Summary

The modified gap method in FA for robot-assisted TKA makes it possible to create an extension gap based on patient-specific soft tissue assessment.

Abstract

Introduction

One of the features of the VELYS (DePuy Synthes), a TKA-assisted robot, is the ease of soft tissue evaluation using a balance graph. At our hospital, we use the VELYS to perform the modified gap technique in functional alignment (FA) based on patient-specific soft tissue evaluation.

Purpose

The purpose of this study was to examine the alignment and intraoperative component gap (C-gap) in this operation method.

Materials And Methods

Twenty-four knees (8 males and 16 females) with a mean age of 68 ± 2.3 years were selected from 24 patients who underwent TKA using the VELYS for varus osteoarthritis of the knee at our hospital. The implants were Attune PS type, and soft tissue balance was evaluated using VELYS to create an extension gap, followed by the modified gap method in FA using a tensor. The gap balance was adjusted and measured using a Bicondylar Type Tensor with patella reduction using a tensor by force of 40 pounds, 20 pounds on each of the medial and lateral condyles. The HKA before and after surgery and the medial and lateral C-gap in extension and flexion were examined.

Results

HKA was 8.7±5.1 before surgery and 2.3±1.6 after surgery. C-gap (mean ± standard deviation mm) was 0°: medial 11.2±1.1, lateral 11.6±1.4, 90°: medial 10.5±1.4, lateral 11.1±1.6.

Discussion

The modified gap method in FA for robot-assisted TKA makes it possible to create an extension gap based on patient-specific soft tissue assessment. In the results of this study, the postoperative HKA was 2.3 degrees, suggesting that the tibial osteotomy is varus to balance the soft tissues in extension. The C-gap obtained with this technique did not differ between medial and lateral in extension and flexion, suggesting that a good gap and balance was achieved.