The Development of Polyaxial Cannulated Screw with Cement Augmentation and Coupling Auxiliary Cement Irrigator for Osteoporotic Vertebrae

This study aims to develop a newly designed polyaxial cannulated screw with cement augmentation and coupling auxiliary cement irrigator in treatment of vertebroplasty or pedicle screw fixation for patients with osteoporosis. Currently, vertebroplasty has been an effect approach to treat the vertebral compression fracture induced by osteoporosis of vertebral body. Vertebroplasty is the percutaneous injection of PMMA cement into the vertebral body, to restore the original spinal curvature. In spinal operation with severe osteoporosis patient, securing the pedicle screw is an even bigger challenge for the surgeon. To solve this problem, 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. However, it often resulted in insufficient interfacial strength due to the lack of cement, or a poor blend between the screw, cement and spine. Currently abroad, only the expandable screw developed by Merck Corporation’s Omega 21 Spine System can assist in increasing the interfacial strength. However, their design only focus on the expandable function at the tip of the screw, the purpose to increase the interfacial strength for patients with osteoporosis might be limited. To date, although cannulated screws have been developed to increase interfacial strength, however, the commercial cannulated screws are all without polyaxial function. In spinal operation with severe osteoporosis patient, neither vertebroplasty or cannulated screw fixation, an easy-operate cement irrigator will be needed to inject PMMA cement into the vertebral body with amount control. In current study, polyaxial cannulated screw with cement augmentation and coupling auxiliary cement irrigator is designed with the following features: Features of cannulated screw: 1. Polyaxial; the direction of screw insertion can be chosen during surgery. 2. With a longitude hole and several side holes for PMMA cement injection. 3. Complied with the coupling auxiliary cement irrigator for PMMA cement injection. Features of the coupling auxiliary cement irrigator: 1. The plastic plunger of the traditional syringe is replaced with a metal-made plunger, and the PMMA cement is injected through the continuous movement of the plunger by mechanism of its outer thread, this particular design effectively improve the efficacy of cement injection. 2. The amount of injected cement can be controlled during surgery. 3. Can be utilized in spinal surgery for both vertebroplasty and cannulated screw fixation. In terms of biomechanical study, the pull-out and torsion and cntilever tests will be performed using the MTS testing machine and artificial test blocks. The difference of the biomechanical characteristics between the newly designed polyaxial cannulated screw and the traditional screw will be evaluated and compared for determination of the design parameters.

Project ID:PB9709-3955
External Project ID:NSC97-2622-E182-001-CC3