Patient-specific instruments for total knee arthroplasty can accurately predict the component size as used peroperative.

Purpose: Patients-specific instruments (PSI) for implantation of total knee arthroplasty (TKA) can be used to predict the implant size for both the femur and the tibia component. This study aims to determine the impact of approval of the PSI planning for TKA on the frequency of, and reason for intraoperative changes of implant sizes.
Methods: The clinical records of 293 patients operated with MRI- (90.4 %) and CT-based (9.6 %) PSI were reviewed for actual used implant size. Preoperative default planning from the technician and approved planning by the operating surgeon were compared with the intraoperative implanted component size for both the femur and tibia. Intraoperative reason for not following the default sizes was outdated. Furthermore, MRI- and CT-based PSI were compared for these outcomes.
Results: In 93.9 and 91.1 % for, respectively, the femur and tibia (n.s.), the surgeon planned size was implanted during surgery. The predicted size of the femur (p < 0.00) and the tibia (p < 0.00) component planned by a technician differed from the implanted component sizes in 62 (21.2 %) and 51 (17.4 %) patients, respectively. In 17 cases, the femoral component size was adapted intraoperative based on the expert opinion of the operating surgeon. In 26 cases, the tibia component was changed during the surgery because of a mediolateral overhang, sclerotic bone, medial or lateral release, limited extension and/or fixed varus deformity. The results between the MRI- and CT-based PSI did not differ (n.s.).
Conclusions: PSI is a tool to help the surgeon to achieve the best possible results during TKA. The planning made by a technician should always be validated and approved by the operating surgeon who has the ultimate responsibility regarding the operation. With PSI, the operating surgeon is able to minimize intraoperative implant size errors in advance to improve operating room efficiency with possible lowering hospital costs per procedure.
Levels of Evidence: III.