Summary

Medial laxity in extension and flexion can lead to inferior postoperative clinical outcomes and functions.

Abstract

Introduction

Proper ligament balance is critical to the success of total knee arthroplasty (TKA). Previous studies have reported the impact of ligament balance on clinical outcomes, but most of these studies have involved relatively small numbers of patients. The purpose of this study was to determine whether intraoperative gap balance influences clinical outcomes in a multi-center study.

Methods

A prospective multi-center study was conducted to collect data on patients undergoing TKA for knee osteoarthritis with a single posterior-stabilized implant. The present study included 656 knees (134 male, 522 female) in 11 centers. Varus-valgus gap angle and joint gap in extension and flexion were measured using a tensor device with 176 N. The varus angle was denoted as positive. The medial and lateral gaps were calculated based on the center gap and the varus-valgus angle. Medial and lateral joint laxity was determined by subtracting the polyethylene thickness from the joint gap. The correlations were evaluated between joint gap angle and clinical score, and between medial and lateral joint laxity and clinical outcomes at one year and two years using Knee Society score (KSS) and the new Knee Society score (KSS 2011).

Results

The average gap angle was 1.5° varus (standard deviation [SD] = 3.1°) in extension and 1.0° varus (SD = 4.3°). The average medial and lateral laxity in extension was -1.4 (SD = 2.7) mm and -0.6 (SD = 3.2) mm, respectively. The corresponding values in flexion was 2.4 (SD = 3.9) mm and 3.0 (SD = 3.9) mm, respectively.
The varus gap angle in flexion was positively correlated with KSS knee score (r = 0.107, p = 0.027), KSS function score (r = 0.140, p = 0.004), KSS 2011 symptoms (r = 0.132, p = 0.006), and KSS 2011 functional activities (r = 0.105, p = 0.030) at two years.
Medial laxity in extension had negative correlation with KSS function score (r = -0.097, p = 0.045), KSS 2011 symptoms (r = -0.130, p = 0.007), and KSS 2011 functional activities (r = -0.118, p = 0.015) at two years. Medial laxity in flexion had negative correlation with KSS 2011 symptoms at one year (r = -0.112, p = 0.016). Lateral gaps did not show a statistically significant correlation with clinical outcomes.

Conclusion

Better clinical outcomes are obtained with varus gap balance than with equal medial and lateral gaps. Medial laxity in extension and flexion can lead to inferior postoperative clinical outcomes and functions. Medial stability is important to improve knee function and symptoms after TKA. Lateral-opening joint gap balance is acceptable and does not jeopardize clinical outcomes.