Rescue Augmentation: Increased Stability in Augmentation After Initial Loosening of Pedicle Screws.

Abstract

Study Design:Biomechanical study.Objectives:Failure of pedicle screws is a major problem in spinal surgery not only postoperatively, but also intraoperatively. The aim of this study was to evaluate whether cement augmentation may restore mounting of initially loosened pedicle screws.Methods:A total of 14 osteoporotic or osteopenic human cadaveric vertebral bodies (L2)—according to quantitative computed tomography (QCT)—were instrumented on both sides by conventional pedicle screws and cement augmented on 1 side. In vitro fatigue loading (cranial-caudal sinusoidal, 0.5 Hz) with increasing peak force (100 N + 0.1 N/cycles) was applied until a screw head displacement of 5.4 mm (∼20°) was reached. After loosening, the nonaugmented screw was rescue augmented, and fatigue testing was repeated.Results:The fatigue load reached 207.3 N for the nonaugmented screws and was significantly (P = .009) exceeded because of initial cement augmentation (300.6 N). The rescue augmentation after screw loosening showed a fatigue load of 370.1 N which was significantly higher (P < .001) compared with the nonaugmented screws. The impact of bone density on fatigue strength decreased from the nonaugmented to the augmented to the rescue-augmented screws and shows the greatest effect of cement augmentation on fatigue strength at low bone density.Conclusions:Rescue augmentation leads to similar or higher fatigue strengths compared with those of the initially augmented screws. Therefore, the cement augmentation of initially loosened pedicle screws is a promising option to restore adequate screw stability.