Efficacy of novel-concept pedicle screw fixation augmented with calcium phosphate cement in the osteoporotic spine

Pedicle screw instrumentation has become increasingly popular for rigid internal stabilization of the thoracolumbar spine. However, when pedicle screws are used in elderly osteoporotic patients, the screw-bone interface is stripped easily. Therefore, the risk of screw loosening and backing-out after surgery has increased. The purpose of this study was to evaluate the efficacy of the novel-concept pedicle screw fixation augmented with calcium phosphate cement (CPC) in the osteoporotic spine. The novel-concept screw has the same shape as the ordinary screw, but it is hollow and fabricated with 20 small holes (1.3mm in diameter) leading to the hollow part on the bottom of the thread. Fifteen embalmed cadaveric lumbar vertebrae were instrumented with two types of pedicle screw (the ordinary screw and the novel-concept screw) in each pedicle. Only the novel-concept screws were augmented with CPC after insertion. Seven days later, axial pull-out testing was performed at a crosshead speed of 10mm/min. The mean maximal pull-out strength of the ordinary screws was 258N, and that of the novel concept screws was 637N. These results suggest that the novel-concept screw augmented with CPC can be useful for pedicle screw fixation of the osteoporotic spine.