This study was designed to evaluate the true accuracy of patient specific instrumentation (PSI) for total knee arthroplasty (TKA) using a new 3D measurement method.
Consecutive 21 patients (30 knees) who underwent TKA using computed tomography (CT)-based PSI were retrospectively evaluated. Mean patient age was 69.2 years (62 to 77). The postoperative three-dimensional (3D) CT image were superimposed onto the preoperative 3D CT plan and measured the absolute difference in the prosthetic alignment using six parameters: coronal, sagittal, and axial alignment of the femoral and tibial prostheses. Cases in which the difference in the prosthetic alignment was greater than 3° were considered outliers.
For the femoral prosthesis, mean absolute differences between the preoperative 3D CT plan and postoperative 3D CT image were not significantly different and the rates of outliers were 10.0, 33.3, 23.3% in the coronal, sagittal, and axial planes. For the tibial prosthesis, mean absolute differences were significantly larger in the axial plane than in the coronal and sagittal planes (p < 0.001) and the rates of outliers were 23.3, 36.7, 63.3% in the coronal, sagittal, and axial planes. The rates of outliers for the axial alignment of tibial prosthesis were significantly higher than for the other five planes (p = 0.006).
The rotation of the tibial prosthesis with CT-based PSI was less accurate in the axial plane than in the other five planes.