Summary

The presence of a Varus thrust, which is a biomechanical marker characterized by a sudden lateral shift of the knee during walking, pre- and post- total knee arthroplasty, may influence clinical outcome measures after surgery.

Abstract

Introduction

The Varus thrust, a biomechanical marker characterized by a sudden lateral shift of the knee during the loading phase of gait, has been largely studied in knee osteoarthritis patients. This dynamic marker is associated with faster disease onset and progression, poorer functional scores, and greater pain levels. While the varus thrust is of great interest in conservative management, little is known about its impact in total knee arthroplasty (TKA). Thus, the aim of this study was to assess if a varus thrust pre- and/or post-surgery influences clinical outcome measures post-TKA.

Methods

This was a secondary data analysis from a TKA prospective study on nineteen patients (63.2% of women, mean age of 61 years). Varus thrust was objectively quantified during gait before and 1-year after surgery with a knee kinesiography exam (KneeKG® system, Emovi inc.). Knee Injury and Osteoarthritis Outcome Score (KOOS) was completed 1-year post-surgery. Scores on this questionnaire range from 0 (extreme symptoms) to 100 (no symptoms). T-tests for independent samples were performed between patients who present with a varus thrust post-surgery (i.e., >2.5°) and those who did not, on all five KOOS subscales. Additionally, comparisons on the KOOS were performed between patients who corrected their varus thrust with the surgery (i.e., varus thrust pre-surgery >2.5° and varus thrust post-surgery <2.5°) and those who developed one after surgery (i.e., varus thrust pre- <2.5° and varus thrust post- >2.5°).

Results

Five (26.3%) patients presented with a varus thrust post-TKA. They reported significantly (i.e., statistically and clinically) poorer KOOS scores on pain, function during daily living activities (ADL), sport-recreation, and quality of life (QOL) subscales compared to those who did not present a varus thrust post-TKA (respectively 53.0 vs 74.9, 59.0 vs 77.4, 16.0 vs 46.1, 37.6 vs 68.9; all p<0.05). Four patients (21.1%) had their pre-surgery varus thrust corrected with TKA while four others developed a varus thrust after surgery. Patients with varus thrust correction showed significantly (i.e., statistically and clinically) better KOOS scores post-TKA in terms of pain (80.0 vs 50.3), ADL (81.3 vs 56.5), and QOL (65.6 vs 31.3) compared to patients who developed a varus thrust (all p<0.05).

Conclusions

The presence of a varus thrust post-TKA is characterized with poorer patient reported outcome measures. Furthermore, the evolution of this biomechanical marker with the surgery (i.e., correction or development) may influence pain, function, and quality of life one year after TKA. Results support the need to objectively assess the varus thrust pre-surgery and integrate this measure in surgical planning to achieve better clinical outcomes. Furthermore, assessing varus thrust post-TKA is clinically valuable since it can be corrected through rehabilitation programs including targeted conservative interventions.