Validation of the in vivo volumetric wear measurement for total knee prostheses in model-based RSA

Abstract

Implant failure related to polyethylene wear remains an important issue in total knee arthroplasty. Polyethylene wear is usually assessed in vivo by measuring the remaining insert thickness on X-ray images of the knee. To reflect the amount of wear debris more accurately, a 3-dimensional overlap measurement has been suggested, which is based on implant component models which are matched on calibrated stereo X-ray images using model-based roentgen stereophotogrammatic analysis. The goal of this study was to determine the influence of pose estimation, insert thickness deviation and variation in the femoral-tibial contact location on the accuracy and precision of the measurement using simulations and a phantom experiment. We found that the pose estimation was the largest source of variation. The 95% prediction interval varied between 111 and 283 mm(3), which is approximately 100-200% of the detected volumetric wear. Insert thickness variation resulted in prediction intervals of 74-174 mm(3). Variation of the femoral-tibial contact location in the phantom experiment gave a prediction interval of 40 mm(3). Large differences in the detected wear volume were found for different flexion angles. At most 56% of the true wear volume was detected (129 of 230 mm(3), 30° of flexion). In summary, both the accuracy and precision of the volumetric wear measurement were low. The prediction interval of the volumetric wear measurement is at least as large as the measurement outcome itself. This is an important limitation to the applicability of the volumetric wear measurement in clinical practice and further clinical validation is required.

Radiostereometric Analysis Permits In Vivo Measurement of Very Small Levels of Wear in TKA

“…RSA has a reported accuracy for linear wear measurements in the range of 0.1 to 0.2 mm [31,47]. Phantom studies have suggested volumetric measurements are likely to be over-or underestimates of wear volume such that volumetric measurements are not as reliable as linear measurements of TKA wear with RSA [41,44]. Wear measurements can be taken at a single time point or serially in a prospective manner.…”

“…For modern, more wear-resistant TKAs, more advanced methodologies for measuring TKA wear have been developed as research tools utilizing radiostereometric analysis (RSA) and single-plane fluoroscopy [13,17,31,41,[44][45][46][47].…”

“…It has been noted that standing examinations are preferred over supine examinations, because joint laxity in the supine position can change the location of contact [45]. Examinations should be acquired at multiple knee flexion angles to enable the femoral component to drop into different wear pools as the location of contact changes throughout flexion [13,41,44]. RSA has a reported accuracy for linear wear measurements in the range of 0.1 to 0.2 mm [31,47].…”

Validation of In Vivo Linear and Volumetric Wear Measurement for Reverse Total Shoulder Arthroplasty Using Model‐Based Radiostereometric Analysis

“…In 2013, van IJsseldijk et al expanded their measurements to volumetric wear, recording measured wear at varying knee flexion angles and observing that large differences in wear were observed at these different angles, and at most, 56% of the true volume was measured, resulting in poor accuracy and precision . The observations and limitations presented by this study in volumetric wear measurement led to our method of recording wear at different arm positions and taking the unique sum of intersecting overlap voxels.…”

CORR Insights®: Radiostereometric Analysis Permits In Vivo Measurement of Very Small Levels of Wear in TKA

“…While volumetric wear measurements have been made using microcomputed tomography (Fig. 1), it remains to be seen if the resolution of clinical radiographs combined with implant manufacturing tolerances and the measurement uncertainties associated with contemporary wear analysis techniques will allow accurate volumetric wear assessments [12]. As a consequence, robust validation of volumetric wear accuracy would be essential since linear measurement uncertainties on the order of 0.1 to 0.2 mm could contribute to volumetric uncertainties of 10 to 20 cubic millimeters for each square centimeter of contact area.…”