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The Charnley Kerboull hip system Results of a 30 years experience in cemented fixation

The Charnley Kerboull hip system Results of a 30 years experience in cemented fixation. L Kerboull, M Kerboull. Marcel Kerboull Institute Imk-forum.com. introduction. basis of the mechanical principles of the cemented fixation Current Controversies Subsidence and collar Surface finish

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The Charnley Kerboull hip system Results of a 30 years experience in cemented fixation

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  1. The Charnley Kerboull hip systemResults of a 30 years experiencein cemented fixation L Kerboull, M Kerboull. Marcel Kerboull Institute Imk-forum.com

  2. introduction • basis of the mechanical principles of the cemented fixation • Current Controversies • Subsidence and collar • Surface finish • Cementing technique and cement thickness • Classification of cemented stem • What must be a perfect cemented stem • Clinical Results to support our theory

  3. 8 % of stem debonding radiolucent line between cement and stem in zone 1 of Amstutz cement mantle crack at the stem tip level even so often asymptomatic, it was for us. a failure of the primary stem fixation The original charnley stem : the golden standard

  4. Modern Cementing technique and cement mantle minimal thickness were identified as solutions to address the problem of femoral stem loosening. Our mechanical theory of the cemented fixation was initiated in 1972 and is very different Introduction : Current options

  5. Taper slip VS Composite beam Taper-slip system Composite-beamsystem Flanged Charnley Exeter CPT, C-stem Harris Precoat ? CMK

  6. Bone, cement and stem make a composite structure - All mentioned materials have different E-Moduli Cortex: 12 - 18 Gpa PMMA: 1.8 Gpa WHN Stainless Steel 250 Gpa - Each of these materials had different strains under cyclic axial and torsional load that induce micromotion at the interfaces Micromotion primary occurs at the stem-cement interface Micromotion can only be partially absorbed by cement elasticity Micromotion is settled by the stem which is the stiffest component Mechanical basis of stem cemented fixation

  7. The mechanical stability of this composite Is depending on the mechanical properties and shape of the 3 components But the most rigid component will always have the most positive or negative influence Mechanical basis of stem cemented fixation

  8. Improve mechanical properties of cement Increase cement layer thickness Improve cementing technique Improve bone-cement interface Modify stem design to decrease stresses supported by cement Look for a secondary fixation through a distal migration : subsidence Increase link between stem and cement through a rough surface How to improve stem cemented fixation Solutions :

  9. Cement is a viscoelastic brittle material characterized by relatively high compressive strength resistance but weakness in tension and bending Acrylic bone cements: mechanical and physical properties Orthop Clin North Am 2005; 36: 29-39 Kuehn KD and coll 1 Improve mechanical properties of cement ? Compressive strength 90 Mpa Shear strength 50 Mpa Tensile strength 25 Mpa

  10. Improve mechanical properties of cement ? « initial migration seems to be independent of the type of cement and of its viscosity » The influence of cement viscosity on early migration of a tapered polished femoral stem Glyn-Jones and coll Int Orthop 2003 ; 27: 362-5 In fact, cement was, is and will ever be the weakest component of this composite structure

  11. Improve mechanical properties of cement Increase cement layer thickness Improve cementing technique Improve bone-cement interface Modify stem design to decrease stresses supported by cement Look for a secondary fixation through a distal migration : subsidence Increase link between stem and cement through a rough surface How to improve stem cemented fixation Solutions :

  12. 2 Increase cement layer thickness ? We found the answer to this question from the observation of our Charnley first cases Wide medullary canal Thick cement Debonding 36 %

  13. 2 Increase cement layer thickness ? Narrow canal Thin cement Debonding 6 %

  14. 2 Increase cement layer thickness ? Dysplastic femur Very Thin cement 25 y Debonding 0 %

  15. 2 Thickening cement layer was not for us the best choice • this observation suggested that a stem fitted to cortical bone with a thin cement layer might improve the cemented fixation • It was also evident that an undersized stem used to get a thick cement mantle was not the good solution to prevent distal migration, because even thicker the cement was not enough resistant to face the stresses transmitted by the stem. « initial migration seems to be independent of the thickness of the cement mantle » Influence of cement viscosity and cement mantle thickness on migration of the Exceter total hip prosthesis Nelissen RG and coll J Arthroplasty 2005;20:521-8

  16. Improve mechanical properties of cement Increase cement layer thickness Improve cementing technique Modify stem design to decrease stresses supported by cement Improve bone-cement interface Look for a secondary fixation through a distal migration : subsidence Increase link between stem and cement through a rough surface How to improve stem cemented fixation Solutions :

  17. Why : To increase resistance of cement to bone interface through a deep penetration of cement to create interdigitation To get an homogeneous and more resistant cement mantle 3 Improve cementing technique ? At least 3 mm

  18. How ? : Low viscosity cement Vacuum preparation to avoid air High Pressure water cleaning High pressure cement insertion Stem tip centralizer undersized stem 3 Improve cement and cementing technique ?

  19. What can we expect from these techniques ? Prevent early distal migration ? Definitely no Prevent late loosening No influence for the shaped closed fixation, like CMK May be for the loaded-taper fixation, like Exceter But with a time consuming, aggressive for the bone and demanding technique With an important increase of the overall price of the proceedure 3 Improve cement and cementing technique ?

  20. Plugging and simple washing of the medullary canal Use of a Standard viscoelasticity cement Simple Cement insertion using a syringe High Pressure is applied by the canal filling stem 3 Improve cement and cementing technique ? Our current routine technique So for us Cementing technique is not a main issue And must remain a friendly and simple technique

  21. Improve mechanical properties of cement Increase cement layer thickness Improve cementing technique Improve bone-cement interface Modify stem design to decrease stresses supported by cement Look for a secondary fixation through a distal migration : subsidence Increase link between stem and cement through a rough surface How to improve stem cemented fixation Solutions :

  22. Bone is twin : cortice and cancellous Does cancellous bone is able to carry the load ? NO : Ebramzabeh E and coll : the cement mantle in total hip arthroplasty : analysis of long term radiographic results JBJS 1994 76-A,77-87 Effect of aging: lowering of mechnical properties of cancellous bone Are Interdigitations between cement and cancellous bone necessary ? Yes if you use a force loaded stem that submit the cement to high tensile stress No, if cement is only submitted to a low level of compressive stresses by a canal filling stem cemented line to line 4 Improve bone-cement interface

  23. Further under loading and aging cancellous bone undergoes compression and becomes uneven In this situation, the cement mantle is subjected to bending and tensile stresses and will crack. So, removing the cancellous in the superomedial part of the metaphysis and in the distal canal gives the cement an even and rigid base and prevents its crack under bending stress 4 Improve bone-cement interface

  24. 4 Improve bone-cement interface Removal of cancellous bone which is not able to carry load with aging Modification of the bone bed preparation Femoral Reamer Instead of broach Less agressive More precise

  25. Improve mechanical properties of cement Increase cement layer thickness Improve cementing technique Improve bone-cement interface Modify stem design to decrease stresses supported by cement Look for a secondary fixation through a distal migration : subsidence Increase link between stem and cement through a rough surface How to improve stem cemented fixation Solutions :

  26. High bending stresses in the supero medial part break the cement mantle This rupture widens the proximal part of the cement mantle decreases the shear stresses along the stem increases the vertical force on the distal cement which breakes under tensile stress and finally allowed varus tilt and subsidence of the stem Mechanical basis of the stem debonding

  27. Because it was for us the most logical way: to decrease the level of stress within and at the cement stem and cement bone interfaces to only subject the cement mantle to compressive stresses and consequently avoid the problems of the cement layer thickness and resistance 5 Modify stem design : WHY ?

  28. Were retained from the Charnley stem 5 Modify stem design Polished surface Ra 0.04  (1.6  inch) Collar Rectangular cross section The cup design

  29. Opening the stem-neck angle to 130° instead of 125° widening the proximal part of the stem Increasing the range of sizes Three main modifications of the stem designresulted in the MK 1 5 Modify stem design

  30. Stem CCD angle and cement loading 5 Modify stem design

  31. to decrease the pressure on the supero medial and infero lateral part of the cement mantle Opening the stem neck angle to 130° • CCD angle 130° 125° 5 Modify stem design Charnley Kerboull

  32. to give it a double tapered shape with a cross-section sufficently decreasing (taper angle > 5°) so that Widening and thickening the stem proximal part 5 Modify stem design

  33. 5 Modify stem design Widening and thickening the stem proximal part • the shear stresses along the stem • would be progressively transformed • into their pressure components • and the vertical distal force • would be dramatically reduced

  34. 5 modify the stem design: A large range of sizes 1 to reconstruct a normal architecture in every case (limb length and abductor muscles off-set).

  35. 2 to get a self alignment of the stem with the femoral diaphysis axis 5 modify the stem design: A large range of sizes “ in our study, line to line stem without distal centralizer were better aligned than undersized stems fitted with a centralizer” T Scheerlinck and coll CT analysis of defects of the cement mantle And alignment of the stem JBJS 88 B,1 19-25

  36. A large range of sizes Symmetrical anatomy

  37. 5 modify the stem design: A large range of sizes • to have between • stem and femoral canal • the best fit to reduce load transmitted to ciment layer

  38. Under these conditions Cement mantle, cement bone interface are no longer subjected to shear stresses and micromotion is reduced to a level tolerated by creep of cement With this canal filling stem, the double tapered shape is acting to decrease the stresses on the cement, but with an undersized stem the distal force increases and the stem subsides

  39. How to choose the appropriate size regarding to the canal filling concept • According to the preoperative planning • Not the largest one that will impose to ream the cortices but • The first size that get • self alignment • primary stability

  40. How is the cement mantle thickness around a CMK stem Ant. Post. Relatively thick > 2 mm Med. Lat. Thin or very thin < 1 mm uneven But never incomplete T Scheerlinck and coll CT analysis of defects of the cement mantle And alignment of the stem JBJS 88 B,1 19-25

  41. Uneven cement mantle but never incomplete And protected of overloading by the stem design

  42. Improve mechanical properties of cement Increase cement layer thickness Improve cementing technique Improve bone-cement interface Modify stem design to decrease stresses supported by cement Look for a secondary fixation through a distal migration : subsidence Increase link between stem and cement through a rough surface How to improve stem cemented fixation Solutions :

  43. How to improve the cemented stem fixation ? • If you consider subsidence as a positive event to lock the fixation of the stem in the cement mantle you will try to favourize it but you will need to reinforce the cement to lower the distal migration • If you consider subsidence as a primary failure of the initial fixation you will try to protect cement of over loading to prevent distal migration and to protect the ciment the only possibility you have is to work on the stem design

  44. Is Subsidence a normal event ? - probably No forthe CMK which is not designed to subside and does not subside. « The French paradox »: Langlais, Ling, Kerboull, Sedel. JBJS Br, 2003. Why ?? - We choose the stem which best fills the medullary canal there is no space for the stem to subside. - The stem does not subside due to the cohesion forces acting on the two polished (cement/stem) surfaces and micromotion stays under its cement fracture level The collar may decrease the distal force applied to ciment plug does not prevent migration if it occurs just an intraoperative reference to set leg length Subsidence and collar ?

  45. Does CMK subsides ? Long-Term Migration Using EBRA-FCA of Stems Cemented Line-to-Line According to the "French Paradox" Principles Hamadouche, Moussa; Kerboull Luc; Kerboull, Marcel ORS 2008 The EBRA-FCA software is a validated method designed to assess migration of a femoral component through comparable pairs of radiographs. Accuracy has been reported to be better than ± 1.5 mm (95% percentile), with a specificity of 100% and a sensitivity of 78% for the detection of migration of more than 1.0 mm, using RSA as the gold standard

  46. Does CMK subsides ? Materials and Methods: In 1988 and 1989, 164 primary THA in 155 patients by the two seniors of us. mean age 63.8 ± 11.6 years. Polished CMK Results: 73 patients (77 hips) still alive F.U 17.3 ± 0.8 years (15-18 years), 8 patients (8 hips revised for high polyethylene wear 66 patients (69hips) deceased 8 patients (10 hips) lost to follow-up. 1689 radiographs (mean 10.3 per hip) were digitized. 263 (15.6%) excluded No migration curve obtained for 22 of the 164 femoral components (13.4%). Mean subsidence of the entire series was 0.63 ± 0.49 mm Using a 1.5 mm threshold for subsidence, 4 of the 142 stems have migrated. Using a threshold of 2 mm for subsidence, none of the 142 stems have migrated.

  47. Does CMK subsides ? NO this study demonstrates that contrary to other cemented femoral components that have also provided excellent survival in the long term but frequently associated with stem subsidence, The CMK Stem, a highly polished double tapered femoral component with a quadrangular cross-section and a collar, filling the medullary canal, and cemented with a simple technique does not subside up to 18-year follow-up.

  48. What is Subsidence ? Subsidence below 2 mm may be probably absorbed by cement creeping and contributes to lock the stem but overloads the cement Subsidence over 2 mm always induces a fracture of the cement mantle and is a loosening that may be tolerated Because distal migration without varus tilt is often well clinically tolerated that might explain the good survival of taper-slip stem if only revision is considered as a failure.

  49. Improve mechanical properties of cement Increase cement layer thickness Improve cementing technique Improve bone-cement interface Modify stem design to decrease stresses supported by cement Look for a secondary fixation through a distal migration : subsidence Increase link between stem and cement through a rough surface : surface finish How to improve stem cemented fixation Solutions :

  50. Why the polished stem became matt ? 1 • Initiation of stem loosening: • debonding of the cement to prosthesis interface • Improvement of the bond through a matt surface • Composite beam concept

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