The articulating surface replacement (ASR) XL stemmed total hip replacement and ASR resurfacing hip systems were recalled by DePuy due to a high prevalence of early failure. The ASR XL has a greater failure rate than the ASR resurfacing, which has been increasingly attributed to wear and corrosion at the taper interface between the female taper surface of the femoral head and the male taper (trunnion) of the femoral stem. The aim of this study was to quantify the prevalence and severity of taper corrosion in retrieved ASR XL hip components.

A peer-reviewed subjective corrosion scoring system was used to quantify corrosion in a consecutive series of the 50 ASR XL hip components (head components – n=44; femoral stems – n=6) at our retrieval centre. Bearing surface wear (femoral head and acetabular cup combined) was quantified and a value of <5 microns was defined as low-wearing. Subsequent profilometry analysis was undertaken in the low-wearing hips to quantify material loss from the taper interface.

90% of components showed evidence of corrosion, with at least moderate corrosion observed in 58%. There were 17 low-wearing hips which had a median material loss from the taper interface of 3.51mm³ (range: 0.612–9.443). The median linear depth of material loss was 33μm (range: 8.5–78.0). No relationship was observed between taper corrosion and serum cobalt (r=0.204, p=0.2712) or chromium (r=0.146, p=0.432) metal ions.

Wear and material loss from metal-on-metal (MoM) hips is associated with pseudotumour formation and adverse soft-tissue reactions. We have shown that taper corrosion is extremely common in failed ASR XL hips and that wear occurs in the same degree of magnitude as at the bearing surface also occurs at the taper interface. Therefore our findings support the emerging concept of ‘taper failure’, whereby the taper is the predominate reason for failure of MoM hips. Future work must determine the relative contributions of the bearing surface and the taper interface to serum cobalt and chromium metal ion levels.

Corrosion at the taper interface between the femoral head and the femoral stem is well described in metal-on-polyethylene (MoP) hips but previously was undetermined in large diameter head metal-on-metal (LHMoM) hips. The high failure rate of the articulating surface replacement (ASR) XL hip system has been partly attributed to susceptibility to corrosive damage at the taper interface. It was not known if other hip manufacturers are liable to taper corrosion. Therefore the aim of this study was to quantify the prevalence and severity of taper corrosion in LHMoM hips and compare corrosion across five different current generation manufacturers.

Taper corrosion was analysed in a consecutive series of the five most common hip types at our retrieval centre: ASR XL, DePuy (n=49); Birmingham hip resurfacing, Smith & Nephew (n=33), Durom, Zimmer (n=31), M2a Magnum, Biomet (n=14) and Cormet, Stryker (n=10). A four-scale peer-reviewed qualitative corrosion scoring system was used to quantify corrosion (none, mild, moderate and severe).

Evidence of corrosion was observed in 86% of components, with at least moderate corrosion observed in 61%. No difference in corrosion was observed between the ASR XL and the other manufacturers (p=0.202). There was still no difference seen when all manufacturers were compared individually (p=0.363). A positive correlation was observed between corrosion and femoral head diameter (r=0.224, p=0.021). However no relationship was observed with implantation time (r=0.163, p=0.118).

Our study indicates that taper corrosion is common in LHMoM hips and affects all hip types equally. The clinical significance of this finding is that all hip types will be susceptible to the complications of corrosion, such as third body wear and osteolysis. Furthermore recent reports indicate that corrosive debris released from the taper interface may play a role in the formation of pseudotumours and adverse soft-tissue reactions. We found that larger femoral head sizes showed greater corrosion, which suggests that high torque increases fretting corrosion of the taper interface. Future work must determine the optimum femoral head size and investigate the chemical composition of the corrosive debris.

In metal-on-metal (MoM) total hip arthroplasty, the taper interface is where the femoral head (female taper surface) attaches to the trunnion (male taper) of the femoral stem. Corrosion is well reported in metal-on-polyethylene hips but little is known about taper corrosion in MoM devices. The aim of this study was to quantify corrosion in modern-generation stemmed MoM hip systems and gain insight into the nature of the underlying corrosive attack.

Taper corrosion was quantified in 161 failed MoM components (head components n=128; femoral stem n=33) from nine hip types with the use of a qualitative subjective scoring system. An unanticipated finding on preliminary inspection of the hips was a region on the female taper surface that contained ridges that directly corresponded with the ridged microthread on the trunnion. The ridges were not present on unimplanted (control) female taper surfaces and therefore a novel four-scale subjective scoring system was devised to quantify the prevalence and severity of this ‘imprinting’ phenomenon.

Evidence of corrosion was observed in 81% (131/161) of components, with at least moderate corrosion observed in 58% (94/161). Corrosion was greater on the female taper surface than on the male taper (p=0.034) and the two scores were associated (r=0.784, p=0.001). Imprinting affected all manufacturers and was observed in 64% (82/128) of head components. The corrosion and imprinting scores were strongly correlated (r=0.694, p=0.001). Corrosion was largely confined to the area of the female taper interface where imprinting had occurred i.e. the region that had been in contact with the trunnion microthread. Scanning electron microscopy showed evidence of fretting corrosion and substantial mechanical wear within the ridged region on the female taper surface.

Our study indicates that MoM hips are susceptible to taper corrosion. We believe it occurs by a process of “mechanically-assisted crevice corrosion,” involving the following sequence of events: joint fluid enters the taper junction as a result of pumping of fluid along the machined microthread of the trunnion. This results in galvanic corrosion of the anodic surface (the cobalt-chromium femoral head or taper sleeve). The pattern of corrosion of the head taper is determined by the surface profile of the screw thread of the trunnion, thus leaving an imprinted appearance. Historically the ridged microthread was introduced to trunnions to minimise the risk of burst fracture of ceramic heads. However this study indicates that the ridges are detrimental in MoM hips by causing extensive mechanical wear. Thus the possibility that cobalt-chrome and ceramic femoral head components require different trunnion designs needs urgent investigation.

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.

Introduction

It has been speculated that impact deformation of thin 1-piece cups used for modern metal-on-metal hip replacement may contribute to early failure. The purpose of this study was to reproduce typical impact deformation and quantify the effect of this on the frictional torque generated at the hip.

Metal on Metal hip resurfacing (MoM HR) can be an effective operation for the young arthritic hip population. However, errors in cup orientation have been associated with increased wear, circulating blood metal ions, and soft tissue abnormalities that can lead to premature failure of the bearing surface and subsequent revision surgery. While image free computer guidance has been shown to increase surgical accuracy in total hip arthroplasty, the role of image based technology in MoM HR is unclear. In this study, we compared the accuracy of cup orientation in MoM HR performed by either freehand technique or CT based navigation.

Seventy five patients (81 hips) underwent either freehand (n=42) or navigation (n=39) surgery, both requiring a three dimensional (3D) CT surgical plan. Surgery was conducted by hip specialists blind to the method of cup implantation until the operation. Deviation in inclination and version from the planned orientation, as well as, number of cups within a 10° safe zone and 5° optimal zone of the target position was calculated using post operative 3D CT analysis.

Error in inclination was significantly reduced with navigation compared to freehand technique (4° vs 6°, p=0.02). We could not detect a difference between the two groups for version error (5° vs 7°, p=0.06). There was a significantly greater number of hips within a 10° (87% vs 67%, p=0.04) and 5° (50% vs 20%, p=0.06) safe zone when navigated.

Image based navigation can substantially improve accuracy in cup orientation. The results of our freehand group appear better than historic controls, suggesting the use of a 3D plan may help to reduce technical error and improve the learning curve in this technically demanding procedure. We advocate the use of image based navigation in MoM hip resurfacing arthroplasty.

The radiographic analysis of over 5000 metal on metal (MoM) hips using Ein Bild Roentgen Analyse (EBRA) software have been recently published in an attempt to determine the influence of cup orientation on bearing function. The validation of this software relies one study, conducted in a phantom pelvis without a femoral head in situ. Three dimensional computed tomographic (3D-CT) has been shown to be more accurate for hip and knee arthroplasty than plain radiographs for measurements of component orientation and position. The accuracy of EBRA when compared to 3D-CT for MoM hips specifically is unclear.

We measured the cup orientation of 96 large diameter MoM hips using EBRA analysis of plain radiographs and compared this to 3D-CT. All measurements were made using the radiographic definition of cup orientation. The mean difference in version between the two imaging modalities was 8°; with wide limits of agreement of −21.2° and +5.6°. Three retroverted cups were not detected by EBRA. The mean difference in inclination values was 0.3°, but there was up to 9°difference between imaging modalities. When measured by 3D CT, 64% of hips were within a 10° safe zone around 45° inclination and 20° version, compared to only 24% when measured by EBRA (Fishers Exact test, p< 0.0001).

The measurement of cup orientation of MoM hips using EBRA software is insufficiently accurate, particularly for the assessment of cup version. The cup rim is obscured by the large diameter femoral head on plain radiographs. Research studies using EBRA analysis for version have limited value if accuracy of more than 20 degrees is required to draw conclusions. This software may not be suitable to measure the performance of a device or surgeon. The limitations of EBRA can be overcome, if 3D-CT with an extended Hounsfield scale for data capture is used.

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 the first use of synchrotron xray spectroscopy to characterize and compare the chemical form and distribution of metals found in tissues surrounding patients with metal-on-metal hip replacements that failed with (Ultima hips) or without (current generation, large diameter hips) corrosion.

INTRODUCTION

There is increasing worldwide interest in the assessment of wear in explanted hip components. This is due is part to high profile failures of orthopaedic components in the US, whilst in the UK hip resurfacings have been experiencing a higher than expected failure rate. The reasons for these failures are not well understood, with data from the NJR suggesting the 43% of MoM resurfacing failures are unexplained.

Wear analysis is a vital tool in determining failure mechanisms and ultimately improving the longevity of joint replacements through improved design and manufacturing control. There are currently no relevant measurement standards for the evaluation of retrieved orthopaedic components. This paper will assess two of the most commonly used techniques namely roundness measurement and co-ordinate measurement. The advantages and disadvantages of both techniques are considered in this paper.

SUMMARY

The relationship between component position, wear rate and edge loading was investigated for 115 explanted current generation Metal-on-Metal (MoM) hips. Edge wear was detected in: 63% of all hips; and 48% of those with cups positioned within Lewinnek's box.

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.

Metal-on-metal (MOM) hip resurfacings release chromium and cobalt wear debris into the surrounding joint. The hip tissue taken from failed MOM hips shows specific histological features including a subsurface band-like infiltrate of macrophages with particulate inclusions, perivascular lymphocytic infiltrate and fibrin exudation. This tissue response has been called Aseptic Lymphocytic Vasculitis Associated Lesion (ALVAL).

There is a recognised carcinogenic potential associated with hexavalent chromium and epidemiological data from first generation MOM arthroplasties may suggest an increased incidence of haematological malignancy. The ALVAL type reaction includes a marked proliferation of lymphocytes in the perivascular space and thorough investigation of this lymphocytic response is warranted.

This study aims to further characterise the lymphocytic infiltrate using immunohistochemistry and to test clonality using polymerase chain reaction (PCR).

Tissues from revised all cause failed MOM hip arthroplasties (n=77) were collected and analysed initially using routine H&E staining. Those that met the diagnostic criteria of ALVAL described above (n=34) were further stained with a panel of immunohistochemical markers (CD3, CD4, CD8 (T-cell markers) and CD20 (B-cell marker)). 10 representative ALVAL cases were selected and sent for gene rearrangement studies using PCR to determine whether the lymphocytes were polyclonal or monoclonal in nature.

The analysis of the lymphocytic aggregates in ALVAL, showed a mixed population of B and T cells. Within the aggregates, there was a predominance of B cells (CD20) over T cells (CD3). Of the 10 cases which were analysed by PCR, 7 were suitable for interpretation. None of these cases showed evidence of monoclonal lymphocyte proliferation.

The carcinogenic potential of wear debris from MOM hips, particularly affecting the haematopoietic system should be investigated. This study has shown a predominantly B-lymphocyte response in tissues surrounding MOM hips which is polyclonal. Although the numbers are small, the study suggests an immune mediated response in MOM hip tissue and excludes a neoplastic proliferation.

However, long term follow up of patients with MOM hips may be prudent.

Early stabilisation after an anterior cruciate ligament (ACL) rupture reduces future meniscal injury. We may therefore expect protection of articular cartilage from ACL reconstruction, but this has yet to be shown.

Our aim wasto determine the effect of meniscal injury on the long term risk of osteoarthritis (OA) following ACL reconstruction using Single Photon Emission Computed Tomography (SPECT, a 3 dimensional radionuclide scan).

We studied a prospective series of 31 patients (mean age at injury of 29 years) who had bone-patellar tendon-bone ACL reconstruction for unstable, ACL deficient knees. Mean follow-up was 10 years (range 9-13). Patients were separated into two groups according to the status of their menisci at the time of ACL reconstruction, those with intact menisci in group 1 (n=15) and those who required partial meniscectomy in group 2 (n=16). The contra-lateral normal knee was used as a control.

All knees were clinically stable with high clinical scores (mean Lysholm score 93 and mean Tegner activity score 6). In group 1 (intact menisci) only one patient (7%) had clinical symptoms of OA and was the only patient with increased uptake on SPECT compatible with early OA. In group 2 (partial meniscectomy), two had clinical symptoms of osteoarthritis, and five patients (32%) had increased uptake on SPECT compatible with early OA. None of the control knees had early OA on SPECT.

The prevalence of OA 10 years post ACL reconstruction, using the most sensitive investigation available, is very low in patients who had intact menisci (7%), but increases 5 fold (32%) if a meniscal tear was present. We recommend early ACL reconstruction to preserve the menisci to minimise the long term risk of OA.

It is thought that metal ions from metal on metal bearing hip replacements cause DNA damage and immune dysfunction in the form of T cell mediated hypersensitivity. To explore the hypothesis that there is a relationship between metal ion levels and DNA damage and immune dysfunction in matched patient groups of hip resurfacings and standard hip replacements reflected in the levels of lymphocyte subtypes (CD3+ T cells, CD4+ T helper cells, CD8 +T cytotoxic/suppressor cells, CD16 +Natural Killer and CD19+ B cells) in peripheral blood samples, we analysed peripheral blood samples from 68 patients: 34 in the hip resurfacing group and 34 in the standard hip arthroplasty group. Samples were analysed for counts of each sub-group of lymphocyte and cytokine production. Whole blood cobalt and chromium ion levels were measured using inductively-coupled mass spectrometry. All hip components were well fixed.

Cobalt and chromium levels were significantly elevated in the resurfacing group compared to the hybrid group (p<0.001). There was a statistically significant decrease in the resurfacing group's level of CD8+ cells (T cytotoxic/suppressor) (p=0.010). No other subgroup of lymphocytes was significantly affected. Gamma interferon levels post antigen challenge were severely depressed in the hip resurfacing group.

A threshold level of blood cobalt and chromium ions for depression of CD8+ T cells was observed. Hip resurfacing patients have levels above this threshold whilst standard hip replacements fall below it. The patients all had normal levels of CD16 +Natural Killer and CD19+ B cells suggesting that this is not a bone marrow toxic effect. Cytokine analysis confirmed that some aspects of T cell function in hip resurfacing patients are severely depressed.

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.

Introduction: Local problems of metal on metal (MOM) hip arthroplasty such as pseudotumours, neck thinning and osteolysis maybe related to concentrations of cobalt and chromium ions in the synovial fluid. There is little reported on these values. Our aim was to determine the range of metal ion levels in synovial fluid, and to investigate the relationship between these samples and simultaneous blood samples.

Methods: Synovial fluid and whole blood samples were taken from 30 consecutive patients at the time of revision surgery for a painful MOM hip. Aspirated fluid was not visibly contaminated with blood. Impants were in situ for a mean period of 31 months. All had normal renal function. Samples were analysed using ICP mass spectrometry and compared with 10 samples from patients without implants.

Results: The mean (and range) of synovial fluid metal ion levels were 1965 ug/l (30 to 13618) and 6265 ug/l (11 to 81630) for Cobalt and Chromium respectively. There was a good correlation between synovial and blood levels for both cobalt (R=0.65, p = 0.0001) and chromium (R = 0.59, p = 0.006).

Discussion and Conclusion: Metal ions in synovial fluid from MOM hips are generated from wear of the bearing surfaces, the correlation with blood metal ion levels, shown in this study, suggest that blood levels may be used as surrogate marker for hip wear rate. Our range of synovial fluid metal ion levels may be useful for those conducting in vitro studies on the biocompatibility of MOM hips.

A 10° deviation from the ideal cup orientation in Metal on Metal (MoM) bearing couples leads to increased wear and the subsequent risk of early revision surgery. We assessed the accuracy of orthopaedic trainees and consultants in achieving optimal acetabular cup orientation.

49 trainees and 18 consultants were asked to orientate an acetabular component to 40° inclination and 20° anteversion in 3 consecutive pelvic models:

osteoarthritic (OA),

The trainee group experience in performing hip arthroplasty procedures ranged from novice to expert (> 100 procedures performed). Performance was measured using an image based navigation system.

Average angular error in all tasks was less than 10°, but the range in anteversion or inclination was up to 65°. Eighteen percent of trainees were +/− 10° of the target orientation in Station A, 29% in B and 2% in C. Forty four percent of consultants achieved the safe zone in A, 16% in B and 0% in C. There was no significant difference in accuracy between the two groups in any of the tasks (p> 0.01). There was no correlation between experience and angular accuracy.

We have been unable to demonstrate trainees have the ability to achieve the optimal cup orientation in a clinically relevant safe zone. A similar range of error is found in experienced surgeons. Focused training or intra-operative computer assistance may provide the solution to improving accuracy in this core orthopaedic skill.

Introduction: The successful outcome from metal-on-metal hip resurfacing is partly dependent on the restoration of the natural biomechanics of the hip joint. Valid measurement of the geometry of the reconstructed hip is challenging using plain radiographs. CT is more accurate and precise yet rarely used to assess hip geometry. Our aims were 1) to quantify the agreement between radiographic and CT measurement of horizontal femoral offset (HFO); 2) to determine the relationship between HFO and patient gender and size; and 3) To compare HFO of the reconstructed hip to the contralateral hip.

Method: We used plain radiograph and CT data from 42 patients (23 male and 19 female) from a consecutive series with unilateral metal-on-metal hip resurfacings. We measured HFO of both hips (component and contralateral) using plain radiographs (with PACS) and CT (with Robin 3D software). Pelvic width and radial head sizes were measured on CT. Measurements were made in triplicate by 2 observers.

We graded the contralateral hip for severity of joint space narrowing on plain radiographs.

Results: There was considerable disagreement between CT and plain radiographs for HFO. HFO was statistically different between genders (p=0.0004). HFO correlated with femoral head radius (0.57, p=0.0002), but not patient size (for height (0.29, p=0.13), or pelvic width (0.25, p=0.11). There was a wide range of HFO of the contralateral hips that was comparable to the reconstructed hip.

Conclusion: To our knowledge this is the first study to show the importance of measuring HFO using CT. HFO was found to be correlated to gender and femoral head radius, but not with any other parameters of patient size. The wide range of offset was considerably greater than is available from current total hip replacement designs. Hip resurfacing may overcome this.

Performing Bilateral Knee replacements simultaneously is a controversial issue with proponents on both sides of the argument. The advantages of simultaneous arthroplasties include the administration of a single anaesthetic, reduced hospital stay and consequent reduced costs. Reuben et al (J. Arthroplasty, 1998) reported a 36% reduction in hospital costs. Patients also have a quicker return to function and Leonard et al (J Arthroplasty 2003) reported a high patient satisfaction rate of 95%.

The primary disadvantages noted in previous studies include an increase in peri operative complications–both cardiac and pulmonary. An increase in mortality figures is perhaps the most serious complication recorded in some studies. Ritter etal (Clin. Orthop. 1997) reported a 30 day mortality rate of 0.99% in bilateral simultaneous TKA as compared to 0.3% in patients who underwent a staged procedure.

Our study comprised a total of 202 patients who underwent bilateral simultaneous total knee replacements at a District General Hospital in Harlow. Harlow is one of the centres involved in the multi centric trials for the PFC Sigma Knee System and is perhaps the only centre in the UK where bilateral simultaneous procedures are carried out in significant numbers. There were 103 males and 99 females. 12 of the patients had Rheumatoid arthritis. 45% of the patients were in the 71–80 years age group, 26% in the 61–70 years age group. The average age across the entire group was 71.3 years. 35% of patients had a BMI of 25–30, 23% a BMI of 30–35, while less than 5% had a BMI of greater than 40. Most patients (44%) were ASA grade 2. The 3 most common co morbidities included hypertension(85%), coronary artery disease(25%) and diabetes mellitus (12%). 90% of the patients had the procedure performed under a General Anaesthetic and Epidural. Tourniquet time ranged from 55–159 minutes. (average 96 minutes). The patella was resurfaced in all patients. Post operatively the average drain collection was 1200 mls(range 7002600mls). Average pre op Hb was 13.8 g/dl, the post op average being 9.7 g/dl. 71% of patients required blood transfusion after surgery (average 2.8 units). Average hospital stay was 12.4 days (range 5–38 days). 6 patients required HDU admission.

Complications: None in 60%; there were 3 deaths in the first 30 days(1.5%), 2 cases of pulmonary embolism(1%); 6 cases of Myocardial Infarction (3%). There were 14 superficial wound infections and 10 patients required wound washouts. An MUA was performed on 8 knees. 2 patients had Revision Knee replacements for infection.

These figures are comparable to those in published literature. We have found Bilateral simultaneous Total Knee replacements to be a safe procedure with quick return to function.