Qualifying CT for wrist arthroplasty: extending techniques for total hip arthroplasty to total wrist arthroplasty

摘要

The purpose of this study was to extend previous work to detect migration of total wrist arthroplasty non-invasively, and with greater accuracy. Two human cadaverous arms, each with a cemented total wrist implant, were used in this study. In one of the arms, 1 mm tantalum balls were implanted, six in the carpal bones and five in the radius. Five CT scans of each arm were acquired, changing the position of the arm each time to mimic different positions patients might take on repeated examinations. Registration of CT volume data sets was performed using an extensively validated, 3D semi-automatic volume fusion tool in which co-homologous point pairs (landmarks) are chosen on each volume to be registered. Three sets of ten cases each were obtained by placing landmarks on 1) bone only (using only arm one), 2) tantalum implants only, and 3) bone and tantalum implants (both using only arm two). The accuracy of the match was assessed visually in 2D and 3D, and numerically by calculating the distance difference between the actual position of the transformed landmarks and their ideal position (i.e., the reference landmark positions). All cases were matched visually within one width of cortical bone and numerically within one half CT voxel (0.32 mm, p = 0.05). This method matched only the bone/arm and not the prosthetic component per se, thus making it possible to detect prosthetic movement and wear. This method was clinically used for one patient with pain. Loosening of the carpal prosthetic component was accurately detected and this was confirmed at surgery.