Assessment of Bone Implant Contact using Microcomputed Tomography

2015-10-25T00:00:00Z (GMT) by Rachna N. Parwani
Osseointegration also known as Bone Implant Contact (BIC) is an important indicator of overall implant fixation. It is defined as the amount of bone that directly contacts an implant. Backscatter Scanning Electron Microscopy (bSEM) is the current gold standard for BIC measurement. However, this is a destructive test which prohibits further mechanical testing. Microcomputed Tomography (µCT) is used for 3D, non-destructive visualization of the bone-implant interface. However, measurement of BIC using µCT has been limited by the presence of metal artifacts and inadequate resolution. The goal of this study was to evaluate a newer very high resolution µCT scanner as a means to measure BIC. Various µCT scan parameters were optimized to minimize the metal artifacts observed. A training set of 6 plastic embedded rat femur slabs, were scanned using µCT with 3 hours, 2 hours and 1 hour µCT scan duration and then imaged using bSEM. The µCT and bSEM images were evaluated for BIC using a line intersect method. Next, 12 slabs were evaluated for independent validation of BIC in the same fashion as the training set. By optimizing the scan parameters, the metal artifact was limited to a region within approximately 6µm of the bone-implant interface. The strength of correlation between µCT and bSEM based BIC values did not differ greatly for the 3 hours (r=0.854, p=0.03), 2 hours (r=0.878, p=0.021) and 1 hour (r=0.839, p=0.037) scans of the training set. The strength of correlation obtained for the µCT and bSEM based BIC values for the validation set was not as strong as the training set(r=0.726, p=0.008) because three specimens which had very thin rims of bone or very small gaps at the bone-implant interface. The nine remaining specimens in the validation set had a much higher correlation between µCT and bSEM based BIC (r=0.909, p=0.001). This study shows that BIC can be estimated with very high resolution µCT which is an improvement from the ability of current high resolution µCT scanners.