Fracture risk during pedicle screw insertion in osteoporotic spine

Although using a larger screw can enhance the stability of screw-bone inter face in pedicular screw instrumentation, it may cause pedicle fracture duri ng screw insertion in osteoporotic spine. We investigated structural change s of the pedicle with the advance of osteoporosis and its implication for t he risk of pedicle fracture. Bone mineral density of trabecular, subcortica l, and cortical bone of pedicle in an osteoporotic group, assessed by perip heral quantitative computed tomography, was significantly lower than that o f those in the normal group. Cortical thickness also declined. There were n o pedicle fractures in normal vertebrae, but seven (41.2%) fractures were o bserved among 17 pedicles in osteoporotic vertebrae in which bone mineral d ensity measured with dual-energy x-ray absorptiometry was <0.7 g/cm(2) and screw diameter >70% of the outer diameter of the pedicle. Our results sugge st that screw diameter should not exceed 70% of the outer diameter of the p edicle in the case of osteoporosis in which vertebral bone mineral density is <0.7 g/cm(2).