after fatigue cycling. The authors highlighted that pedicle screws augmented using the kyphoplasty technique had signicantly greater pullout strength than those augmented with a vertebro­plasty augmentation technique and those placed in healthy control vertebrae with no augmenta­tion (see Fig.18.4).

Pedicle screw augmentation with PMMA cement has been shown to signicantly improve the xation strength even in a severely osteo­porotic spine. Costa and colleagues further evaluated the difference in pullout strength between ve different cement augmentation techniques [31]. Uniform synthetic bone (Sawbones, Washington, USA) was used to simulate severe osteoporosis by providing a platform for each augmentation technique; polyaxial screws and acrylic cement (PMMA) at medium viscosity were used. Five groups were analyzed: (I) screw only without PMMA (control group), (II) retrograde cement prell­ing of the tapped pedicle screw pilot hole, (III) cannulated and fenestrated screw with cement injection through perforations in the screw, (IV) injection using a standard trocar of PMMA (vertebroplasty) with retrograde prelling of the tapped pilot hole, and (V) injection through a fenestrated trocar and retrograde prelling of the tapped pilot hole (Fig. 18.5). Standard X-rays were taken in order to conrm cement distribution in each group. A total of 30 pedicle screws at full insertion were then tested for axial pullout failure using a mechanical testing machine. The results of pullout analysis revealed better resistance to pull out in all groups as compared to the control group with­out cement augmentation. In particular, the sta­tistical analysis showed a difference between Group V (P=0.001) and all other groups, sug­gesting better load resistance to axial forces when the distribution of the PMMA is uniform and elongated along the screw stem due to combining a fenestrated trocar and prelling augmentation technique (see Fig.18.5).