Dual-taper implants provide surgeons with options to optimise patients' anatomy intraoperatively but are at risk of early revision due to adverse tissue reactions to corrosion debris. Risk factors for failure and linkage with symptoms however are not fully understood. We related retrieval findings to clinical and implant variables.

This study involved 88 failed dual-taper implants with TMZF femoral stems and cobalt-chromium necks, revised for pain, elevated Co (median = 7.3μg/L) and Cr (median = 2.15μg/L) ions levels and fluid collection on MRI.

Stem-neck surfaces were assessed for: 1) severity of corrosion using a published visual method and 2) severity of material lost and location of damage with a roundness-measuring machine. Five traces were taken on each round section of the taper surface at 45° increments to compute the relative depth of damage. The total area of these traces provided a measure of surface damage for comparative purposes.

The stem-neck taper junctions were severely corroded; the deepest areas of damage were on the inferior-proximal and superior-distal part of the necks, compatible with cantilever bending. Elemental analysis revealed chromium rich deposits indicative of corrosion processes and metal transfer from the stem to the neck.

There was a positive correlation between the severity of damage and time of implantation (p<0.0001). Co and Cr levels in the blood were also strongly correlated (p<0.0001, p=0.0002). No other implant or patient variables were linked.

The stem-neck junction was severely corroded in all cases. The severity and location of the areas of surface damage did not link with implant or patient characteristics in this big cohort suggesting that the design and material combination is the predominant source of failure in these designs.

Dual-taper hips are severely corroded at the stem-neck junction; this appears to be due to the use of a TMZF alloy stem paired with CoCrMo necks.

Trunnionosis, due to mechanical wear and/or corrosion at the head stem taper junction, can occur in metal on polyethylene (MOP) hip implants. In some patients this results in severe soft tissue destruction or Adverse Reaction to Metal Debris (ARMD). The amount of material required to cause ARMD is unknown but analyses of retrieved hips may provide the answer to this clinically important question.

We collected implants from 20 patients with failed hips with MOP bearings, revised due to ARMD. We collected clinical, imaging and blood test data. We graded the severity of taper corrosion (1 to 4), and quantified the volume of material loss from this junction. We compared our results with previous data collected for metal-on-metal (MOM) hips.

The median time to revision of the MOP hips was 51.3 (23.1–56.4) months. All head tapers were moderately to severely corroded with a median corrosion score of 4. The median (range) of total material loss at the taper of the MOP hips was 3.9 mm³ (2.96 – 7.85 mm³) and the material loss rate was 1.4 mm³ / year (0.56 – 1.82).

Comparison with MOM hips revealed no significant difference in taper material loss (p=0.7344) with a median rate of 0.81 mm³ / year (0.01–3.45).

We are the first to quantify the volume of material loss at the head taper of hip implants with MOP bearings that were revised due to trunnionosis. This data indicates that a clinically significant dose of cobalt and chromium to induce ARMD is approximately 1.4 mm³ / year.

We have identified a clinically significant volume of taper material loss in MOP hips.

Total hip arthroplasties are known to corrode predominantly at the taper junctions between Cobalt Chromium Molybedenum (CoCrMo) and Titanium (Ti) alloy components.

We aimed to understand the modes underlying clinically significant tissue reactions to metals from corroded implants by determining: (1) what type of metal is present in the tissues, (2) which cells contain the metal species and (3) how this compares with results from metal-on-metal (MOM) hip resurfacings (HRs).

This study involved periprosthetic tissue from patients that had undergone revision surgery due to adverse reactions to metal debris (ARMD) from dual-taper prostheses consisting of Ti-based alloy stems paired with CoCrMo necks. We used Synchrotron micro X-ray Fluorescence Spectroscopy (µXRF) and micro X-ray Absorption Near Edge Spectroscopy (µXANES) for detection of Co, Cr and Ti, and determination of their oxidation state.

Synchrotron radiation has shown that the chromium in tissues is Cr₂O₃ when derived from corroded CoCrMo/Ti junctions beside the CrPO₄ species found when hip implants release CoCrMo nanoparticles from their bearing surfaces (MoM HRs). Presence of Cr₂O₃ was associated with titanium oxide TiO₂. This may be the outcome of the chemical interaction between the two species. Histological examination showed corrosion products present within viable macrophages and in the extracellular connective tissue, Figure 1.

Understanding corrosion at taper junctions and the pathogenesis of the biological response is of significant clinical importance. This is the first study to co-register histology and metal distribution maps and to explore the potential synergy effect of CoCrMo with Ti alloy.

This study provides guidance for toxicological studies on wear/corrosion particles, how they stimulate the host response and the cellular mechanisms involved in the pathogenesis of ARMD.

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Objectives

The use of ceramic femoral heads in total hip arthroplasty (THA) has increased due to their proven low bearing wear characteristics. Ceramic femoral heads are also thought to reduce wear and corrosion at the head-stem junction with titanium (Ti) stems when compared with metal heads. We sought to evaluate taper damage of ceramic compared with metal heads when paired with cobalt chromium (CoCr) alloy stems in a single stem design.

Aims

The aim of this study was to compare the design of the generic OptiStem XTR femoral stem with the established Exeter femoral stem.

Background

Surgeons are waiting for a hassle free, time saving, precise and accurate guide for hip arthroplasty. Industry are waiting for instruments to reduce manufacturing costs associated with washing, assembling, sterilization and transportation. Patient specific / custom made surgical guides may deliver these goals but current systems have had limited assessments.

We comprehensively assessed a new guiding system for the acetabular component of hip replacement, “Bullseye”.

Objectives

Mechanical wear and corrosion at the head-stem junction of total hip arthroplasties (THAs) (trunnionosis) have been implicated in their early revision, most commonly in metal-on-metal (MOM) hips. We can isolate the role of the head-stem junction as the predominant source of metal release by investigating non-MOM hips; this can help to identify clinically significant volumes of material loss and corrosion from these surfaces.

Osteoarthritis (OA) affects bone cartilage and underlying bone. Mechanically, the underlying bone provides support to the healthy growth of the overlying cartilage. However, with the progress of OA, bone losses and cysts occur in the bone and these would alter the biomechanical behaviour of the joint, and further leading to bone remodelling adversely affect the overlying cartilage.

Human femoral head and femoral condyle were collected during hip or knee replacement operation due to the end stage of osteoarthritis (age 50–70), and the cartilage patches were graded and marked. A volunteer patient, with minor cartilage injury in his left knee while the right knee is intact, was used as control. Peripheral quantitative computed tomography (pQCT) was used to scan the bone and to determine the volumetric bone mineral density (vBMD) distribution.

The examination of retrieved tissue explants from osteoarthritic patients revealed that patches of cartilage were worn away from the articular surface, and patches of intact cartilage were left. The cysts, ranging from 1 to 10mm were existed in all osteoarthritic bones, and were located close to cartilage defects in the weight-bearing regions, and closely associated with the grade of cartilage defect as measured by pQCT. The bone mineral density (vBMD) distribution demonstrated that the bones around cysts had much higher vBMD than the trabecular bone away from the cysts. Compared to the subchondral bone under thicker cartilage, subchondral bone within cartilage defect has higher vBMD. This may result from the mechanical stimulation as a result of bone-bone direct contact with less protection of cartilage in cartilage defect regions.

This study showed an association between cartilage defect and subchondral bone mineral density distribution. Cysts were observed in all osteoarthritic samples and they are located close to cartilage defects in the weight-bearing regions. Cartilage defect altered the loading pattern of the joints, this leading to the bone remodelling and resultant bone structural changes as compared to the normal bone tissues.

This work was financially supported by The ARUK Proof of Concept Award (grant no: 21160).

Introduction

Surgical simulation and ‘virtual’ surgical tools are becoming recognised as essential aids for speciality training in Trauma & Orthopaedics, as evidenced by the BOA T&O Simulation Curriculum 2013^1,2. The current generation of hip arthroplasty simulators, including cadaveric workshops, offers the trainee limited exposure to reproducible real life bony pathology. We developed and implemented a novel training course using pathological dry bone models generated from real patient cases to support senior orthopaedic trainees and new consultants in developing knowledge and hands on skills in complex total hip arthroplasty.

Introduction

We report 10-year clinical outcomes of a prospective randomised controlled study on uni-compartmental knee arthroplasty using an active constraint robot.

Measuring the clinical impact of CAOS systems has generally been based around surrogate radiological measures with currently few long-term functional follow-up studies reported. We present 10 year clinical follow up results of robotic vs conventional surgery in UKA.

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.

Introduction

The National Joint Registry (NJR) for England, Wales and Northern Ireland contributes important information on the performance of implants and surgeons. However, the quality of this data is not known. This study aimed to perform an independent validation of primary metal-on-metal hip procedures recorded on the NJR through linkage to the London Implant Retrieval Centre (LIRC).

Introduction

Retrieved metal-on-metal acetabular components are invaluable resources from which to investigate the wear behaviour of failed hip implants. New forensic and investigative techniques continue to be developed to help the surgeon further understand factors which contribute to early failure. We have developed a novel technique to locate the in vivo location of the primary wear scar of an explanted cup.

Arthroplasty registries are important for the surveillance of joint replacements and the evaluation of outcome. Independent validation of registry data ensures high quality. The ability for orthopaedic implant retrieval centres to validate registry data is not known. We analysed data from the National Joint Registry for England, Wales and Northern Ireland (NJR) for primary metal-on-metal hip arthroplasties performed between 2003 and 2013. Records were linked to the London Implant Retrieval Centre (RC) for validation. A total of 67 045 procedures on the NJR and 782 revised pairs of components from the RC were included. We were able to link 476 procedures (60.9%) recorded with the RC to the NJR successfully. However, 306 procedures (39.1%) could not be linked. The outcome recorded by the NJR (as either revised, unrevised or death) for a primary procedure was incorrect in 79 linked cases (16.6%). The rate of registry-retrieval linkage and correct assignment of outcome code improved over time. The rates of error for component reference numbers on the NJR were as follows: femoral head category number 14/229 (5.0%); femoral head batch number 13/232 (5.3%); acetabular component category number 2/293 (0.7%) and acetabular component batch number 24/347 (6.5%).

Registry-retrieval linkage provided a novel means for the validation of data, particularly for component fields. This study suggests that NJR reports may underestimate rates of revision for many types of metal-on-metal hip replacement. This is topical given the increasing scope for NJR data. We recommend a system for continuous independent evaluation of the quality and validity of NJR data.

Cite this article: Bone Joint J 2015;97-B:10–18.

There are several component position and design variables that increase the risk of edge loading and high wear in metal-on-metal hip resurfacing (MOM-HR). In this study we combined all of these variables to calculate the ‘contact patch to rim distance’ (CPRD) in patients undergoing revision of their MOM-HR. We then determined whether CPRD was more strongly correlated with component wear and blood metal ion levels, when compared to any other commonly reported clinical variable. This was a retrospective study of 168 consecutively collected MOM-HR retrieval cases. All relevant clinical data was documented, including pre-revision whole blood cobalt and chromium ion levels. Wear of the bearing surfaces was then measured using a roundness-measuring machine. We found four variables to be significantly (p < 0.05) correlated with component wear and blood metal ion levels: (1) cup inclination angle, (2) cup version angle, (3) arc of cover, and (4) CPRD. The correlations between CPRD and both wear and ion levels were significantly stronger than those seen with any other variable (all p < 0.0001). Our study has shown that CPRD is the best predictor of component wear and blood metal ion levels, and may therefore be a useful parameter to help determine those patients who are at risk of high wear and require more frequent clinical surveillance.

Introduction

Edge loading is a common wear mechanism in Metal-on-Metal (MOM) hip resurfacing and is associated with higher wear rates and the incidence of pseudotumour. The purpose of this study was to develop a method to investigate the contributions of patient, surgical and implant design variables on the risk of edge loading.

Improvements in the surgical technique of total knee replacement (TKR) are continually being sought. There has recently been interest in three-dimensional (3D) pre-operative planning using magnetic resonance imaging (MRI) and CT. The 3D images are increasingly used for the production of patient-specific models, surgical guides and custom-made implants for TKR.

The users of patient-specific instrumentation (PSI) claim that they allow the optimum balance of technology and conventional surgery by reducing the complexity of conventional alignment and sizing tools. In this way the advantages of accuracy and precision claimed by computer navigation techniques are achieved without the disadvantages of additional intra-operative inventory, new skills or surgical time.

This review describes the terminology used in this area and debates the advantages and disadvantages of PSI.

Introduction

Metal Artefact Reduction Sequence (MARS) MRI is being increasingly used to detect soft tissue inflammatory reactions surrounding metal-on-metal hip replacements. The UK MHRA safety alert announced in April 2010 recommended cross-sectional imaging such as MRI for all patients with painful MOM hips. The terms used to describe the findings include bursae, cystic lesions and solid masses. A recently used term, pseudotumour, incorporates all of these lesions. We aimed to correlate the pattern of abnormalities on MRI with clinical symptoms.

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.

We measured the orientation of the acetabular and femoral components in 45 patients (33 men, 12 women) with a mean age of 53.4 years (30 to 74) who had undergone revision of metal-on-metal hip resurfacings. Three-dimensional CT was used to measure the inclination and version of the acetabular component, femoral version and the horizontal femoral offset, and the linear wear of the removed acetabular components was measured using a roundness machine.

We found that acetabular version and combined version of the acetabular and femoral components were weakly positively correlated with the rate of wear. The acetabular inclination angle was strongly positively correlated with the rate of wear. Femoral version was weakly negatively correlated with the rate of wear. Application of a threshold of > 5 μm/year for the rate of wear in order to separate the revisions into low or high wearing groups showed that more high wearing components were implanted outside Lewinnek’s safe zone, but that this was mainly due to the inclination of the acetabular component, which was the only parameter that significantly differed between the groups.

We were unable to show that excess version of the acetabular component alone or combined with femoral version was associated with an increase in the rate of wear based on our assessment of version using CT.