Penetration of Acrylic Bone Cements into Cancellous Bone

The depth of penetration of five commercial acrylic bone cements into cancellous bone was measured in vitro. Under standard, idealized conditions, cement penetration was found to vary significantly with different cements. Penetration was critically influenced by the coarseness of the cancellous bone and increased directly with the effective volume of the “cells” within the osseous matrix. An inverse correlation was determined between the mean cement viscosity during flow into the bone and final penetration depth. The dough time, set time and working time of each acrylic formulation was found to have no significant effect upon the depth of cement penetration.

It is suggested that in addition to the techniques adopted for introduction of cement to the bone, the selection of the bone cement itself may critically influence the incidence of late loosening following total joint replacement.     

Penetration of acrylic bone cements into cancellous bone

The depth of penetration of five commercial acrylic bone cements into cancellous bone was measured in vitro. Under standard, idealized conditions, cement penetration was found to vary significantly with different cements. Penetration was critically influenced by the coarseness of the cancellous bone and increased directly with the effective volume of the "cells" within the osseous matrix. An inverse correlation was determined between the mean cement viscosity during flow into the bone and final penetration depth. The dough time, set time and working time of each acrylic formulation was found to have no significant effect upon the depth of cement penetration. It is suggested that in addition to the techniques adopted for introduction of cement to the bone, the selection of the bone cement itself may critically influence the incidence of late loosening following total joint replacement.     

Cement penetration in the proximal femur does not depend on broach surface finish

In a cadaver study, we prepared 29 paired human cadaver femora using 3 different broaches of identical geometry but different surface characteristics. In one group of 20 pairs, preparation with chipped-toothed broaches was compared to diamond-shaped broaches; in the other group of 9 pairs, polished tamps for compaction of cancellous bone were compared with chipped-tooth broaches. Cancellous bone was irrigated with 1 liter pulsed lavage. The specimens were embedded in specially-designed pots. Palacos R and Simplex bone cements were used. After vacuum mixing, the cement was applied in a retrograde manner and subjected to a standard pressure protocol with a constant force of 3000 N. Radiographs were taken and horizontal sections were obtained at predefined levels using a diamond saw. Microradiographs were taken, digitized and analyzed to assess cement penetration into cancellous bone. In 6 of 9 femora prepared using smooth tamps, femoral fractures occurred despite careful preparation technique. The microradiographic evaluation showed no significant morphometric differences between diamond and chipped tooth or between polished and chipped-tooth broaches with regard to cement penetration into cancellous bone. Therefore, in the presence of pulsed lavage, one finds no significant effect of broach surface characteristics on cement penetration into cancellous bone of the proximal end of the femur.     

Sustained pressurization of polymethylmethacrylate: a comparison of low- and moderate-viscosity bone cements

There is at present great uncertainty relating to the fixation of joint implants. The deficiencies of acrylic bone cement are well documented, but the limitations of cementless fixation are as yet imcompletely identified. The purpose of this study was to investigate the potential of sustained external pressurization to improve the mechanical characteristics of conventional acrylic bone cement. The effect of serially increasing sustained pressurization of two commerically available acrylic bone cements (Simplex-P and LVC) was evaluated in human cadaver femora. A new method for determination of the shear strength of the bone-cement interface in place of the traditional pushout tests was used. In this model, there was a significant increase in the bone-cement interfacial shear strength with increasing pressure, but no difference in the shear strength was found between the two cements. At all pressure levels, the shear strength of the cement was greater than that previously reported. Increased cement penetration into the cortical bone was demonstrated with increasing pressure and low-viscosity cement, but the extent of cement penetration did not correlate with the shear strength of the bone-cement interface.     

Metal/cement interface strength in cemented stem fixation

To characterize the strength of the interface between stem-type metal implants and bone cements, a fracture mechanics parameter was used. This parameter, the critical strain energy release rate (G_c), was determined from “push-out” tests of cylindrical specimens. The specimens, formed using molds of bone, were maintained and tested at body temperature. The strength of interfaces formed with cancellous bone surrounding the cement mantle was significantly less than the strength of those formed in apposition to cortical bone. A marked degradation of strength was found with saline immersion for SS316LVM/cement interfaces formed with Zimmer regular, Simplex-P, and Zimmer LVC cements. After 60 days of immersion the interface G_c was only 10–20% of the value for bulk cement. Interfaces formed with thin-film polymethylmetharcrylate-precoated metals (SS316LVM, Co-Cr-Mo, and Ti-6A1-4V) yielded “dry” G_c values one order of magnitude greater than those measured with interfaces formed with uncoated metals. Moreover, the strength of precoated SS316LVM/cement interfaces formed with all three brands of cement did not change after saline immersion for 60 days.     

The Relaxation of Some Acrylic Bone Cements

The creep and relaxation of acrylic cements during conditions simulating the conditions in the acetabulum have been examined. CMW and Simplex were found to reach stresses of about 10 N/cm² after 1 year whereas Palacos had lost most of its stress after 6 weeks.     

Cement penetration in the proximal femur does not depend on broach surface finish

In a cadaver study, we prepared 29 paired human cadaver femora using 3 different broaches of identical geometry but different surface characteristics. In one group of 20 pairs, preparation with chipped-toothed broaches was compared to diamond-shaped broaches; in the other group of 9 pairs, polished tamps for compaction of cancellous bone were compared with chipped-tooth broaches. Cancellous bone was irrigated with 1 liter pulsed lavage. The specimens were embedded in specially-designed pots. Palacos R and Simplex bone cements were used. After vacuum mixing, the cement was applied in a retrograde manner and subjected to a standard pressure protocol with a constant force of 3000 N. Radiographs were taken and horizontal sections were obtained at predefined levels using a diamond saw. Microradiographs were taken, digitized and analyzed to assess cement penetration into cancellous bone. In 6 of 9 femora prepared using smooth tamps, femoral fractures occurred despite careful preparation technique. The microradiographic evaluation showed no significant morphometric differences between diamond and chipped tooth or between polished and chipped-tooth broaches with regard to cement penetration into cancellous bone. Therefore, in the presence of pulsed lavage, one finds no significant effect of broach surface characteristics on cement penetration into cancellous bone of the proximal end of the femur.     

Cement penetration in the proximal femur does not depend on broach surface finish

In a cadaver study, we prepared 29 paired human cadaver femora using 3 different broaches of identical geometry but different surface characteristics. In one group of 20 pairs, preparation with chipped-toothed broaches was compared to diamond-shaped broaches; in the other group of 9 pairs, polished tamps for compaction of cancellous bone were compared with chipped-tooth broaches. Cancellous bone was irrigated with 1 liter pulsed lavage. The specimens were embedded in specially-designed pots. Palacos R and Simplex bone cements were used. After vacuum mixing, the cement was applied in a retrograde manner and subjected to a standard pressure protocol with a constant force of 3,000 N. Radiographs were taken and horizontal sections were obtained at predefined levels using a diamond saw. Microradiographs were taken, digitized and analyzed to assess cement penetration into cancellous bone. In 6 of 9 femora prepared using smooth tamps, femoral fractures occurred despite careful preparation technique. The microradiographic evaluation showed no significant morphometric differences between diamond and chipped-tooth or between polished and chipped-tooth broaches with regard to cement penetration into cancellous bone. Therefore, in the presence of pulsed lavage, one finds no significant effect of broach surface characteristics on cement penetration into cancellous bone of the proximal end of the femur.     

An experimental comparison of different devices for pulsatile high-pressure lavage and their relevance to cement intrusion into cancellous bone

Introduction Some of the systems marketed for pulsatile high-pressure lavage are clearly different in their mechanical pulse characteristics. To take the matter further we set up an experimental in vitro model to determine whether these different lavage systems might produce different cementation results because of their differing pulse characteristics, and whether the systems differed significantly in terms of cement depth penetration. Materials and methods A total of 48 femoral heads were obtained at operation from patients who had undergone endoprosthetic hip replacement. The specimens were subjected to manual rinsing or semiautomatic cleansing procedures with five different pulsatile lavage devices. After the cleansing procedures, polymethylmetacrylate bone cement was intruded into the cancellous bone under standardised conditions. Determination of cement penetration was done by computed tomography using an image processing software. Results Irrespective of the nature of the lavage system tested, superficial cement penetration, both up to 2 mm and up to 3 mm, was significantly better after pulsatile high-pressure lavage than it was after manual rinsing of the specimens with a bladder syringe (P < 0.001 in each case). Whereas our experimental model did not show any significant differences between the lavage systems as regards the cementation results to a depth of up to 2 mm (P = 0.996), there were significant differences at a target depth of 3 mm (P < 0.05). Conclusion As compared with manual rinsing, pulsatile high-pressure lavage in vitro makes highly significant improvements in cement penetration into cancellous bone and should be regarded as an indispensable component of modern cementation techniques for endoprosthetic surgery. Up to the present we have not been able to ascertain what influence the different pulse characteristics of a pulsatile lavage system may have on the intended cementation result, whether it is impact force, pulse shape, pulse duration, flow rate or frequency. Appropriate investigations will be necessary.     

Stress transfer at the femoral bone/bone cement interface as a function of the cement thickness

Summary When a cement canal prosthesis is used as the femoral component in total hip replacement (THR), the penetration depth of the bone cement can be varied according to the cement implantation pressure. Using experimental data which give a relation between the pressure applied to the cement at implantation and the resulting shape of the cement layer, a three-dimensional finite element study was performed to calculate the stress distribution at the bone/bone cement interface. The calculations show that the interface stresses increase with increasing depth of penetration by the cement layer. The explanation of this effect is that as the bone cement penetrates further into the cancellous bone, the cancellous bone is stiffened and can no longer act as a soft interposition between cortical bone and bone cement. From these results and from the clinical requirement that as little bone as possible be destroyed in any kind of alloarthroplasty, we conclude that the penetration depth of bone cement into cancellous bone in THR should be minimized to the depth necessary in order to achieve sufficient initial stability of the implant. The results show that a cement-canal prosthesis meets these requirements if a cement implantation pressure of 1.0 bar is used.     

Effect of cement pressure and bone strength on polymethylmethacrylate fixation

The effect of the quality of the bone and of the cement pressurization magnitude and duration on the fixation achieved with polymethylmethacrylate (PMMA) bone cement is studied in vitro. Seventy-one cementbone interface specimens, prepared under various conditions of pressurization of low-viscosity bone cement, are tested in tension. The load at failure and the maximum cement penetration are measured to assess the fixation achieved, and the quality of the bone is assessed by determining the compressive strength of each of the bone specimens. Statistical analysis of the data indicates that the pressure magnitude is the most influential of the factors considered in the cement penetration behavior and in the development of failure load capacity. The duration of the pressure does not appear to be a significant factor. The cement penetration is a decreasing function of the bone strength, reflecting a decrease in the porosity and an increase in the area fraction. Although not directly measured in these tests, these latter bone properties are indirectly measured by the bone compressive strength. The effect of increasing bone strength on the failure load is nonlinear. The development of adequate failure load capacity is the result of a balance between the cement penetration allowed by the porosity of the bone and the inherent strength of the cancellous bone itself. Weak bone, although adequately penetrated by cement, cannot provide strong fixation. Stronger, denser bone limits cement penetration, but pressurization enhances development of failure load capacity through more complete infusion and interlocking of the cement in the available pore space. The strength of the fixation achievable for any bone is limited by the intrinsic strength of the bone. An optimal depth of cement penetration of 4 mm and an optimal bone area fraction of 0.20 are suggested for the most effective fixation.     

Antibiotics and Bone Cements: Experimental and Clinical Long-Term Observations

Comparing several antibiotics and different bone cements, the mixture of Palacos® R (polymethylmethacrylate, PMMA) with gentamicin proved to be the most suitable one as far as a high and sustained release of the antibiotic from the artificial resin is concerned. A continuous leaching of gentamicin was observed for more than 5 years. Gentamicin proved to be stable in Palacos R for the whole period of time.

The release of 12 antibiotics from Palaes R was evaluated in vitro. Four other bone cements were included in this ttudy as well, in order to evaluate the leaching of gentamicin from these materials. the combination Gentamicin-Palacos R (GP) showed a 2–3 fold higher and much more prolonged release than did the other mixtures. From this investigation, which also included studies of commercially available antibiotic bone cement mixtures, it is quite obvious that there exist distinct differences in the various bone cements as well as in the various antibiotics as regards their qualification for use in alloarthroplasty.

Pharmacokinetic studies in patients after implantation of GP showed low gentamicin concentrations in serum (on average 1.8μg/ml) and urine. However, in wound exudate, derived directly from the vicinity of the implanted cement, gentamicin concentrations up to 150μg/ml were observed. Also in tissue samples from the vicinity of the implant, high concentrations were measurable for a long period of time (up to 5 1/2 years).     

Daptomycin‐Loaded Polymethylmethacrylate Bone Cement for Joint Arthroplasty Surgery

Antibiotic‐loaded acrylic bone cement has been frequently used as an infection prophylaxis or antibiotic‐loaded spacer in infected arthroplasty. In addition, daptomycin has been used recently against broad spectrum Gram‐positive organisms. The goal of this in vitro study is to investigate the bacteriacidal and mechanical properties of daptomycin‐incorporated polymethylmethacrylate (PMMA) bone cement and evaluate its feasibility for clinical use. Daptomycin (0.5, 1, or 2 g) was premixed with 40 g of PMMA bone cement powder before curing. The mechanical properties of the daptomycin‐loaded acrylic bone cement (DLABC) were estimated following standard guidance, and the release profile and kinetics of daptomycin from PMMA were analyzed. The antimicrobial efficacy of DLABC was determined with a zone of inhibition (ZOI) assay against Staphylococcus aureus, Staphylococcus epidermis, Enterococcus faecalis, and Enterococcus faecium, respectively. The results showed that the compressive strength, of PMMA bone cement, which was higher than 100 MPa in all groups, was sufficient according to ISO 5833 after incorporation of daptomycin. The encapsulated daptomycin was released for 2 weeks with a 9.59 ± 0.85%, 15.25 ± 0.69%, and 20.64 ± 20.33% released percentage on the first day in the low, mid, and high groups, respectively. According to the calculated release kinetics, incorporated daptomycin should be 3.3 times the original dose to double its release. Although all recipes of DLABC had a microbial inhibitory effect, the effect with a higher encapsulated amount of daptomycin was more significant. Therefore, we believe that daptomycin can be locally delivered from PMMA bone cement at the surgical site as a prophylactic or treatment for osteomyelitis against Gram‐positive organisms with intact cement function.     

A study of intrusion characteristics of low viscosity cement Simplex-P and Palacos cements in a bovine cancellous bone model

Aseptic loosening is the most common long-term complication of cemented total hip arthroplasties (THA). The functional longevity of these implants depends on the bone-cement interface. The influence of cement injection pressure, type of cement, ambient temperature, chilling of the monomer, and centrifugation of cement-on-cement intrusion depth was investigated in specimens of bovine cancellous bone. In order to validate the bovine model for comparative purposes relative to use in man, a linear relationship between human and bovine cancellous bone was first demonstrated for various porosities and cement intrusion depth. Three cements (Low Viscosity Cement [LVC], Simplex-P, and Palacos) were intruded at three different pressures (20, 40, and 60 PSI) at the same ambient temperature and relative humidity into commercially prepared plugs of bovine cancellous bone. Cement intrusion depth was proportional to injection pressure for all three cements, but was significantly different for each cement at a given pressure. At 20, 40, and 60 PSI, Palacos had a cement intrusion depth of 1.4, 2.4, and 2.8 mm respectively, while the figures for Simplex-P were 2.2, 4.2, and 5.0 mm, and for LVC were 8.0, 12.0, and 14.6 mm. Ambient temperature had an inverse relationship with cement intrusion depth for all three cements given the same experimental conditions. Chilling the monomer increased the intrusion of Simplex-P to 5.8, 8.2, and 12.7 mm at 20, 40, and 60 PSI injection pressure respectively. Simplex-P intrusion depth was not modified by cement centrifugation at any of the three injection pressures tested.(ABSTRACT TRUNCATED AT 250 WORDS)     

The Effect of Tourniquet Use and Sterile Carbon Dioxide Gas Bone Preparation on Cement Penetration in Primary Total Knee Arthroplasty

BackgroundTourniquetless total knee arthroplasty (TKA) is experiencing resurgence in popularity due to potential pain control benefits. Furthermore, optimal cement technique and implant fixation remain paramount to long-term cemented TKA success, as aseptic loosening continues to be a leading cause of revision. The purpose of this study is to determine how tourniquet use and/or novel bone preparation using sterile, compressed carbon dioxide (CO₂) gas affected cement penetration in TKA.MethodsA retrospective review was performed on 303 consecutive primary TKAs with the same implant in 3 groups: (1) a tourniquet without sterile CO₂ compressed gas used for bone preparation, (2) no tourniquet with CO₂ gas, and (3) tourniquet use and CO₂ gas bone preparation. Cement penetration was measured on radiographs by two independent, blinded raters across 7 zones defined by the Knee Society Radiographic Evaluation System.ResultsThe 3 groups did not differ on age, body mass index, or gender (P ≥ .1). Cement penetration was greater in 6 of 7 zones with significantly greater cement penetration in 3 zones (tibial anteroposterior zone 2, femoral lateral zones 3A and 3P) in groups that utilized CO₂ gas bone preparation compared to the tourniquet only group (P ≤ .039).ConclusionBone prepared with CO₂ gas showed significantly more cement penetration in 3 zones with greater cancellous bone. The results suggest that use of CO₂ gas bone preparation may achieve greater cement penetration than using a tourniquet with lavage only.     

Einfluss der femoralen Zementiertechnik auf das Zementierergebnis

METHODS: To evaluate the penetration depth of cement into trabecular femoral bone, femora of 14 sheep were subjected to simultaneous bilateral cementing. After femoral neck osteotomy, preparation of the bone cavities and jet lavage, cement was applied simultaneously using the conventional retrograde method for one side and vacuum application for the contralateral limb. Bilateral simultaneous pressurisation was then applied. All femoral specimens were X-rayed, sawed into standardised, horizontal, stereometric, identical slices and microradiographed. Cement penetration was assessed using a morphometric software system. RESULTS: No significant differences in depth of cement penetration between sheep femora cemented with the vacuum application method and the standard retrograde method could be found or between the ratio of cement-consolidated and non-cement-consolidated cancellous bone. CONCLUSION: The more complicated and technically challenging method of cement application under vacuum had no advantage in terms of cement interdigitation over the standard retrograde method.     

Effect of bone porosity on the mechanical integrity of the bone-cement interface

BACKGROUND: Osteopenia is one factor that may influence the decision about the type of implant fixation to use in total hip arthroplasty. However, clinical studies generally do not associate the outcome of an arthroplasty with the degree of osteopenia. The mechanical integrity of the cement fixation of an implant may be affected by the relative degree of osteopenia, which could account for some of the variable long-term results after total hip arthroplasty performed with cement. The purpose of this study was to determine the effects of bone porosity, trabecular orientation, cement pressure, and cement penetration depth on fracture toughness at the bone-cement interface. METHODS: Trabecular bone from the proximal part of bovine femora was used with a single brand of commercial acrylic bone cement to form compact-tension interface specimens representing a range of bone porosities, orientations, and cement pressures within a clinically achievable range. All specimens were loaded to failure with use of a servohydraulic testing machine, and fracture toughness at the interface was calculated. After testing, images of a representative sample of specimens were made with use of computed tomography to measure the penetration depth of the cement into the bone. RESULTS: Significant correlations were found between fracture toughness and bone porosity, trabecular orientation, and cement pressure, with bone porosity having the strongest effect (p < 0.000015). Examination of the computed tomographic images also showed a significant correlation between fracture toughness and maximum cement penetration depth (p < 0.033), as well as significant partial correlations between maximum and mean penetration depth and bone porosity (p < 0.0037 and p < 0.0028). CONCLUSION: The fracture resistance of the bone-cement interface is greatly improved when the ability of the cement to flow into the intertrabecular spaces is enhanced.     

Treatment of 10-mm-Deep or Greater Uncontained Tibial Bone Defects in Primary Total Knee Reconstruction without Metal Augmentation: Autologous Oblique Structural Peg Bone and Cancellous Chip Bone Grafting

BackgroudIn this study, we report satisfactory clinical and radiological outcomes after autologous oblique structural peg bone and cancellous chip bone grafting without metal augmentation, including the use of a metal wedge, block, or additional stem, for patients with ≥ 10-mm-deep uncontained medial proximal tibial bone defects in primary total knee replacement.MethodsThe study group included 40 patients with primary total knee replacement with ≥ 10-mm-deep uncontained tibial bone defects who underwent autologous oblique structural peg bone and cancellous chip bone grafting and were followed-up for at least 1 year. Tibial cutting was performed up to a depth of 10 mm from the articular surface of the lateral tibial condyle, after which the height and area of the remaining bone defect in the medial condyle were measured. The bone defect was treated by making a peg bone and chip bone using excised segments of the tibia and femur. In all cases, the standard tibial stem and full cemented fixation techniques were used without metal augmentation. Preoperative and final follow-up radiologic changes and clinical measures were compared, and prosthesis loosening and bone union were checked radiologically at final follow-up.ResultsThe mean depth of the bone defects was 10.9 mm, and the mean percentage of the area occupied by bone defects in the axial plane was 18.4%. The mean mechanical femorotibial angle was corrected from 19.5° varus preoperatively to 0.2° varus postoperatively (p < 0.002). There was no prosthesis loosening, and all cases showed bone union at the 1-year postoperative follow-up.ConclusionsEven in patients with uncontained tibial bone defects ≥ 10-mm deep in primary total knee replacement, if the defect occupies less than 30% of the cut surface, autologous oblique structural peg bone and cancellous chip bone grafting can be used to achieve satisfactory outcomes with a standard tibial stem and no metal augmentation.     

Estrogen and Cancellous Bone Loss in the Fowl

Female birds model a type of woven bone prior to egg laying which is known as medullary bone. Medullary bone modeling is estrogen dependent and in the female fowl coincides with a decrease in cancellous bone volume. Medullary bone modeling was induced in male laying-strain fowl by the administration of estrogen and prevented in females by the administration of tamoxifen. In estrogen-treated males, medullary bone modeling was accompanied by cancellous bone loss; cancellous bone volume was significantly lower than in control males (P < 0.001). In females, the prevention of medullary bone modeling by tamoxifen treatment resulted in significantly higher cancellous bone volumes than in control females (P < 0.001). Estrogen therefore appears to play a role in cancellous bone loss in the fowl. Received: 29 April 1997 / Accepted: 3 September 1997