Highly Crosslinked Polyethylene for Total Hip Arthroplasty. William H Harris, MD, D.Sc

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1 Highly Crosslinked Polyethylene for Total Hip Arthroplasty William H Harris, MD, D.Sc Alan Gerry Clinical Professor of Orthopædic Surgery Harvard Medical School Massachusetts General Hospital

2 Reduction of the Particle Burden generated at the articulation in THA can be done several ways Ceramic on Ceramic Metal on Metal Crosslinked Polyethylene

3 Estimated Utilization of Crosslinled POLY Crosslinked Poly Centerpulse 80% Stryker 80% Smith Nephew 50% Depuy / Johnson & Johnson 80% Zimmer 90%

4 What are the lessons to be learned from the Hylamer Failure? Not highly crosslinked Not shown to decrease wear Not studied after oxidation Oxidized rapidly Failed early No prior human use

5 What does the Hylamer failure tell us about highly crosslinked polyethylene that has been melted? NOTHING

6 To understand the new polyethylenes introduced in the past 5 years, you need to consider 1) Crosslinking 2) Free radical production 3) Free radical reduction

7 In short, crosslinking: 1) reduces wear 2) almost linearly 3) And optimumly at 9.5 or 10 MRad

8 Residual Free Radicals Residual Free Radicals left in the UHMWP after radiation lead to oxidation, white banding, embrittlement and reduced properties. Melting eliminates all detetable free radicals.

9 Metal on Metal,Ceramic on Ceramic, and HXPE: Advantages in common Long duration human use Low lysis incidence Relatively inert material

10 Long term in vivo human experience with highly crosslinked polyethylenes come from Oonishi & coworkers Grobbelaar & coworkers Wroblewski and coworkers

11 Charnley (1975) No wear No osteolysis Pta 4yr PO No wear Charnley 9yr PO 2mm wear Pta 19yr PO No wear Charnley 24yr PO 4.5mm wear (Ref. C.W.C. 65 Yrs)

12 85 of the 103 hips had no detectable wear at an average follow-up of 15.5 years.

13 In total, 145 total hip replacements in patients with highly crosslinked polyethylene were followed years. The data on wear and lysis are outstanding.

14 Challenge: There were no in vivo wear data on the new E-Beam highly crosslinked poly

15 In vivo wear data on e-beam, melted, highly crosslinked polyethylene 3 Studies RSA Longevity Prospective, randomized, controlled, bilateral simultaneous THA RSA Durasul Prospective, randomized, controlled,tha Martell Method Prospective, controlled compared against traditional poly

16 Bilateral Simultaneous THR RSA Study of Longevity versus Conventional Poly 54 2 years proximal penetration (micra) Gamma in Nitrogen 210 Longevity 80 Stat. Sig. P<0.005 Malchau, Herberts 03

17 Longitudinal penetration at 24 months (Mean; 2 yrs p=0,0005) Plus = proximal

18 Randomized, Controlled, Prospective RSA Study of Durasul versus Conventional Poly 61 3 years Less penetration in both supine and standing films proximal penetration supine Gamma /nitrogen 250 Durasul 130 Stat. Sig. P<0.002 Malchau, Herberts 03

19 Randomized, Controlled, Prospective RSA Study of Durasul versus Conventional Poly Note Well: After the first year there was no measurable further penetrations of the femoral head into the Durasul Polyethylene Malchau, Herberts 03

20 Martell Study of Electron Beam irradiated, subsequently melted UHMWP versus traditional poly Gamma / air E-Beam duration up to 48 mo. up to 44 mo xray pairs steady state wear 136 micra 8 micra Manning Martell Galante Harris 03

21 Martell Study of Electron Beam irradiated, subsequently melted UHMWP versus traditional poly Note Well: None of the traditional factors that influence traditional poly wear namely age gender activity level BMI head size Manning Martell Galante Harris 03

22 These three studies are remarkable in showing: E-Beam highly crosslinked poly is extremely wear resistant in vivo in humans The penetration rate is extremely low, in the same range as metal on metal and ceramic on ceramic Uniform results from three different population groups and 2 different measuring techniques None of the traditional wear factors, activity, gender, age, head size, appears to make a difference

23 Now, the key decision of which Alternate Bearing hinges on 5 key features--- Adverse Characteristics of each Material Adaptability Forgiveness Familiarity Cost

24 Adverse Characteristics of each Material : Metal on Metal metalosis, head damage on dislocation, metal ion release, hypersensitivity, renal challenge, stripe wear, third body intolerance, accelerated wear with microseparation, no constrained liners.

25 Adverse Characteristics of the Material: Ceramic on Ceramic chipping, no constrained or extended lip liners stripe wear, accelerated wear if abducted head fracture, socket fracture requires a fresh trunion - often only 3 head neck lengths

26 Adverse Characteristics of the Material Highy Crosslinked Polyethylene reduced fatigue crack propagation reduced modulus Actually reduced modulus is an advantage because it reduces the contact stresses

27 What about their Mechanical Properties All the new polys have reduced properties but all within ASTM, ISO and FDA guidelines All new polys have properties that are better than Himont 1900, which has served well in hips and knees for over 2 decades

28 ADAPTABILITY In contrast to the hard on hard bearings, highly crosslinked poly allows the widely used and highly valuable; extended lip liners offset liners eccentric liners constrained liners

29 Forgiveness Crosslinked Polyethylene is the only alternative bearing surface for which : Impingement is more benign Slight degrees of excessive abduction does not lead to stripe wear

30 Forgiveness (continued) Third body wear is very well tolerated Dislocation and/or reduction does not damage the surface of the head The surgeon does not have to risk metalosis or to avoid chipping

31 Familiarity no learning curve no changes in surgical technique looks, feels, smells and acts just like polyethylene you have always used, except no oxidation and remarkably little wear no need to leave your customary techniques to get extended lip liners, offset liners or constrained liners

32 And finally, keep in mind cost With the increasing pressure on hospitals & health care costs, justification of high cost alternative bearing over highly crosslinked polyethylene becomes even more difficult.

33 In fact, highly crosslinked polyethylene is a very attractive alternate bearing surface Many feel it is the most attractive

34 OVER 250,000 PATIENTS ARE NOW WALKING ON e-beam IRRADIATED,SUBSEQUENTLY MELTED, HIGHLY CROSSLINKED POLYETHYLENE

35 Thank You