisingly high among these sports items compared with ordinary people. The mechanical breakdown owing to heavy loads at the pars interarticularis is thought to be one of the causautive factors of spondylolysis. In order to prove this hypothesis, we performed the experimental studies using fresh cadavers. In these experiments the strain at various points was measurad during three directional movements of the spinal column with continuous loading, antero-posterior, lateral and rotational ones. Regarding to antero-posterior bending, remarkable deformities were recognized on the pars interarticularis of the fifth lumbar vertebra during posterior bending compared with anterior bending. At the time of rotational bending, of the spinal column in extention deformities at the pars interarticularis showed twice as large as those in neutral position. Furthermore, at rotational bending the deformities at that site considerably increased according to increasing axial loads on the spinal column.
These results suggest that the repetitive stress on the pars interarticularis during sports activity may cause fatigue fracture on that part.
