Precision and accuracy measurement of radiostereometric analysis applied to movement of the sacroiliac joint

Abstract

Background: Different techniques have been used to quantify the movement of sacroiliac (SI) joints. These include radiostereometric analysis (RSA), but the accuracy and precision of this method have not been properly evaluated and it is unclear how many markers are required and where they should be placed to achieve proper accuracy and precision.

Purpose: The purpose of this study was to test accuracy and precision of RSA, applied to the SI joint, in a phantom model and in patients.

Methods: We used a plastic phantom attached to a micrometer to obtain a true value of the movement of the SI joint and compared this value with the measured value obtained by RSA; the difference represented the accuracy. The precision of the system was measured by double examination in the phantom and in six patients, and was expressed by a limit of significance (LOS). We analyzed different marker distributions to find optimal marker placement and number of markers needed.

Results: The accuracy was high and we identified no systematic errors. The precision of the phantom was high with a LOS less than 0.25° and 0.16 mm for all directions, and in patients, the precision was less than 0.71° for rotations and 0.47 mm translations. No markers were needed in the pubic symphysis to obtain good precision.

Conclusions: The accuracy and precision are high when RSA is used to measure movement in the SI joint and support the use of RSA in research of SI joint motion.

Figures

Fig. 1A–C

The setup of the pelvic phantom with the sacrum attached to a translation stage and a rotation rod are shown for (A) Y rotation and all translations, (B) X rotations, and (C) Z rotations.

Fig. 2

The RSA markers were divided into different marker segments (MS): MS A = five dorsal markers in the ilium; MS B = three frontal markers in the inferior pubic ramus; MS C = six sacral markers; and MS D = two cranial markers in the sacrum. Circles = three randomly selected markers in the ilium and three randomly selected markers in the sacrum.

Fig. 3

A graph shows the accuracy in setups with different marker distributions. The accuracy is presented as the mean difference between the true value and the measurement obtained by RSA. Trans = translation (mm); Rot = rotation (°).