Summary

Postoperative WBLR correlated with the synovial gene expressions of IL1B and IL6. The postoperative alignment needed to predict an improvement in IL6 gene expression was a WBLR of 52%, which is considered the minimum postoperative alignment for biological improvement.

Abstract

High tibial osteotomy (HTO) is widely performed for medial compartment knee osteoarthritis (OA) and can relieve symptoms while preserving the OA joint. Recently, several studies have reported the effect of HTO on the intra-articular environment, suggesting that the biological environment could be improved by HTO. Many clinical and biomechanical studies have been conducted to determine the ideal lower limb alignment with the goal of improving clinical outcomes and survival. However, the relationship between the corrected lower limb alignment achieved by HTO and joint inflammation remains poorly understood. The purposes of this study were to investigate the relationship between pre- and postoperative knee alignment and synovial gene expression, and to identify the cutoff point of postoperative knee alignment where the gene expressions associated with synovial inflammation improve.
A total of 36 OA patients who underwent medial open-wedge HTO (MOWHTO) were included. Synovial tissue was collected from the affected knees during the initial MOWHTO and plate removal surgeries. Gene expressions associated with the pathogenesis of OA in synovial tissue were investigated by real-time polymerase chain reaction. The correlation between the weight-bearing line ratio (WBLR) and synovial gene expressions was determined. A receiver operating characteristic curve (ROC) analysis was used to determine the cutoff values of WBLR for the improvement of gene expression. The subjects were divided into two groups according to the cutoff values of WBLR and were compared for Knee injury and Osteoarthritis Outcome Score (KOOS) and synovial gene expression.
The postoperative WBLR correlated with IL1B (ρ = −0.43, p = 0.008) and IL6 (ρ = −0.41, p = 0.01). The cutoff value to predict the improvement of IL6 was a postoperative WBLR of 52%, with an area under the curve of 0.74 (p = 0.03). Patients with a WBLR <52% showed higher postoperative inflammatory gene expression (IL1B (p = 0.03), IL6 (p = 0.02)) and inferior postoperative KOOS across all scales compared to those with a WBLR >52%.
From a biological point of view, the postoperative WBLR after OWHTO should be greater than 52% to avoid residual intra-articular inflammation and poor clinical outcomes. We recommend aiming for several degrees of varus to 52% as the target alignment for biological improvement, taking into account potential surgical inaccuracies in correction.