Summary

This study retrospectively analyzed 180 knees that underwent bicruciate stabilized total knee arthroplasty (BCS TKA) to assess the relationship between lateral joint laxity at 90° flexion and postoperative patient satisfaction, finding that lateral joint laxity of less than 3mm may result in decreased satisfaction.

Abstract

Introduction

Bicruciate stabilized total knee arthroplasty (BCS TKA) features a distinctive implant design aimed at reproducing normal knee kinematics. Previous reports have demonstrated favorable outcomes for BCS TKA compared to other implants. We have previously shown that medial stability and lateral laxity during flexion in BCS TKA can influence patient-reported outcomes. However, few studies have explored the optimal degree of lateral laxity in BCS TKA.

Purpose

The purpose of this study is to examine the appropriate level of lateral laxity in BCS TKA to improve patient satisfaction.

Methods

This study was a retrospective review of data obtained from patients who underwent BCS TKA between April 2018 and April 2023 at our institution. A total of 180 knees (patients) were analyzed, with a mean age of 75.2 ± 7.6 years; 29 men and 151 women were included. One year postoperatively, patient satisfaction was evaluated using a five-point scale (very satisfied, satisfied, neutral, dissatisfied, very dissatisfied) and a visual analog scale (VAS), with scores ranging from 0 (very dissatisfied) to 100 (very satisfied). Intraoperative lateral laxity was measured using a tensor with a 60N distraction force for the medial and lateral compartments. "Lateral joint laxity" was defined as the component gap minus the thickness of the selected polyethylene insert. Patients were divided into two groups based on satisfaction, and a comparative analysis was performed. Receiver operating characteristic (ROC) curve analysis was performed to determine the optimal cut-off value for lateral joint laxity at 90° flexion, which best distinguished between satisfied and dissatisfied patients.

Results

The dissatisfied group had significantly smaller lateral joint laxity at 90° flexion compared to the satisfied group (1.8±2.7mm vs. 4.1±2.6mm, p<0.01). A positive correlation between lateral joint laxity at 90° flexion and patient satisfaction (VAS) was observed (r=0.230, p<0.01). ROC curve analysis yielded an area under the curve of 0.72. The optimal cut-off value for lateral joint laxity at 90° flexion was identified as 3mm.

Conclusion

In BCS TKA, lateral laxity at 90° flexion is associated with postoperative patient satisfaction. Lateral joint laxity of less than 3mm at flexion may result in decreased patient satisfaction, highlighting the importance of maintaining sufficient lateral laxity.