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heer van den Eeden


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heer van den Eeden

  1. 1. Metal on Metal resurfacing Tot. Hip. Dr F M C van den Eeden F.M.C. Orthopedisch chirurg M.C.A. M C A Alkmaar In 2007 : > 23000 artificial total hips implanted in the Netherlands Less than 1000 Resurfacing type In 2010 RECALL of hipprosthesis by Depuy orthopedics (Johnson & Johnson) -ASR Resurfacing system -ASR XL Acetabular system
  2. 2. 13% reoperations before 5 y p 93000 recall worldwide Early revisions MOM related to wear Metal on Metal Hip Resurfacing - Tribology and Critical Issues Jack Thomas Regional Director - Europe Corin Group p p plc
  3. 3. Background Resurfacing is not new R f i i t Metal-metal bearings are not new Development of modern metal-metal resurfacing What went wrong with historical Resurfacing Arthroplasty What went wrong with historical Metal-metal Arthroplasty Technical theory behind the Cormet Clinical and In Vitro Studies Clinical Follow-up p Hip Tribology Tribology is: ‘a study that deals with the design, friction, wear friction wear, and lubrication of interacting surfaces in relative motion (as in bearings or gears)’ (WWWebsters) What factors affect the tribology of hip bearings? Materials Loads Geometry Sliding speeds Lubrication theory L b i ti th
  4. 4. Lubrication Theory y Lubricating films can separate bearing surfaces Dental drills, air hockey etc drills Thickness of the lubricant thickness primarily depends on: Material Load (up to 3.5x Bw) Contact stress Sliding velocity Conformity (Radial Clearance/Sphericity) Rotation frequency Radial Clearance The Bottom line… h l Lubricant films are formed during relative motion If the lubricant film is thicker than the relative roughness the surfaces will separate separate. Define lambda ratio: Minimum Film Thickness O Cumulative Surface Roughness
  5. 5. Hydrodynamic Lubrication O ! 3 Lubricant film fully separates the surfaces This is the ideal regime – effectively zero wear Motion M ti Bearing Surface B i S f Bearing Surface Motion Boundary Lubrication O < 1 Lubricant is present but not thick enough to separate the surfaces Surfaces can be protected b b S f b t t d by boundary l b i d lubricants ( t i t (proteins, lipids etc) Asperities on opposing surfaces contact leading to friction and p pp g g wear Motion Bearing Surface Bearing Surface Motion
  6. 6. Mixed Lubrication 1 < O < 3 Combination of boundary and fluid film lubrication Occurs with intermittent motions Sometimes the surfaces are separated and sometimes not There is occasional surface contact leading to some surface wear Bearing Surface g Motion Bearing Surface Motion So… So How do we engineer Hydrodynamic Lubrication? 1. Engineer the materials 2. Engineer the geometry Diameter Radial Clearance Sphericity
  7. 7. Effect of Material Stiffness (Elastic modulus) Surface roughness Bearing Material Elastic Modulus (Gpa) Typical Surface Roughness, Ra (microns) Alumina 400 0.005 High Carbon CoCr 200 0.005-0.01 UHMWPE 1 1 Stiffness has a small effect on lubricating film thickness Surface roughness has a massive effect: UHMWPE is 200 times rougher than metal or ceramic Minimum Fil Thi k Mi i Film Thickness O Cumulative Surface Roughness Effect of Bearing Diameter Large Bearing Diameters Large bearing = lower contact stress Increased sliding speed generates an increased fluid film BUT sliding distance is increased!
  8. 8. What does it all mean? Metal/ceramic UHMWPE bearings Rough surfaces/Large radial clearances/Poor sphericity R h f /L di l l /P h i i ¾ Boundary lubrication ¾ Wear is directly proportional to load and sliding distance ¾ More wear with larger bearing diameters For Example… Example THARIES/Wagner/Freeman Metal-UHMWPE Resurfacings Massive wear due to large diameter Metal-UHMWPE articulation Metal UHMWPE - Wrong Tribology
  9. 9. What does it all mean? Metal on metal bearings We can achieve very smooth surfaces (Ra = 0.05 microns) 0 05 We can achieve excellent sphericity (<10 microns) We can achieve optimum radial clearances Therefore we can achieve a lubricated contact! • Especially with Larger diameter bearings For Example: Metal on metal simulator study, Smith et al* study al 7 llion cycles s 6 5 We Rate mm per mil 4 m3 3 2 ear 1 0 16mm 16 22.225mm 22 225 28mm (new) 28 ( ) 28mm (worn) 28 ( ) 36mm 36 Joint Diameter * Proc Inst Mech Eng [H] 2001; 215(2): 161-170
  10. 10. What went wrong with Historical M-M h ih i i l Hip Arthroplasty? p p y Poor Manufacturing tolerances Equatorial bearing! Poor design Component fixation Impingement p g The result? Early incidence of loosening with metallosis No such problems with the Charnley at the time. Summary of Tribology We know how to engineer the bearing We know what not to do with reference to historical Resurfacing and Metal-metal THRs So what are the current critical issues in Metal-metal Hip Resurfacing?
  11. 11. Critical Issues? C iti l I ? Wear Do Standard Heat-Treatment Processes Influence Heat- Large Diameter Metal-on-Metal Wear ? Metal-on- – An In Vitro Study Under Normal & Adverse Gait Conditions John G. Bowsher, Jim Nevelos, Julia C. Shelton Trans 49th ORS, New Orleans, 2003 Metal Ion Release Medium Term Serum Cobalt and Chromium Levels in Patients with Metal-metal Resurfacing V Reddy MD, J Dorairajan MD, J Nevelos PhD, S Krikler PhD FRCS(Orth). Trans 70th AAOS, New Orleans, 2003. Do Standard Heat-Treatment Processes Influence Heat- Large Diameter Metal-on-Metal Wear ? Metal-on- – An In Vitro Study Under Normal & Adverse Gait Conditions Physiological Hip Self-Centring Bearing Anti-Rotate Anti Rotate Arm (x2) Simulator Study Horizontal Torque y Cell ± 20 Nm z As Cast vs HIPed Torque Cell Adapter x and Solution d S l ti Cup Fixturing Annealed 40mm Serum Chamber Direction of Torque Measurement T Bearings 360q (y-axis) 23q Fixed in Standard and y-x plane Severe Testing r23q Biaxial Rocking Motion g Joint Conditions Force ABD / ADD FLEX / EXT (a)(b) Fig. 1. Schematics showing (a) hip joint simulator, and (b) torque measurement and definition of biaxial rocking motion.
  12. 12. Results (a) Running-In (b) Steady-State (c) Simulated (d) Simulated 0 to 1 mc 1-3, 4-6 mc Fast Walking Fast Jogging Normal Walking Normal Walking 7.0 ** 6.0 ** (m m 3 /1 0 6 C y c le s ) M ean W ear R ate 5.0 ** 4.0 3.0 2.0 m 1.0 0.0 (n=6) (n=8) (n=18) (n=22) (n=6) (n=6) (n=8) (n =8) (n`=8) As cast HIPed & Solution Annealed ** - statistically significant Conclusions – Wear Study r HIPing and solution annealing did not adversely affect the wear rates of large diameter metal-on-metal articulations, even under severe gait conditions. r Both alloys possessed very different micro-structures and surface carbide structure, Fig 2a-2b, however, this appeared to have little affect on the wear mechanisms mechanisms. r A combined head and cup wear rate of 0.45 mm3/106 cycles (k = 1.5 x10-8 mm3 N-1 m-1) for the 40 mm diameter metal bearings is lower than that reported for smaller head diameters, thus suggesting improved lubrication for larger bearing sizes. r The wear of both groups was found to be highly sensitive to the type of patient activity tested, with fast jogging activities generating a 10–fold increase in metal wear generation compared to normal walking, k = 2.4 x10-7 mm3 N-1 m-1.
  13. 13. Medium Term Serum C b l and Chromium Levels di S Cobalt d Ch i l in Patients with Metal-metal Resurfacing Metal- 39 patients followed for up to 6 years Blood serum levels of Co and Cr measured using a standardized technique Two distinct patient groups: General Population Outliers No effect: Corin McMinn vs. Cormet resurfacing Bilateral (few data points) Results – General Population 250 Ov e rall av e rage ion le v e ls Co Cr 200 ion level (nmo l/l) 150 100 n 50 0 Pre Pre- 3 10 16 22 28 34 38 45 52 57 63 76 op Time (months)
  14. 14. Younger vs. Older Patient Groups 250 250 ion levels patients under 50 at primary operation ion levels patients over 60 at primary operation Co 200 200 Co Cr Cr ion level nmol/l l 150 150 ion level nmol/l 100 100 50 50 0 0 0 3 10 16 22 28 34 39 46 54 0 4 10 16 22 28 33 38 53 Months months Decrease in ion levels could be due to a decrease in wear after ‘running-in’ plus improved joint stability. Outliers - Results 4000 AP Co Outliers Compared with Average Population AP Cr LB Co 3500 LB Cr SM Co 3000 SM Cr Ave Co Ave Cr 2500 Ion level (nm ol/l) 2000 1500 1000 500 0 0 12 24 36 48 60 72 Months Post-op
  15. 15. Conclusions – Metal Ion Study In the vast majority of patients with metal-metal hip resurfacing there is a small but early rise in serum metal ions over the first 2-3 years but the levels then gradually diminish over time . g y Steep cups seem to be associated with increased levels, which could be due to wear and therefore increased ion release into the body. Summary Cormet has the right tribology for clinical success and is the product of 11 years continuous controlled evolution Cormet is the only resurfacing hi prosthesis C t i th l f i hip th i with peer reviewed published wear data and l long term i release measurements t ion l t
  16. 16. Cormet Update – July ‘03 Jack Thomas Regional Director - Europe Corin Group p p plc
  17. 17. Latest Developments p McMinn published a paper in Hip International The paper attacks Cormet and g heat treatments in general General Paper is in a Supplement with the proceedings from a symposium at EFORT 2002 o sy pos u O 00 Guest editor was G Bannister (MMT user) Not peer reviewed as such Lots of inaccuracies Lots of very poor science No surprises there then
  18. 18. Key points Alleged: ’94 –HIPed; ’95 – SA ’96 – HIP d and SA All d HIP d SA, HIPed d Fact: ’91-’95 – Trucast (94% HIPed) Fact 1996 – C F Centaur HIP d and SA ( HIPed d (reverse engineered i d from the original McMinn castings). Difference between HIPed and HIPed and SA? Negligible Current Cormet Metallurgy Unchanged and re-validated
  19. 19. More failures in 1996 ?? 94-95 – three failures (1 infection, 1 head collapse, 1 loosening with dysplasia) 1996 - 5 failures (1 infection, 3 cup loosenings, 1 awaiting revision) Metallosis and osteolysis seen with the cup loosenings Plus one from Belgium with pain (and alleged severe wear) at 50 months but well fixed. ) McMinn Sales by Year Year No of Implantations. 1991 23 1992 56 1993 57 1994 95 1995 238 1996 440 Total 909
  20. 20. Failures with wear Case from Belgium with l ith low carbide bid content (allegedly) Cup is open and anteverted. Could be a yp y hypersensitivity reaction Cup Loosenings Cups have tilted HA on smooth Wear secondary to cup movement or cup movement secondary to wear?
  21. 21. Wear as related to carbide content MMT data (Calowear) from Treacy presentation 1.4E-03 1 4E 03 Error Bars = 1 standard 90% confidence interval 1.2E-03 Wear Coefficien K (mm3 N-1 m-1) 1.0E-03 1.26E-03 1.03E-03 1.03E-03 8.0E-04 9.46E-04 nt, 6.0E-04 4.0E-04 W 2.0E-04 0.0E+00 As Cast HT High N2 HIP & HT Material Type 100,000 times the wear factors seen clinically!! Hang on. McMinn alleges that some 1996 resurfacings are fine and other have metallosis Ah, this is because HIP and SA produces a range of microstructures. microstructures A very convenient excuse . HIP and SA is used because it gives the most reproducible results
  22. 22. Remember… The data shown by McMinn would lead us to believe that forged materials also have high wear 200,000 Metasul since 1988 would suggest otherwise Conserve plus is also HIP and SA with no reported problems with wear These arguments are fabrications made up to support a faulty hypothesis Published wear data Mean Volumetric Wear at 3M cycles 7 6 metic Wear (m ) 3 mm 5 4 3 Volum 2 1 0 28mm low C 36mm wrought, 36mm wrought, 36mm wrought, 40mm as cast 40mm HIPed and 54mm as cast, 54.5mm as cast, head/High C cup mean 143 (142-146, mean 123 (120-126, mean 105 (105, (mean 220) SA Mean 220 mean 276 (254-307, mean 108 (83-129, mean 50 n=3) n=4) n=3) n=3) n=4)
  23. 23. Wear Data Wear is dependant on head size and radial clearance and NOT metallurgy Although low carbon/low carbon couples are not great This was supported at the recent Second International Conference on Metal-metal Hip Prostheses: Past Performance and Future Directions. Montreal 2003. Directions 2003 McMinn d M Mi and MMT are b becoming i i increasingly i l t d i l isolated by the scientific community and are losing credibility in the eyes of surgeons. surgeons Thank you