Effect of Cup Inclination and Anteversion on the Risk of Impingement and Edge Contact in Total Hip Replacement: Geometrical and Finite Element Modelling

Lin Wang^1-2, Gregory Pryce², Mazen Al Hajjar^1-2, Sophie Williams², Jonathan Thompson^1-2

¹DePuy Synthes Joint Reconstruction, Leeds, United Kingdom

²Institute of Medical and Biological Engineering, School of Mechanical Engineering, University of Leeds, Leeds, United Kingdom

Keywords: acetabular cup positioning, impingement, edge contact, PINNACLE^®, computational simulation.

INTRODUCTION

Surgical positioning plays a key role in the function and durability of an artificial hip joint. Preclinical numerical investigations have been conducted to evaluate the effects of various acetabular cup inclination and anteversion angles on the risk of impingement [1]and edge contact[2], which could lead to implant dislocation and accelerated wear.

METHOD

A rigid geometrical model[1] that can predict occurrence and location of impingement was developed in SOLIDWORKDS (Dassault Systèmes, France), consisting of the right hemi-pelvis and femur bone geometry, PINNACLE^® Shell with MARATHON^®Neutral Liner (36x56mm), CORAIL^® Stem (size 12) and 36mm diameter head (DePuy Synthes, UK). 3D kinematic motions of seven daily living activities, which are prone to posterior and anterior dislocation, were simulated for various cup inclination (30º to 70º) and anteversion (0º to 50º), with an increment of 5º. By contrast, to investigate edge contact condition, elastic-plastic Finite Element Analysis (FEA) [2], which simulates metal-on-polyethylene wear under ISO 14242-1 gait cycle, have been developed in Ansys v18.2 (ANSYS, Inc. PA USA). In total, nine FEA runs were generated by incorporating response surface method, with three levels of inclination (35º, 45º, 55º) and anteversion (0º, 15º, 30º).

RESULT

For the specific activities and bony geometry studied, the geometrical modelling identified an implant impingement-free zone, i.e. inclination (50º to 70º) and anteversion (15º to 25º). Moreover, the higher inclination is, the lower anteversion is required to avoid impingement. However, according to the FEA, increased volumetric wear, contact pressure, wear depth and stress were associated with a combination of steep cup inclination (55º) and anteversion (30º), resulting from the edge contact, where a decreased contact area that intersects with cup rim.

CONLUSION

Optimisation of impingement and edge contact have different requirements for cup positioning, hence requiring evaluating combined risk in surgical planning.

REFERENCE

1. Pryce, G., et al. Development of a Geometric Model of THR to Assess Occurrence and Location of Impingement. in Orthopaedic Research Society Annual Meeting. 2018. New Orleans, USA.

2. Wang, L., D. Beedall, and J. Thompson, Effect Of Cup Positioning On Wear Of Metal-On-Polyethylene Total Hip Arthroplasty: A Finite Element Analysis. Orthopaedic Proceedings, 2019. 101-B(SUPP_5): p. 27-27.

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