Inter- and intra-batch variability in the handling characteristics and viscosity of commonly used antibiotic-loaded bone cements

Two-year fixation and ten-year clinical outcomes of total knee arthroplasty inserted with normal-curing bone cement and slow-curing bone cement: A randomized controlled trial in 54 patients

BACKGROUND

The normal-curing Refobacin® Bone Cement R (RR) and slow-curing Refobacin® Plus Bone Cement (RP) were introduced after discontinuation of the historically most used bone cement, Refobacin®-Palacos® R, in 2005. The aim of this study was to compare total knee arthroplasty component fixation with the two bone cements.

METHODS

54 patients with primary knee osteoarthritis were randomized to either RR (N = 27) or RP (N = 27) bone cement and followed for two years with radiostereometric analysis of tibial and femoral component migration and dual-energy x-ray absorptiometry measured periprosthetic bone mineral density (BMD). Further, patients were followed up at ten years with clinical outcome scores (OKS and KOOS).

RESULTS

At two-years follow-up, tibial total translation was 0.31 mm (95% CI: 0.19 - 0.42) for the RP group and 0.56 mm (95% CI: 0.45 - 0.67) (p < 0.01) for the RR group. There was continuous tibial component migration from one to two years follow-up (MTPM > 0.2 mm) in 13/27 patients from the RR and in 12/26 patients from the RP group. There was no difference between groups in BMD baseline values or changes during follow-up, as well as no correlation between change in BMD and tibial component migration. At ten-years follow-up, the improvement in the clinical outcome scores was similar between groups. There were no prosthesis related complications during the 10-year follow-up.

CONCLUSION

At two years, tibial total translation was lower in the RP compared with the RR cement group, but BMD changes were similar. At ten years, no components were revised and clinical outcome scores were similar between groups.

Effect of shape on bone cement polymerization time in knee joint replacement surgery

BACKGROUND

Although many factors are known to influence the polymerization time of bone cement, it remains unclear which bone cement shape predicts the precise polymerization time. The purpose of this study was to investigate whether different cement shapes influenced polymerization time and to identify the relationship between cement shape and ambient operating theater temperature, relative humidity, and equilibration time.

METHODS

Samples were gathered prospectively from 237 patients undergoing primary total knee arthroplasty. The cement components were made into 2 different shapes: lump and pan. The time at which no macroscopic indentation of both cement models was possible was recorded as the polymerization time.

RESULTS

There was no significant difference between hand mixing (lump shape: 789.3 ± 128.4 seconds, P = .591; pan shape: 899.3 ± 152.2 seconds, P = .584) and vacuum mixing (lump shape: 780.2 ± 131.1 seconds, P = .591; pan shape: 909.9 ± 143.3 seconds, P = .584) in terms of polymerization time. Conversely, the polymerization time was significantly shorter for Antibiotic Simplex (lump shape: 757.4 ± 114.9 seconds, P = .001; pan shape: 879.5 ± 125.0 seconds, P < .001) when compared with Palacos R+G (lump shape: 829.0 ± 139.3 seconds, P = .001; pan shape: 942.9 ± 172.0 seconds, P < .001). Polymerization time was also significantly longer (P < .001) for the pan shape model (904 ± 148.0 seconds) when compared with the lump shape model (785.2 ± 129.4 seconds). In addition, the polymerization time decreased with increasing temperature (lump shape: R = 0.334, P < .001; pan shape: R = 0.375, P < .001), humidity (lump shape: R = 0.091, P < .001; pan shape: R = 0.106, P < .001), and equilibration time (lump shape: R = 0.073, P < .001; pan shape: R = 0.044, P < .001).

CONCLUSIONS

The polymerization time was equally affected by temperature, relative humidity, and equilibration time regardless of bone cement shape. Furthermore, the pan shape model better reflected the cement polymerization time between implant and bone compared with the lump shape model. The current findings suggest that, clinically, constant pressure with the knee in <45° of flexion needs to be applied until remaining pan shaped cement is completely polymerized.

Bone cement product and failure in total knee arthroplasty

Background and purpose - The bone cement market for total knee arthroplasty (TKA) in Norway has been dominated by a few products and distributors. Palacos with gentamicin had a market share exceeding 90% before 2005, but it was then withdrawn from the market and replaced by new slightly altered products. We have compared the survival of TKAs fixated with Palacos with gentamicin with the survival of TKAs fixated with the bone cements that took over the market. Patients and methods - Using data from the Norwegian Arthroplasty Register for the period 1997-2013, we included 26,147 primary TKAs in the study. The inclusion criteria were TKAs fixated with the 5 most used bone cements and the 5 most common total knee prostheses for that time period. 6-year Kaplan-Meier survival probabilities were established for each cement product. The Cox proportional hazards regression model was used to assess the association between bone cement product and revision risk. Separate analyses were performed with revision for any reason and revision due to deep infection within 1 year postoperatively as endpoints. Adjustments were made for age, sex, diagnosis, and prosthesis brand. Results - Survival was similar for the prostheses in the follow-up period, between the 5 bone cements included: Palacos with gentamicin, Refobacin Palacos R, Refobacin Bone Cement R (Refobacin BCR), Optipac Refobacin Bone Cement R (Optipac Refobacin BCR), and Palacos R + G. Interpretation - According to our findings, the use of the new bone cements led to a survival rate that was as good as with the old bone cement (Palacos with gentamicin).

Not all approved antibiotic-loaded PMMA bone cement brands are the same: ranking using the utility materials selection concept

In the literature on in vitro characterization of approved antibiotic-loaded poly(methyl methacrylate) bone cement brands, there is no information on the basis for selection of a given brand for use in cemented arthroplasties. This shortcoming is addressed in the present study. It involved determining four key properties (fatigue limit, fracture toughness, polymerization rate, and phosphate buffered saline diffusion coefficient) for six brands and then using the mean property values, in conjunction with a materials selection methodology, called the utility concept, to rank the brands. It is emphasized that the present work is an illustration of a rational approach to selection of a cement brand and, as such, the study findings are not intended to be recommendations regarding clinical use or otherwise of a brand.

Is the Stryker Revolution mixing system fit for purpose? Reliability and a micro-CT assessment of cement porosity

The Stryker Revolution(TM) is a new mixing system that employs a high vacuum and a motorised mixing spatula in an effort to reduce cement porosity. We have compared Revolution(TM) with Depuy Cemvac(®), in terms of system reliability and cement porosity. Standardised Simplex P(®) and SmartSet(®) HV cement samples were produced using both mixing systems and analysed using a micro-CT scanner. The overall porosity, number and volume of voids were measured. Void analysis was subdivided into macro-pores (>0.5 mm3) and micro-pores (0.0005-0.5 mm3). Both systems were easy to use and no breakages were encountered. There was no significant difference in overall porosity between Revolution(TM) and Cemvac(®). Revolution(TM) produced over a five-fold decrease in average macro-pore size with medium viscosity cement (p=0.02), but produced a greater number of micro-pores (p<0.01). SmartSet(®) HV specimens had a higher porosity compared to Simplex P(®). This study demonstrated that the Revolution(TM) system was reliable and reduced porosity at least as effectively as the established Cemvac(®) system. The Revolution(TM) produced a greater number of smaller pores and further testing is required to establish if this results in a significant mechanical benefit.

The long-term in vivo behavior of polymethyl methacrylate bone cement in total hip arthroplasty

BACKGROUND AND PURPOSE

The long-term success of cemented total hip arthroplasty (THA) has been well established. Improved outcomes, both radiographically and clinically, have resulted mainly from advances in stem design and improvements in operating techniques. However, there is concern about the durability of bone cement in vivo. We evaluated the physical and chemical properties of CMW1 bone cements retrieved from patients undergoing revision THA.

METHODS

CMW1 cements were retrieved from 14 patients who underwent acetabular revision because of aseptic loosening. The time in vivo before revision was 7-30 years. The bending properties of the retrieved bone cement were assessed using the three-point bending method. The molecular weight and chemical structure were analyzed by gel permeation chromatography and Fourier-transform infrared spectroscopy. The porosity of the bone cements was evaluated by 3-D microcomputer tomography.

RESULTS

The bending strength decreased with increasing time in vivo and depended on the density of the bone cement, which we assume to be determined by the porosity. There was no correlation between molecular weight and time in vivo. The infrared spectra were similar in the retrieved cements and in the control CMW1 cements.

INTERPRETATION

Our results indicate that polymer chain scission and significant hydrolysis do not occur in CMW1 cement after implantation in vivo, even in the long term. CMW1 cement was stable through long-term implantation and functional loading.

Gentamicin release from commercially-available gentamicin-loaded PMMA bone cements in a prosthesis-related interfacial gap model and their antibacterial efficacy

Background

Around about 1970, a gentamicin-loaded poly (methylmethacrylate) (PMMA) bone cement brand (Refobacin Palacos R) was introduced to control infection in joint arthroplasties. In 2005, this brand was replaced by two gentamicin-loaded follow-up brands, Refobacin Bone Cement R and Palacos R + G. In addition, another gentamicin-loaded cement brand, SmartSet GHV, was introduced in Europe in 2003. In the present study, we investigated differences in gentamicin release and the antibacterial efficacy of the eluent between these four cement brands.

Methods

200 μm-wide gaps were made in samples of each cement and filled with buffer in order to measure the gentamicin release. Release kinetics were related to bone cement powder particle characteristics and wettabilities of the cement surfaces. Gaps were also inoculated with bacteria isolated from infected prostheses for 24 h and their survival determined. Gentamicin release and bacterial survival were statistically analysed using the Student's t-test.

Results

All three Palacos variants showed equal burst releases but each of the successor Palacos cements showed significantly higher sustained releases. SmartSet GHV showed a significantly higher burst release, while its sustained release was comparable with original Palacos. A gentamicin-sensitive bacterium did not survive in the high gentamicin concentrations in the interfacial gaps, while a gentamicin-resistant strain did, regardless of the type of cement used. Survival was independent of the level of burst release by the bone cement.

Conclusions

Although marketed as the original gentamicin-loaded Palacos cement, orthopaedic surgeons should be aware that the successor cements do not appear to have the same release characteristics as the original one. Overall, high gentamicin concentrations were reached inside our prosthesis-related interfacial gap model. These concentrations may be expected to effectively decontaminate the prosthesis-related interfacial gap directly after implantation, provided that these bacteria are sensitive for gentamicin.

Comparison of two methods of fatigue testing bone cement

Two different methods have been used to fatigue test four bone cements. Each method has been used previously, but the results have not been compared. The ISO 527-based method tests a minimum of 10 samples over a single stress range in tension only and uses Weibull analysis to calculate the median number of cycles to failure and the Weibull modulus. The ASTM F2118 test regime uses fewer specimens at various stress levels tested in fully reversed tension-compression, and generates a stress vs. number of cycles to failure (S-N) or Wöhler curve. Data from specimens with pores greater than 1mm across is rejected. The ISO 527-based test while quicker to perform, provides only tensile fatigue data, but the material tested includes pores, thus the cement is closer to cement in clinical application. The ASTM regime uses tension and compression loading and multiple stress levels, thus is closer to physiological loading, but excludes specimens with defects obviously greater than 1mm, so is less representative of cement in vivo. The fatigue lives between the cements were up to a factor 15 different for the single stress level tension only tests, while they were only a factor of 2 different in the fully reversed tension-compression testing. The ISO 527-based results are more sensitive to surface flaws, thus the differences found using ASTM F2118 are more indicative of differences in the fatigue lives. However, ISO 527-based tests are quicker, so are useful for initial screening.

Orthopaedic bone cement: do we know what we are using?

Bone cements produced by different manufacturers vary in their mechanical properties and antibiotic elution characteristics. Small changes in the formulation of a bone cement, which may not be apparent to surgeons, can also affect these properties. The supplier of Palacos bone cement with added gentamicin changed in 2005. We carried out a study to examine the mechanical characteristics and antibiotic elution of Schering-Plough Palacos, Heraeus Palacos and Depuy CMW Smartset bone cements. Both Heraeus Palacos and Smartset bone cements performed significantly better than Schering-Plough Palacos in terms of mechanical characteristics, with and without additional vancomycin (p < 0.001). All cements show a deterioration in flexural strength with increasing addition of vancomycin, albeit staying above ISO minimum levels. Both Heraeus Palacos and Smartset elute significantly more gentamicin cumulatively than Schering-Plough Palacos. Smartset elutes significantly more vancomycin cumulatively than Heraeus Palacos. The improved antibiotic elution characteristics of Smartset and Heraeus Palacos are not associated with a deterioration in mechanical properties. Although marketed as the 'original' Palacos, Heraeus Palacos has significantly altered mechanical and antibiotic elution characteristics compared with the most commonly-used previous version.

In vitro comparison of Refobacin-Palacos R with Refobacin Bone Cement and Palacos R + G

BACKGROUND

Refobacin Palacos R (RPR) is no longer produced and Palacos R + G (PRG) and Refobacin Bone Cement R (RBC) have been introduced to supersede it. We performed an in vitro study to ascertain whether the handling and mechanical properties of the more recent cement preparations are different to those of their predecessor.

METHODS

The 3 cements were tested to ISO 5833 and German DIN 53435 standards. In addition, their gentamicin elution, shrinkage, viscosity, and handling characteristics were studied.

RESULTS

All 3 cements had comparable mechanical properties exceeding the ISO 5833 and DIN 53435 standards. They eluted similar amounts of gentamicin and had comparable shrinkage. In the batches tested, RBC showed statistically significantly longer handling curves. Both PRG and RBC had statistically significantly lower viscosities as they cured compared to their predecessor.

INTERPRETATION

Surgeons must be aware that both successor cements do not appear to have handling curves and viscoelastic properties identical to those of RPR.