Pseudotumours have recently been reported in non-metal-on-metal total hip replacements (non-MoM THRs), however the magnitude and risk factors for this complication are unknown, as is the outcome of its treatment. 3340 primary THR undergoing revision for pseudotumour between 2008 and 2015 were identified in the National Joint Registry for England and Wales. 7.5% (n=249) of these pseudotumour revisions, had non-MoM bearing surfaces. The risk of revision for pseudotumour in non-MoM hips was 0.032% (249/789,397; 95% CI 0.028%–0.036%). The risk of pseudotumour revision was 2.35 times (95% CI 1.76–3.11) higher in ceramic-on-ceramic compared with hard-on-soft bearings, and 2.80 times (95% CI 1.74–4.36) higher in 36mm metal-on-polyethylene bearings compared to 28mm and 32mm metal-on-polyethylene bearings. The outcome of revision for pseudotumour non-MoM hips was studied in 185 hips. 13.5% (n=25) had re-revisions at a mean of 1.2 years (range 0.1–3.1 years). Infection (32%), dislocation/subluxation (24%), and aseptic loosening (24%) were the commonest indications for re-revision. The 4-year survival rate was 83.8% (95% CI=76.7%–88.9%). Multiple revision indications (Hazard Ratio (HR)=2.78; 95% CI=1.03–7.49) and incomplete revision procedures (HR=5.76; 95% CI=1.28–25.9) increased the risk of re-revision. Although the overall risk of revision for pseudotumour in non-MoM THRs is low, the risk is increasing and is significantly higher in ceramic-on-ceramic and large head metal-on-polyethylene THR. These revisions have a high early failure rate

Pseudotumours (soft-tissue masses relating to the hip joint) following metal-on-metal hip resurfacing arthroplasty (MoMHRA) have been associated with elevated serum and hip aspirate metal ion levels, suggesting that pseudotumours occur when there is increased wear. This study aimed to quantify the wear of implants revised for pseudotumours and a control group of implants revised for other reasons of failure. A total of 30 contemporary MoMHRA implants in two groups were investigated: (1) 8 MoMHRA implants revised due to pseudotumour; (2) 22 MoMHRA implants revised due to other reasons of failure. The linear wear of retrieved implants was measured using a Taylor-Hobson Roundness machine. The average linear wear rate was defined as the maximum linear wear depth divided by the duration of the implant in vivo. In comparison with the non-pseudotumour implant group, the pseudotumour implant group was associated with: (1) significantly higher median linear wear rate of the femoral component: 8.1 um/year (range 2.75-25.4 um/year) vs. 1.97 um/year (range 0.82-13.00 um/year), p=0.002; and (2) significantly higher median linear wear rate of the acetabular component: 7.36 um/year (range 1.61-24.9 um/year) vs. 1.28 um/year (range 0.18-3.33 um/year), p=0.001. Wear on the acetabular cup components in the pseudotumour group always involved the edge, indicating edge-loading of the bearing. Significantly greater linear wear rates of the MoMHRA implants revised due to pseudotumour support the in vivo elevated metal ion concentrations in patients with pseudotumours. This study is the first to confirm that pseudotumour occurs when there is increased wear at the MoM articulation. Furthermore, edge-loading may be the dominant wear generation mechanism in patients with pseudotumour

Introduction: Edge-loading, a phenomenon whereby the femoral component comes into contact with the edge of the acetabular component, has been suggested to increase wear in metal-on-metal hip resurfacing arthroplasty (MoMHRA). Pseudotumours (soft-tissue mass relating to the hip joint) have been associated with elevated serum and hip aspirate metal ion levels. This study aimed to investigate in vivo edge-loading in MoMHRA patients with pseudotumours by quantifying dynamic loci of the hip joint segment force relative to the acetabular component during functional activities. Materials and Methods: A total of 21 MoMHRA patients (30 hips) in two groups were investigated in this Ethics approved study:. 6 patients with pseudo-tumours detected using ultrasound/MRI;. 15 patients without pseudotumours. Three-dimensional lower limb motion analysis (12 camera Vicon System) was performed to estimate hip joint segment force during walking, chair-rising and stair-climbing. CT scans were used to determine each patient’s specific hip joint centre and acetabular component orientation. Edge-loading was defined to occur when a hip joint segment force vector/ cup intersection was located within 10% of the cup radius from the edge of the cup. Serum cobalt and chromium levels were analysed using Inductively-Coupled Plasma Spectrometer. Results: Edge-loading in the pseudotumour group occurred with significantly (p=0.02) longer (4-fold increase) duration as well as greater magnitude (7-fold increase) of force, compared to the non-pseudotumour group. The duration and force of the edge-loading were activity-dependent, with proportionally greater difference observed during stair climbing. The acetabular cup orientation values in the pseudotumour group were found within the safe zone of Lewinnek in one third of the hips with the remaining two thirds outside the safe zone. The presence of pseudotumour was associated with:. significantly higher median serum cobalt levels: 14.3ug/l (range 10.6–64.1) vs. 1.9ug/l (range 1.2–5.0), p< 0.001;. significantly higher median serum chromium levels: 21.2ug/l (range 13.8–45.2) vs. 1.8ug/l (range 0.7–7.6), p< 0.001. Discussion: Edge-loading in MoMHRA patients with pseudotumours occurred in vivo with significantly longer duration and greater magnitude of force impulse compared to the patients with a well functioning MoMHRA during activities of daily living. This suggests that edge-loading may be an important mechanism that leads to localised high wear, with subsequent elevation of metal ion levels in MoMHRA patients with pseudotumours. Although the acetabular component malposition, such as increase in both inclination and anteversion angles, appears to be an important factor in edge-loading, the aetiology of edge-loading is likely to be multi-factorial

Introduction: Pseudotumours (soft-tissue masses relating to the hip joint) following metal-on-metal hip resurfacing arthroplasty (MoMHRA) have been associated with elevated serum and hip aspirate metal ion levels, suggesting that pseudotumours occur when there is increased wear. This study aimed to quantify in vivo wear of implants revised for pseudotumours and a control group of implants revised for other reasons of failure. Methods: A total of 30 contemporary MoMHRA implants in two groups were investigated in this Institutional Review Board approved study:. 8 MoMHRA implants revised due to pseudotumour;. 22 MoMHRA implants revised due to other reasons of failure (femoral neck fracture and infection). The linear wear of retrieved implants was measured using a Taylor-Hobson Roundness machine. The average linear wear rate was defined as the maximum linear wear depth divided by the duration of the implant in vivo. Results: In comparison with the non-pseudotumour implant group, the pseudotumour implant group was associated with:. significantly higher median linear wear rate of the femoral component: 8.1um/year (range 2.75–25.4um/year) vs. 1.79um/year (range 0.82–4.15um/year), p=0.002; and. significantly higher median linear wear rate of the acetabular component: 7.36um/year (range1.61–24.9um/year) vs. 1.28um/year (range 0.18–3.33um/year), p=0.001. Similarly, differences were also measured in absolute wear values. The median absolute linear wear was significantly higher in the pseudotumour implant group:. 21.05um (range 2.74–164.80um) vs. 4.44um (range 1.50–8.80um) for the femoral component, p=0.005; and. 14.87um (range 1.93–161.68um) vs. 2.51um (range 0.23–6.04um) for the acetabular component, p=0.008. Wear on the acetabular cup components in the pseudotumour group always involved the edge, indicating edge-loading of the bearing. In contrast, edge-loading was observed in only one acetabular component in the non-pseudotumour group of implants. The deepest wear was observed well within the bearing surface for the rest of the non-pseudotumour group. The difference in the incidence of edge-loading between the two groups was statistically significant (Fisher’s exact test, p=0.03). Discussion: Significantly greater linear wear rates of the MoMHRA implants revised due to pseudotumour support the in vivo elevated metal ion concentrations in patients with pseudotumours. This study provides the first direct evidence to confirm that pseudotumour is associated with increased wear at the MoM articulation. Furthermore, edge-loading with the loss of fluid film lubrication may be the dominant wear generation mechanism in patients with pseudotumour

Introduction: Symptomatic abnormal soft-tissue masses relating to the hip joint, such as those described as pseudotumours, are being increasingly reported following metal-on-metal hip resurfacing arthroplasty (MoMHRA). These were found to be locally destructive, requiring revision surgery in a high proportion (75%) of patients. Lymphocyte infiltrations seen in pseudotumours were similar to aseptic lymphocyte vascular associated lesion (ALVAL), which is thought to represent a T-lymphocyte-mediated delayed type hypersensitivity. Therefore, a delayed hypersensitivity reaction to nickel (Ni), chromium (Cr) or cobalt (Co) has been suggested to play a role in pseudotumour aetiology. In patients with bilateral MoMHRA who presented with symptoms on one side, subsequent scans have demonstrated pseudotumours both on the symptomatic and asymptomatic side. Thus, there are concerns that there may be an appreciable number of asymptomatic pseudotumours that surgeons are unaware of and these may eventually become symptomatic. Aim: The aims of this study were:. to determine the prevalence of asymptomatic pseudotumours after MoMHRA; and. to measure Co and Cr ion levels as well as lymphocyte proliferation responses to Ni, Co and Cr (the principal elements in the CoCr alloy used in MoMHRA) in MoMHRA patients with and without asymptomatic pseudotumours. Methods: A total of 201 MoMHRA implanted hips in 158 patients (97 male, 61 female) with a mean age of 56 years (range 33–73 years) were evaluated. The mean follow-up was 61 months (range 13–88 months). Resurfacing devices implanted included 128 Birmingham Hip Resurfacing, 66 Conserve Plus and seven ReCap. The control groups included additional 20 patients, 10 male and 10 female (a mean age 68 years, range 57–80 years) with metal-on-polyethylene total hip arthroplasty and a further 22 age-matched patients (a mean age 55 years) without any metal implants. Ultrasound was used as the initial imaging modality and MRI was used to assess the extent of the identified masses. Patients with a soft-tissue mass had ultrasound-guided aspiration or core biopsy performed. Venous blood samples were collected in all patients for serum cobalt and chromium ion levels analysis using Inductively-Coupled Plasma Mass Spectrometer and lymphocyte transformation tests (LTT). The Oxford Hip Score (OHS) was used to measure the functional outcomes of patients. Acetabular component abduction angle was measured from standardised anteroposterior pelvis radiographs. Results: Prevalence – Pseudotumours were found in 7 patients (6 female and 1 male). The overall prevalence of asymptomatic pseudotumours was 4%, with a relatively very high (30%) prevalence in females with bilateral implants. Histological examinations showed extensive necrosis of connective tissue, in which there were scattered aggregates of metal particles and a diffuse lymphocyte infiltrate. Metal Ion Levels – The presence of pseudotumour was associated with significantly higher median serum cobalt levels (9.2mg/L vs. 1.9mg/L, p< 0.001), chromium levels (12.0mg/L vs. 2.1mg/L, p< 0.001), hip aspirate cobalt levels (1182 mg/L vs. 86.2mg/L, p=0.003), and aspirate chromium levels (883mg/L vs. 114.8mg/ L, p=0.006), as well as with inferior functional scores (OHS 41 vs. 47 p< 0.001). There was no significant difference in acetabular cup inclination angle (p=0.51). Lymphocyte Reactivity: A higher incidence and level of enhanced lymphocyte reactivity to Ni (p=0.001), but not to Co or Cr (the principal elements in the CoCr alloy used in metal-on-metal hip resurfacing implants), was found in patients with MoMHRA compared to the patients without MoM implants. However, lymphocyte reactivity to Co, Cr and Ni did not significantly differ in patients with pseudotumours compared to those patients without pseudotumours. Conclusion: The prevalence of asymptomatic pseudotumours in females was high, especially in females with bilateral MoMHRA implants (30%). The patients with ‘asymptomatic’ pseudotumours were in fact mildly symptomatic. Lymphocyte reactivity to Co, Cr and Ni did not differ in patients with pseudotumour compared to those patients without pseudotumours, suggesting that systemic hypersensitivity type IV reactions, mediated by lymphocyte reactivity to these metals, is not the dominant mechanism in pathogenesis of the soft tissue pseudotumours. Furthermore, pseudotumours were not detected in those patients who had normal levels of cobalt and chromium ions. This suggests that pseudotumours do not occur if MoM articulations are well functioning. Therefore, pseudotumours are likely to be a biological consequence of the large amount of metal debris generated in vivo due to excessive wear

Hip resurfacing may be a useful surgical procedure when patient selection is correct and only implants with superior performance are used. In order to establish a body of evidence in relation to hip resurfacing, pseudotumour formation and its genetic predisposition, we performed a case-control study investigating the role of HLA genotype in the development of pseudotumour around MoM hip resurfacings.

All metal-on-metal (MoM) hip resurfacings performed in the history of the institution were assessed. A total of 392 hip resurfacings were performed by 12 surgeons between February 1st 2005 and October 31st 2007. In all cases, pseudotumour was confirmed in the preoperative setting on Metal Artefact Reduction Sequencing (MARS) MRI. Controls were matched by implant (ASR or BHR) and absence of pseudotumour was confirmed on MRI. Blood samples from all cases and controls underwent genetic analysis using Next Generation Sequencing (NGS) assessing for the following alleles of 11 HLA loci (A, B, C, DRB1, DRB3/4/5, DQA1, DQB1, DPB1, DPA1). Statistical significance was determined using a Fisher's exact test or Chi-Squared test given the small sample size to quantify the clinical association between HLA genotype and the need for revision surgery due to pseudotumour.

Both groups were matched for implant type (55% ASR, 45% BHR in both the case and control groups). According to the ALVAL histological classification described by Kurmis et al., the majority of cases (63%, n=10) were found to have group 2 histological findings. Four cases (25%) had group 3 histological findings and 2 (12%) patients had group 4 findings. Of the 11 HLA loci analysed, 2 were significantly associated with a higher risk of pseudotumour formation (DQB1*05:03:01 and DRB1*14:54:01) and 4 were noted to be protective against pseudotumour formation (DQA1*03:01:01, DRB1*04:04:01, C*01:02:01, B*27:05:02).

These findings further develop the knowledge base around specific HLA genotypes and their role in the development of pseudotumour formation in MoM hip resurfacing. Specifically, the two alleles at higher risk of pseudotumour formation (DQB1*05:03:01 and DRB1*14:54:01) in MoM hip resurfacing should be noted, particularly as patient-specific genotype-dependent surgical treatments continue to develop in the future.

Objectives. Pseudotumours (abnormal peri-prosthetic soft-tissue reactions) following metal-on-metal hip resurfacing arthroplasty (MoMHRA) have been associated with elevated metal ion levels, suggesting that excessive wear may occur due to edge-loading of these MoM implants. This study aimed to quantify in vivo edge-loading in MoMHRA patients with and without pseudotumours during functional activities. Methods. The duration and magnitude of edge-loading in vivo was quantified during functional activities by combining the dynamic hip joint segment contact force calculated from the three-dimensional (3D) motion analysis system with the 3D reconstruction of orientation of the acetabular component and each patient’s specific hip joint centre, based on CT scans. Results. Edge-loading in the hips with pseudotumours occurred with a four-fold increase in duration and magnitude of force compared with the hips without pseudotumours (p = 0.02). Conclusions. The study provides the first in vivo evidence to support that edge-loading is an important mechanism that leads to localised excessive wear (edge-wear), with subsequent elevation of metal ion levels in MoMHRA patients with pseudotumours

We report on a group of 20 metal-on-metal resurfaced hips (17 patients) presenting with a soft tissue mass associated with various symptoms. We describe these masses as pseudotumours.

All patients underwent plain radiography and fuller investigation with CT, MRI and ultrasound. Where samples were available, histology was performed. All patients in this series were female. Presentation was variable; the most common symptom was pain or discomfort in the hip region. Other symptoms included spontaneous dislocation, nerve palsy, an enlarging mass or a rash. The common histological features were extensive necrosis and lymphocytic infiltration. Fourteen of the 20 cases (70%) have so far required revision to a conventional hip replacement and their symptoms have either settled completely or improved substantially since the revision surgery. Two of the three bilateral cases have asymptomatic pseudotumours on the opposite side.

We estimate that about 1% of patients develop a pseudotumour in the first five postoperative years after a hip resurfacing. The cause of these pseudotumours is unknown and is probably multi-factorial, further work is required to define this; they may be manifestations of a metal sensitivity response. We are concerned that with time the incidence of these pseudotumours will increase.

Introduction

Pseudotumors have been reported following metal-on-metal total hip arthroplasty (THA); however, the natural history and longitudinal imaging findings of pseudotumors have yet to be fully analyzed. Our hypothesis was that pseudotumor size might change over time following metal-on-metal THA. This hypothesis was studied longitudinally using magnetic resonance imaging (MRI).

Introduction: We report on a group of 20 metal-onmetal resurfaced hips (17 patients) presenting with a soft tissue mass associated with various symptoms; these masses we termed pseudotumours.

Methods: All patients underwent plane radiography; CT, MRI and ultrasound investigations were also performed for some patients. Where samples were available histology was performed. Metal ion levels were measured in six patients and one patient had the metal ion levels in the joint fluid measured.

Results: All patients in this series were female. Presentation was variable; the most common symptom was pain or discomfort in the hip region. Other symptoms included spontaneous dislocation, nerve palsy, a noticeable mass or a rash. In all cases a soft tissue mass was present in the region of the hip, this was either solid or cystic. The common histological features were extensive necrosis and lymphocytic infiltration. The blood cobalt and chromium levels varied considerably between the six patients that had these measurements. The median blood chromium level was 3.8 μg/L (range 0.8 to 23 μg/L) and that for cobalt was 11.5 μg/L (range 2.1 to 15 μg/L). The synovial fluid sample taken from a single joint contained much higher metal levels, 701 μg/L for chromium and 329 μg/L for cobalt. Twelve of the 20 cases have so far required revision to a conventional hip replacement.

Discussion: This complication is best imaged with ultrasound, and is not detected by normal xray. We estimate that about 1% of patients develop a pseudotumour in the first five postoperative years. The cause of these pseudotumours is unknown and is probably multifactorial, further work is required to define this; they may be manifestations of a metal sensitivity response. We are concerned that with time the incidence of these pseudo-tumours will increase.

Background

Pseudotumor or high grade ALVAL (aseptic lymphocyte-dominated vasculitis-associated lesion) development around total hip replacements secondary to local metal debris generation – especially in the setting of metal-on-metal bearings – is a well-recognised histopathologic phenomenon. Recent work has suggested a strong genetic correlation with an individual's risk of such lesion development following metal exposure. Emerging data have highlighted a similar potential concern around total knee replacements (TKRs), particularly with increasing construct modularity. To date, the body-of-knowledge pertaining to TKR-associated ALVALs has largely been limited to individual case reports or small retrospective case series’, with no large-scale investigation looking at this potential complication. This study sought to establish the preliminary prevalence of pseudotumor or high grade ALVAL formation seen at the revision of primary TKRs and to establish the correlation between histologic ALVAL grade and patient-reported functional outcomes.

Introduction: The development of Inflammatory Pseudotumour (IP) is a recognised complication following Metal on Metal Hip Resurfacing Arthroplasty (MoMHRA), thought to occur secondary to wear and elevated ion levels. Studies have shown that acetabular component orientation influences the wear of metal-on-metal hip replacement bearings. The aims of this study were to investigate the significance of cup orientation in the development of IP, and to identify a ‘safe-zone’ for cup placement with lower-risk for IP development.

Methods: Twenty six patients (n=27 hips) with IP confirmed radiologically, intra-operatively and histologically were matched for sex, age, pre-operative diagnosis, component size and follow-up with a cohort of asymptomatic MoMHRA patients (Control n=58). Radiographic acetabular anteversion and inclination were measured using EBRA. We calculated the distance in degree space of each acetabular component from the optimum position of 40° inclination and 20° anteversion, recommended by the designers, and thus compared acetabular component position between the two groups. Three different zones were tested as possibly optimum for acetabular placement. These were Lewinneck’s Zone (LZ) (inclination/anteversion; 30–50°/5–25°), and two zones defined by ±5° (Zone 1) or ± 10° (Zone 2) about the suggested target of 40°/20°. An optimal placement zone was determined based on a significant difference in IP incidence between components in the zone versus those outside.

Results: There was a wide range in cup orientations; mean inclination and anteversion were similar in the two groups: IP 47.5° (10.1°–80.6°)/14.1° (4.1°–33.6°) Vs Control 46.1° (28.8°–59.8°)/15.6° (4.3°–32.9°). Acetabular components in the IP group were significantly further away from the optimum position of 40°/20° in comparison to the controls (p=0.023). There was no difference in IP incidence between cups positioned within (IP:13/27, Control:35/58) or out of LZ (p=0.09) and within (IP: 2/27, Control: 10/58) or out of Zone 1 (p=0.156). Cups placed in Zone 2 (IP:6/27, Control:27/58) had significantly lower IP incidence versus those outside this zone (p=0.01). The odd’s ratio of developing IP when the cup is positioned out-of Zone 2 was 3.7.

Discussion: This study highlights the importance of ace-tabular component orientation in IP development. On the whole, patients with pseudotumour had acetabular components that were further away from the optimum position in comparison to the controls. However, a small number of IP patients had well-placed components implying that additional factors, possibly patient and/or gender specific, are involved in the development of pseudotumour. Furthermore, we defined an optimum, ‘safe-zone’ of ±10° around the cup position of 40°/20°. Patients with acetabular components outside this safe zone have an increased risk of IP development.

Purpose

Our primary purpose was to study the rate of occurrence and the natural course of pseudotumors in patients who had not required a revision procedure. Our secondary purpose was to see if there is a relationship between serum metal ion analysis and clinical symptoms with metal-on-metal (MOM) hip arthroplasty.

Between April 2008 and February 2012, we implanted 159 large-diameter MOM stemmed THA with head diameters of 38–50mm. There were 6–38mm, 22–40mm, 42–42mm, 42–44mm, 24–46mm, 13–48mm, 4–50mm, 5–52mm, and one-54mm heads implanted in 138 patients (21 males and 117 females). The pre-operative diagnoses included: 120 OAs, 12 IONs, 4 femoral neck fractures, one RA, and one post-traumatic OA. Their ages were 40–86 years (avg. 63.6 yrs). Follow up was 4 to 67 months post implantation (avg. 40.4 months). All implants were manufactured by one company (Wright Medical Technology, Arlington, TN, USA). The stems were of a standard titanium-aluminum alloy, either 44 ANCA-FIT or 115 PROFEMUR Z non-cemented stems. Acetabular components were all CONSERVE PLUS cobalt-chromium monoblock shells. Heads were also fabricated out of cobalt-chromium alloy, with modular junctions. Patients with complaints of groin pain and/or swelling or hip instability underwent MRI examination in order to detect the presence of fluid collections or soft tissue masses. The statistical correlation between abnormal findings on MRI and age, gender, head diameter, component position and duration post-surgery was performed.

35 hips in 31 patients (22.0%) were found to have either a fluid collection or “pseudotumor” on MRI. These were in 5 males and 26 female patients. According to Hart's MRI classification, they were classified 21 hips in Type 1, twelve hips in Type 2, and two hips in Type 3 (Fig. 1, 2 and 3). 8 hips in 8 patients who had any pseudotumors were undergone revision THA (Fig. 4, 5 and 6). All hips had corrosions at head-neck taper junctions (Fig. 7). There was no difference in age between these two groups of patients (63.7 vs. 63.6 yrs.), but a significant difference in duration from the time of implantation of two groups (23.9 vs. 44.8 months). There appeared to be no significant difference between the mean head diameter of the two groups, 43.2mm and 44.0mm respectively. There was no statistical difference between the two groups with regard to implant orientation: cup inclination 18–70 degrees (41.8 vs. 43.6 degrees); cup anteversion −13–49 degrees (15.1 vs. 14.7 degrees); stem anteversion 2–48 degrees (20.1 vs. 23.3 degrees); and stem offset 17.5–56.2mm (38.2 vs. 37.8mm). Furthermore, according to Lewinnek's safe zone, there was no difference in cup orientation between the two groups (Fig. 8). When we investigated the types of modular neck, the hips having any pesudotumors tended to have long or varus necks.

In this study, it is important to emphasize that the appearance of symptoms and development of a pseudotumor occurred early after a MOM THA in some patients. Also it will be important to subject all patients to MRI examination to evaluate the possibility of “silent” fluid collections and pseudotumors. In large-diameter head metal-on-metal stemmed THAs, femoral stems having long or varus neck may contribute to head-neck junction failure.

Tribological studies of hip arthroplasty suggest that larger diameter metal-on-metal (MOM) articulations would produce less wear than smaller diameter articulations. Other advantages using these large femoral heads implants include better stability with lower dislocation rates and improved range of motion. The aim of the present study was to compare chromium (Cr), cobalt (Co) and titanium (Ti) ion concentrations up to 1-year after implantation of different large diameter MOM total hip arthroplasty (THA).

Methods: Cr, Co and Ti concentrations were measured using a high resolution mass spectrometer (HR-ICP-MS) by an independent laboratory in 110 patients, randomized to receive a large metal-on-metal articulation unce-mented Ti THA from one of the following companies: Zimmer, Smith & Nephew, Biomet or Depuy. Samples of whole blood were collected pre-operatively, and postoperatively at six months and one year.

Summary of Results: At 6 months, whole blood cobalt levels were: (table removed)

Statistical group comparison revealed significant difference for Cr (p=0.006), Co (p=0.047) and Ti (p=< 0.001). With Biomet implants presenting the best results for Cr and Co and Zimmer the highest Ti level.

Discussion: Different implant factors may influence measured metal ion level in whole blood: articular surface wear and implant passive corrosion. Bearing wear may be related to its diameter, quality of the surface finish, component sphericity, radial clearance, manufacturing process (forged vs cast metal) and metal carbon content. Biomet articulation seems to present the best factors selection. Passive corrosion of exposed metallic surfaces is represented by the elevated Ti levels found in all tested systems (Ti was not part of the bearing surfaces). The plasma sprayed acetabular component surface of the Zimmer’s component seems to be responsible for the significant difference in Ti versus the other implants.

Introduction: Metal on metal hip resurfacing arthroplasty-induced pseudotumours are a serious complication, which occur in 4% of patients who undergo this procedure. The aim of this study was to measure the 3D in vivo wear on the surface of resurfacing components revised for pseudotumour, compared to a control group.

Method: Thirty-nine hip resurfacing implants were examined; these were sourced from our institutions prosthesis retrieval bank. They were divided into two groups; 22 patients with a clinical and histopathological diagnosis of pseudotumour and 17 controls. Patient demographics and time to revision were known. Three dimensional contactless metrology (Redlux™ Ltd) was used to scan the surface of the femoral and acetabular components, to a resolution of 20 nanometers. The location, depth and area of the wear scar was determined for each component. Volumetric wear was determined, along with the presence of absence of edge-loading. A separate blinded analysis to determine the presence of absence of impingement was performed by one of the authors. ANOVA was used to test for differences in wear and Fishers Exact test was used to compare the incidence of edge-loading between the groups.

Results: The volumetric wear rate for femoral component of the pseudotumour group was 4.7mm3/yr (SD3.5) and 1.7 mm3/yr (SD1.5) for the control group (p=0.03). In the pseudotumour group, the volumetric wear rate of the acetabular component was 3.5 mm3/yr (SD3.6) compared to 0.02 mm3/yr (SD0.07) for the control group (p=0.01). Edge-loading was detected in 74% of acetabular components in the pseudotumour group and 22% of those in the control group (p=0.01). Anterior or posterior edge-loading, consistent with impingement was present on the femoral components of 73% of patients in the pseudotumour group and 22% in the control group (p=0.01).

Discussion: This work demonstrates that implants revised for pseudotumour have significantly higher volumetric wear rates than controls. They also have a significantly higher incidence of edge-loading and impingement than controls. Edge-loading significantly increases wear. We suggest that pseudotumours are caused by high concentrations of metal wear debris, which have been shown to have a toxic effect on osteocytes and macrophages. This is the one of the first studies to demonstrate a clear link between pseudotumours and increased bearing surface wear. It is also the first to demonstrate that edge-loading, due to impingement, occurs in a significant number of patients who develop this condition. Improved implantation techniques and resurfacing designs may help avoid this serious complication of hip resurfacing.

Pseudotumour formation is being reported with increasing frequency in failing metal-on-metal hip resurfacings and replacements. This mode of failure complication has also been reported with metal-on-polyethylene bearing bearings when it is usually associated with evidence of surface corrosion and no apparent wear at the head–neck taper.

We present a case with evidence of taper wear and damage secondary to corrosion in an uncemented total hip replacement with a metal on polyethylene articulation (TMZF (Titanium, Molybdenum, Zirconium and Ferrous) Accolade® stem, Trident® HA coated acetabular shell, Low Friction Ion Treatment (LFIT™) Cobalt-Chrome anatomic head (40 mm), X3® polyethylene liner)

Recently, a series of locally destructive soft tissue pseudotumour has been reported in patients following metal-on-metal hip resurfacing arthroplasty (MoMHRA), requiring revision surgery in a high percentage of patients. Based on the histological evidence of lymphocytic infiltration, a delayed hypersensitivity reaction to nickel (Ni), chromium (Cr) or cobalt (Co) has been suggested to play a role in its aetiology. The aim of this study was to investigate the incidence and level of hypersensitivity reaction to metals in patients with pseudotumour.

Materials and Methods: 25 patients were investigated in this Ethics approved study:

Group 1: MoMHRA patients with pseudotumours, detected on the ultrasound and confirmed with MRI (n=6, 5 F:1 M, mean age 53 years);

Lymphocyte transformation tests (LTT) were used to measure lymphocyte proliferation responses to metals. Peripheral blood mononuclear cells were isolated from heparinized blood samples using standard Ficoll–Hypaque® (Pharmacia). The PBMC were cultured at a cell density of 106 cells/mL. Culture was set up in the presence of either:

medium alone;

After 5 days of culture, cells were pulsed with [3H]-thymidine and proliferation was assessed by scintillation counting. The stimulation index (SI) was calculated by the ratio of mean counts per minute of stimulated to unstimulated cultures. A SI value of greater than 2.0 was interpreted as a positive result.

Results: A clinical history of metal allergy was reported in 2/6 in Group 1, 2/13 in Group 2, and none in Group 3. In pseudotumour group, the incidence of reactivity to Ni, Co and Cr was 60%, 17% and 0%, respectively. Within Group 2, the reactivity to Ni, Co and Cr was 69%, 8% and 15%, respectively. One control subject had reactivity to Ni. Inter-group comparisons of mean SI values (Kruskal-Wallis non-parametric analysis of variance) showed no significant differences (p> 0.05).

Discussion: The incidence of enhanced lymphocyte response to metals in patients with MoMHRA was more common than the control group. However, in comparison with non-pseudotumour patients, there was no significant difference in the incidence or the level of lymphocyte reactivity in patients with pseudotumour. We conclude that patients with MoMHRA have an enhanced lymphocyte response to metal ions, reflecting exposure and immune reactivity. However, patients with pseudotumours have a similar proliferative response to those without pseudotumours, which suggests that type IV hypersensitivity may not be the cause of the pseudotumours.

Aims

Large-diameter metal-on-metal (MoM) total hip arthroplasty (THA) has demonstrated unexpected high failure rates and pseudotumour formation. The purpose of this prospective cohort study is to report ten-year results in order to establish revision rate, prevalence of pseudotumour formation, and relation with whole blood cobalt levels.

Purpose: Recently, there has been concern raised on the occurrence of pseudotumors after metal on metal hip resurfacing. A pseudotumor is defined as a local soft tissue mass associated with localized bony and/or tissue (muscle) destruction. The primary purpose of this study is to determine the incidence of this complication in several high volume Canadian academic centres.

Method: Nine of the 11 Canadian academic centres who perform metal on metal hip resurfacings were surveyed. The number of metal on metal hip resurfacing arthroplasties performed at each centre was first determined, as were the number of those who have presented with a pseudotumour, and subsequently gone on to revision surgery. The basic demographics of the group were recorded, as were the radiographic and implant design variables for those cases presenting with a pseudotumour.

Results: A sample of 3,400 hip resurfacing arthroplasties performed between 2002 and December 2008 were surveyed. Demographics were tabulated for a sub-sample of these patients. 76% were male, the mean length of follow-up was 3.02 years, mean BMI was 28.65, and mean age was 52.10 years. Three of 3,400 cases presented with a pseudotumour, an incidence of .09%.

Conclusion: Although pseudotumors remain a concern after metal on metal hip resurfacing, the incidence at short to mid term follow-up is very low in this multi-centre academic survey. This information is significantly lower than what other groups have recently reported. Continued close monitoring is required in order to determine what clinical factors are at play.