Summary

Decreased knee adduction moment after unilateral total knee arthroplasty improved patient outcome, but contralateral residual osteoarthritis knee did not due to increased pain with high gait speed.

Abstract

Introduction

The knee adduction moment (KAM) is often focused on total knee arthroplasty (TKA) research for assessing postoperative functional outcome. The impact of the operative knee on contralateral nonoperative osteoarthritis (OA) knee about gait analysis also remain unclear. The aim of this study was to investigate pre- and postoperative changes of gait parameters based on an interactive musculoskeletal modelling software and knee joint pain in patients who underwent unilateral TKA for bilateral knee OA.

Methods

In this prospective study, 10 patients (mean age, 74 years) with bi-lateral varus knee OA were participated, which included Kellgren–Lawrence grade 2 or greater severity by knee radiographs and underwent posterior cruciate-substituting TKA with follow-up for more than 2 years. The gait measurements in bilateral knees preoperatively and 1-year follow-up after TKA were analyzed using the point cluster technique and three force plates. An interactive musculoskeletal modelling software was used for calculating the KAM, knee flexion moment, and tibiofemoral (TF) joint force during each gait phase. The 2011 Knee Society Knee Scoring System (2011 KSS) were also measured pre- and postoperatively.

Results

For operative knee, peak KAM was lower, and TF joint force was higher postoperatively than preoperatively, but all parameters including the nonoperative knees did not have significantly different before and after TKA. However, gait analyses showed that postoperative KAM was significantly lower than preoperative KAM at the 30%, 40%, and 50% phases for the operative knee, and only at the 60% phase for nonoperative knee, all in stance phase. Postoperative gait flexion moment was higher than preoperative moment at 100 % swing phase only in nonoperative knee. Meanwhile, in operative knee, postoperative TF joint force was significantly larger than preoperative force at 10% stance phase and 70% swing phase. Operative knees with postoperative decreased KAM had high 2011 KSS total and functional score improvement, while increased knee flexion moment in gait analysis was correlated with only total score. On the other hand, in nonoperative knees, the only factor that correlated with decreased symptom score was increased postoperative gait speed.

Discussion

Gait analysis particularly showed that postoperative KAM significantly decreased in mid to late stance phase, and postoperative TF joint force increased in heel strike and early swing phases. This suggests that preoperative avoidance gait from knee pain was improved by post-TKA pain relief. As a result, an improvement in 2011 KSS might be achieved. On the other hand, contralateral TKA did not improve postoperative symptom score in the nonoperative knees. This is because postoperative decreased symptoms score was significantly correlated with only increased gait speed due to contralateral TKA; patients with advanced nonoperative knee OA increased gait speed after successful contralateral TKA and might easily feel more knee pain postoperatively than preoperatively. We believe that patients with increased gait speed after contralateral TKA might reasonably be considered for TKA in the nonoperative knees.