抄録
Since 1969 the investigation has been performed concerning low back pain among top athletes and in 27 percent of the subjects spondylolysis was found. This high frequency led the author to suspect the possibility of some non-congenital cause. Therefore, an experiment was undertaken with an artificial model of a spinal element.
The spinal model was constructed with Methacrylic Methyl resin and was subjected to compressive and tortional loads. Stress distributions in the posterior portion of the vertebra were measured. In addition, destructive tests were conducted with continuous and repetitive application of loads
Three axis strain gauge measurements confirmed that the fracture surface was perpendicular to the direction of the maximum strain. A compressive strain was observed in the dorsal side, whereas tensile strain in the ventral. An increasing strain was observed with an increasing degree of extention both in the continuous and repetitive loading experiment. The maximum strain was noticed at the lateroventral area of the pars interarticularis and its value at the maximum extension was approximately seven times that of the maximum flexion. In the repetitive loading experiment, a fatique fracture was found more likely to occur in the extensional posture. The destructive experiment resulted in fracture of the pars interarticularis.
Judging from the above results, frequent lifting of a heavy load in the extentional posture corresponds to repetitive stress and causes an eventual fracture at the pars interarticularis, which in turn could cause spondylolysis.
