• Kazumasa Yamamura, Yukihide Minoda, Ryo Sugama, Yoichi Ohta, Suguru Nakamura, Hideki Ueyama, and Hiroaki Nakamura.
• Department of Orthopaedic Surgery, Osaka City University Graduate School of Medicine, 1-4-3 Asahi-machi Abeno-ku, Osaka, 545-8585, Japan.
• Knee Surg Sports Traumatol Arthrosc. 2020 May 1; 28 (5): 1560-1567.

PurposeThe accuracy of patient-specific instrumentation (PSI) in total knee arthroplasty (TKA) is still controversial, especially in the tibial prosthesis. It was hypothesized that the design modification of PSI improved the tibial prosthetic alignment and reduced the associated complications. The aim of this study was to compare the accuracy of a conventional PSI with that of a newly designed PSI for total knee arthroplasty (TKA) using a new three-dimensional (3D) measurement method.MethodsThirty TKAs each using the conventional and newly designed PSIs were studied. The postoperative 3D-computed tomography (3D CT) image was superimposed on the preoperative 3D CT plan. The absolute differences in the tibial prosthetic alignment between the preoperative and postoperative 3D CT images were directly measured in the coronal, sagittal, and axial planes. Knees in which the difference in the prosthetic alignment was > 3° were considered deviations.ResultsThe new PSI showed less mean absolute differences and lower rate of deviations than the conventional PSI in the coronal and axial planes (p = 0.045 and p = 0.004, respectively). The deviations (> 3°) of the tibial prosthesis using the conventional PSI were 27, 30, and 63% and of those using the new PSI were 0, 20, and 20% in the coronal, sagittal, and axial planes, respectively.ConclusionsThis is the first report to evaluate the effect of improvement in PSI design on the postoperative alignment using 3D method, and it clearly showed that the modification significantly improved the accuracy of alignment and reduced the deviations.Level Of EvidenceTherapeutic study, case-control study, Level III.

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