Improvement of Biomechanical Performance for Spinal Pedicle Screws with Cement Augmentation in Severe Osteoporosis---A Comparative Study between Cannulated Screw with Cement Injection and Solid Screw with Cement Pre-Filling

In spinal operation with severe osteoporosis patient, securing the pedicle screw is a challenge for the surgeon. To solve this problem, the number of vertebrae needs to be secured was increased in order to strengthen the securing effect. However, it often required bigger wound and more screws and thus increased the operation time and cost. Another frequently used method is to pour cement into the spine then install the screw to increase the interfacial strength between the screw and vertebral bodies. In our previous experience, the fixation strength of pedicle screws can be improved with use of cannulated screws by injecting bone cement, via the central hole of the screw, into vertebral bodies. Although both above-mentioned surgical techniques can increase interfacial strength, however, lack of literatures had compared the mechanical performance between these two surgical techniques on view point of biomechanics. By using self-designed cannulated and solid screws, this study is designed to compare the biomechanical performance for pedicle screw fixation in severe osteoporosis on circumstances of: (A) Cannulated screw with cement injection and (B) Solid screw with cement pre-filling. Both interfacial strength of fixation screw and mechanical stability of spinal construct following assemble of spinal units (screw, rod and nut) will be evaluated accordingly. A brief explanation of the screw design is as follows: Design a hollow pedicle screw and drill a number of holes at the end of the screw. After the screw was inserted into the spine, the cement was poured in via the hollow screw with a compressor and thus enabled the cement to penetrate the hole on the screw to the outside and then into the spine. This will blend the cement, spine and screw together, increase the pullout strength and thus resolve the problem with the screw treatment of severe osteoporosis patients. We propose to perform this study within two years. Interfacial characteristics of fixation screws (cannulated and solid) together with integral stability of the spinal construct assembly will be conducted to compare the differences of the mechanical behaviors between these two fixation techniques. The contents of this two-year study are summarized as follows: A. The first-year study: Static tests for fixation screws Commercially available test block will be used as a substrate for vertebrae with severe osteoporosity to eliminate the experimental errors caused by the variability of bone properties and morphometry. Mechanical tests involving: (1). screw pullout, (2). screw bending, and (3). screw torsion will be performed according to the related ASTM testing standards with use of MTS testing machine. The interfacial characteristics of cannulated screw and solid screw, augmented with bone cement based on the above-mentioned surgical techniques, will be evaluated and compared. B. The second-year study: Dynamic tests for spinal construct assembly According to ASTM P5-94 testing standards, dynamic tests for spinal construct following assemble of spinal units (screw, rod and nut) will be conducted to compare the integral stability in between the two fixation techniques (cannulated and solid screws). The biomechanical performance for osteoporotic vertebrae treated with cannulated and solid screws will be examined.

Project ID:PC9808-0586
External Project ID:NSC98-2314-B182-013-MY2