# Restricted kinematic alignment total knee arthroplasty using augmented reality technology to maintain limb alignment within targeted boundaries

## TL;DR

A smartphone-based augmented reality system helps surgeons align knee implants more precisely during surgery, leading to better soft-tissue balance.

## Contribution

Integration of AR navigation into restricted kinematic alignment TKA and evaluation of its clinical effectiveness.

## Key findings

- AR-aided restricted kinematic alignment reduced soft-tissue imbalance compared to mechanical alignment.
- Postoperative walking speed was similar between AR-aided and mechanical alignment groups.
- AR system enabled real-time confirmation of limb alignment within safe boundaries.

## Abstract

An augmented reality (AR)-aided navigation system that utilizes a standard smartphone enables accurate alignment of femoral and tibial components in total knee arthroplasty (TKA) and provides real-time intraoperative quantification of joint gaps. This study aimed to integrate the AR-aided navigation system into the surgical technique of restricted kinematic alignment and to evaluate its clinical effectiveness.

We compared 45 restricted kinematic alignment TKAs performed using posterior cruciate ligament (PCL) retaining medial-congruent prosthesis with an AR-aided navigation system and 40 mechanically aligned TKAs performed using PCL resecting posterior-stabilized prosthesis in patients with preoperative varus or neutral lower limb alignment. In the restricted kinematic alignment group, femoral and tibial alignments were determined using calipered and soft tissue–guided techniques, respectively, with the AR-aided navigation system providing real-time confirmation that angular values remained within safe boundaries. The target intraoperative extension gap was a rectangular configuration with equal medial and lateral widths.

Intraoperative measured value of the soft-tissue imbalance with the knee in extension was significantly smaller in the restricted kinematic alignment group than in the mechanical alignment group (1.1 ± 1.1° vs 2.5 ± 2.2°; 95% CI, 0.7 to 2.2°; P < 0.001; Cohen’s d = 0.85). After propensity score matching, no significant differences were observed between the groups in either the timed up-and-go test or the 10-m walk test at 1 week postoperatively (12.6 ± 3.5 s vs 13.2 ± 5.3 s; 95% CI, − 3.0 to 1.7; P = 0.60; and 11.7 ± 2.5 s vs 11.9 ± 3.2 s; 95% CI, − 1.7 to 1.3; P = 0.82, respectively).

Restricted kinematic alignment TKA using PCL retaining medial-congruent prosthesis achieved more balanced intraoperative soft-tissue tension than the mechanical alignment TKA using posterior-stabilized prosthesis. However, early postoperative walking speed did not differ between the two groups.