Accuracy of the CT-Implant Movement Analysis. A Feasibility Study.

Abstract Background: Radiostereometric analysis (RSA) is a high precision in vivo measuring method and regarded as the gold standard for motion analysis. RSA has been around for over 40 years and its accuracy is properly evaluated. The CT technics have evolved and now low dose CT scans can reproduce 3-D models of bone and joints. The Sectra Implant Movement analysis (IMA) is a new method using a low dose CT for high accuracy measurement. There is no study evaluating the precision and accuracy of the new CT based method.The investigator want to compare the accuracy of the two methods.

Method/design: The RSA method will be tested in patients that already have tantalum markers inserted around the SI joints from earlier studies conducted at Ullevål University Hospital. There are 2-6 patients in the age of 40-50 years available for RSA analysis with and without provocation of the SI joints. Some are fused in one SI joint after insertion of the tantalum markers, but the contralateral joint can then be used for the analysis. At the same time,the investigator will perform low dose CT with and without provocation of the SI joints. The results of the analysis will be compared.

Discussion: The conventional RSA is an invasive method using tantalum markers inserted in to bone. If the CT method has the same accuracy, then the tantalum markers will become obsolete and future studies can easily be performed using non-invasive low dose CT scans.

Keywords: RSA, CT method, low dose CT, IS joint, movement

Introduction: