We have developed a novel technique to analyse bone, using imaging mass cytometry (IMC) without the constraints of using immunofluorescent histochemistry. IMC can measure the expression of over 40 proteins simultaneously, without autofluorescence. We analysed mitochondrial respiratory chain (RC) protein deficiencies in human bone which are thought to contribute to osteoporosis with increasing age.

Osteoporosis is characterised by reduced bone mineral density (BMD) and fragility fractures. Humans accumulate mitochondrial mutations and RC deficiency with age and this has been linked to the changing phenotype in advancing age and age-related disease. Mitochondrial mutations are detectable from the age of 30 onwards, coincidently the age BMD begins to decline. Mitochondria contain their own genome which accumulates somatic variants at around 10 times the rate of nuclear DNA. Once these mutations exceed a threshold, RC deficiency and cellular dysfunction occur. The PolgD257A/D257A mouse model expresses a proof-reading deficient version of PolgA, a mtDNA polymerase. These mice accumulate mutations 3-5 times higher than wild-type mice showing enhanced levels of age-related osteoporosis and RC deficiency in osteoblasts.

Bone samples were analysed from young and old patients, developing a protocol and analysis framework for IMC in bone tissue sections to analyse osteoblasts in-situ for RC deficiency.

Samples from the femoral neck of 10 older healthy volunteers aged 40 – 85 were compared with samples from young patients aged 1-19. We have identified RC complex I defect in osteoblasts from 6 of the older volunteers, complex II defects in 2 of the older volunteers, complex IV defect in just 1 older volunteer, and complex V defect in 4 of the older volunteers.

These observations are consistent with the PolgD257A/D257A mouse-model and suggest that RC deficiency, due to age-related pathogenic mitochondrial DNA mutations, may play a significant role in the pathogenesis of human age-related osteoporosis.

The most common reason for revision surgery of total hip replacements is aseptic loosening of implants secondary to osteolysis, which is caused by immune-mediated reactions to implant debris. These debris can cause pseudotumour formation. As revision surgery is associated with higher mortality and infection, it is important to understand the pro-inflammatory process to improve implant survival. Toll-like receptor 4 (TLR4) has been shown to mediate immune responses to cobalt ions. Statin use in epidemiological studies has been associated with reduced risk of revision surgery. In-vitro studies have demonstrated the potential for statins to reduce orthopaedic debris-induced immune responses and there is evidence that statins can modulate TLR4 activity. This study investigates simvastatin's effect on orthopaedic biomaterial-mediated changes in protein expression of key inflammatory markers and soluble-ICAM-1 (sICAM-1), an angiogenic factor implicated in pseudotumour formation.

Human macrophage THP-1 cells were pre-incubated with 50µM simvastatin for 2-hours or a vehicle control (VC), before being exposed to 0.75mM cobalt chloride, 50μm3 per cell zirconium oxide or LPS as a positive control, in addition to a further 24-hour co-incubation with 50µM simvastatin or VC. Interleukin −8 (IL-8), sICAM-1, chemokine ligand 2 (CCL2), CCL3 and CCL4 protein secretion was measured by enzyme-linked immunosorbent assay (ELISA). GraphPad Prism 10 was used for statistical analysis including a one-way ANOVA.

Pre-treatment with simvastatin significantly reduced LPS and cobalt-mediated IL-8 secretion (n=3) and sICAM-1 protein secretion (n=2) in THP-1 cells. Pre-treatment with simvastatin significantly reduced LPS-mediated but not cobalt ion-mediated CCL2 (n=3) and CCL3 protein (n=3) secretion in THP-1 cells. Simvastatin significantly reduced zirconium oxide-mediated CCL4 secretion (n=3).

Simvastatin significantly reduced cobalt-ion mediated IL-8 and sICAM-1 protein secretion in THP-1 cells. This in-vitro finding demonstrates the potential for simvastatin to reduce recruitment of leukocytes which mediate the deleterious inflammatory processes driving implant failure.

Aims

Hip fracture commonly affects the frailest patients, of whom many are care-dependent, with a disproportionate risk of contracting COVID-19. We examined the impact of COVID-19 infection on hip fracture mortality in England.

Aims

To identify the responsiveness, minimal clinically important difference (MCID), minimal clinical important change (MIC), and patient-acceptable symptom state (PASS) thresholds in the 36-item Short Form Health Survey questionnaire (SF-36) (v2) for each of the eight dimensions and the total score following total knee arthroplasty (TKA).

Abstract

Hip fracture principally affects the frailest in society, many of whom are care dependent, and are disproportionately at risk of contracting COVID-19. We examined the impact of COVID-19 infection on hip fracture mortality in England.

We conducted a cohort study of patients with hip fracture recorded in the National Hip Fracture Database between 1st February 2019 and 31st October 2020, in England. Data were linked to Hospital Episode Statistics to quantify patient characteristics and comorbidities, Office for National Statistics mortality data, and Public Health England's SARS-CoV-2 testing results. Multivariable Cox regression examined determinants of 90-day mortality. Excess mortality attributable to COVID-19 was quantified using Quasi-Poisson models.

Analysis of 102,900 hip fractures (42,630 occurring during the pandemic) revealed that amongst those with COVID-19 infection at presentation (n=1,120) there was a doubling of 90-day mortality; hazard ratio (HR) 2.05 (95%CI 1.86–2.26), while for infections arising between 8–30 days after presentation (n=1,644) the figure was even higher at 2.52 (2.32–2.73). Malnutrition [1.44 (1.19–1.75)] and non-operative treatment [2.89 (2.16–3.86)] were the only modifiable risk factors for death in COVID-19 positive patients. Patients with previous COVID-19 initially had better survival compared to those who contracted COVID-19 around the time of their hip fracture; however, survival rapidly declined and by 365 days the combination of hip fracture and COVID-19 infection was associated with a 50% mortality rate. Between 1st January and 30th June 2020, 1,273 (99.7%CI 1,077–1,465) excess deaths occurred within 90 days of hip fracture, representing an excess mortality of 23% (20%–26%), with most deaths occurring within 30 days.

COVID-19 infection more than doubled early hip fracture mortality; the first 30-days after injury were most critical, suggesting that targeted interventions in this period may have most benefit in improving survival.

Introduction and Objective

Total joint replacement is indicated for osteoarthritis where conservative treatment has failed, and in the UK the number of patients requiring hip and knee replacements is set to increase with an ageing population. Survival of total hip replacements is around 85% at 20 years with the most common reason for revision being aseptic loosening of the implant secondary to osteolysis, which is caused by immune-mediated reactions to implant debris. These debris can also cause pseudotumour formation. As revision surgery is associated with higher morbidity, mortality, infection rates, venous thromboembolism, resource demand and poorer subsequent function it is important to understand the mechanisms underlying the pro-inflammatory process to improve implant survival. Toll-like receptor 4 (TLR4), an innate immune receptor, has been demonstrated to mediate deleterious immune responses by the Tyson-Capper research group, including inflammatory cytokine interleukin-8 (IL-8) secretion. Statin use in epidemiological studies has been associated with reduced overall risk of revision surgery after hip replacement. In-vitro studies have demonstrated the potential for statins to reduce orthopaedic debris-induced immune responses which can lead to osteolysis and pseudotumour formation. As literature from cardiological investigations demonstrate that statins can reduce the expression and responsiveness of TLR4, this could be an exciting mechanism to exploit to reduce the host immune response to orthopaedic wear debris, thereby improving implant survival by reducing immune mediated osteolysis. This ongoing study investigates simvastatin's effect on cobalt ion-mediated changes in gene and protein expression of interleukin-8 and soluble-ICAM-1 (sICAM-1) which is an angiogenic factor implicated in pseudotumour formation.

Introduction

We aimed to identify genes associated with the development of ALVAL at relatively low levels of wear.

Aims

There are limited published data detailing the volumetric material loss from tapers of conventional metal-on-polyethylene (MoP) total hip arthroplasties (THAs). Our aim was to address this by comparing the taper wear rates measured in an explanted cohort of the widely used Exeter THA with those measured in a group of metal-on-metal (MoM) THAs.

Objectives

We have encountered patients who developed large joint fluid collections with massive elevations in chromium (Cr) and cobalt (Co) concentrations following metal-on-metal (MoM) hip arthroplasties. In some cases, retrieval analysis determined that these ion concentrations could not be explained simply by the wear rates of the components. We hypothesized that these effects may be associated with aseptic lymphocyte-dominated vasculitis-associated lesion (ALVAL).

Aims

We sought to determine whether cobalt-chromium alloy (CoCr) femoral stem tapers (trunnions) wear more than titanium (Ti) alloy stem tapers (trunnions) when used in a large diameter (LD) metal-on-metal (MoM) hip arthroplasty system.

Modular un-cemented acetabular components are used in over 50% of UK hip replacements. Mal-seating of hard liners has been reported as a cause of failure which may be a result of errors in assembly, but also could be affected by deformation of the acetabular shell on insertion. Little information exists on in vivo shell deformation. Previous work has confirmed the importance of shell diameter and thickness upon shell behaviour, but mostly using single measurements in models or cold cadavers.

Exploration of deformation and its relaxation over the first twenty minutes after implantation of eight generic metal cups at body temperature.

Using a previously validated cadaveric model at controlled physiological temperature with standardised surgical technique, we tested the null hypothesis that there was no consistency for time dependent or directional change in deformation for a standard metal shell inserted under controlled conditions into the hip joint. Eight custom made titanium alloy (TiAl6V4) cups were implanted into 4 cadavers (8 hips). Time dependent cup deformation was determined using the previously validated ATOS Triple Scan III (ATOS) optical measurement system. The pattern of change in the shape of the surgically implanted cup was measured at 3 time points after insertion.

We found consistency for quantitative and directional deformation of the shells. There was consistency for relaxation of the deformation with time. Immediate mean change in cup radius was 104μm (sd 32, range 67–153) relaxing to mean 96 μm (sd 32, range 63–150) after 10 minutes and mean 92 μm (sd 28, range 66–138) after 20 minutes.

This work shows the time dependent deformation and relaxation of acetabular titanium shells and may aid determining the optimal time for insertion of the inner liner at surgery.

Background

Increased revision rates and early failure of Metal-on-Metal (MoM) hip replacements are often due to adverse reaction to metal debris (ARMD). ARMD describes numerous symptoms in patients such as pain, osteolysis and soft tissue damage. Cobalt is a major component of MoM joints and can initiate an immune response via activation of the innate immune receptor Toll-like receptor 4 (TLR4). This leads to increased secretion of inflammatory cytokines e.g. interleukin-8 (IL-8). This study investigates whether TLR4-specific antagonists inhibit the inflammatory response to cobalt using IL-8 gene expression and protein secretion as a marker of TLR4 activation.

Background

Adverse reactions to metal debris are implicated in the failure of metal-on-metal hip arthroplasty. The peri-implant tissues are often infiltrated by leukocytes which may cause observed immunological effects, including soft tissue necrosis and osteolysis. Cobalt ions from orthopaedic implants aberrantly activate the innate immune receptor human toll-like receptor-4 (TLR4), leading to inflammatory cytokine release including interleukin-8 (IL-8). IL-8 has been shown to increase expression of intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1). These factors are essential for leukocyte adhesion to endothelium, which is required for leukocyte migration into tissues. This study investigates cobalt's effect on gene and protein changes in IL-8, ICAM-1 and VCAM-1 to determine their potential role in immune cell infiltration of peri-implant tissues.

Background

Metal-on-metal (MoM) hip arthroplasty has been associated with adverse reactions including pseudotumours, and osteolysis. Tissues surrounding failed MoM hip implants are often infiltrated by inflammatory cells such as monocytes and neutrophils. The mechanisms by which these cells are recruited to the tissues remain unclear. Cobalt from MoM implants activates Toll-like receptor 4 (TLR4), an immune cell surface receptor usually responsible for recognition of bacteria and prevention of sepsis. Activation by bacteria leads to secretion of pro-inflammatory cytokines which guide other immune cells to the site of inflammation. The effect of cobalt on this response is unknown and therefore this study aims to determine the effect of cobalt-mediated TLR4 activation on the migration of inflammatory cells.

Introduction

There is little information available to surgeons regarding how the lateral soft-tissue structures prevent instability in knees implanted with total knee arthroplasty (TKA). The aim of this study was to quantify the lateral soft-tissue contributions to stability following cruciate retaining (CR) TKA.

The pathogenesis of falling bone mineral density (BMD) as a universal feature of advancing age is poorly understood¹. Frequently culminating in the development of osteoporosis, the process is attributable to more than 500,000 fragility fractures occurring every year in the UK Such injuries are associated with great levels of morbidity, mortality and a £3.5 billion cost to the healthcare economy².

With age, humans are known to accumulate somatic mitochondrial DNA (mtDNA) mutations in mitotic and post mitotic tissue, and stem cell precursors³. Compelling evidence in recent years, particularly that provided by animal models suggests that these mutations are intrinsic to the ageing process^4–6. We provide evidence for the first time that mitochondrial dysfunction contributes significantly to the failure of bone homeostasis and falling BMD.

We have utilised a mouse model that accumulates mtDNA mutations at 3–5 times the rate of normal mice, consequently ageing and developing osteoporosis prematurely⁷, to clearly demonstrate that osteoblasts are vulnerable to mtDNA mutations. We have developed a new quadruple immunofluorescent assay to show that mitochondrial respiratory chain dysfunction occurs in osteoblasts as a consequence (p < 0.0001). We show that this mitochondrial dysfunction is associated with reduced BMD in female and male mice by 7 (p = 0.003) and 11 (p = 0.0003) months of age respectively. Using osteoblasts derived from mesenchymal stem cells extracted from male and female mice with mitochondrial dysfunction aged 4, 7 and 11 months, we demonstrate a vastly reduced capacity to produce new mineralised bone in vitro when compared to wild type cell lines (p < 0.0001). Exercise was found to have no beneficial effect on osteoblast and whole bone phenotype in this mouse model. It is likely that mtDNA mutations accumulating over a longer time period in human ageing have significantly detrimental effects on bone biology and diminishing BMD.

INTRODUCTION

Deformation of modular acetabular press-fit shells is of much interest for surgeons and manufacturers. Initial fixation is achieved through press-fit between shell and acetabulum with the shell mechanically deforming upon insertion. Shell deformation may disrupt the assembly process of modular systems and may adversely affect integrity and durability of the components and tribology of the bearing. The aim of the study was to show shell deformation as a function of bone and shell stiffness.

INTRODUCTION

Deformation of modular acetabular press-fit shells is a topic of much interest for surgeons and manufacturer. Such modular components utilise a titanium shell with a liner manufactured from metal, polyethylene or ceramic. Initial fixation is achieved through a press-fit between shell and acetabulum with the shell mechanically deforming upon insertion. Shell deformation may disrupt the assembly process of inserting the bearing liner into the acetabular shell for modular systems. This may adversely affect the integrity and durability of the components and the tribology of the bearing.

Concerns have been raised that deformation of acetabular shells may disrupt the assembly process of modular prostheses. In this study we aimed to examine the effect that the strength of bone has on the amount of deformation of the acetabular shell. The hypothesis was that stronger bone would result in greater deformation. A total of 17 acetabular shells were inserted into the acetabula of eight cadavers, and deformation was measured using an optical measuring system. Cores of bone from the femoral head were taken from each cadaver and compressed using a materials testing machine. The highest peak modulus and yield stress for each cadaver were used to represent the strength of the bone and compared with the values for the deformation and the surgeon’s subjective assessment of the hardness of the bone. The mean deformation of the shell was 129 µm (3 to 340). No correlation was found between deformation and either the maximum peak modulus (r² = 0.011, t = 0.426, p = 0.676) or the yield stress (r² = 0.024, t = 0.614, p = 0.549) of the bone. Although no correlation was found between the strength of the bone and deformation, the values for the deformation observed could be sufficient to disrupt the assembly process of modular acetabular components.

Cite this article: Bone Joint J 2015; 97-B:473–7.