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.
- Phase I will evaluate implant spacing, orientation and length both computationally and with experimental validation. Computationally, the Finite Element method (with Abaqus) will be 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.
- Phase II will repeat Sawbones testing with the use of a bone void filler to provide additional stability on the best and worst case implant configurations identified during Phase I.
- Phase III of the study will utilize the left and right SIJs of cadaveric specimens to perform cyclic testing on the best and worst case constructs identified during Sawbones testing in Phase I. The placement of implants in the cadaveric specimens will be performed using the O-arm, an intraoperative CT scanner with navigation capabilities. The O-arm is is frequently used interoperatively at this institution to ensure accurate implant positioning.
The specific aims of this project will be evaluated using the outcome measures of construct stiffness, implant pullout strength, and implant loosening by way of volumetric gap measurement from micro CT scanning and visualization of loosening using X-ray.