Sensor Assessment of Gap Balance in Mobile-Bearing Unicompartmental Knee Arthroplasty

Summary

Here, we present a protocol to measure the gap contact force and gap balance in mobile-bearing unicompartmental knee arthroplasty (UKA). Along with the clinical and radiographic data, we hope to determine the normal range of the contact force and set up the threshold of the gap balance.

Abstract

The most important procedure of mobile-bearing unicompartmental knee arthroplasty (UKA) is to balance the knee flexion and extension gap. Conventionally, the balance was determined by the subjective assessment of plugging out the feeling gauge. Since it mainly depended on the surgeons' experience, the accuracy was always in doubt. In the past 10 years, pressure sensors have been introduced to guide the gap balance in total knee arthroplasty (TKA). However, the sensor technique was introduced to UKA very recently. Herein is our sensor assessment of the gap balance in 20 cases UKA by one experienced surgeon. The sensor was a custom-designed force sensor matrix according to the shape of the tibial trial of mobile-bearing UKA. The postoperative clinical outcomes and radiographic results were recorded for future comparison. We aim to use this method to assess more than 200 cases of UKA by various surgeons to ultimately standardize the gap-balance result.

Introduction

The mobile-bearing UKA is currently one of the most successful treating methods for anteromedial osteoarthritis (AMOA) of the knee¹. The balance of the flexion and extension gap during the operation is the key to a successful UKA^2,3. The gap overload might aggravate the wear of the mobile bearing. Moreover, the elevated gap contact force might lead to postoperative valgus deformity and degeneration of the lateral compartment⁴. Therefore, achieving an optimal gap tightness as well as an acceptable gap balance in UKA is an important part of the learning curve

Protocol

This study was approved by the human ethics committee of the China-Japan Friendship Hospital (approval number 2020-50-k28).

1. Preparation and sterilization of the force sensor

1. Use abrasion-resistant adhesive tape to fix the force sensor on the upper surface of the tibial trial before sterilization.
2. Pack and sterilize the force sensor using low-temperature sterilization with hydrogen peroxide gas plasma (Figure 1).
   NOTE: The sensor should be fixed on the tibial trial to prevent the effect of the shear force.

2. Procedure of m....

Results

Cohort demographics
The first 20 patients who undertook mobile-bearing UKA were enrolled in the China-Japan Friendship Hospital from March to June 2021. The surgeries were all done by a senior doctor with over 2,000 cases of UKA experience. The demographic along with prothesis data is shown in Table 1. The age ranged from 58-82 years, and the diagnoses were all AMOA.

Results of gap force and balance measurements
The pattern of gap forc.......

Discussion

This study provided a detailed protocol of sensor technology in assessing the joint gap contact force and balance in mobile-bearing UKA. We hope to set up a goal of standard contact force as well as gap-balancing difference, which would allow the orthopedic surgeons to determine the bearing thickness and gap-balancing more easily in the future.

The overload of the joint gap may lead to postoperative valgus deformity of the limb, future degeneration of the lateral compartment, and even OA progr.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Oxford UKA	Zimmer/Biomet		For the catalog numbers refer to Oxford Partial Knee Microplasty Instrumentation (femoral component, tibial component, meniscus bearing)
Teflon Tape	3M		Abrasion resistant adhesive tape widely used in biomechanical experiments
Verasense	OrthoSensor	Verasense	TKA sensor
Excel	Microsoft		digital table software
STERRAD 100S sterilization system	Johnson&Johnson	STERRAD 100S	Low-temperature sterilizing with hydrogen peroxide gas plasma
UKA force sensor	Qingrui Boyuan	in house	Co-designed and produced by Qingrui Boyuan Technology
Computer program for recording raw data	Qingrui Boyuan	in house	Co-designed and produced by Qingrui Boyuan Technology
Protractor	Shanghai M&G Stationery Inc.	any	Sterilized in the sterilization system
USB line	Lenovo		any
Laptop	Lenovo		any basic configuration