Abstract
Purpose
To compare the in vitro elution characteristics of CMW1 and Palacos R bone cement loaded with gentamicin, teicoplanin, or in combination.
Methods
Four bone cement discs were prepared for each cement type. Disc 1 contained no antibiotics; disc 2 contained 0.5 g gentamicin; disc 3 contained 2 g teicoplanin; disc 4 contained 0.5 g gentamicin and 2 g teicoplanin. Elution studies were conducted using a fluorescence polarisation immunoassay technique and performed at intervals of 6 weeks.
Results
For CMW1, gentamicin and teicoplanin elution levels in combination discs were higher than those in the single antibiotic discs (p < 0.001 & p < 0.06). For Palacos R, gentamicin elution levels in combination discs were higher than those in the single antibiotic discs (p < 0.001), but teicoplanin elution levels in combination discs were lesser than that from the single antibiotic discs (p < 0.02). In single and combination discs, gentamicin elution levels in Palacos R were higher than those in CMW1 (p < 0.001 & p < 0.001). Palacos R eluted more teicoplanin than CMW1, except in combined disc with gentamicin, when less teicoplanin was eluted.
Conclusion
Antibiotic elution is higher in Palacos R than CMW1. Antibiotic combination in both cement types has the synergistic effect of increasing antibiotic elution, except for teicoplanin from Palacos R. When high elution of gentamicin is required, Palacos R is preferable. When high elution of teicoplanin is required, Palacos R with only teicoplanin is superior to CMW1.
Keywords: Antibiotic elution, Bone cement, Arthroplasty, CMW, Palacos
Level of evidence
Level IV (experimental study).
1. Introduction
Periprosthetic joint infection can lead to serious complications that often require multiple procedures and prolonged antimicrobial treatment, which lead to poor functional outcomes and increase the economic burden for healthcare services.1 The use of antibiotics in bone cement to prevent and treat infection was first reported by Buchholz in 1970, and the results of the management of prosthetic joint infection using antibiotic-loaded cement heralded a significant change in joint replacement surgery in primary arthroplasty surgery and revision surgery using a spacer as a delivery system.2 Since then, the process of antibiotic elution from bone cement has been extensively researched in vitro and in vivo studies to assess its role in primary and revision surgeries where biofilm formation is one of the main obstacles in the treatment of infections.3 A variety of antibiotics have been used alone or in combination in different types of bone cement with different results.4,5,7, 8, 9 Cement is used as grout in primary and revision surgeries to bond the implant to the bone and vehicle for the elution of antibiotics into the operative field. It is also used as a spacer in first-stage revision surgery to maintain a soft tissue envelope around the joint space but principally to act as a localised antibiotic delivery system. The synergistic effect of elution may have been previously reported with a combination of gentamicin and teicoplanin showing a longer period of bactericidal action than a combination of gentamicin and vancomycin although the latter combination showed higher concentrations in the first 4 days.10 There is a paucity of evidence on the elution characteristics of teicoplanin9. Therefore; we conducted an in vitro observational study to compare the elution characteristics of gentamicin and teicoplanin used alone and in combination in CMW1 and Palacos bone cement. These two antibiotics were chosen as they constitute the most commonly used combination for the treatment of prosthetic joint infections in first-stage revision hip and knee surgery in clinical practise at our institution.
2. Materials and methods
A total of 24 cement discs were made using customised identical moulds 28 mm in diameter and 20 mm in depth. Twelve discs were made of CMW1 cement (DePuy CMW, UK), and another 12 discs were made of Palacos R cement (Heraeus Medical, UK). For each cement type used, four different disc types were made in triplicate with different antibiotic amounts to account for the variance of elution rate in each disc type. Each disc type was loaded with the same amount of antibiotic. Disc 1 was not loaded with antibiotics (control group); three discs were made of Palacos R cement, and another three discs were made of CMW1 cement. Disc 2 was loaded with 0.5 g of gentamicin; three discs were made of Palacos R cement, and another three discs were made of CMW1 cement. Disc 3 was loaded with 2 g of teicoplanin; three discs were made of Palacos R cement, another three were made of CMW1 cement. Disc 4 was loaded with 0.5 g of gentamicin and 2 g of teicoplanin; three discs were made of Palacos R cement, and another three discs were made of CMW1 cement.
The discs were made in a theatre environment using standard mixing bowls and spatulas, and each disc was made from 40 g of cement powder. The antibiotics (gentamicin, teicoplanin or a combination of both) were first added to the polymethyl methacrylate cement powder and thoroughly mixed under sterile conditions. A senior theatre scrub nurse (AN) then prepared the respective cement by adding the liquid monomer to the powder polymer or polymer–antibiotic mixture according to the manufacturer's instructions using vacuum mixing (Summit Medical, Gloucestershire, UK) in a sterile operating theatre environment. The cement dough was then transferred into standard-sized pre-prepared sterile moulds to produce cement discs of dimensions 28 mm × 20 mm. The cement was compressed into the moulds by hand to minimise the risk of lamination or air bubbles in the discs. The pressure was applied until the cement was fully set, and the setup was left at the theatre room temperature for 1 h. The discs were transferred from the moulds to sterile pots containing 50 ml of buffered normal saline bath and maintained at a constant temperature of 37 °C in the laboratory incubator. All 24 discs were made identically, at the same time and in the same theatre setting.
After 24 h, a 5-ml sample from the saline bath was taken from each pot and stored in a separate smaller sterile container. These containers were kept at −20 °C in the laboratory until the assays were performed. The 5 ml sample was used to determine the amount of eluted antibiotic using a fluorescence polarisation immunoassay technique (TDxFKx, Abbott, UK). The discs were then removed from the pots, washed with 30 ml of normal saline, and re-immersed into fresh 50 ml saline pots. This procedure was repeated for all discs at the following time intervals: 48 h, 72 h, 120 h, 1 week, 2 weeks, 3 weeks, and 6 weeks. All antibiotic elution levels were measured in microgram/millilitre (μg/ml). The results were analysed by comparing the elution characteristics of the antibiotics alone and in combination in both cement types.
2.1. Statistical considerations
There are two treatment factors of interest for each antibiotic, namely, type of administration (single or combination) and type of cement block (CMW1 cement or Palacos R cement). Data analysis was performed by a medical statistician (RJ). Data were measured on the log scale to ensure normality. Analyses were performed using repeated-measures analysis of variance. The results are expressed as means and standard error of the difference between means. Significance was set at the 5% level.
3. Results
Elution assays of control discs were randomly performed for both gentamicin and teicoplanin levels, and they revealed no detectable levels of either antibiotic. The mean values of the triplicate discs in each of the four-disc types were calculated for the different time points and are shown in Table 1.
Table 1.
Gentamicin and Teicoplanin elution levels from Palacos R and CMW1 cement discs (loaded with Gentamicin or Teicoplanin or combination of both) at different time points and total elution for 6 weeks.
| GENTAMICIN RELEASE (mcg/ml) |
TEICOPLANIN RELEASE (mcg/ml) |
||||
|---|---|---|---|---|---|
| Disc with Gentamicin alone | Combination disc Gentamicin & Teicoplanin | Disc with Teicoplanin alone | Combination disc Gentamicin & Teicoplanin | ||
| CMW 1 | 24 h | 25 | 53 | 101.4 | 116.9 |
| 48 h | 1.87 | 9.3 | 9.4 | 21.97 | |
| 72 h | 0.97 | 5.93 | 5.03 | 10.67 | |
| 120 h | 1.00 | 4.7 | 6.03 | 10.3 | |
| 1 week | 0.93 | 3.07 | 4 | 7.67 | |
| 2 weeks | 1.60 | 6.24 | 8.2 | 12.97 | |
| 3 weeks | 1.17 | 4.4 | 5.03 | 8.5 | |
| 6 weeks | 1.83 | 7.63 | 8.47 | 13.13 | |
| Total for 6 weeks | 34.37 | 94.27 | 147.56 | 202.11 | |
| PALACOS R | 24 h | 44 | 55.17 | 130.2 | 88.83 |
| 48 h | 8.53 | 18.2 | 20.53 | 14.83 | |
| 72 h | 5.1 | 10.3 | 8.47 | 6.6 | |
| 120 h | 5.3 | 12.23 | 7.83 | 5.87 | |
| 1 week | 4 | 7.27 | 5.17 | 3.37 | |
| 2 weeks | 6.56 | 15.13 | 11.2 | 6.67 | |
| 3 weeks | 4.67 | 9.63 | 8.8 | 5.2 | |
| 6 weeks | 8.27 | 16.23 | 21.53 | 8.8 | |
| Total for 6 weeks | 86.43 | 144.16 | 213.73 | 140.17 | |
Fig. 1 shows the elution profiles of the log antibiotic measures from each disc type at each time point. The results for the two antibiotics are shown separately and reveal a greater level of variability for gentamicin than for teicoplanin. Therefore, the two antibiotics were analysed separately.
Fig. 1.
Elution profiles of the log antibiotic measures from each disc type at each time point.
These figures clearly show that there is a greater level of variability for gentamicin than for teicoplanin.
CMW1 – Single, CMW1 cement disc loaded with a single antibiotic; CMW1 – Comb., CMW1 cement disc loaded with a combination of antibiotics; PAL–R – Single, Palacos R cement disc loaded with a single antibiotic; PAL–R – Comb., Palacos R cement loaded with a combination of antibiotics.
3.1. CMW1 cement
All disc types with gentamicin and/or teicoplanin showed maximum elution level at 24 h, a subsequent steep reduction in antibiotic elution level up to 48 h, and steady elution at the next time points. Antibiotic levels were detectable at 6 weeks, and this suggests continued elution.
Gentamicin elution (Fig. 2): The total level of gentamicin eluted from the combination disc was significantly higher than that from the disc loaded with only gentamicin (94.9 μg/ml versus 34.7 μg/ml; p = 0.001). This was observed at all time points.
Fig. 2.
Gentamicin elution levels from CMW1 cement discs loaded with only gentamicin (blue) and a combination of gentamicin and teicoplanin (red).
Teicoplanin elution (Fig. 3): Statistical analysis revealed that the total level of teicoplanin eluted and level of teicoplanin eluted at each time point were higher from combination discs than those from discs loaded with only teicoplanin. However, due to large in-group variability in the combination discs, the result is not statistically significant (202.1 μg/ml versus 147.57 μg/ml; p = 0.6).
Fig. 3.
Teicoplanin elution levels from CMW1 cement discs loaded with only teicoplanin (blue) and a combination of gentamicin and teicoplanin (red).
Conclusion: In CMW1 cement, the combination of gentamicin and teicoplanin has the synergistic effect of increased elution levels of both antibiotics in total and at each time point.
3.2. Palacos R cement
For all disc types with gentamicin and/or teicoplanin, maximum elution levels were reached at 24 h, followed by a steep fall in antibiotic levels up to 48 h, and steady elution at subsequent time intervals. Antibiotic levels were detectable even at 6 weeks, and this finding suggests continued elution.
Gentamicin elution (Fig. 4): The total level of gentamicin eluted from the combination disc was significantly higher than that from the disc loaded with only gentamicin (144.17 μg/ml versus 86.4 μg/ml; p = 0.001). This was observed at all time points.
Fig. 4.
Gentamicin elution levels from Palacos R cement discs loaded with only gentamicin (blue) and a combination of gentamicin and teicoplanin (red).
Teicoplanin elution (Fig. 5): The total level of teicoplanin eluted from the combination disc was significantly lower than that from the disc loaded with only teicoplanin (140 μg/ml versus 213.7 μg/ml; p = 0.02). This was observed at all time points. In other words, with Palacos R cement, more teicoplanin is eluted from discs loaded with only teicoplanin than from combination discs.
Fig. 5.
Teicoplanin elution levels from Palacos R cement discs loaded with only teicoplanin (blue) and a combination of gentamicin and teicoplanin (red).
Conclusion: In Palacos R cement, the combination of gentamicin and teicoplanin significantly increased the gentamicin elution level and significantly reduced the teicoplanin elution level.
3.3. Comparison of CMW1 and Palacos R cement
Gentamicin elution: The total gentamicin elution level from discs loaded with only gentamicin and from combination discs is significantly higher when Palacos R cement is used than when CMW1 cement is used (86.43 μg/ml versus 34.37 μg/ml; p = 0.001 and 144.17 μg/ml versus 94.9 μg/ml; p = 0.001). This is observed at all time points (Fig. 6).
Fig. 6.
Total gentamicin elution levels for 6 weeks from Palacos R and CMW1 cement discs loaded with only gentamicin (blue) and a combination of gentamicin and teicoplanin (red).
Teicoplanin elution: The total teicoplanin elution level from discs loaded with only teicoplanin is significantly higher when Palacos R cement is used than when CMW1 cement is used (213.73 μg/ml versus 147.57 μg/ml; p = 0.03). However, the total teicoplanin elution level from combination discs is significantly less when Palacos R cement is used than when CMW1 cement is used (202.1 μg/ml versus 140.17 μg/ml; p = 0.04). In other words, with Palacos R cement, less teicoplanin is eluted from combination discs than from discs loaded with only teicoplanin. This is observed at all time points (Fig. 7).
Fig. 7.
Total teicoplanin elution levels for 6 weeks from Palacos R and CMW1 cement discs loaded with only teicoplanin (blue) and a combination of gentamicin and teicoplanin (red).
Conclusion: More gentamicin is eluted from antibiotic combination discs made from Palacos R cement than from combination discs made from CMW1 cement, and more teicoplanin from discs loaded with only teicoplanin, and more gentamicin from discs loaded with only gentamicin are eluted when the discs are made from Palacos R cement than when the discs are made from CMW1 cement. However, with Palacos R cement, less teicoplanin is eluted from antibiotic combination discs than from discs loaded with only teicoplanin.
4. Discussion
Since the first reported use of antibiotics in bone cement by Buchholz and Engelbrecht in 1970,2 the use of antibiotic-loaded bone cement has become standard practice in cemented joint arthroplasty.4 Most bone cement types are now manufactured with added antibiotics, most commonly gentamicin. Antibiotic-loaded bone cement is used as prophylaxis against infection in primary arthroplasty and as part of the treatment for infected joint replacements in revision surgery, where it acts as a local delivery system for antibiotic elution around implants.5 The addition of another antibiotic to the antibiotic-loaded bone cement is accepted practice in the surgical management of infected joints, especially in the first stage of revision surgery, and typically after obtaining the results of sensitivity studies of organisms identified from the microbiological assessment of synovial fluid aspirates or biopsies acquired pre-operatively.6 The problem of an infected joint replacement is magnified by the emergence of multi-resistant organisms and failure to eradicate the joint infection with routinely used antibiotics, thereby emphasizing the need to use more than one antibiotic.7 A combination of antibiotics in bone cement may solve the problem of resistant organisms around implants.8
Elution has been described as a passive surface phenomenon, as diffusion from the cement matrix through the voids and cracks in the cement, and as a process termed passive opportunism in antibiotic combinations.11 Antibiotic elution from bone cement is dependent on a number of factors, including the type of antibiotic, type of bone cement (with regard to viscosity and porosity), the quantity of antibiotic used, the molecular weight of antibiotic, the surface area of cement, method of preparation of bone cement (including mixing speed), and effect of the combination of two or more antibiotics.9
When antibiotic combinations are used in bone cement, a synergistic effect of increased release of the individual antibiotics is often observed. This is attributed to several factors, including increased porosity and voids in bone cement due to the addition of a second antibiotic or the second antibiotic acting as a soluble additive, thereby increasing the surface area of the bone cement; this is referred to as passive opportunism.12 When two antibiotics are incorporated in bone cement, more voids and cracks exist in the cement and are subsequently released, resulting in the release of the remaining antibiotics. Anagnostakos et al. studied antibiotic release and bacterial growth inhibition in Palacos R cement with various combinations of gentamicin, vancomycin, and teicoplanin or synercid and tested them against Staphylococcus epidermidis, Staphylococcus aureus, Enterococcus faecalis, and methicillin‐resistant S aureus (MRSA).9 There was a wide variation in antibiotic activity with the longest growth inhibition of S. epidermidis and MRSA observed with the gentamicin–vancomycin combination and the longest growth inhibition of E. faecalis and S. aureus observed with the gentamicin–teicoplanin combination. The highest gentamicin and vancomycin levels were observed in the first 4 days, teicoplanin was detected only in the first 72 h, and synercid was not detected at all. The level of gentamicin released was higher than the level of vancomycin released. The aminoglycoside–glycopeptide combination had a synergistic effect on the release of gentamicin, but not on vancomycin or teicoplanin. Overall, they concluded that cement with a combination of antibiotics was superior to cement with a single antibiotic. In contrast, Trippel reported that antibiotic combination did not result in increased elution.13 This may be due to factors such as the relative decrease in available cement surface area for diffusion; the quantity of trantibiotic added, and decreased porosity and voids due to vacuum mixing of cement. Elution characteristics differ with each type of cement, and it has been reported in numerous studies that antibiotic elution is better with Palacos R cement than with other cement types. This is attributed to the higher porosity of Palacos R cement.
Our study showed that antibiotic elution level peaks at 24 h and an exponential fall follows thereafter. This was observed in all disc types studied. This finding is consistent with the reports of other studies.14 The detection of antibiotic elution at 6 weeks validates similar results of other studies that reported antibiotic elution at even longer periods.15
We showed that elution from Palacos R cement is superior to that from CMW1 cement for single antibiotics and gentamicin used in combination, but not for teicoplanin used in combination. The increased elution of gentamicin from Palacos R cement with gentamicin–teicoplanin combination supports the theory of the synergistic effect of teicoplanin on gentamicin release, but not vice versa, which is similar to the pattern reported by Anagnostakos et al.6 This may be due to vacuum mixing, which has been proven to reduce porosity and voids in bone cement, or due to the physical characteristics of teicoplanin when mixed in cement containing another antibiotic.
Although a level of mechanical strength is required in cement used in primary arthroplasty or the second stage of a revision arthroplasty, it is not as important in the first stage of revision procedure where antibiotic elution and maintenance of soft tissue space are the primary concerns. Mechanical fracture and fatigue properties were not assessed in this study, but they are critical in primary surgery and may be affected by the addition of antibiotics. Our results reveal the elution characteristics that may be expected in first-stage revision surgery, but conclusions from this study and the other studies cited herein need to be interpreted with consideration for the potential alteration of mechanical properties caused by the addition of antibiotics.
This study has limitations as we considered only two antibiotics and two types of cement that are relevant to our practice, but many other combinations are used in clinical practice. The results of this study cannot be extrapolated to other antibiotic–cement combinations. Although our results show high antibiotic elution levels, we did not investigate the minimum inhibitory antibiotic concentration or antibiotic sensitivity against specific bacteria. In theory, the porosity of each disc may be different and hence affect the outcome; however, care was taken to mix the cement in an identical manner in a theatre setting such that all discs were identical and variation in porosity was minimal. In addition, as our study is an in vitro study, our results may not exactly mimic in vivo elution characteristics in any given clinical scenario but may give an indication of what may be expected. However, we tried to replicate in vivo conditions with regard to fluid concentrations and temperature.
The practical implications of this study are that antibiotic elution levels are higher with Palacos R cement than with CMW1 cement and that antibiotic elution levels with both cement types are highest at 24 h. Antibiotic combination in CMW1 and Palacos R cement has the synergistic effect of increased elution of individual antibiotics, with the exception of higher teicoplanin elution levels from Palacos R cement in discs with only teicoplanin than in combination discs. Antibiotics have different elution characteristics in the two-bone cement studied, and a combination of two or more antibiotics is shown to have synergistic action on elution rate and quantity. This has clinical implications in revision arthroplasty surgery. If high gentamicin elution is required with or without teicoplanin, Palacos R cement loaded with teicoplanin is superior to CMW1 cement, and maximum elution level is reached at 24 h. If high teicoplanin elution is required as a single antibiotic, Palacos R cement with only teicoplanin is superior to CMW1 cement, and maximum elution level is reached at 24 h.
Declaration of competing interest
All authors declare no conflict of interests.
Acknowledgements
The authors would like to thank De Puy, UK, and Heraeus Medical, UK, for their material support in this study.
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