Strategy for Salvage Pedicle Screw- Biomaterials Filling, Modified Cement Augmentation and Cortical Bone Trajectory

Pedicle screw fixation has been widely accepted for treatment of spinal disorders, including degeneration, trauma, infection, and other pathological diseases of thoracolumbar spine. To date, however, in cases of pedicle screw loosening, salvage surgery for failed pedicle screw in an enlarged pedicle hole remains challenge. Numerous reports have addressed on the efficacy of specific biomaterial for treatment of failed pedicle screws. These include the augmentation with PMMA cement, calcium phosphate cement, or hydroxyapatite granules. However, under the same platform, few literatures are available to systematically evaluate the association among the screw anchoring strength, augmentation materials, enlarged hole size, and bone quality. Furthermore, previous reports have demonstrated that screw fixation strength can be effectively improved when revision pedicle screw is augmented with PMMA cement. However, the use of large amounts of PMMA increases the risk of cement leakage, which evaluates complication rates. To solve this problem, with less amount of PMMA, we propose to devise a modified PMMA-augmented technique, to achieve a more safety and more robust fixation for salvage pedicle screw placement. Recently, cortical bone trajectory (CBT) screws were developed as an alternative to traditional pedicle trajectory (TPT) in the lumbar spine. Previous reports have shown that CBT fixation provided similar stability as traditional pedicle screw fixation. However, literatures examining the possibility of CBT screws rescue failed pedicle screws and pedicle screws rescue failed CBT screws is lacking. To address the aforementioned issues, this three-year study aims to systematically explore the strategy for salvage pedicle screws in three ways: biomaterials augmentation, modified PMMA augmentation technique and cortical bone trajectory. The contents of this three-year study are summarized as follows:The first-year study: Biomaterials augmentationThree types of commercially available test blocks are used to mimic different BMD degrees of vertebral bones. Following preparation of two different enlarged screw-hole sizes, PMMA, CaSO4, HAP and bone chips are used for salvage pedicle screw. The association among screw anchoring strength, augmentation materials, screw-hole size, and bone quality will be evaluated.The second-year study: Modified PMMA augmentation techniqueSinge-level porcine lumbar vertebrae are used to evaluate the efficacy of the modified technique. Following the filling of the space of the enlarged screw hole using a small amount of PMMA, a small-diameter screw is then inserted. After the PMMA has hardened, the screw is then carefully removed, leaving a high-stiffness threaded PMMA hole. A larger-diameter screw (with identical thread type) is then inserted to “expand” the smaller PMMA-threaded hole to achieve a more safety and robust fixation.The third-year study: Cortical bone trajectoryTwo-level (L3-L4) porcine lumbar spines are used. Specimens are divided to TPT and CBT groups. For the TPT, both L3 and L4 are bilaterally instrumented with pedicle screws; whereas in CBT, they are instrumented with cortical screws. The possibility of TPT and CBT screws when each is used to rescue the other is assessed on condition that bilateral screw loosening occurs on superior (L3) level.

Project ID:PB10707-0613
External Project ID:MOST107-2221-E182-013