Bauze, Adrian

Costi, John Jack

Hearn, Trevor Charles

Krishnan, Jeganath

Rankin, Wayne

Slavotinek, John Paul

Stavrou, Peter

English

Flinders Academic Commons

Archived at the Flinders Academic Commons:  http://dspace.flinders.edu.au/dspace/  This is the publisher’s copyrighted version of this article.  The original can be found at: http://www.josonline.org/pdf/v12i2p194.pdf  © 2004 Journal of Orthopaedic Surgery Published version of the paper reproduced here in accordance with the copyright policy of the publisher. Personal use of this material is permitted. However, permission to reprint/republishthis material for advertising or promotional purposes or for creating new collective works forresale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from Journal of Orthopaedic Surgery. Cement penetration and stiffness of thecement-bone composite in the proximal tibia ina porcine modelAJ Bauze, JJ Costi, P Stavrou, WA Rankin, TC Hearn, J KrishnanDepartment of Orthopaedic Surgery, Flinders University School of Medicine, Flinders Medical Centre and RepatriationGeneral Hospital, Adelaide, AustraliaJP SlavotinekDepartment of Medical Imaging, Flinders University School of Medicine, Flinders Medical Centre and Repatriation GeneralHospital, Adelaide, Australiadevice group and either of the 2 other groups at anylevel (p>0.3 in all cases). Differences in surface stiffnessby tibial plateau region were found in tibiae that hadbeen cemented using finger-packing and in those thathad had their undersurface coated, but not in tibiaethat had been cemented using the tibial-pressurisingdevice.Conclusion. The tibial cement-pressurising deviceeliminated regional differences in stiffness seen withother cementing methods. Elimination of thesedifferences by using this device should reducemicromotion and the incidence of aseptic loosening oftibial base plates in total knee arthroplasty.Key words: arthroplasty; bone cements; knee joint; tibiaINTRODUCTIONA major problem affecting the success of total kneereplacement (TKR) is loosening of the tibial component,Address correspondence and reprint requests to: Prof Jegan Krishnan, Department of Orthopaedic Surgery, Flinders MedicalCentre, Bedford Park, South Australia 5042, Australia. E-mail: jegan.krishnan@flinders.edu.auABSTRACTPurpose. To assess the stiffness of the cement bonecomposite and the depth and uniformity of cementpenetration into the surface of the tibial componentduring total knee reconstruction in a porcine model.Methods. The effectiveness of 3 protocols werecompared: 2 commonly used cementing techniques—finger-packing of cement on the cut surface followedby impaction, and coating of the undersurface of theprosthesis with cement followed by impaction—anda new method using a tibial cement-pressurisingdevice. Cement penetration was measured bycomputed tomography; stiffness was determined byhydraulic penetration testing.Results. Cement penetration at a depth of 1 mmwas significantly greater following coating theundersurface of the prosthesis than following finger-packing (p=0.008). There was no significant differenceat deeper levels or between the tibial-pressurisingJournal of Orthopaedic Surgery 2004;12(2):194–198Vol. 12 No. 2, December 2004 Penetration and stiffness of cement-bone composite in tibia 195which is believed to be due to micromotion at thecement-bone interface.1,2  Micromotion is themicroscopic rocking of an implant against the cut tibialsurface, leading to depression of one side of theimplant and elevation of the contralateral side. Thedegree of fixation at the cement-bone interface, andhence the amount of micromotion, is thought todepend on the penetration of cement into thetrabecular bone.2,3 Deep penetration of cancellous boneby cement has been shown to reduce micromotion andposterior lift-off, and to be important in achievingdurable rigid fixation.2Cement penetration into bone is directlyproportional to the bone pore diameter and the squareroot of the pressure applied to the cement; it is alsoinversely proportional to the time from initial mixingof the cement.4 Penetration of cement is increased byusing high-volume, high-pressure pulsatile lavage toclean the cut surface, by ensuring that the cementviscosity is low,4–6 and by increasing the duration thatpressure is applied to the cement.4 In contrast,penetration of cement is decreased in sclerotic bone7;peripheral penetration is decreased by cement leakagearound the edges of the prosthesis.4,7,8Increased cement penetration has been shown toincrease tensile and shear strengths of the cement boneinterface.4,6 Although less than 1 to 2 mm of cementpenetration results in a weak cement-bone interface,predisposes to micromotion,7,9 and can lead toradiological evidence of loosening,4  greater than 5 mmof penetration can lead to heat-induced necrosis ofbone, does not increase the strength of the interface,and results in increased loss of bone stock if revisionarthroplasty is required.4,7 Optimal cement penetrationthus occurs at a depth of 3 to 5 mm.4,7 In addition, theuse of clamp fixation, which has been described forthe proximal tibia,10 provides a large initial pressure,a lack of variance in force over time, and deep cementpenetration, and also allows the surgeon toconcurrently cement the other components.The tensile and shear strengths of the cement-boneinterface have been assessed.4,6 Nevertheless, theirrelevance to the clinical setting has not beenestablished, because tensile and shear stresses thatmay pull the tibial component from the bone are notcommonly experienced during TKR in situ. It has beenpostulated that increasing the tensile and shearstrengths of the cement-bone interface shoulddecrease micromotion.4,6 Hence, the stiffness of thecement-bone composite being compressed is likely tobe relevant to micromotion and loosening of the tibialcomponent. This concept is supported by evidence ofincreased subsidence of uncemented tibialcomponents in tibiae with low bone mineral density(although this relationship is eliminated by the use ofcement).11Although the stiffness of trabecular bone innormal, osteoarthritic, and rheumatoid knees haspreviously been examined,12,13 the stiffness of thecement-bone composite has not. This study sought toinvestigate cement-bone stiffness in an in vitro porcinemodel, by using 2 commonly practised cementingtechniques and a novel clamp-cement pressuriser thatwas developed by our group in 2002. This tibial-pressurising device (TPD) allows constant pressure tobe applied to the surface of the tibial component duringTKR. The TPD is mounted firmly onto the anteriorsurface of the tibia via fixation pins, and pressure isapplied with a removable screw-clamp mechanismthat is attached to the main body of the TPD. Thefixation pins use the same holes as those used by thetibial cutting guides during bone removal in thepreparation of the tibial component.METHODS20 cadaveric juvenile porcine tibiae were randomlyallocated into 4 groups. The tibiae were cut throughat the metaphysis using an oscillating saw, andthe metaphyseal bone was analysed in a bonedensitometer (DEXA; Lunar Prodigy BoneDensitometer, GE Lunar Corporation, Madison [WI],US) to ensure uniformity of the 4 groups. The cutsurface was then prepared with high-pressure, high-volume pulsatile lavage with normal saline.Polymethylmethacrylate cement (Surgical Simplex;Stryker Howmedica Osteonics, Allendale [NJ], US)was prepared according to the manufacturer’sinstructions at the ambient temperature of 22ΟC andapplied 3 minutes after mixing. A 10.0 cm x 10.0 cm x0.5 cm flat, cold-worked piece of stainless steel wasused to simulate a prosthesis.In the first group of tibiae (the finger-packedgroup), cement was packed into the cut surface withdigital pressure. In the second group (the undersurfacegroup), undersurface of the model prosthesis wascoated with cement. In these two groups, the modelprosthesis was then impacted with a mallet andmanual pressure was applied until the cement cured.For the third group (the pressuriser group), cementwas applied to the cut tibial surface, the modelprosthesis was impacted in the same way as in the firsttwo groups, and pressure was then applied with theTPD. The fourth group (the controls) received nocement or implant.The specimens were wrapped in saline-soakedtowels and frozen at -30ΟC until analysis. Computed196 AJ Bauze et al. Journal of Orthopaedic Surgerytomography (CT) was performed using a High SpeedAdvantage CT system (General Electric, Milwaukee[WI], US), which scanned 1-mm slices parallel to thecut surface of the tibia. Imaging conditions were thesame for all scans. One researcher analysed the digitalCT images to a depth of 5 mm, using special software(IDL Version 4; Research Systems Inc., Boulder [CO],US). On each image, the cortical rim of each slice wasoutlined manually so that cortical bone and soft tissuecould be excluded from the analysis. The penetrationof cement into the cancellous metaphyseal bone wascalculated as the percentage of pixels within themanually traced area that had a grey-scale reading ofgreater than 150. This 150 level was chosen as thethreshold because scans through metaphysealtrabecular bone that did not contain cement yieldedno pixels when the background grey-scale readingwas adjusted to greater than 150. To assess themeasurement precision, the analysis was repeated 10times at a depth of 2 mm on one specimen chosen atrandom (the fourth specimen from the undersurfacegroup).The tibiae were then thawed and tested forindentation. A 1.5-cm thick slice was cut from the tibialplateau of each specimen, and the cemented surfacewas placed face-down on a cleaned latex-coveredstainless-steel plate and encircled by a 2-cm deepstainless steel cylindrical mould, which was then filledwith polymethylmethacrylate cement. After thecement had set, the specimen was inverted and thetibial plateau, which was embedded horizontally inthe cement, was examined. A line was drawn acrossthe plateau between points defining the maximummediolateral width of the specimen. This line wasdivided into thirds by perpendicular lines creating 6regions: anteromedial, anterior intercondylar,anterolateral, posterolateral, posterior intercondylar,and posteromedial. Indentation tests were performedto a depth of 0.5 mm at a rate of 2 mm per minute,12after the flat end of a cylindrical indenter (diameter,4 mm) had been fixed to the actuator of a hydraulicmaterials-testing machine (Instron model 8511; InstronPty Ltd, High Wycombe, UK). Four tests wereperformed in each region. We determined stiffness bycalculating the slope of the linear region of the loadingcurve.Statistical analysis was performed using univariateand repeated measures analysis of variance, as wellas Tukey’s Honestly Significant Difference post-hoctests (SPSS 11.5 for Windows, SPSS Inc., Chicago [IL],US).RESULTSThe mean bone mineral density of the tibiae was0.88 g/cm2 (standard deviation [SD], 0.40 g/cm2),and no statistically significant differences in bonemineral density were seen between the 4 groups(univariate ANOVA, p=0.317).In the assessment of measurement precision, thecoefficient of variation (SD as a percentage of the mean)for the determination of the extent of cementpenetration was 0.65% (mean, 27.6%; SD, 0.18%). Thisvery low coefficient of variation indicates that theresults are precise. Cement penetration data, by depthof analysis are shown in Table 1. Independent ANOVAswere performed for each depth. Cement penetrationat 1 mm was significantly greater for a prosthesis witha cement-coated undersurface than for one that hadbeen finger-packed (p=0.008). There was no significantdifference at deeper levels or between the TPD groupand either of the 2 other groups at any level (p>0.3 inall cases).The surface stiffness results are shown in Table 2.The mean overall stiffness of each cemented group wassignificantly greater than that of the control group(p<0.001). Coating the undersurface of the prosthesiswith cement produced a greater mean overall stiffnessthan did the other two cementing techniques (p<0.001).Significant differences were found between differentregions in the control group (p<0.001), finger-packedcement group (p=0.019), and undersurface cementgroup (p=0.038). Differences, however, were not foundafter TPD use (p=0.621).DISCUSSIONCement penetration of the tibial metaphysis wassignificantly affected by the method of cementpressurisation. Coating the undersurface of theprosthesis with cement followed by impaction with amallet produced significantly greater cementpenetration at a depth of 1 mm than did finger-packingof the cut tibial surface followed by impaction. NoTable 1Cement penetration for each study group, expressed as thepercentage of total surface area, by depth of analysisp u o r G h t p e d y b , n o i t a r t e n e p f o %) D S ( n a e Mm m 1 m m 2 m m 3 m m 4 m m 5d e k c a p - r e g n i Fe c a f r u s r e d n Ur e s i r u s s e r P) 4 1 ( 5 5) 8 ( 8 7 1) 6 ( 4 6 1) 9 ( 2 4 1) 1 1 ( 6 4) 9 1 ( 3 4) 4 ( 4 1 1) 0 1 ( 1 2) 8 ( 5 1 1) 2 ( 4) 4 ( 7) 4 ( 6) 2 ( 3) 4 ( 4) 5 ( 5Vol. 12 No. 2, December 2004 Penetration and stiffness of cement-bone composite in tibia 197significant differences were shown between use of thenew TPD and use of the other two techniques. Thestiffness of the cement-bone composite was alsosignificantly affected by the cementing technique.Coating of the undersurface of the prosthesis withcement followed by impaction produced the mostuniform distribution of cement-bone compositestiffness, which was consistent with the cementpenetration results.Regional differences in surface stiffness were foundin the control tibiae that were not cemented. The TPDwas the only method of cementing that eliminatedthese regional differences. This greater uniformity ofstiffness across the tibial plateau may reducemicromotion and loosening of the tibial componentafter total knee arthroplasty.The mean bone mineral density of the tibialmetaphysis of a population undergoing TKR has beenfound to be 0.81 g/cm2 (range, 0.15–1.33 g/cm2),11which is similar to that found in the porcine tibiae ofthis study. The mean stiffness of different regions ofthe cut surface of the tibia from patients undergoingTKR for osteoarthritis shows wide variation, rangingfrom 586 N/mm (SD, 203 N/mm) to 1786 N/mm(SD, 807 N/mm).12 The stiffness of the control porcinetibiae in our study fell within this range. These 2properties support the validity of the porcine modelthat we used.When we mounted the tibiae for indentationtesting, we needed to hold the cement surroundingREFERENCES1. Sherman RM, Byrick RJ, Kay JC, Sullivan TR, Waddell JP. The role of lavage in preventing hemodynamic and blood-gaschanges during cemented arthroplasty. J Bone Joint Surg Am 1983;65:500–6.the sample with clamps; when there was an unevenbase, washers were used for support. It is possible thatsome settling occurred at the site of these supportsduring testing. There may also have been some errorin the angle of indentation, despite efforts to ensurethat it was perpendicular to the area being tested.However, these potential errors would not havefavoured any particular study group.The use of cement increases the stiffness ofcancellous bone and should reduce micromotionand the incidence of aseptic loosening of tibial baseplates in TKR. The cementing technique should aimat producing consistent stiffness across the cement-bone composite. In this study, penetration wasmaximised by coating the undersurface of theprosthesis and impacting the cement with a mallet;however, this method also produced regionalvariations in stiffness. The most uniform stiffnesswas achieved by the use of the TPD. The TPD alsoleaves the surgeons’ hands free to work on thefemur during tibial cement pressurisation.ACKNOWLEDGEMENTSWe  thank Jane Shearer and Julia Serrada forperforming the bone densitometry; Ashley Wallageand Jan Crook for assistance in computed tomography;and Richard Stanley for technical assistance with theindentation testing.* AM denotes anteromedial, AI anterior intercondylar, AL anterolateral, PL posterolateral, PI posterior intercondylar, PM posteromedial† Univariate ANOVA‡ Non-cemented boneTable 2Bone-composite stiffness for each study group, by tibial plateau regionp u o r G n o i g e r y b , s s e n f f i t S) m m / N ( ) D S ( n a e Me u l a v pM A I A L A L P I P M P l l a r e v Ol o r t n o Cd e k c a p - r e g n i Fe c a f r u s r e d n Ur e s i r u s s e r P1 ) 9 9 1 ( 3 2 6) 2 2 4 ( 8 3 4 1) 8 5 4 ( 1 4 9 1) 9 4 5 ( 5 2 5 11 ) 9 1 3 ( 1 9 5) 8 7 3 ( 5 3 2 1) 3 8 3 ( 1 7 7 1) 8 2 5 ( 6 1 3 1) 4 5 4 ( 4 0 1 1) 4 6 4 ( 1 9 2 1) 5 7 4 ( 8 5 0 2) 9 1 5 ( 5 2 4 1) 7 6 4 ( 2 0 2 1) 7 3 3 ( 6 1 4 1) 6 3 5 ( 9 3 1 2) 0 1 4 ( 7 6 3 11 ) 1 3 5 ( 2 2 9) 1 2 4 ( 6 6 5 1) 1 2 5 ( 8 2 2 2) 1 9 2 ( 5 2 4 11 ) 6 9 2 ( 9 3 9) 5 3 4 ( 0 4 6 1) 7 1 6 ( 3 5 1 2) 0 3 3 ( 7 5 3 11 ) 1 4 4 ( 7 9 8) 7 2 4 ( 1 3 4 1) 7 1 5 ( 8 3 0 2) 8 5 4 ( 1 7 4 11 0 0 . 0 << 9 1 0 . 0< 8 3 0 . 0< 1 2 6 . 0* †‡198 AJ Bauze et al. Journal of Orthopaedic Surgery2. Miskovsky C, Whiteside LA, White SE. The cemented unicondylar knee arthroplasty. An in vitro comparison of threecement techniques. Clin Orthop 1992;284:215–20.3. Goldstein SA, Wilson DL, Sonstegard DA, Matthews LS. The mechanical properties of human tibial trabecular bone as afunction of metaphyseal location. J Biomech 1983;16:965–9.4. Walker PS, Soudry M, Ewald FC, McVickar H. Control of cement penetration in total knee arthroplasty. Clin Orthop 1984;185:155–64.5. Krause WR, Krug W, Miller J. Strength of the cement-bone interface. Clin Orthop 1982;163:290–9.6. Ritter MA, Herbst SA, Keating EM, Faris PM. Radiolucency at the bone-cement interface in total knee replacement. Theeffects of bone-surface preparation and cement technique. J Bone Joint Surg Am 1994;76:60–5.7. Kim YH, Walker PS, Deland JT. A cement impactor for uniform cement penetration in the upper tibia. Clin Orthop 1984;182:206–10.8. Vertullo CJ, Davey JR. The effect of a tibial baseplate undersurface peripheral lip on cement penetration in total kneearthroplasty. J Arthroplasty 2001;16:487–92.9. Bert JM, McShane M. Is it necessary to cement the tibial stem in cemented total knee arthroplasty? Clin Orthop 1998;356:73–8.10. Kanekasu K, Yamakado K, Hayashi H. The clamp fixation method in cemented total knee arthroplasty. Dynamic experimentaland radiographic studies of the tibial baseplate clamper. Bull Hosp Jt Dis 1997;56:218–21.11. Li MG, Nilsson KG. The effect of the preoperative bone quality on the fixation of the tibial component in total kneearthroplasty. J Arthroplasty 2000;15:744–53.12. Finlay JB, Bourne RB, Kraemer WJ, Moroz TK, Rorabeck CH. Stiffness of bone underlying the tibial plateaus of osteoarthriticand normal knees. Clin Orthop 1989;247:193–201.13. Yang JP, Bogoch ER, Woodside TD, Hearn TC. Stiffness of trabecular bone of the tibial plateau in patients with rheumatoidarthritis of the knee. J Arthroplasty 1997;12:798–803.

Cement penetration and stiffness of the
            cement-bone composite in the proximal tibia in a porcine model

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Cement penetration and stiffness of the cement-bone composite in the proximal tibia in a porcine model

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