Summary

Monitoring the real-time tibial component rotational alignment using Augmented Reality Guidance NextAR with the smart grasses during surgery allowed surgeons to place tibial components more accurately in rotation compared to the conventional navigation system, which may lead to better patient-reported outcomes.

Abstract

Introduction

Computer-assisted surgery (CAS) for total knee arthroplasty (TKA) represents several advancements, such as implant placement and bony resection accuracy. However, achieving accurate rotational alignment of the tibial component remains challenging. We have previously reported that the tibial components of TKA tend to be implanted more internally rotated than the preoperative plan using the 3D planning software, ZedKnee. This observational study aimed to evaluate the accuracy of the tibial component rotational alignment using an Augmented Reality (AR) navigation system with smart glasses, NextAR.

Methods

We retrospectively analyzed the patients who underwent TKA using the NextAR with smart glasses and Medacta GMK Sphere CS implant and took postoperative whole-leg CT. The NextAR group (14 knees) and the conventional group (14 knees) were included. The NextAR group consisted of 4/7 male/female, 77.3 ± 5.7 years, 24.7 ± 3.5 body mass index (BMI). The tibial anatomical AP axis was used as a rotational reference for the NextAR group. Surgeons can see real-time tibial component rotation during surgery through smart glasses. The conventional group consisted of 5/5 males/females, 74.2 ± 5.7 years, 28.7 ± 4.8 BMI, and using Akagi’s line as a rotational reference. We defined the anteroposterior (AP) axis of the tibia as a line perpendicular to the tibial posterior wall axis connecting the medial and lateral sides of the posterior tibia and passing through the center of the proximal tibia. The tibial external/ internal rotation angle of the tibial components was defined as the angle between the tibial AP and implant AP axes. We compared the postoperative tibial tray installation accuracy between the NextAR and conventional groups, evaluating the error of the implanted tibial component rotational angle from the tibial anatomical AP axis.

Results

The NextAR group showed a mean internal rotation of 0.9 ± 1.2°, while the conventional group had an average internal rotation of 5.4 ± 4.6°compared to the preoperative plan, which was statistically significant. (P= .0090*) Furthermore, the NextAR group had an average deviation of 4.7 ± 3.2° internal rotation from the Akagi line. In contrast, the conventional group had 5.4 ± 4.6° (P= .8542), which suggests that the tibial anatomical rotational alignment is comparable to the Akagi line that had been proved as a reliable reference line in the previous literature.

Discussion

This study had some limitations: the retrospective study design, small sample size, and patient outcomes analysis and intra-/ interobserver variations of the measurements have yet to be performed. The tibial anatomy varies significantly among patients, making it difficult to establish a one-size-fits-all approach for rotational alignment. We have previously reported that the tibial components tended to be implanted more internally rotated (6.5 ± 7.4°) than the preoperative plan referring to the Akagi line using the 3D planning software ZedKnee, even with the CT-free navigation system. Mitsuhashi et al. reported that navigation systems, particularly those combining CT-based preoperative planning with intraoperative image-free navigation, significantly improve the rotational alignment of the tibial component in TKA. The current study indicated that the NextAR system may enable more accurate placement of the tibial component in rotation by allowing surgeons to see the rotation angle through smart glasses during the surgery.