CT data used to predict pullout strength of orthopedic screws

The PI of this project was: Paul Anderson, MD

This project was funded by: Department of Orthopedic Surgery

The term of this project was: April 2011 to June 2012

The number of subjects scanned during this project was: 10

In this study we will be using CT derived data to calculate Bone Mineral Density (BMD) at focal areas of interest (screw paths) and comparing this to the pullout strength of the screws. We will be testing the pullout strength of standard orthopedic screws and spine pedicle screws in both human and animal bone. We will be performing CT scans of these same bone samples before and after screw placement to evaluate the exact screw path. Pullout testing will then be performed on theses samples to find the actual pullout strength. From the CT scans we will be able to determine the Hounsfield Units in the exact path of the screw. Hounsfield units will then be converted into Bone Mineral Density using new computer software and known mathematical techniques. The Bone Mineral Density for a specified screw path will then be compared to pullout strength. The young bovine and sheep spines are very homogenous bone samples and very affordable and available. These will be used initially to set up a valid model for human cadaveric bone samples, which are more heterogeneous and less available. The animal samples will also be used to study the isotropic and anisotropic properties of screw pullout strength, which mainly involves studying the different outcomes when screws are placed at different angles into bony samples. A biostatistician will be consulted to define the appropriate number of samples necessary to make a significant conclusion.