Micro-Computed Tomography-Based Finite Element Analysis Of The Mechanical Integrity Of In Vivo Biodegradable Magnesium-Alloy Screw And Surrounding Bone
The anterior cruciate ligament (ACL) tear, the most common knee injury, affects 100,000 to 200,000 persons in the US annually. Surgical repair is employed to restore the knee to its full range of motion. In the surgery, an interference screw is used to a secure a soft tissue graft that is used to replace the torn ACL. In 2012, orthopedic devices for knees accounted for the largest share of the $29.2 billion overall revenue for orthopedic devices. Biodegradable implants are expected to lead growth in the orthopedic sector by increasing the quality of life and decreasing recovery time after orthopedic injury for athletes and non-athletes and aging, osteoporotic, osteoarthritic and obese populations. Magnesium-based orthopedic devices, including interference screws, are being investigated because of their ability to provide high strength as a metal, but degrade like a polymer. One objective of this study was to compare the pull-out forces of an unnamed magnesium-alloy against a commercially available copolymer, 82:18 PLLA:PLGA, in woven bone using finite element analysis. The reaction forces in bone and displacement of the screws were used to assess the overall performance of each material in a pull-out test. The second objective of this work was to develop and evaluate micro-computed tomography-based finite element models of in vivo biodegradable screws of the unnamed magnesium-alloy over time in rabbit femurs. Several foundational observations were made about modeling in vivo degrading magnesium devices with a micro-CT to FEA protocol. The results of this work have shown that an unnamed biodegradable magnesium-alloy and a biodegradable 82:18 PLLA:PLGA copolymer performed equally in nodal displacement and that the Mg-based device only outperformed the copolymer in Emin woven bone
