Improving Function of Orthopedic Medical Devices

Abstract: 

Improving Function of Orthopedic Medical Devices

The purpose of this research is to investigate factors leading to the loss of sacral-side implant fixation during sacroiliac joint (SIJ) fusions for low back pain, and to develop a set of guidance criteria to aid the surgeon in obtaining optimal implant choice and placements. Recently available surgical treatment options consisting of press-fit triangular titanium implants have been specifically designed to reduce pain by minimizing SIJ motion. Although their effectiveness in improving patient quality of life has been well-established, loss of implant fixation in the sacrum remains problematic and is a major cause of failed treatment. This study will evaluate multiple implant placement parameters including depth, angular orientation (divergence), and spatial distribution to elucidate which factors contribute most to construct fixation strength.

This project will evaluate implant spacing, orientation and length both computationally and with experimental validation. Computationally, the finite element (FE) method (with Abaqus) is used to develop and implement a model of the instrumented sacroiliac joint with static torsional and shear loading, for the parametric analysis of implant parameters. Experimentally, the validation will utilize a Sawbones foam model for cyclic testing in both torsion (simulating the physiologic motions of nutation/counternutation) and vertical shear to simulate the early post-operative time when sacral loosening is most likely to occur. In addition, micro CT scanning after cyclic testing will be used to provide a quantitative measure of the degree of loosening at the implant/bone/foam interface. The FE model will be validated by the Sawbones model tests and CT scans. 

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