Design and analysis of biodegradable buttress threaded screws for fracture fixation in orthopedics: a finite element analysis.

Screws made up of non-biodegradable materials (Ti-alloy, etc.) have been used since long for temporary joining/fixation in applications involving skeleton damage or bone fracture. These screws need to be removed after complete healing as their sustained presence results in many complications, such as - micro-fracturing, stress shielding, etc. The removal of these screws is a little difficult too as it may result in the healed bone getting broken/damaged again. These problems can be overcome by employing metallic implants (plate, screws, etc.) made up of biodegradable metallic materials (Mg-alloy, etc.). Such implants exhibit optimal mechanical performance, are biocompatible, have adequate biodegradation rates, and rely on a unique design. Internal fracture fixation makes usage of screws with or without an accompanying plate. Buttress-threaded screws are the most frequently used ones. These screws must have the capacity to bear usually occurring loads and hold fractured segments of bone all through the process of healing. Finite element analysis (FEA) is an effective technique used for testing and validation of desired characteristics for Mg-based biodegradable buttress-threaded screw (BBTS). The characteristics of interest include maximum possible pullout resistance to tightly hold segments of bone, torsional ability for tightening or tapping, bending ability during providing plate support by screw head, and resistance to combined loading (tensile/compressive and bending) during the self-support stage using merely the screw(s). According to test results and subsequent validation through discretization error and convergence plot, BBTS made up of Mg-alloy are found safe for regular applications under usually encountered impact loads. Topological optimization and vibration analysis are also performed wherein it is observed that design of BBTS is good enough for possible usage in fracture fixation in orthopaedics.