Citation for published version (APA):
Waal Malefijt, de, J., Slooff, T. J. J. H., & Huiskes, H. W. J. (1987). The actual status of acrylic bone cement in total hip replacement : a review. Acta Orthopaedica Belgica, 53(1), 52-58.
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'52
THE ACTUAL STATUS OF ACRYLIC BONE CEMENT
IN TOTAL HIP REPLACEMENT
A
review
by J. DE WAAL MALEFIJT, T.J.J.H. SLOOF and R. HUISKES"
The utilization of polymethylmethacrylate to sta· hilize· total hip replacements has tremendously in· creased since Charnley introduced the acrylic cement as a fixative in 1960.
M~ny contemporary studies and experiments have resulted in increased knowledge about cement pro· perties and side.effects.
In tbis article the present status of acrylic cement
in
total hip replacement is contemplated, with the aid of a comprehensive and actual review of the Uierature, and supplemented with remarks and recommendations resulting from a longlasting expe· rience with cemented hip arthroplasties in our clinic.Native knowledge of mixing and handling instruc· tions regarding the application of each separate cement is indespensable, while also the importance of practising meticulous cementing techniques in order to obtain optimal primary implant fixation, is .strongly emphasized. When hip replacements are performed according to these developments, a reduc· tion of mechanical loosening of cemented hip arthro· plasties is liable to be achieved.
Keywords, hip arthroplasty; polymethylmetha-crylate; improved techniques.
Mots cles, hanche ; prothese".tDtale; polymethyl. methacrylate; teChniques avancees.
INTRODUCTION
A slirvey of the extensives literature concerning utilization of polymethylmethacrylate (PMMA) for fixamon of joint implants suggests how revolutionary ,ACJ8,Or,thopredica B!;llglca.- Tome 53, Fasc. 1, 1987
Charnley was in 1960 when he stabilized his first arthroplasty of the hip with acrylic cement (3).
Since then, the properties and side-effects of acrylic cement have been studied by many investigators. These studies have resnlted in major and dramatic improvements in the use of PMMA heralding an entire new ero of cemented arthroplasties.
Long term follow-up studies will have to demon-strate whether all changes lead to an improvement of results.
THE INTERLOCKING OF ACRYLIC CEMENT AND BONE
The durability of a cemented arthroplasry is clo-sely related to the quality of fixation of aorylic cement to the bone, and is also dependent on the interfacial bond between cement and prosthesis.
Acrylic cement is exclusively a «filler », adapting the surface irregularities of the surrounding bone tis-sue to the relatively smooth surface of the inserted proslhesis (macro-interlock).
In this way the area -of contact between cement and bone is increased and forces are distributed over a larger bone surface area, so that local overloading is avoided.
By pressurizing the cement during insertion, the aarylic cement penetrates into cancellous bone inter-stices with better mechanical interdigitation as a result (micro-interlock).
This bonding between bone and acrylic cement by interdigitation is caIled «primary mechanical ancho-rage ».
.. Department of Orthopedics, St. Radboud Hospital, Univer-sity of Nijmegen.
mechanical anchorage» as the steady svate, which can be obtained when all biological reactions in the surrounding tissues following an arthroplasty, have
become stationary.
PRIMARY MECHANICAL ANCHORAGE The quality of the primary mechanical stability
of
the cemented prosthesis mainly depends on :- the viscosity of the acrylic cement,
- cement pres'5urization,
- blood pressure,
- structure of the .surrounding bone tissue, - cleanliness of the bone tissue,
- implant design,
- implant insertion technique,
dimensional changes of the cemen t.
In the past, several acrylic cements have beeo developed which produce different viscosity during the «mixing» and «handling» ph.,es in the
poly-merization process. A number of experiments,
inclu-ding our owns have shown that there are no signi-ficant differences between these cements as far as mechanical properties are concerned, if the mixing
technique is properly standardized (7).
Low viscosity cement penetrates easier in
trabe-cular hone. Noble and Swarts (22) (1983) per-formed an in vitro study, in which they demonstrated
a clear correlation between the viscosity of cement
and final penetration depth. (22).
The depth of penetration also depends on the size of the interstitial cavities ,in cancellous bone.
It is impossible to obtain adequate primary anchorage
in a sclerotic bone cavity, Furthermore, the time at
which the cement is pressurized within the prepared hone is of critical importance··in achieving the desired mechanical interdigitation (20).
Only if the cancellous bone has been thoroughly cleaned with a la"age system (waterpick), and sub-sequently dried, the hony structure can be optimally utilized (16). Hwskes and Slooff have shown, that thermal damage to the hone is likely to occur with a cement penetration of 5 mm or more (15). Walker et al. (31) (1984) found, that there seems to be
a correlation between an increase of the strength of
the cement-bone composite and the depth of
pene-tration under similar conditions of bone preparation.
ideal penetration depth amounts 3 to 4 mm: Other . researchers have proposed a penet",tion depth"
"of
5-10 mm (16) Considering all vhese fadors, it is extremely difficult to develop a standardized technique which guarantees 0 ceDtoin penetratiort depth in the clinical situation. Although the viscosity of the cement should be low in order toobhln adequate cement penetration, a sufficiently high visco' sity is needed to enable pressurization (22). In this respect, exact knowledge of the mising conditions for PMMA hone cements is i.ndispensable. Preferably, the pressure exerted on the bone tissue by the cement dough is maintained at a level substantially above the bleeding pressure, until the viscosity of the dough is high enough to resis t the occurrence of a hematoma between cement and bone, which will compromise the strength of the i.nterface (13).The distvibution of the cement and the direction in whioh the acrylic flows during prosthetic insertion, also depends on the geometry of the hone cavity as well as the desi!Jll of tbe implant. During insertion into the cement, a prosthesis should only be moved in one direction; the contact force must be applied starically and must be maintained until polymeriza-tion is complete. Any movements of the pressing aid by the surgeon in this stage, always leads to undesirable migration of the cement and often to disruption of the integrity of the cement mantle.
During and after the polymerization process, the cement dough undergoes dimensional changes. In the litera tINe, an overall expansion of 2 to 5 volume percent has been mentioned, as a result of expansion of enclosed air and vaporized monomer bubbles, fol-lowed by thermal shvinkage (25).
The shrinkage may result in a gap between the bone and the cement mass, which may constitute a threat to primary mechanical anchorage.
SECONDARY ANCHORAGE
A large number of !J'lrameters are involved in the long-term quality of the hone-cement bonding: the initial damage to the bone as a result of
the operation,
side-effects of acrylic cement, - positioning of the prosthesis,
54 J. DE WAAL .MALEFIJT, T.J.J.H. SLOOFF, R. HUISKES
. .,-ith~ load on the artificial joint,
, ,..,..,.,genera1 condition, age and in particular the weight of the patient,
.0;-,trauma/infections,
. ageing of the cement,
. , .'C"C ,changes ;n bone diameter in elderly patients ( osteoporosis).
Some of these parameters areas follows: ~) Damage to the bone, causeJ by cement con-stituents.
b) Other influences on secondary anchorage.
a) . Damage to the bone, caused by cement
proper-ties' ;or constituents.
Polymerization heat.
. 'in
nearly all publications on this subject, the beat fr~ .the polymerizing bone cement is unanimously considered to be an important causative factor of initial bone necrosis. Feith concluded from rabbit experiments that the thermic tissue damage far ex<;eeds the necrosis which results from ischemia by the operative interference with the blood supply (8). '. In a finite element model, Huiskes demonstrated atheoretical relationship between the maximum tem-perature, the cement layer thickness, and the amount of . bone necro.is, whereby the stem of a metal femotal endoprosthesis in .the cement leads to a reducvion of the maximum temperature, acting as a« heat sink» (14) .... :He also established that geometrical! conditions, a hil1her initial bone temperature, and the inferior t~erm~l properties of HDPE compared to metal, a~tI:ibute to a greater chance for thermal damage during acetabular cup fixation with cement than dllring fixation of intramedullary (metal) implants. :, 'Furthermore, Huiskes evolved the hypothesis, that
a
higher temperature may have an Jndirect effect on tissue necrosis by increasing the cytotoxicity of residual monomer (14).Of course the amount of bone necrosis depends on the. duration of exposure to polymerization tempera-tures .. Eriksson demonstrated, that bone developes necrosis when exposed to a temperarure of 47" C or higher during one minute or more (6).
As previously stated, it remains uncert';n what will be the exact effect of deep penetration of acrylic cement in trabecular bone, as a result of pressuriza-tion techniques.
Acta' Orthopmdic8"Belgica, Tome 53, Fasc. 1, 1987
As long as no definite clinical data are available on this subject, it is advisible to take all possible mea8mes to reduce the maximal temperarure (cooling the bone with a waterpick, avoiding thick cement mantles etc.) .
Considerable precooling of the prosthetic
compo-nents, before insertion and/or the cement consti-tuents prior to mixing, may lead to a reduction of the -temperature at the bone cement interface.
A disadvantage however is, that the setting time is prolonged, resulting in a compromise of the mecha· nical properties of the cement (14).
Monomer.
In the past, methylmethactylate intoxication was considered to be the principal cause of circulatory
disturbances and even cardiac arrest, during implan-tation of cemented joint arthroplasties, in particular
in the femur.
Recent studies have now suggested, that this so called «implantation syndrome» is imtiated by fat, bone marrow cells and probably entrapped air, being forced into the vascular system by the pressure under which bone cement is implanted into the medullary canal. This can be visualized using intraoperative transoesophageal two dimensional echocardiography continuously (12).
Utilization of a vent during cement insertion, but
also cleaning of the trabecular structure of the bone with a lavage system, reduces the likelyhood of this embolization to occur (28).
Many in vitro and in vivo studies have been designed to evaluate the cytotoxicity of monomer. Linder established that monomer, even when ther-mal effects and pressure on the tissue are elimi-nated, causes microcirculatory dis·rurbances resulting in tissue -necrosis (19).
Therefore, waiting with the introduction of cement until just prior to the setting time, has no beneficial effect with respect to the possibility of introducing less monomer to the patient (17)_
Furthermore, it has been shown that the concen-tration of unpolymerized monomer at the interface is
only high enough to cause tissue necrosis until a maximum of 4 hours after insertion of the cement dough (29).
Dimethylparatoluidine.
The catalyst NN-dimethyl-p-toluidine (DMpT) is
By means of gaschromatographic analysis, they identified DMpT in acrylic cement even 10 years after total hip replacement (2). The clinical significance of these findings however, is yet unknown.
Other cement constituents.
The effect of additives like antibiotics, colourants and contrast media on the mechanical properties of the cement can not be neglected. Barium sulphate (Roentgen contrast medium) for instaoce, was found to be associated with necrosis of lamellar bone. However, it seems unlikely that these reactions will
occur when this contrast medium is utilized within acrylic cement.
Ageing of polymethylmethacrylate.
As the age of implanted cement increases, its strength slowly reduces.
By diffusion processes leading to volume changes, and cyclic loading of the material, the acrylic turns
into a more rigid substance with a decrease in
resi-lience (9, 14).
The abrasion of particles of acrylic cement, in
the presence of relative motions, may subsequently lead to agressive granulomatous tissue reactions,
which in turn will contribute to bone resorption and further loosening of the implant (33).
b) Other influences on secundary anchorage. It has been 'shown, that the diameter of long bones increases with aging, by subperiosteal expansion and endosteal bone resorption (27). It remains to be seen, whether these reactions also take place after intramedullary fixated arthtOplasties.
Theoretically the gap which is thus formed hetween implant and bone, may initiate a definite loosening of the prosthesis. But also, the design and mechanical properties of the implant, bodyweight of the patient and the loading on the prosthesis play an important role in bone remodeling.
DISCUSSION
In terms of polymerization heat, toxicity of cement constituents, dimensional changes and unfavourable
cemented arthroplasties, which in most publications' have been reported as a mean of. 90 % good: results a£.ter ten years (4). Moreover, it appears reasonable to assume thatoptlmization of implant desig!lS\ cements and cementing techniques will even imProve these results and increase the average . expected lifespan of cemented total hip replacement. The firSt clinical results of modern techruques subsmutiare this assumption (10).
Improvements in implant design.
FemOTal components were provided with abroad and rounded medial border, and sharp edges «< stteSs-raisers») were eliminated. Preferably, .he width of the stem 's more than half the width of the medul: lary canal (1).
Concerns over the incidence of acetabula:r com· ponent loosening have motivated further research into acetabular cups. The addition of" metal backing to a polyethylene component serves to stiffen the otherwise flexible cup, and this stiffening serves mnch the same purpose as the subchondral bone in the natural acetabulum.
Metal backing thus tends to di.tribute loading around the prosthetic component more uniformly, which results in lower peak stresses ;n cement, sub-chondral bone, and trabecular bone within the aceta-bular region. Furthermore, metal backing probably establishes a heat"sink effect with respect to the polymerization heat generated by the acrylic cement. The first clinical results of hip arthroplasry with the use of metal backed acetabular components are encouraging (11). Having a unifonn cemellrt mantle is considered to be advantageous in terms of stress in the cement. For that reason, spacers have been added to acetabular components, to guarantee a uniform cement mantle thickness.
Preferably, these spacers are made of PMMA, in order to have the same mechanical properties as the
cement mantle.
In the past, the critical importance of the inter' facial bond betwee1?a metal implant and bone cement. has been underestimated. Raab et al; demonstrated, that the implant-cement interface deteriorates over time when exposed to 37" C saline. They established
1;6 J. DE WAAL J~ALEFIJT, T.J.J.H. SLOOFF, R. HUISKES pqor:.&t.;tic and fatigue properties of these interfaces
compared to the &arne properties for bone cement, sllggejlrlngtbat failure of tbis interface may be a precursor' as well as a major cause of cement failure and. subsequent implant loosening ( 26 ). This was cOnfirmed by Huiskes, who srated that the cement stress is dramatically increa&ed when the implant. acryLic cemeOtt ·interface is loose (14).
The strength of tbe cement-metal. interface can be increased by PMMA1"recoating. In this process, a thin layer of bone· cement is added to ·the metal sur· face of the prosthesis by the manufacturer.
Improvement of acrylic cement.'
In orthopaedic research, many =periments bave the objectivl" to develop a new aery lie cement with reduced polymerization and enhanced mechanical pro· petties, by alternating polymer formulations, addition of· reinforcing agents and changejl in !!he particle size . distribution of the prepolymerized powder.
As hand mixed cement isa brittle material, several methods have been explored to enhance cement pro· peDties through reduction of cement porosity. These methods include centrifugation of tbe cement mixture, ,vacuum mixing techniques or mixing under ultra· sonk vibrations. The fatigue life of cement can thus be increased by porosity reduction, while the implant· c.ement interface strength as well as the bone-<:ement interface strength are enhanced (7). The success of these techniques depends on the viscosity of cement during the mixing and handling phase. Vacuum· mixing can lead to a 70 % reduction of cementporo-sity, resulrlng in a 20 to 40 % increase of cement· strength (24). A major di&advantage of centrifuga. tion might be, that cement constituents or additives,
IlS a);'esuk of densrty differences compared to PMMA,
are tbrCIW" to the periphery of the cement. Thus, the crementstrength is locally reduced. This isparllicularly :marked· in « cold» specimens, in which the viscosity
·bas ~i:tot yet inctea&ed, while die rorce of centrifuga· tion also is of significant influence (30).
. There is no general agreement about the benefits fiommurasonic vibrabion of the cement mixture (7). Cement porosity is not only dependent on the mixing technique. Noble et al. used Surgical Simplex bone .cement in a laboratory study on cadaver femurs. They. found that the degree and distributJion of the pqres in the cement also depended on the cement .thickness and the position of the cement in the femur,
:'A~a Ortoop~dica Belglca. Tome 53, Fasc. f, 1987
both of which are related to the prosthetic design
(23 ).
Improvements in cementing techniques.
Several measures to improve implant £ixation with acry'ic cement have a.lr£Jldy been mentioned pre-viously. The bulk shape of the bone cavity has to be
meticulously prepared in such a manner, that a con-gruous cement mantle geometry can be obtained aftee insertion of the implant. Large bone defects are preferably filled with bone grafts. The use of pul-sating saHne lavage to mechanically debr,ide the
pre-pared bone surfaces and scrupulous cleaning and drying of the bone cavity before inserti()n of acrylic cement has significantly altered tbe primary quality of the bone cement interface.
Miller et al. demonstrated, that thorough cleaning of the bone surface in a cortical tube model in the dog produced a virtual doubling of the cement-bone surface shear strength (21) .
In terms of cement distribution, it is well esta-blished that plugging the medullary canal leads to a much stronger bone-cement interface. Insertion of
the acrylic with a cement syringe, using a vent to allow air to escape, is recommended.
Knowledge of the exact mixing and handling time of the utilized cement is indispensible. In order to perform a proper cement technique one should no~
insert the cement until the appropriate viscosity is obtained, which enables us to pressurize the cement resulting in adequate penetration in the trabecular bone. The pressurization techniques as described by
Ling, Weber and Harris deserve aHention.
They introduced several methods and instrumen ts to maintain pressure on ,the cement dough until i1: has cured (10, 18, 32).
CONCLUSION
The critical importance of ,an optimal primary fixa-tion of cemented arthroplasties to improve long. term results, is now gaining wide acceptance. The little additional time which is needed to practice all new cementing techniques, can absolutely be neglected compared to the duration of the revision surgery. It: is not to be expected that other fixation techniques will equal the quality of the primary anchorage as obtained with acrylic cement. Meticulous surgery
RESUME
]. de WAAL MALEFIJT, T.J.J.H. SWOFF et R_ HUISKES. - Le paint sur I'usage du ciment acrylique en arthroplastie totale de hanche.
Depuis l'introduction en 1960 par Charnley du metha-crylate de methyle pour fixer les protheses totales de hanche. cette technique connut un essort peu ordinaire. Nos connaissances des proprietes et des ef£ets secondaires du dment se sont considerablement developpees grace
a
de nombreuses etudes qui permirent une notable amelioration des techniques d'emploi de ce materiau.Dans eet article, les auteurs font Ie point sur l'abon-dante litterature parue au sujet des techniques d'emploi du dment acrylique. Ces donnees, ainsi que la tres longue experience des auteurs menent
a
un certain nombre de conclusions pratiques formuIees sous forme de recom-mandations pour l'emploi du ciment. Les auteurs sou-lignent !'importance d'avoir une connaissence approfon-die des proprietes du ciment employe et surtout de possedera
fond une technique de cirnentage precise qui perrnet une fixation optimale de !'implant. Vne ame-lioration des techniques de cimentage, grace aces prescriptions pratiques, amenera logiquementa
une reduc-don du nombre de descellements.SAMENV ATTING
]. de WAAL MALEFIJT, T.].J.H. SWOFF en R. HUISIKES. - Huidige positie bii bet gebruik van
aerylcement fer fixatie van totale heupprofhesen.
Sinds Charnley in 1960 het polymethylmethacrylaat introduceerde ter fixatie van totale heupprothesen, is het gebruik van het acrylcement enorm toegenomen. T ege-lijkertijd hebben vele studies met betrekking tot de eigenschappen en bijwerking.ep_ van het cement, de ken-nis hieromtrent vergroot.
Dit resulteerde in sterke verbeteringen in de prak-tische toepassing van het acrylcement bij gewrichts-vervangende operaties.
In dit artike1 wordt de huidige positie en de gebruiks-methode van het acrylcement bij de totale heupprothese besproken aan de hand van een uitgebreide en aktuele literatuurstudie.
Voorts zijn daarin aanbevelingen en opmerkingen ver-werkt, die resulteren uit de jarenlange ervaring met gecementeerde heuparthroplastieken binnen onze eigen kliniek.
De noodzaak van een gedegen kennis omtrent de ver-werkingsvoorschriften van het gebruikte cement en
mechanische losrakingen worden' verwacht.
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J.
de W AAL MALEFIJT Sint Radboud ZiekenhuisAfdeling Orthopaedie Postbus 9101
