The properties of shape memory alloys, specifically the equiatomic intermetallic NiTi, are unique and significant in that they offer simple and effective solutions for some of the biomechanical issues encountered in orthopedics. Pedicle screws, used as an anchoring point for the implantation of spinal instrumentations in the spinal fracture and deformity treatments, entail the major drawback of loosening and backing out in osteoporotic bone. The strength of the screw contact with the surrounding bone diminishes as the bone degrades due to osteoporosis. The SMArtTM pedicle screw design is developed to address the existing issue in degraded bone. It is based on the interaction of bi-stable shape memory-superelastic elements. The bi-stable assembly acts antagonistically and consists of an external superelastic tube that expands the design protrusions when body temperature is attained; also an internal shape memory wire, inserted into the tube, retracts the assembly while locally heated to above the body temperature. This innovative bi-stable solution augments the pull-out resistance while still allowing for screw removal. The antagonistic wire-tube assembly was evaluated and parametrically analyzed as for the interaction of the superelastic tube and shape memory wire using a finite element model developed in COMSOL Multiphysics®. The outcomes of the simulation suggest that shape memory NiTi inserts on the SMArtTM pedicle screw can achieve the desired antagonistic functionality of expansion and retraction. Consequently, a parametric analysis was conducted over the effect of different sizes of wires and tubes. The dimensions for the first sample of this innovative pedicle screw were determined based on the results of this analysis.
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September 2012
Technical Briefs
Shape Memory Alloy Expandable Pedicle Screw to Enhance Fixation in Osteoporotic Bone: Primary Design and Finite Element Simulation
Majid Tabesh,
Majid Tabesh
Dynamic and Smart Systems Laboratory, Engineering Center for Orthopedic Research Excellence, University of Toledo
, 2801 West Bancroft, Toledo, Ohio, 43606
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Vijay Goel,
Vijay Goel
Dynamic and Smart Systems Laboratory, Engineering Center for Orthopedic Research Excellence, University of Toledo
, 2801 West Bancroft, Toledo, Ohio, 43606
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Mohammad H. Elahinia
Mohammad H. Elahinia
Dynamic and Smart Systems Laboratory, Engineering Center for Orthopedic Research Excellence, University of Toledo
, 2801 West Bancroft, Toledo, Ohio, 43606
Search for other works by this author on:
Majid Tabesh
Dynamic and Smart Systems Laboratory, Engineering Center for Orthopedic Research Excellence, University of Toledo
, 2801 West Bancroft, Toledo, Ohio, 43606
Vijay Goel
Dynamic and Smart Systems Laboratory, Engineering Center for Orthopedic Research Excellence, University of Toledo
, 2801 West Bancroft, Toledo, Ohio, 43606
Mohammad H. Elahinia
Dynamic and Smart Systems Laboratory, Engineering Center for Orthopedic Research Excellence, University of Toledo
, 2801 West Bancroft, Toledo, Ohio, 43606J. Med. Devices. Sep 2012, 6(3): 034501 (8 pages)
Published Online: August 20, 2012
Article history
Received:
May 15, 2010
Revised:
July 5, 2012
Online:
August 20, 2012
Published:
August 20, 2012
Citation
Tabesh, M., Goel, V., and Elahinia, M. H. (August 20, 2012). "Shape Memory Alloy Expandable Pedicle Screw to Enhance Fixation in Osteoporotic Bone: Primary Design and Finite Element Simulation." ASME. J. Med. Devices. September 2012; 6(3): 034501. https://doi.org/10.1115/1.4007179
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