The relationship between alignment, function and loading in total knee replacement: In-vivo analysis of a unique patient population

David Williams,Andrew Metcalfe,June Madete,Gemma Whatling,Peter Kempshall,Mark Forster,Kathleen Lyons,Cathy Holt

doi:10.1016/j.jbiomech.2020.110042

Abstract

The purpose of this study was to quantify the effect of total knee replacement (TKR) alignment on in-vivo knee function and loading in a unique patient cohort who have been identified as having a high rate of component mal-alignment. Post-TKR (82.4 ± 6.7 months), gait analysis was performed on 25 patients (27 knees), to calculate knee kinematics and kinetics. For a step activity, video fluoroscopic analysis quantified in-vivo implant kinematics. Frontal plane lower-limb alignment was defined by the Hip-Knee-Ankle angle (HKA) measured on long leg static X-rays. Transverse plane component rotation was calculated from computed tomography scans. Sagittal plane alignment was defined by measuring the flexion angle of the femoral component and the posterior tibial slope angle (PTSA). For gait analysis, a more varus HKA correlated with increased peak and dynamic joint kinetics, predicting 47.6% of Knee Adduction Angular Impulse variance. For the step activity, during step-up and single leg loaded, higher PTSA correlated with a posterior shift in medial compartment Anterior-Posterior (AP) translation. During step-down, higher PTSA correlated with reduced lateral compartment AP translation with a posterior shift in AP translation in both compartments. A more varus HKA correlated with a more posterior medial AP translation and inter-component rotation was related to transverse plan range of motion. This in-vivo study found that frontal plane lower-limb alignment had a significant effect on joint forces during gait but had minimal influence on in-vivo implant kinematics for step activity. PTSA was found to influence in-vivo TKR translations and is therefore an important surgical factor.

Highlights

Total knee replacement (TKR) is a successful operation for treating pain and improving function in end stage osteoarthritis, with 102,177 replacements performed in the United KingdomAbbreviations: TKR, Total knee replacement; TCWSM, Treatment Centre Weston Super Mare; HKA, Hip-Knee-Ankle angle; PTSA, Posterior Tibial Slope Angle; Patient Reported Outcome Measures (PROMS), Patient Reported Outcome Measure; KOS, Knee Outcome Survey; Ground reaction forces (GRF), Ground Reaction Force; KAAI, Knee Adduction Angular Impulse; EKAM, External Knee Adduction Moment; AP, Anterior-Posterior; range of motion (ROM), Range of Motion; PE, Polyethylene.⇑ Corresponding author at: Cardiff School of Engineering, Cardiff University,(excluding Scotland) in 2017 (National Joint Registry, 2018)
This study revealed that for this unique cohort of patients a more varus HKA angle was associated with increased peak and dynamic frontal plane loading during gait, indicated by the peak EKAM and KAAI
PTSA was found to have the greatest influence on implant kinematics during the step-up-step-down activity with HKA being shown to have limited influence on implant kinematics

Summary

Introduction

Total knee replacement (TKR) is a successful operation for treating pain and improving function in end stage osteoarthritis, with 102,177 replacements performed in the United Kingdom⇑ Corresponding author at: Cardiff School of Engineering, Cardiff University,(excluding Scotland) in 2017 (National Joint Registry, 2018). For optimal TKR function (restoration of near normal motion and function), implant components should be correctly aligned either to mechanical frontal plane parameters (Mechanical alignment) or to recreate native knee anatomy (Kinematic alignment) (Bäthis et al, 2004; Sikorski, 2008). It is currently unclear which is optimum.

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