Following the Anatomy of the Proximal Tibia With a Standard Anatomic Technique and the Use of an Asymmetrical Tibial Base Plate can Lead to a Mismatched Internal Components’ Rotation in Mechanically Aligned Total Knee Arthroplasty

Background: Tibiofemoral components rotational congruency affects the total knee arthroplasty (TKA) success. The smart insert sensor (I-S) helps to establish tibial component rotation reciprocally to a fixed femoral rotation. We aimed (1) to validate the use of I-S as a possible tool to reach reproducible recip- rocal femorotibial rotation (RftR) in TKA independently from anatomic landmarks, reducing outliers in combined and mismatched femorotibial rotation (CftR and MMftR, respectively) positioning and (2) to validate the “curve-on-curve” method for a specific type of asymmetrical tibial component. Methods: From February 2018, we conducted a prospective case-control study including 106 patients undergoing TKA. Patients were divided into 2 groups based on the method used to establish tibial component rotation: with the I-S use (group A, n 1⁄4 53) and with the standard “curve-on-curve” tech- nique (group B, n 1⁄4 53). Rotational alignment was calculated using the Berger protocol with post- operative computed tomography scanning. Alignment parameters measured were tibial and femoral component rotations (tR, fR), the CftR, the MMftR, and the RftR. Results: Intraoperative rotation measured by I-S correlated the best with RftR (r 1⁄4 0.84; P < .001) at the post-operative CT scanning. No significant differences were found between groups A and B regarding all types of rotation (fR: P 1⁄4 .774; tR: P 1⁄4 .467; CftR: P 1⁄4 .847) except for MMftR (P 1⁄4 .036) and RftR (P 1⁄4 .023). There were no outliers in group A but 27 and 12 outliers in group B for MMftR and CftR respectively (P < .001; P 1⁄4 .032). Conclusions: The TKA components’ rotation established using a smart I-S intraoperatively is ascribable to the RftR at postoperative computed tomography scan. The I-S helps reduce outliers in the CftR and MMftR. An asymmetrical tibial base plate implanted using the curve-on-curve technique does not create a neutral reciprocal femorotibial rotation significantly increasing the number of cases with mismatched femorotibial internal rotation.