Method for the location of primary wear scars from retrieved metal on metal hip replacements

Retrieved metal-on-metal acetabular cups are valuable resources in investigating the wear behaviour of failed hip implants, but adequate methods to do so are lacking. To further contribute to addressing this issue, we developed a method to detect the in vivo location of the primary wear scar of an explanted cup

Does diametrical clearance influence the wear of Pinnacle hip implants?

Aims: The optimum clearance between the bearing surfaces of hip arthroplasties is unknown. Theoretically, to minimize wear, it is understood that clearances must be low enough to maintain optimal contact pressure and fluid film lubrication, while being large enough to allow lubricant recovery and reduce contact patch size. This study aimed to identify the relationship between diametrical clearance and volumetric wear, through the analysis of retrieved components. / Methods: A total of 81 metal-on-metal Pinnacle hips paired with 12/14 stems were included in this study. Geometrical analysis was performed on each component, using coordinate and roundness measuring machines. The relationship between their as-manufactured diametrical clearance and volumetric wear was investigated. The Mann-Whitney U test and unpaired t-test were used, in addition to calculating the non-parametric Spearman's correlation coefficient, to statistically evaluate the acquired data. / Results: The hips in this study were found to have had a median unworn diametrical clearance of 90.31 μm (interquartile range (IQR) 77.59 to 97.40); 32% (n = 26) were found to have been below the manufacturing tolerance. There was no correlation found between clearance and bearing (rs = -0.0004, p = 0.997) or taper (rs = 0.0048, p = 0.966) wear rates. The wear performance of hips manufactured within and below these specifications was not significantly different (bearing: p = 0.395; taper: p = 0.653). Pinnacles manufactured from 2007 onwards had a greater prevalence of bearing clearance below tolerance (p = 0.004). / Conclusion: The diametrical clearance of Pinnacle hips did not influence their wear performance, even when below the manufacturing tolerance. The optimum clearance for minimizing hip implant wear remains unclear

Quantifying material loss from the bearing surfaces of retrieved hip replacements: Method validation

Computational methods used to quantify wear in failed hip arthroplasties are often limited by human and sampling errors. An automated software solution has been developed to overcome these shortcomings. The overarching aim of the current study was to validate this method through a comparison with gravimetric measurements. Seventy-two different wear volumes were quantified to within a mean error of 0.14 mm3 and 0.10 mm3 of gravimetric results for simulated cup and head components, respectively. This approach had an improved accuracy, repeatability and reproducibility over a commonly used, commercially available software solution, which bears many of the common sources of error

An integrated discrete event simulation and particle swarm optimisation model for optimising efficiency of cancer diagnosis pathways

The National Health Service (NHS) constitution sets out minimum standards for rights of access of patients to NHS services. The ‘Faster Diagnosis Standard’ (FDS) states that 75% of patients should be told whether they have a diagnosis of cancer or not within 28 days of an urgent GP referral. Timely diagnosis and treatment lead to improved outcomes for cancer patients, however, compliance with these standards has recently been challenged, particularly in the context of operational pressures and resource constraints relating to the COVID-19 pandemic. In order to minimise diagnostic delays, the National Physical Laboratory in collaboration with the Royal Free London (RFL) NHS Foundation Trust address this problem by treating it as a formal resource optimisation, aiming to minimise the number of patients who breach the FDS. We use discrete event simulation and particle swarm optimisation to identify areas for improving the efficiency of cancer diagnosis at the RFL. We highlight capacity-demand mismatches in the current cancer diagnosis pathways at the RFL, including imaging and endoscopy investigations. This is due to the volume of patients requiring these investigations to meet the 28-day FDS target. We find that increasing resources in one area alone does not fully solve the problem. By looking at the system as a whole we identify areas for improvement which will have system-wide impact even though individually they do not necessarily seem significant. The outcomes and impact of this project have the potential to make a valuable impact on shaping future hospital activity

Are all metal-on-metal hip revision operations contributing to the National Joint Registry implant survival curves? : a study comparing the London Implant Retrieval Centre and National Joint Registry datasets

AIMS: The National Joint Registry for England, Wales and Northern Ireland (NJR) has extended its scope to report on hospital, surgeon and implant performance. Data linkage of the NJR to the London Implant Retrieval Centre (LIRC) has previously evaluated data quality for hip primary procedures, but did not assess revision records. METHODS: We analysed metal-on-metal hip revision procedures performed between 2003 and 2013. A total of 69 929 revision procedures from the NJR and 929 revised pairs of components from the LIRC were included. RESULTS: We were able to link 716 (77.1%) revision procedures on the NJR to the LIRC. This meant that 213 (22.9%) revision procedures at the LIRC could not be identified on the NJR. We found that 349 (37.6%) explants at the LIRC completed the full linkage process to both NJR primary and revision databases. Data completion was excellent (> 99.9%) for revision procedures reported to the NJR. DISCUSSION: This study has shown that only approximately one third of retrieved components at the LIRC, contributed to survival curves on the NJR. We recommend prospective registry-retrieval linkage as a tool to feedback missing and erroneous data to the NJR and improve data quality. TAKE HOME MESSAGE: Prospective Registry - retrieval linkage is a simple tool to evaluate and improve data quality on the NJR. Cite this article: Bone Joint J 2016;98-B:33-9

Dimensional analysis of 3D-printed acetabular cups for hip arthroplasty using X-ray microcomputed tomography

Purpose Three-dimensional (3D) printing is increasingly used to produce orthopaedic components for hip arthroplasty, such as acetabular cups, which show complex lattice porous structures and shapes. However, limitations on the quality of the final implants are present; thus, investigations are needed to ensure adequate quality and patients safety. X-ray microcomputed tomography (micro-CT) has been recognised to be the most suitable method to evaluate the complexity of 3D-printed parts. The purpose of this study was to assess the reliability of a micro-CT analysis method comparing it with reference systems, such as coordinate measuring machine and electron microscopy. Design/methodology/approach 3D-printed acetabular components for hip arthroplasty (n = 2) were investigated. Dimensions related to the dense and porous regions of the samples were measured. The micro-CT scanning parameters (voltage – kV, current – µA) were optimised selecting six combinations of beam voltage and current. Findings Micro-CT showed good correlation and agreement with both coordinate measuring machine and scanning electron microscopy when optimal scanning parameters were selected (130 kV – 100 µA to 180 kV – 80 µA). Mean discrepancies of 50 µm (± 300) and 20 µm (± 60) were found between the techniques for dense and porous dimensions. Investigation method such as micro-CT imaging may help to better understand the impact of 3D printing manufacturing technology on the properties of orthopaedic implants. Originality/value The optimisation of the scanning parameters and the validation of this method with reference techniques may guide further analysis of similar orthopaedic components

Wear of dual-mobility cups: a review article

Dual-mobility (DM) cups have been clinically used in hip surgery in Europe for more than 35 years and continue to gain popularity worldwide due to promising results at reducing instability. Concerns related to polyethylene wear apply as in conventional standard bearings but are accentuated by the larger-diameter articulations with multiple surfaces. We critically reviewed the reported literature regarding the in vivo and in vitro wear occurring on all surfaces involved. We looked for patterns to create a rational classification of sites of wear and to identify areas for future research. Wear was a significant problem for first-generation designs and appeared to be design related. Improved polyethylene, thinner and smoother trunnions, chamfered rims and eccentric configuration of insert and shell seem to enhance outcome performance; however, long-term clinical evidence and retrieval studies are needed to better understand the balance of benefit and risk when opting for DM bearings