Accuracy of the CT-Implant Movement Analysis. A Feasibility Study.
Phase: NA
Conditions: Sacroiliac Instability
Sponsor: University of Bergen

 
Sponsor 
Bergen University 
 
Movement analysis of the sacroiliac joint part of the  
Indication and treatment of adult spinal deformity 
The INTRAKS-study 
 
 
 
 
 
 
09.12.2020 

Movement of the Sacroiliac (SI) Joint, comparing conventional RSA 
with the Sectra Implant Movement analysis using a low dose CT for 
high accuracy measurement 
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. We 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 
two 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, we 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: 
Because of the high accuracy and precision, radiostereometric analysis (RSA), has become a well- 
established method for three-dimensional (3-D) measurements of micro motion in joints [1-6]. The 
implantation of tantalum markers is invasive, but no reports of patient injuries are reported. The 
markers might be inserted through the approach used during a surgical intervention or in an extra 
stab incisions in the skin to get the markers to the necessary position in the bony structures. The 
placements of the markers are of outmost importance to achieve good quality measurements. At 
least three no collinear markers in each segment and a good distance and distribution in all three 
axes (X, Z, Y) is essential for a good 3-D configuration.  
The CT techniques have evolved and now low dose CT scans can reproduce 3-D models of bone and 
joints. The Sectra Implant movement analysis (IMA) [7-10] is a non-invasive method using a low dose 
CT scan. No tantalum markers are needed and joint provocation can easily be conducted in the CT. 
The CT scan is then sent to the Sectra AB for analysis. 
Method: 
Patients and methods:  
The RSA method will be tested in patients that already have tantalum markers inserted around the SI 
joints from earlier studies [11, 12], approximately five years ago, conducted at Ullevål University 
Hospital. These are patients with long lasting severe sacroiliac joint pain. There are two patients in 

the age of 40-50 years available for RSA analysis with and without provocation of the SI joints, at the 
same time we will perform low dose CT with and without provocation of the SI joints. For the non-
provocation, the patient will be in a supine-position. The provocation x-ray/low dose CT will be 
performed; 1: anterior straight legraise 2: One side figure of four position, both with 1kg of load. 
Some are fused in one SI joint after insertion of the tantalum markers, but the contralateral joint can 
then be used for the analysis. We will also measure eventual movement in the fused joint and the 
symphysis (if tantalum markers present). The Center for Implant and Radiostereometric Research 
Oslo has extensive experience with RSA and established state of the art measuring method of 
movement in the SI joint. They will perform the RSA measurements. The CT scan is send to the Sectra 
AB for analysis. 
Statistical analysis: 
Null hypothesis (H0): There is no difference in the accuracy  
Alternate Hypothesis (H1): There is a difference in the accuracy 
Continuous variables will be described with mean and standard deviation\, and the normality of the 
data will be checked using the histograms, QQ-plots and the Kolmogorov-Smirnov-Test of normality. 
The differences of motion will also be tested for normality. The paired sample T-test will be used to 
detect possible significance in the difference between the two groups. Non-parametric tests are used 
if the assumption of normality does not hold. All analysis will be conducted using commercially 
available software (SPSS version 24, IBM Inc.) and the level of significance is set to p<0.05 in a two-
sided test.