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 reciprocal 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 = 53) and with the standard "curve-on-curve" technique (group B, n = 53). Rotational alignment was calculated using the Berger protocol with postoperative 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 = 0.84; < .001) at the post-operative CT scanning. No significant differences were found between groups A and B regarding all types of rotation (fR:  = .774; tR:  = .467; CftR:  = .847) except for MMftR ( = .036) and RftR ( = .023). There were no outliers in group A but 27 and 12 outliers in group B for MMftR and CftR respectively ( < .001;  = .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.