Evaluation of automated radiostereometric image registration in total knee arthroplasty utilizing a synthetic‐based and a CT‐based volumetric model

Radiostereometic analysis (RSA) is an accurate method for rigid body pose (position and orientation) in three‐dimensional space. Traditionally, RSA is based on insertion of periprosthetic tantalum markers and manual implant contour selection which limit clinically application. We propose an automated image registration technique utilizing digitally reconstructed radiographs (DRR) of computed tomography (CT) volumetric bone models (autorsa‐bone) as a substitute for tantalum markers. Furthermore, an automated synthetic volumetric representation of total knee arthroplasty implant models (autorsa‐volume) to improve previous silhouette‐projection methods (autorsa‐surface). As reference, we investigated the accuracy of implanted tantalum markers (marker) or a conventional manually contour‐based method (mbrsa) for the femur and tibia. The data are presented as mean (standard deviation). The autorsa‐bone method displayed similar accuracy of −0.013 (0.075) mm compared to the gold standard method (marker) of −0.013 (0.085). The autorsa‐volume with 0.034 (0.106) mm did not markedly improve the autorsa‐surface with 0.002 (0.129) mm, and none of these reached the mbrsa method of −0.009 (0.094) mm. In conclusion, marker‐free RSA is feasible with similar accuracy as gold standard utilizing DRR and CT obtained volumetric bone models. Furthermore, utilizing synthetic generated volumetric implant models could not improve the silhouette‐based method. However, with a slight loss of accuracy the autorsa methods provide a feasible automated alternative to the semi‐automated method.