Journal
JOURNAL OF BIOMECHANICS
Volume 49, Issue 9, Pages 1836-1844Publisher
ELSEVIER SCI LTD
DOI: 10.1016/j.jbiomech.2016.04.021
Keywords
Bone-screw interface; Continuum finite element analysis; Proximal humerus; Fracture fixation
Categories
Funding
- AO Foundation via the AOTRAUMA Network [AR2008_01]
- Whitaker International Program Post-doctoral Research Scholarship
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Finite element analysis is commonly used to assist in the development and evaluation of orthopedic devices. The physics of these models are simplified through approximations that enable more efficient simulations, without compromising the accuracy of the relative comparisons between implant designs or configurations. This study developed and evaluated a technique to approximate the behavior of a finely threaded screw using a smooth cylinder with the threads implicitly represented through interfacial contact conditions. This pseudo-threaded model was calibrated by comparing to simulations that explicitly modeled the thread geometry with frictional contact. A parametric analysis was performed with a single screw-in bone system, five loading directions, and three Young's moduli that span the range of cancellous bone (200, 600, and 1,000 MPa). Considering that screw cut-out from cancellous bone is a critical clinical issue in the osteoporotic proximal humerus, the pseudo-threaded model was compared with a bonded interface to examine three different screw configurations in a 3-part proximal humerus fracture across 10 patients. In the single screw-in-bone system, the pseudo-threaded model predicted the screw displacement of the explicitly threaded model with 1-5% difference and estimated the strain distributions and magnitudes more accurately than a bonded interface. Yet, the relative comparisons of implant stability across the three different screw configurations in the proximal humerus were not affected by the modeling choice for the bone-screw interface. Therefore, the bonded interface could serve as a more efficient methodology for making relative comparisons between implants that utilize the same thread profile. (C) 2016 Elsevier Ltd. All rights reserved.
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