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.

Development, construction, and validation of a thinner uniplanar calibration cage for radiostereometry

Radiostereometric analysis (RSA) is an accurate and precise radiographic method that can be used to measure micromotion of implants and study joint kinematics in vivo. A calibration cage with radiopaque markers is used to calibrate the RSA images; however, the thickness (250 mm) of the calibration cage restricts the available area for the patient and equipment during RSA recordings. A thinner calibration cage would increase the recording area, facilitate handling of the cage, and ease integration of the cage with the RSA system. We developed a thinner calibration cage without compromise of accuracy and precision. First, we performed numerical simulations of an RSA system, and showed that the calibration cage thickness could be decreased to 140 mm maintaining accuracy and precision using 40 fiducial and 30 control markers. Second, we constructed a new calibration cage (NRT cage) according to the simulation results. Third, we validated the new calibration cage against two state-of-the-art calibration cages (Umeaa cage and Leiden cage) in a phantom study. All cages performed similar for marker-based analysis, except for y-rotation, where the Umeaa cage (SD = 0.064 mm) was less precise compared to the NRT (SD = 0.038 mm) and Leiden cages (0.042 mm) (p = .01). For model-based analysis the NRT cage had superior precision for translations (SD ≤ 0.054 mm) over the Leiden cage (SD ≤ 0.118 mm) and Umeaa cage (SD ≤ 0.093 mm) (p < .01). The combined study confirmed that the new and thinner calibration cage maintained accuracy and precision at the level of existing thicker calibration cages.

Ten-year comparison of two different techniques for femoral bone cavity preparation-broaching versus compaction in patients with cementless total hip arthroplasty : a randomized radiostereometric study of 30 total hip arthroplasties in 15 patients operated bilaterally

Aims

Femoral bone preparation using compaction technique has been shown to preserve bone and improve implant fixation in animal models. No long-term clinical outcomes are available. There are no significant long-term differences between compaction and broaching techniques for primary total hip arthroplasty (THA) in terms of migration, clinical, and radiological outcomes.

Methods

A total of 28 patients received one-stage bilateral primary THA with cementless femoral stems (56 hips). They were randomized to compaction on one femur and broaching on the contralateral femur. Overall, 13 patients were lost to the ten-year follow-up leaving 30 hips to be evaluated in terms of stem migration (using radiostereometry), radiological changes, Harris Hip Score, Oxford Hip Score, and complications.

Results

Over a mean follow-up period of 10.6 years, the mean stem subsidence was similar between groups, with a mean of -1.20 mm (95% confidence interval (CI) -2.28 to -0.12) in the broaching group and a mean of -0.73 mm (95% CI -1.65 to 0.20) in the compaction group (p = 0.07). The long-term migration patterns of all stems were similar. The clinical and radiological outcomes were similar between groups. There were two intraoperative fractures in the compaction group that were fixed with cable wire and healed without complications. No stems were revised.

Conclusion

Similar stem subsidence and radiological and clinical outcomes were identified after the use of compaction and broaching techniques of the femur at long-term follow-up. Only the compaction group had intraoperative periprosthetic femur fractures, but there were no long-term consequences of these.

Cite this article: Bone Jt Open 2021;2(12):1035–1042.