Aspects of glenoid component wear and disassembly in the Nottingham Total Shoulder Arthroplasty

Gyorgy, Kocsis (2019) Aspects of glenoid component wear and disassembly in the Nottingham Total Shoulder Arthroplasty. PhD thesis, University of Nottingham.

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Abstract

Introduction

Glenoid component wear and loosening is the Achilles heel of total shoulder replacement. Analysis of failed, revised implants may give an insight into the causes of component failure.

The Nottingham Total Shoulder Arthroplasty System (NTSA) is an anatomical prosthesis design with an UHMWPE bearing captured onto a metal glenoid baseplate. The two most frequent modes of failure were component loosening and polyethylene bearing disassembly from the metal glenoid baseplate.

Component loosening is complex; an insight into the mechanisms is provided by a comprehensive literature review. As polyethylene wear plays a central role in the process, volumetric assessment of the NTSA glenoid liner wear rate and scanning electron microscopy were carried out in this study. For 3D scanning of ex vivo implants, the use of coherence scanning interferometry (white light scanner) was proposed, acquiring 3D images without contact, ionising radiation or extensive surface preparation.

A potential mechanism for the UHMWPE bearing disassembly from the metal glenoid baseplate - vacuum forces between the glenoid liner and the artificial humeral head components - is suggested from this work.

Methods

Polyethylene glenoid liner wear analysis

Twenty-four Nottingham total shoulder replacement metal-back glenoid liners were explanted from revision shoulder arthroplasty cases. A Phase Vision Quartz DBE 800 scanner was used to scan the explanted polyethylene liners. The images of worn liners were registered to the reference image. Differences in wear and wear rate were quantified and central and non-central wear groups were distinguished.

A Hitachi S-2600N Variable Pressure Scanning Electron Microscope (VPSEM) was used.

Vacuum phenomenon

New NTSA components were mounted on a materials test machine, surrounded by bovine synovial fluid which was restrained by a commercially available latex condom. Forces were measured continuously as the components were quickly distracted from each other.

The force that may lead to glenoid disassembly was approximated using cyclic testing. The glenoid component of the NTSA system was mounted on the tensile test machine and the polyethylene liner was repeatedly pushed outwards, along an axis perpendicular to the plane of the baseplate, using 40N, 60N, 80N and 300N of force.

Results

Polyethylene glenoid liner wear analysis

The central wear group had a polyethylene wear rate of 115 ± 55mm3/year (mean ± SD). The non-central group showed a wear rate of 112 ± 42 mm3/year (mean ± SD), which was not significantly different from the central wear group (p=0.426) Polyethylene liners with rapid edge wear showed a wear rate of 545 mm3/year. Scanning electron microscopy images showed that the polyethylene was wearing in laminar flakes which indicated fatigue wear.

Vacuum phenomenon

The vacuum tests showed a peak force of 50.4N (SD 3.8) from which an average of 10.2N (SD 0.015) was attributed to the resistance of the artificial capsule; thus, approximately 40N of vacuum force was present.

An SN (stress versus number of cycles) curve for push-out failure load for the plastic liner was prepared and failure at 12500 cycles was predicted for the vacuum forces that we observed in the actual vacuum forces measurements.

Conclusion

The volumetric wear rate was found to be faster than data suggested by previous studies on all polyethylene cemented glenoid components and more than twice as fast as in the case of total hip replacement with the acetabular liner made of the same type of polyethylene. Use of coherence scanning interferometry is proposed for wear analysis.

Vacuum forces may play an important role in glenoid component disassembly in the NTSA system.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Bayston, Roger
McNally, Donal
Wallace, Angus
Keywords: Total shoulder replacement; Shoulder prosthesis; Polyethylene glenoid liner wear analysis; Vacuum forces
Subjects: W Medicine and related subjects (NLM Classification) > WE Muscoskeletal system
Faculties/Schools: UK Campuses > Faculty of Medicine and Health Sciences > School of Medicine
Item ID: 56229
Depositing User: Kocsis, Gyorgy
Date Deposited: 19 Jul 2019 04:40
Last Modified: 07 May 2020 11:46
URI: http://eprints.nottingham.ac.uk/id/eprint/56229

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