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Orthopaedic Proceedings
Vol. 99-B, Issue SUPP_5 | Pages 77 - 77
1 Mar 2017
Parkes M Sayer K Goldhofer M Cann P Walter W Jeffers J
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Introduction

The continued improvement of ceramic materials for total hip arthroplasty led to the development of Zirconia and Zirconia toughened Alumina materials such as BIOLOX® delta. Zirconia exists in a tetragonal phase in new ceramic heads and can transform to a monoclinic phase in response to loading giving the material improved fracture toughness. It is known that surface transformation occurs in this material under hydrothermal conditions (i.e. in vivo condition), and ISO standards recommend parts are artificially aged prior to testing to include any effect of surface transformation on new designs. Accelerated aging procedures have been used to predict the amount of phase transformation that will occur in vivo, but validation of these models requires the study of retrieved hip joints. Here 26 BIOLOX® delta retrievals are analysed to determine the degree of phase transformation that occurs in vivo. The levels of phase transformation measured are compared with those predicted based on accelerated aging tests.

Methods

Twenty-six retrieved BIOLOX® delta (CeramTec AG, Germany) femoral heads were investigated. Retrievals were obtained after implantation of between 1 month and 7 years with an average follow-up of 1.5 years. All retrievals were from ceramic-on-ceramic hip joints that were implanted between 2004 and 2012. Mean patient age was 69 years (range 48–87 years).

Raman spectra were collected using a confocal Raman spectrometer (WITec Gmbh, Germany) a laser wavelength of 532nm, a 50× objective and a 100μm pinhole. Twenty-five measurements were made on each retrieval at random locations outside any visible wear scars and inside visible wear scars. The average monoclinic content was calculated based on the method of Clarke and Adar [1]. For comparison 5 new BIOLOX® delta femoral head resurfacings were measured using the same procedure.


Orthopaedic Proceedings
Vol. 94-B, Issue SUPP_XVIII | Pages 14 - 14
1 May 2012
Accardi M Dini D Lim N Yamamoto K Cann P
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INTRODUCTION

Osteoarthritis (OA) can be artificially simulated ex vivo on healthy articular cartilage (AC) samples by use of proteolytic enzymes. In this article we will present preliminary analyses of the physical degradation of AC when subjected to alternating mechanical stresses. Since AC damage due to OA is believed to be mechanically induced, the first step towards the realisation of an improved understanding of degenerative behaviour of AC under physiological loading conditions is to perform ex vivo tests which mimic such conditions at best.

METHODS

Porcine AC was subjected to biochemical stimulation or left as native AC. Biochemical degradation was performed using combinations of trypsin and Matrix Metalloproteinases (MMPs) to induce the loss of proteoglycan and collagen. A comparison of the biochemical and mechanical properties, topography and difference in response to mechanical damage between the digested AC and healthy AC was made using White Light Interferometry (WLI), Atomic Force Microscopy (AFM) and mechanical testing. The mechanical damage was induced by subjecting AC to shear under physiological and non physiological conditions. The AC was mechanically tested in a Phosphate Buffered Saline (PBS) bath. After mechanical testing, biochemical analysis of the collagen and aggrecan content of the tissue and PBS present in the bath during the mechanical test was performed. Collagen content was determined by measurement of the amount of hydroxyproline (HPRO), and aggrecan content by the amount of glycosaminoglycans (GAG). The mechanical test was either performed on healthy (native) AC or on AC which had first been digested.


Orthopaedic Proceedings
Vol. 94-B, Issue SUPP_XVIII | Pages 65 - 65
1 May 2012
Hart A Lloyd G Sabah S Sampson B Underwood R Cann P Henckel J Cobb PJ Lewis A Porter M Muirhead-Allwood S Skinner J
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SUMMARY

We report a prospective study of clinical data collected pre, intra and post operation to remove both cup and head components of 118 failed, current generation metal on metal (MOM) hips. Whilst component position was important, the majority were unexplained failures and of these the majority (63%) had cup inclination angles of less than 55 degrees. Poor biocompatibility of the wear debris may explain many of the failures.

BACKGROUND

Morlock et al reported a retrospective analysis of 267 MOM hips but only 34 head and cup couples (ie most were femoral neck fractures) and without data necessary to define cause of failure. The commonest cause of failure in the National Joint Registry (NJR) is unexplained.


Orthopaedic Proceedings
Vol. 93-B, Issue SUPP_IV | Pages 547 - 548
1 Nov 2011
Underwood R Cann P Ilo K Wagner C Skinner J Cobb J Porter M Muirhead-Allwood S Hart A
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Introduction: The London Implant Retrieval Centre (LIRC) was founded to investigate the high incidence of unexplained failures of Metal-on-Metal (MoM) hips. A multidisciplinary team analyse the failed hips, investigations include CT and MRI scans, blood and synovial fluid tests, wear measurements, X-rays and clinical data from the explanting surgeons.

Wear measurements of 100 explanted hips have been carried out on a Taylor Hobson 365 Roundness Machine using the LIRC Wear Protocol. It was found that 50% of explanted cups were wearing less than 5 μm/year and 60% of components were wearing less than 10 μm/year. Wear tests on hip joint simulators predict wear rates between 2 and 8 μm/year. However, 6% of cups are wearing faster than 100 μm/year, with 16% of cups have wear patches deeper than 100 μm and that 4% have a wear patch deeper than 300 μm.

Discussion: This paper considers the common characteristics of components in this very high wearing category. Engineering parameters such as head/cup clearance, surface finish, form errors and head cup contact conditions are investigated. This is correlated with clinical data and other results from the LIRC.

Cup position is an important factor, all of the high wearing components are outside the Lewinick’s Box, however it is shown that mal position is does not always lead to extreme wear. Further analysis is taking place to calculate the size of the contact patch between head and cup (based on patient data and biomechanics) and the proximity of the contact patch to the edge of the cup.

Conclusion: The study of explanted components shows that 6% exhibit extreme wear, and although several “risk” factors can be identified, it is not clear why only a proportion of these components show extremely high wear rates. This is the subject of current investigation.


Orthopaedic Proceedings
Vol. 92-B, Issue SUPP_III | Pages 400 - 400
1 Jul 2010
Hart AJ Bandi A Maggiore P Skinner JA Underwood R Cann P
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Data on retrieval analysis of current generation metal on metal hip replacements is scarce. Such analysis may help to reduce the incidence of failure and revision procedures. Our aim was to investigate the wear characteristics of explanted (ie failed) metal on metal (MOM) acetabular components in terms of; 1) wear rate; and 2) distribution of the wear (specifically edge loading).

30 hips were collected from 20 centres. The types of prostheses were: 15 BHR; 10 Cormet and 5 ASR. Wear of the acetabular components of the prostheses was measured using an out of roundness (Rondcom 60A) machine. We recorded the implantation and removal date of each hip.

The median linear wear rate was 7.32μm/year; this is at least 3 times greater than steady state wear rates reported for similar components worn in hip simulator studies. For 24 out of 30 cups, the greatest linear wear was recorded at the cup edge.

Failed metal-on-metal acetabular components were associated with higher than expected wear rates. The highest wear was seen closest to the cup edge in the majority of patients suggesting edge loading had occurred and probably explained the high wear rates. Accurate cup placement (to avoid edge loading) may reduce the failure of MOM hips.


Orthopaedic Proceedings
Vol. 91-B, Issue SUPP_III | Pages 406 - 406
1 Sep 2009
Hart A Maggiore P Sandison A Sampson B Muirhead-Allwood S Cann P Skinner J
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Introduction: Approximately 0.5 % of patients with metal on metal hip replacements develop post operative pain which is thought to be due to an immune reaction to metal wear particles, known as Aseptic Lymphocyte Dominated Vasculitis Associated Lesion (ALVAL). Treatment usually requires revision to a non metal on metal hip.. Is the development of ALVAL more likely in those patients with high wear rates?

Methods: Retrieved Metal on Metal (MOM) hip implants; periprosthetic tissue and blood samples were obtained from patients (n = 18) undergoing revision for unexplained pain at a mean of 2 years post operatively. The following variables were measured:

linear wear rate (depth of the femoral head and acetabular socket wear patch/time from operation);

the diagnosis and severity of ALVAL from histological sections of periprosthetic tissue (Wilhert grading system);

pre-revision whole blood cobalt, and chromium levels using Inductively Coupled Plasma Mass Spectrometry.

All implants and tissue samples were analysed against control samples from patients undergoing revision of MOM hips for fractured femoral neck or impingement.

Results: Linear wear rates of retrieved implants, and blood levels of cobalt and chromium from patients with unexplained plain were greater than from control patients. Histolopathological analysis of tissue showed dense inflammatory infiltrates with healthy looking endothelial cells in all vessels from both patient groups.

Discussion and Conclusion: A painful MOM hip was associated with high wear rates and blood metal levels. The local inflammatory response was similar to “ALVAL”, ie lymphocyte dominated, but not exclusive to those patients with unexplained pain. We question whether ALVAL represents a vasculitis, or merely a classical lymphocyte driven inflammatory tissue response to metal debris particles.