Metal on Metal Hips. Total Hip Replacement. Total Hip Replacement

Transcription

1 Metal on metal hips: Questions Metal on Metal Hips Jim Sullivan Why were metal on metal hips popular? Are all metal on metal hips the same? What are the problems with the ASR hip? What are the issues with chromium and cobalt? Who needs revision surgery? What are the findings at surgery? Do the metal levels drop after revision? Total Hip Replacement Total Hip Replacement Hip replacement is one of the most successful and cost effective operations performed today. 35,000 procedures in Australia annually Expectations have evolved Patients younger, more active and living longer 40 years post Charnley LFAs

2 Australian Joint Replacement Registry Aseptic loosening (linear osteolysis) and focal or expansileosteolysisare the same biological process Most common causes of revision (31335 revisions) Loosening / osteolysis 55.4% Dislocation 14.4% Infection 11.7% Fracture 9.0% Generation of particulate debris Access of joint fluid to implant/bone interface Biological response to particulate debris Others causes: pain, implant breakage, wear, malposition, leg length discrepancy Theoretical advantages of metal on metal STEADY-STATE WEAR PERIOD to FIELD one PINHEAD (0.9 mm3) of WEAR DEBRIS M-o-M compared to UHMWPE - Volumetric Wear Rate MATERIALS DIAMETER (mm) IMPLANTATION PERIOD Metal-on-Polymer days Ceramic-on-Polymer days Metal-on-Metal days years Eileen Ingham & John Fisher - Institute of Medical and Biological Engineering University of Leeds years Source: Prof D. Dowson, University of Leeds

3 Australian Joint Replacement Registry Head size and dislocation Most common causes of revision (31335 revisions) Loosening / osteolysis 55.4% Dislocation 14.4% Infection 11.7% Fracture 9.0% Metal on metal articulations allow large diameter bearings which increase inherent stability of the hip 28mm 32mm ROM Others causes: pain, implant breakage, wear, malposition, leg length discrepancy 38mm Metal on Metal Hips Metal on metal bearings > 300,000 hips > 15 years follow-up Clinical outcomes same as other bearings No gross material failures No run-away wear Rare osteolysis Operate under mixed lubrication (boundary and fluid film) in ideal circumstances Very low wear rate and particle debris generation Allow large diameters - minimizing dislocation risk Weber: Clin.Orthop., 1996 Wagner and Wagner: Clin.Orthop., 2000 Hilton et al.: Clin.Orthop., 1996 Schmalzried et al: Clin.Orthop., 1996 Wagner and Wagner: Clin.Orthop., 1996 Dorr et al: J.Bone Joint Surg.Am., 2000 Sensitive to sub-optimal implant alignment Metal ion release

4 Problems with the ASR hip Are all metal on metal hips the same? ASR resurfacing released in Australia in 2003 ASR conventional THR released in 2004 Resurfacing identified as an outlier in 2007 AOA NJRR annual report with a revision rate twice other resurfacings Resurfacing and conventional implants identified in 2008 and 2009 reports as outliers. Depuy voluntarily recalled ASR implants at the end of patients in Australia had received these implants (4410 conventional and 1167 resurfacing) One British centre (Langton, 2011) reports a revision rate of almost 50% for conventional THR and 25% for resurfacing at 7 years No, but The AOA NJRR reports a higher revision rate for all metal/metal when the head size is greater than 28mm The risk is even greater with conventional THR than resurfacing The yearly cumulative percent revision at 5 years for conventional THR is Cormet 7.1 ASR 7.8 BHR 4.9 Are all metal on metal hips the same? Are all metal on metal hips the same? The yearly cumulative percent revision at 5 years for resurfacing is ASR 10.9 Durom 7.6 Cormet 6.0 BHR 3.5 McMinn (designer of the BHR) reports personal results of 98% survivorship at 13 years in men Oswestry Resurfacing Registry reports 95% survivorship at 10 years for 4000 BHRs from 141 surgeons. 11 year post BHR

5 What are the problems with the ASR hip? What are the problems with the ASR hip? Some differences from Birmingham Hip Resurfacing ASR BHR Subtendedarticular surface angle 144 to Mean radial clearance (µm) Wall thickness at rim (mm) / 4.6 Manufacturing method of head As cast As cast Manufacturing method of cup HIP/SA As cast The thinner more flexible shell may be subject to deformation on insertion Equatorial contact with increased wear or spin out What are the problems with the ASR hip? What are the issues with chromium and cobalt? The sub-hemispherical design (reduced subtended articular surface angle) may predispose to edge loading and increased wear It reduces the tolerated margin of error for cup placement Cobalt, chromium, molybdenum and nickel are important trace elements required for normal physiology Following MOM hip replacement blood levels of these metal ions increase and can be grossly elevated in loose or wearing implants Wear leads to release of metal ions and nanoparticles. The relative surface area and biological activity usually increases as particle size reduces The wear debris is phagocytosed by macrophages and giant cells. In the lysosomes the metal particles are subjected to corrosion producing high intracellular levels of ions causing cell death The result is excessive generation of metal ion debris which causes local reaction and possible systemic effects

6 What are the issues with chromium and cobalt? What are the issues with chromium and cobalt? The local cytotoxic response in not directly dose dependent but may be caused by a vasculitis or a cell-mediated hypersensitivity The local response of the tissues is now grouped under the term - Adverse Reaction to Metal Debris ARMD includes Metallosis Aseptic lymphocytic vasculitis-associated lesions pseudotumours Chromium most commonly exists in 3 forms: Cr(VI), Cr(III) phosphate and Cr(0) metallic form Hexavalent chromium is a known respiratory carcinogen (not found in tissue) Cr(III) is less reactive Cobalt at toxic levels is associated with neurological symptoms (hand tremor, incoordination, vertigo, cognitive decline, depression, hearing loss and visual disturbance Peripheral neuropathy cardiac symptoms (arrhythmias and cardiomyopathy) rash What are the issues with chromium and cobalt? ASR recall Chromium and cobalt levels are measured by inductively-coupled plasma mass spectometry (ICP-MS) technique The 2 laboratories in Sydney have different normal reference ranges RPA: Cobalt <10 nmol/l and Chromium <26 nmol/l Douglass: Cobalt <20 nmol/l and Chromium nmol/l Pathology reports state serum/plasma cobalt levels >85 nmol/l indicate toxicity Clinical symptoms not expected at levels < 100 nmol/l In most cases of clinical symptoms levels exceed 1000 nmol/l 367 patients with 380 ASR hips (includes 26 bilaterals), performed between March 2004 and November 2008 were reviewed Follow-up assessment History of symptoms Examination Radiograph MRI or Ultrasound Cobalt and Chromium levels

7 ASR recall ASR recall Most patients asymptomatic Local symptoms Pain Tightness, loss of movement Lump Weakness Systemic symptoms Fatigue Poor concentration, memory loss Irritabilty Poor balance Hearing loss Rash Cardiac symptoms Examination generally unremarkable Trochanteric bursitis Radiographs Cup inclination angle Osteolysis ASR recall ASR recall MRI and Ultrasound defined fluid around hip, pseudotumour and bursitis Cobalt Levels 76.6% < 85 nmol/l 12.5% > 150 nmol/l 3.65% > 500 nmol/l 1.6% > 1000 nmol/l 367 patients with 380 ASR hips (includes 26 bilaterals), performed between March 2004 and November 2008 were reviewed 12 prior to recall (3.3%) These revision were indicated on pain, loosening or fracture and equate to a cumulative rate of 0.7% per year Since the recall a further 62 revision have been performed (17.4%)

8 Indications for revision surgery Findings at surgery Since the recall revisions are precipitated by Staining or Metallosis High metal ion levels without or without symptoms Joint effusion Cobalt > 1000 nmol/l Cobalt > 250 nmol/l in younger patient Cobalt > 150 nmol/l rising by 50 over time Pseudotumour Osteolysis Soft tissue necrosis Adverse reaction to metal debris identified on imaging, again with or without symptoms Osteolysis Large bursal collection or pseudotumour with elevated metal levels Elevated ion levels with implant malalignment Patient reques Findings at surgery Findings at surgery Local soft tissue reaction or ARMD is not proportional to metal ion levels 52 year old male, complains of occasional ache but no loss of function Cobalt 70nmol/L

9 Findings at surgery Findings at surgery In only one case has there been any significant soft tissue necrosis 63 year old female 40 months post primary with symptoms of pain and weakness Cobalt 183, Chromium 164 Necrosis of hip abductor insertion with exposed bone of the trochanter, but no osteolysis Acetabular revision is not technically difficult Most cases revised to explant only 1-2mm larger in size Only one case of stem revision (not radiologically loose) Co 129, Cr 88 Ongoing hip adbuctor weakness post revision Do the levels drop after revision? Reviews After revision to ceramic on ceramic, or ceramic on poly articulation The cobalt level does drop dramatically after removal of the articulation and soft tissue debridement Retesting at 3 months (1057 to 66), (1049 to 60), (2348 to 111), with lower pre-op levels near normal by 3 months Mean ion levels of revision patients Chromium Cobalt Pre-revision Post-revision A meta-analysis (Onega, Baron and MacKenzie, 2006) comprising 1,435,356 person-years of follow-up, and a recent analysis (Visuri et al, 2010) of 310,341 person-years have shown no overall increase in cancers Some cancers such as bowel and lung are less numerous, others such as prostate were more common The Onega study suggested a late increase in melanoma, and cancers of the bladder, kidney and oro-pharynx, which raises the question of metal exposure The effects of exposure to higher metal ion levels are unknown

10 Conclusions Thankyou Results of large diameter metal on metal hips are variable and indications under review Hip resurfacing (BHR types) remains a successful procedure in young males UK Register (2010) found 5 year mortality rate for resurfacing 1.8% compared with total hip replacement 9.9%, even after adjustment for age, gender and activity level Surgical technique critical with small margin for error Ongoing monitoring required with ion measurement and imaging Low threshold for revision in patients with symptoms, evidence of ARMD or high metal ion levels 3rd Generation 350K Cycles ASR