High-precision measurements of cementless acetabular components using model-based RSA: an experimental study

Background In RSA, tantalum markers attached to metal-backed acetabular cups are often difficult to detect on stereo radiographs due to the high density of the metal shell. This results in occlusion of the prosthesis markers and may lead to inconclusive migration results. Within the last few years, new software systems have been developed to solve this problem. We compared the precision of 3 RSA systems in migration analysis of the acetabular component.

Material and methods A hemispherical and a nonhemispherical acetabular component were mounted in a phantom. Both acetabular components underwent migration analyses with 3 different RSA systems: conventional RSA using tantalum markers, an RSA system using a hemispherical cup algorithm, and a novel modelbased RSA system.

Results We found narrow confidence intervals, indicating high precision of the conventional marker system and model-based RSA with regard to migration and rotation. The confidence intervals of conventional RSA and model-based RSA were narrower than those of the hemispherical cup algorithm-based system regarding cup migration and rotation.

Interpretation The model-based RSA software combines the precision of the conventional RSA software with the convenience of the hemispherical cup algo-rithm-based system. Based on our findings, we believe that these new tools offer an improvement in the measurement of acetabular component migration.