L4-L5 disc herniation in spontaneous fusion of L5-S1: A biomechanical and clinical study

Anatomical structures at L5-S1 level may be subjected to extremely high stresses and, then, a clinical lesion may arise. Rupture of the annulus fibrosus may lead to L5-S1 disc herniation: actually this is the most common site of occurrence. A clinical direct evidence of the biomechanical nature of lumbar disc herniation is reported by describing rare cases where a spontaneous L5-S1 fusion has been followed, in the long tern, by L4-L5 disc herniation. As L5-S1 fused, L4-L5 took over becoming the functional lumbo-sacral mechanical passage.