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The Charnley Kerboull hip systemThe Charnley Kerboull hip system
Results of a 30 years experienceResults of a 30 years experience in cemented fixationin cemented fixation
L Kerboull, M Kerboull.L Kerboull, M Kerboull.
Marcel Kerboull InstituteMarcel Kerboull Institute
Imk-forum.comImk-forum.com
introductionintroduction
• basis of the mechanical principles of the basis of the mechanical principles of the cemented fixation cemented fixation
• Current ControversiesCurrent Controversies• Subsidence and collarSubsidence and collar• Surface finishSurface finish• Cementing technique and cement thicknessCementing technique and cement thickness• Classification of cemented stemClassification of cemented stem
• What must be a perfect cemented stem What must be a perfect cemented stem
• Clinical Results to support our theoryClinical Results to support our theory
The original charnley stem : the golden The original charnley stem : the golden standardstandard
8 % of stem debonding8 % of stem debonding– radiolucent line between cement radiolucent line between cement and stem in zone 1 of Amstutzand stem in zone 1 of Amstutz
– cement mantle crack cement mantle crack at the stem tip levelat the stem tip level
even so often asymptomatic, even so often asymptomatic, it was for us. it was for us. a failure of the primary stem fixationa failure of the primary stem fixation
Introduction : Current optionsIntroduction : Current options
• Modern Cementing technique and cement Modern Cementing technique and cement mantle minimal thickness were identified as mantle minimal thickness were identified as solutions to address the problem of femoral solutions to address the problem of femoral stem loosening.stem loosening.
• Our mechanical theory of the cemented fixation Our mechanical theory of the cemented fixation was initiated in 1972 and is very differentwas initiated in 1972 and is very different
Taper slip VS Composite beam
Taper-slip system
CMK
Exeter Flanged Charnley
Harris Precoat
Composite-beam system
CPT, C-stem
?
Mechanical basis Mechanical basis of stem cemented fixationof stem cemented fixation
Bone, cement and stem make Bone, cement and stem make a composite structurea composite structure- All mentioned materials have different E-Moduli- All mentioned materials have different E-Moduli
Cortex:Cortex: 12 - 18 Gpa 12 - 18 GpaPMMA:PMMA: 1.8 Gpa 1.8 GpaWHN Stainless SteelWHN Stainless Steel 250 Gpa250 Gpa
- Each of these materials had different strains under cyclic axial - Each of these materials had different strains under cyclic axial and torsional load that induce micromotion at the interfacesand torsional load that induce micromotion at the interfaces
- Micromotion primary occurs at the stem-cement interfaceMicromotion primary occurs at the stem-cement interface
- Micromotion can only be partially absorbed by cement Micromotion can only be partially absorbed by cement elasticityelasticity
- Micromotion is settled by the stem which is the stiffest Micromotion is settled by the stem which is the stiffest component component
MechanicalMechanical basis basis of stem cemented fixationof stem cemented fixation
The mechanical stability The mechanical stability
of this composite of this composite
Is depending on the mechanical properties Is depending on the mechanical properties and shape of the 3 componentsand shape of the 3 components
But the most rigid component will always But the most rigid component will always have the most positive or negative influencehave the most positive or negative influence
How to improve stem cemented fixationHow to improve stem cemented fixation
1.1. Improve mechanical properties of cement Improve mechanical properties of cement 2.2. Increase cement layer thicknessIncrease cement layer thickness3.3. Improve cementing technique Improve cementing technique 4.4. Improve bone-cement interfaceImprove bone-cement interface5.5. Modify stem design to decrease stresses Modify stem design to decrease stresses
supported by cement supported by cement 6.6. Look for a secondary fixation through a Look for a secondary fixation through a
distal migration : subsidencedistal migration : subsidence7.7. Increase link between stem and cement Increase link between stem and cement
through a rough surfacethrough a rough surface
Solutions :Solutions :
1 Improve mechanical properties of cement ?1 Improve mechanical properties of cement ?
Cement is a viscoelastic brittle material Cement is a viscoelastic brittle material characterized by relatively high characterized by relatively high
compressive strength resistance but compressive strength resistance but weakness in tension and bendingweakness in tension and bending
Acrylic bone cements: mechanical and physical Acrylic bone cements: mechanical and physical propertiesproperties
Orthop Clin North Am 2005; 36: 29-39Orthop Clin North Am 2005; 36: 29-39Kuehn KD and collKuehn KD and coll
Compressive strengthCompressive strength 90 Mpa90 Mpa
Shear strengthShear strength 50 Mpa50 Mpa
Tensile strengthTensile strength 25 Mpa25 Mpa
Improve mechanical properties of cement ?Improve mechanical properties of cement ?
« initial migration seems to be independent of « initial migration seems to be independent of the type of cement and of its viscosity »the type of cement and of its viscosity »
The influence of cement viscosity on early migration of The influence of cement viscosity on early migration of a tapered polished femoral stema tapered polished femoral stem
Glyn-Jones and collGlyn-Jones and collInt Orthop 2003 ; 27: 362-5Int Orthop 2003 ; 27: 362-5
In fact, cement was, is and will ever beIn fact, cement was, is and will ever be the weakest component of this composite the weakest component of this composite
structurestructure
How to improve stem cemented fixationHow to improve stem cemented fixation
1.1. Improve mechanical properties of cement Improve mechanical properties of cement 2.2. Increase cement layer thicknessIncrease cement layer thickness3.3. Improve cementing technique Improve cementing technique 4.4. Improve bone-cement interfaceImprove bone-cement interface5.5. Modify stem design to decrease stresses Modify stem design to decrease stresses
supported by cement supported by cement 6.6. Look for a secondary fixation through a Look for a secondary fixation through a
distal migration : subsidencedistal migration : subsidence7.7. Increase link between stem and cement Increase link between stem and cement
through a rough surfacethrough a rough surface
Solutions :Solutions :
2 Increase cement layer thickness ?2 Increase cement layer thickness ?
Wide medullary canalWide medullary canalThick cementThick cementDebonding 36 %Debonding 36 %
We found the answer to this We found the answer to this questionquestionfrom the observation of our from the observation of our Charnley first casesCharnley first cases
2 Increase cement layer thickness ?2 Increase cement layer thickness ?
Narrow canalNarrow canalThin cement Thin cement Debonding 6 %Debonding 6 %
2 Increase cement layer thickness ?2 Increase cement layer thickness ?
Dysplastic femurDysplastic femurVery Thin cement Very Thin cement
Debonding 0 %Debonding 0 %
25 y
2 Thickening cement layer was not for 2 Thickening cement layer was not for us the best choiceus the best choice
• this observation suggested that a stem fitted to cortical this observation suggested that a stem fitted to cortical bone with a thin cement layer might improve the bone with a thin cement layer might improve the cemented fixationcemented fixation
• It was also evident that an undersized stem used to get a It was also evident that an undersized stem used to get a thick cement mantle was not the good solution to prevent thick cement mantle was not the good solution to prevent distal migration, because even thicker the cement was distal migration, because even thicker the cement was not enough resistant to face the stresses transmitted by not enough resistant to face the stresses transmitted by the stem.the stem.
« initial migration seems to be independent of the thickness « initial migration seems to be independent of the thickness of the cement mantle »of the cement mantle »
Influence of cement viscosity and cement mantle thickness Influence of cement viscosity and cement mantle thickness on migration of the Exceter total hip prosthesison migration of the Exceter total hip prosthesis
Nelissen RG and collNelissen RG and coll
J Arthroplasty 2005;20:521-8J Arthroplasty 2005;20:521-8
How to improve stem cemented fixationHow to improve stem cemented fixation
1.1. Improve mechanical properties of cement Improve mechanical properties of cement 2.2. Increase cement layer thicknessIncrease cement layer thickness3.3. Improve cementing technique Improve cementing technique 4.4. Modify stem design to decrease stresses Modify stem design to decrease stresses
supported by cement supported by cement 5.5. Improve bone-cement interfaceImprove bone-cement interface6.6. Look for a secondary fixation through a Look for a secondary fixation through a
distal migration : subsidencedistal migration : subsidence7.7. Increase link between stem and cement Increase link between stem and cement
through a rough surfacethrough a rough surface
Solutions :Solutions :
3 Improve cementing technique ? 3 Improve cementing technique ?
• 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
At least 3 mm
3 Improve cement and cementing technique ? 3 Improve cement and cementing technique ?
• 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 ? 3 Improve cement and cementing technique ?
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 ? 3 Improve cement and cementing technique ?
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
So for us Cementing technique is not a main issue And must remain a friendly and simple technique
Our current routine technique
How to improve stem cemented fixationHow to improve stem cemented fixation
1.1. Improve mechanical properties of cement Improve mechanical properties of cement 2.2. Increase cement layer thicknessIncrease cement layer thickness3.3. Improve cementing technique Improve cementing technique 4.4. Improve bone-cement interfaceImprove bone-cement interface5.5. Modify stem design to decrease stresses Modify stem design to decrease stresses
supported by cement supported by cement 6.6. Look for a secondary fixation through a Look for a secondary fixation through a
distal migration : subsidencedistal migration : subsidence7.7. Increase link between stem and cement Increase link between stem and cement
through a rough surfacethrough a rough surface
Solutions :Solutions :
4 Improve bone-cement interface4 Improve bone-cement interface
Bone is twin : cortice and cancellousBone is twin : cortice and cancellous
Does cancellous bone is able to carry the load ?Does cancellous bone is able to carry the load ?NO : Ebramzabeh E and coll : the cement mantle in total hip arthroplasty : NO : Ebramzabeh E and coll : the cement mantle in total hip arthroplasty :
analysis of long term radiographic resultsanalysis of long term radiographic resultsJBJS 1994 76-A,77-87JBJS 1994 76-A,77-87
Effect of aging: Effect of aging: lowering of mechnical properties of cancellous bonelowering of mechnical properties of cancellous bone
Are Interdigitations between cement and cancellous bone necessary ?Are Interdigitations between cement and cancellous bone necessary ?
Yes if you use a force loaded stem that submit the cement to high tensile Yes if you use a force loaded stem that submit the cement to high tensile stressstress
No, if cement is only submitted to a low level of compressive stresses by a No, if cement is only submitted to a low level of compressive stresses by a canal filling stem cemented line to linecanal filling stem cemented line to line
4 Improve bone-cement interface4 Improve bone-cement interface
• Further under loading and aging cancellous bone Further under loading and aging cancellous bone undergoes compression and becomes unevenundergoes compression and becomes uneven
• In this situation, the cement mantle is subjected In this situation, the cement mantle is subjected to bending and tensile stresses and will crack.to bending and tensile stresses and will crack.
• So, removing the cancellous in the superomedial So, removing the cancellous in the superomedial part of the metaphysis and in the distal canal part of the metaphysis and in the distal canal gives the cement an even and rigid base and gives the cement an even and rigid base and prevents its crack under bending stressprevents its crack under bending stress
4 Improve bone-cement interface4 Improve bone-cement interface
FemorFemoralalReameReamerr
Modification of the bone bed Modification of the bone bed preparationpreparation
Less agressiveLess agressiveMore preciseMore precise
Instead of broachInstead of broach
Removal of cancellous bone Removal of cancellous bone which is not able to which is not able to carrycarry load with aging load with aging
How to improve stem cemented fixationHow to improve stem cemented fixation
1.1. Improve mechanical properties of cement Improve mechanical properties of cement 2.2. Increase cement layer thicknessIncrease cement layer thickness3.3. Improve cementing technique Improve cementing technique 4.4. Improve bone-cement interfaceImprove bone-cement interface5.5. Modify stem design to decrease stresses Modify stem design to decrease stresses
supported by cement supported by cement 6.6. Look for a secondary fixation through a Look for a secondary fixation through a
distal migration : subsidencedistal migration : subsidence7.7. Increase link between stem and cement Increase link between stem and cement
through a rough surfacethrough a rough surface
Solutions :Solutions :
Mechanical basis of the stem debondingMechanical basis of the stem debonding
High bending stresses in the supero medial High bending stresses in the supero medial part part break the cement mantlebreak the cement mantle
This ruptureThis rupturewidenswidens the proximal part the proximal part of the cement mantleof the cement mantledecreasesdecreases the shear stresses the shear stresses along the stemalong the stemincreasesincreases the vertical force on the distal cement the vertical force on the distal cement which breakes under tensile stress which breakes under tensile stress and finally and finally allowedallowed varus tilt varus tilt and subsidence of the stem and subsidence of the stem
Because it was for us the most logical way:Because it was for us the most logical way:
to decrease the level of stress within and at to decrease the level of stress within and at the cement stem and cement bone the cement stem and cement bone interfaces interfaces
to only subject the cement mantle to to only subject the cement mantle to compressive stressescompressive stresses
and consequently avoid the problems of and consequently avoid the problems of the cement layer thickness and resistancethe cement layer thickness and resistance
5 Modify stem design : WHY ?5 Modify stem design : WHY ?
Were retained from the Charnley stemWere retained from the Charnley stem
Polished surface Polished surface Ra 0.04 Ra 0.04 (1.6 (1.6 inch)inch)
CollarCollar
Rectangular cross sectionRectangular cross section
The cup designThe cup design
5 Modify stem design5 Modify stem design
Three main modifications of the stem Three main modifications of the stem designdesignresulted in the MK 1resulted in the MK 1
1.1. Opening the stem-neck angle to Opening the stem-neck angle to 130° instead of 125°130° instead of 125°
2.2. widening the proximal part of the widening the proximal part of the stemstem
3.3. Increasing the range of sizesIncreasing the range of sizes
5 Modify stem design5 Modify stem design
CCD angle & equal neck length
Geometrical dependence of CCD and cement mantle pressure
M1 M2
M1 < M2
Force in the superomedial partis higher with a flater CCD angledue to bigger offset
Stem CCD angle and cement loadingStem CCD angle and cement loading
5 Modify stem design5 Modify stem design
Opening the stem neck angle to 130°Opening the stem neck angle to 130°
to decrease the pressure on the supero medial and to decrease the pressure on the supero medial and infero lateral part of the cement mantleinfero lateral part of the cement mantle
• CCD angle
125° 130°
CharnleyCharnley KerboullKerboull
5 Modify stem design5 Modify stem design
Widening and thickeningWidening and thickening the stem proximal part the stem proximal part
to give it a double tapered shapeto give it a double tapered shape
with a cross-section sufficently decreasingwith a cross-section sufficently decreasing
(taper angle > 5°) (taper angle > 5°)
so thatso that
5 Modify stem design5 Modify stem design
Widening and thickeningWidening and thickening the stem proximal part the stem proximal part
–the shear stresses the shear stresses along the stem along the stem
would be would be progressively progressively transformed transformed
into their pressure into their pressure componentscomponents
–and the vertical distal and the vertical distal force force
would be would be dramatically reduceddramatically reduced
5 Modify stem design5 Modify stem design
5 modify the stem design: A large range 5 modify the stem design: A large range of sizesof sizes
1 to reconstruct a normal architecture in every case 1 to reconstruct a normal architecture in every case (limb length and abductor muscles off-set).(limb length and abductor muscles off-set).
30
40
50
60
Offset 42.4 43.0 44.2 49.2 50.6 52.2 57.1 58.5 59.9
Neck Length 32 32 32 36 36 36 40 40 40
201 202 203 301 302 303 401 402 403
2 to get a self alignment of the stem with the 2 to get a self alignment of the stem with the femoral diaphysis axisfemoral diaphysis axis
5 modify the stem design: A large range 5 modify the stem design: A large range of sizesof sizes
“ in our study, line to line stem without distal centralizer were better aligned than undersized stems fitted with a centralizer”
T Scheerlinck and collCT analysis of defects of the cement mantleAnd alignment of the stemJBJS 88 B,1 19-25
A large range of sizesA large range of sizes
Symmetrical anatomy
33 to have between to have between stem and femoral canalstem and femoral canalthe best fitthe best fit
to reduce load transmitted to reduce load transmitted to ciment layer to ciment layer
5 modify the stem design: A large range 5 modify the stem design: A large range of sizesof sizes
Under these conditionsUnder these conditions
Cement mantle, cement bone Cement mantle, cement bone interface are no longer subjected interface are no longer subjected to shear stresses to shear stresses
and micromotion is reduced to a and micromotion is reduced to a level tolerated by creep of cementlevel tolerated by creep of cement
With this canal filling stem, the With this canal filling stem, the double tapered shape is acting to double tapered shape is acting to decrease the stresses on the decrease the stresses on the cement, but with an undersized cement, but with an undersized stem the distal force increases and stem the distal force increases and the stem subsidesthe stem subsides
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
Ant. Post.Ant. Post.
Relatively thick > 2 Relatively thick > 2 mmmm
Med. Lat. Med. Lat.
Thin or very thin < 1 Thin or very thin < 1 mmmm
How is the cement mantle thickness How is the cement mantle thickness around a CMK stemaround a CMK stem
unevenunevenBut never incompleteBut never incomplete
T Scheerlinck and collCT analysis of defects of the cement mantleAnd alignment of the stemJBJS 88 B,1 19-25
Uneven cement mantle but never incompleteUneven cement mantle but never incomplete
And protected of overloading by the stem designAnd protected of overloading by the stem design
How to improve stem cemented fixationHow to improve stem cemented fixation
1.1. Improve mechanical properties of cement Improve mechanical properties of cement 2.2. Increase cement layer thicknessIncrease cement layer thickness3.3. Improve cementing technique Improve cementing technique 4.4. Improve bone-cement interfaceImprove bone-cement interface5.5. Modify stem design to decrease stresses Modify stem design to decrease stresses
supported by cement supported by cement 6.6. Look for a secondary fixation through a Look for a secondary fixation through a
distal migration : subsidencedistal migration : subsidence7.7. Increase link between stem and cement Increase link between stem and cement
through a rough surfacethrough a rough surface
Solutions :Solutions :
How to improve the cemented stem How to improve the cemented stem fixation ?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
Subsidence and collar ?Subsidence and collar ?
Is Subsidence a normal event ?Is Subsidence a normal event ? - probably - probably No forNo for the CMK which the CMK which is not designed to subside is not designed to subside
and does not subside.and does not subside.
« The French paradox »: Langlais, Ling, Kerboull, « The French paradox »: Langlais, Ling, Kerboull, Sedel. JBJS Br, 2003. Sedel. JBJS Br, 2003.
Why ??Why ?? - We choose the stem which best fills the medullary canal - We choose the stem which best fills the medullary canal there is no space for the stem to subside.there is no space for the stem to subside.- The stem does not subside due to the cohesion forces acting on - The stem does not subside due to the cohesion forces acting on
the two polished (cement/stem) surfaces and micromotion the two polished (cement/stem) surfaces and micromotion stays under its cement fracture levelstays under its cement fracture level
The collarThe collar may decrease the distal force applied to ciment plugmay decrease the distal force applied to ciment plugdoes not prevent migration if it occursdoes not prevent migration if it occursjust an intraoperative reference to set leg lengthjust an intraoperative reference to set leg length
Does CMK subsides ?Does CMK subsides ?
Long-Term Migration Using EBRA-FCA of Stems Cemented Line-to-Line According to the "French Paradox" PrinciplesHamadouche, Moussa; Kerboull Luc; Kerboull, MarcelORS 2008
The EBRA-FCA software is a validated method designed to assess migration of afemoral component through comparable pairs of radiographs. Accuracy has been reported to be better than ± 1.5 mm (95% percentile), with a specificity of100% and a sensitivity of 78% for the detection of migration of more than 1.0 mm, usingRSA as the gold standard
Does CMK subsides ?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) deceased8 patients (10 hips) lost to follow-up.
1689 radiographs (mean 10.3 per hip) were digitized. 263 (15.6%) excludedNo 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.
Does CMK subsides ? NODoes 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.
What is Subsidence ?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.
How to improve stem cemented fixationHow to improve stem cemented fixation
1.1. Improve mechanical properties of cement Improve mechanical properties of cement 2.2. Increase cement layer thicknessIncrease cement layer thickness3.3. Improve cementing technique Improve cementing technique 4.4. Improve bone-cement interfaceImprove bone-cement interface5.5. Modify stem design to decrease stresses Modify stem design to decrease stresses
supported by cement supported by cement 6.6. Look for a secondary fixation through a Look for a secondary fixation through a
distal migration : subsidencedistal migration : subsidence7.7. Increase link between stem and cement Increase link between stem and cement
through a rough surface : surface finishthrough a rough surface : surface finish
Solutions :Solutions :
Why the polished stem became matt ?Why the polished stem became matt ?
•Initiation of stem loosening: Initiation of stem loosening:
debonding of the cement to prosthesis interfacedebonding of the cement to prosthesis interface
Improvement of the bond through a matt surfaceImprovement of the bond through a matt surface
Composite beam conceptComposite beam concept
11
Why the polished stem became matt ?Why the polished stem became matt ?
Manufacturer request to facilitate productionManufacturer request to facilitate production
22
Matt stem (CMK3)Vecteur Orthopédique
Polished stem (MKIII)Stryker Howmedica
Ra = 3m Ra = 0.4m
Ovalcross-section
Quadrangularcross-section
Stem Radiological loosening
Polished stems: 1 hip (revised)
related to PE socket wear
Matt stems:16 hips (9 revised)
3 related to PE socket
13 debonding at the bone cement interface
associated to femoral osteolysis
Matte stems loosening (CMK3)
1y 3y 5y
Matte stems loosening (CMK3)
0
20
40
60
80
100
0 2 4 6 8 10 12 14
Follow-up (Years)
% n
ot lo
osen
ed Polished stems
Matte stems
Femoral stems survival with radiologic loosening as the end-point
97.3%97.3%
78.9%78.9%
Log-rank test, p < 0.001
Significant lower survival for matt stems
Similar observations made with other stems designs:
- Exeter stem: Howie et al., JBJS Br, 1998
40 matt VS 40 polished stems, Minimum 9 year-FU
4 matt stems loosened, 0 polished stem
- Iowa Stem: Collis et al., JBJS Am, 2002
122 grit-blasted VS 122 polished stems, mean 5,8
year-FU
6 gritt-blasted stems loosened, 0 polished stem
DISCUSSION
Surface finish change Surface finish change
cross section change ?cross section change ?
What was our main mistakeWhat was our main mistake
VSVS
do not forget Micromotiondo not forget Micromotion
Fact:- Bone, cement and stem form a composite
- All mentioned materials have different E-ModuliCortex: 12 - 18 GpaPMMA: 1.8 GpaWHN Stainless Steel 250 Gpa
- As all material deform differently As all material deform differently under loadunder load
micromotion, settled by the stem, micromotion, settled by the stem, occursoccurs
SO ……… SO ………
With a Matt surface – No relative movement between stem and cement
possible
– Micromotions result in localy debonded areas at the bone cement interface which create an abrasive medium that induce osteolisys
Bon
e
PM
MA
Ste
m
While a polished surface (associated with a While a polished surface (associated with a good design)good design)
micro movements occurs at the stem-cement viscoelastic micro movements occurs at the stem-cement viscoelastic interface and the bone-cement interface is protectedinterface and the bone-cement interface is protected
Bon
e
PM
MA
Ste
m
- An increased cement-
prosthesis bond
- increases shear stresses at the
cement-bone interface
- and finally induces loosening
at the bone-cement interface
We conclude that
Round or Rectangular cross Round or Rectangular cross section ?section ?
Fact : Fact : Stems are prone to relative rotation Stems are prone to relative rotation when torque forces are appliedwhen torque forces are applied
Round vs Rectangular : peak stressesRound vs Rectangular : peak stresses
M2
M1
shear stressshear stress compressive stresscompressive stress
M1
F1a
F1b
a
b
Rounder cross section–Prevents peak stresses at the angle–But Increased shear stresses at the interface
Rectangular cross Rectangular cross sectionsection
–Might induce peak Might induce peak stressesstresses–Applies compressive Applies compressive stresses on the stresses on the cementcement
Too round results in problemsToo round results in problems
Too edgy might result in problemsToo edgy might result in problems
(increased hoop stresses)(increased hoop stresses)
Look for a Look for a compromisecompromiseAlmost rectangular with smooth anglesAlmost rectangular with smooth angles
cross section design : delicate choicecross section design : delicate choice
Results of the first generation of CMKResults of the first generation of CMK
Charnley: Radiological aseptic femoral looseningCharnley: Radiological aseptic femoral loosening220 hips220 hips
Charnley: Radiological aseptic femoral looseningCharnley: Radiological aseptic femoral loosening220 hips220 hips
50%50%
60%60%
70%70%
80%80%
90%90%
100%100%
00 55 1010 1515 2020
74%74%
Long term results : elderly patientsLong term results : elderly patients
Charnley Kerboull stem aseptic femoral loosening200hips mean age 65 years old
Charnley Kerboull Charnley Kerboull stemstem aseptic femoral looseningaseptic femoral loosening200200hips mean hips mean age 65 age 65 years oldyears old
70%70%
80%80%
90%90%
100%100%
00 55 1010 1515 2020
98%98%
CharnleyCharnley rate : 74%rate : 74%
polishpolish
RCO, 1995RCO, 1995
Long term results : patients < 40 years oldLong term results : patients < 40 years old
European Journal of Orthopaedic Surgery and TraumatologyEuropean Journal of Orthopaedic Surgery and Traumatology1996, 6, 241-2461996, 6, 241-246
Long term results : Long term results : CDHCDH
Journal of ArthroplastyJournal of Arthroplasty2001, 16, N°82001, 16, N°8
Charnley vs CMKCharnley vs CMK
30 Y14 Y
Longterm featuresLongterm features
No cement under the tip
Dysplastic stems and acetabular Dysplastic stems and acetabular reconstructionreconstruction
20 years
Results of the next generations of CMKResults of the next generations of CMK
Long term results in patients under 50Long term results in patients under 50CORR, 418, Jan 2004CORR, 418, Jan 2004riesries
• 287 THR performed from 1975 to 1990287 THR performed from 1975 to 1990• Randomly sorted from a cohort of 2804 patientsRandomly sorted from a cohort of 2804 patients• Senior and junior surgeonsSenior and junior surgeons• 222 patients, 144 females and 78 males222 patients, 144 females and 78 males• MeanMean age : 40,1 y ( ± 8 y ; 15,5 - 50 y). age : 40,1 y ( ± 8 y ; 15,5 - 50 y).• Mean weight : 63 kg (Mean weight : 63 kg (± 18,2 kg ; 37 – 116 kg) ± 18,2 kg ; 37 – 116 kg)
0
20
40
60
80
100
120
StatusStatus Mean follow-up Mean follow-up (years)(years)
Number of hipsNumber of hips
ReviewedReviewed 16,1 16,1 ± 4,6± 4,6 210 ( 73,2%)210 ( 73,2%)
Died of Died of unrelated causesunrelated causes
5,4 5,4 ± 3,1± 3,1 10 (3,5%)10 (3,5%)
Lost to follow-Lost to follow-upup
10,8 ± 5,110,8 ± 5,1 42 (14,6%)42 (14,6%)
RevisedRevised 12,6 ± 6,112,6 ± 6,1 25 (8,7%)25 (8,7%)
Mean follow-up : 14,5 years Mean follow-up : 14,5 years ( (±± 5.1, 6m to 25 y) 5.1, 6m to 25 y)
52 hips had a follow-up greater than 20 years52 hips had a follow-up greater than 20 years
Radiological results : Stem looseningRadiological results : Stem loosening
No No looseningloosening
Definite or Definite or probable probable looseningloosening
Potential Potential looseningloosening
Number Number
of hipsof hips
271271
95,1%95,1%12124,2%4,2%
44
0,7%0,7%
10 aseptic, 1 septic, 1 after a periprosthetic fracture
Radiological loosening : stemRadiological loosening : stem
Implants Implants designdesign
SurfaceSurface SectionSection AsepticAseptic
looseninglooseningHipsHips
MK IMK I PolishedPolished QuadrangulQuadrangularar
1 0,7%1 0,7% 139139
CMK 2CMK 2 MatteMatte OvalOval 2 4%2 4% 5151
MK IIIMK III PolishedPolished QuadrangulQuadrangularar
00 2727
CMK 3CMK 3 MatteMatte OvalOval 8 8 11,5%11,5%
7070
Matt vs Polished : p = 0,0001
Survival rate : revision for any reasonSurvival rate : revision for any reason
0
,2
,4
,6
,8
1
0 5 10 15 20 25 30
20 years85,4%
95% sup : 92,4 %95% inf : 78,4 %S
uv
iva
l rat
e %
Su
viv
al r
ate
%
Follow-up yearsFollow-up years
P= 0,0001P= 0,0001
Survival rate : stem loosening, surface Survival rate : stem loosening, surface finishfinish
Su
viv
al r
ate
%S
uv
iva
l rat
e %
Follow-up yearsFollow-up years
0
,2
,4
,6
,8
1
0 5 10 15 20 25 30
polishedpolishedmattmatt
88,5%
96,4%
Survival rate : PE wear dependantSurvival rate : PE wear dependant
0
,2
,4
,6
,8
1
0 5 10 15 20 25 30
Wear <= 0,1 94,8 %
Wear > 0,1 70,6 %P = 0,002
Su
viv
al r
ate
%S
uv
iva
l rat
e %
Follow-up yearsFollow-up years
What we learnt at the end of this studyWhat we learnt at the end of this study
• The Kerboull cemented prosthesis The Kerboull cemented prosthesis
could provide satisfactory and could provide satisfactory and
durable results for 20 years in 85 durable results for 20 years in 85
% of patients younger than 50 % of patients younger than 50
years.years.
• The stem has a reliable fixation The stem has a reliable fixation
without subsidence and without subsidence and with a with a
simple surgical techniquesimple surgical technique
• So in our mind it remains a good So in our mind it remains a good
solution and reliable solution even solution and reliable solution even
for young patientfor young patient
What we learnt at the end of this studyWhat we learnt at the end of this study
• Stem design and surface finish are the most important Stem design and surface finish are the most important
factors. factors.
• Surface must be definitely polished to protect bone-Surface must be definitely polished to protect bone-
cement interface from overloading.cement interface from overloading.
• Cement is weak, and must be protected by the stem of Cement is weak, and must be protected by the stem of
excessive tensile and shear stresses, and just used to excessive tensile and shear stresses, and just used to
fill the gap between the bone and a canal-filling stem. fill the gap between the bone and a canal-filling stem.
• Following these mechanical principles cement quality, Following these mechanical principles cement quality,
cement thickness and cementing technique become cement thickness and cementing technique become
minor concernsminor concerns
• Be careful, the classifications and terminology used in Be careful, the classifications and terminology used in
the literature are confusing because they mainly refer the literature are confusing because they mainly refer
to the cementing technique and not to the design and to the cementing technique and not to the design and
the surfacethe surface
• The CMK is a loaded taper but initially stable due to its The CMK is a loaded taper but initially stable due to its
fitting to the medullary canalfitting to the medullary canal
Thank you for Thank you for your attentionyour attention
• Trust the stem design more than
the cement mantle .