Effective bactericidal activity of tobramycin and vancomycin eluted from acrylic bone cement

Point-of-Care Coating of Revision Femoral Stems With Antibiotic-Loaded Calcium Sulfate: Reduction in Infection After 2nd Stage Reimplantation but Not With Aseptic Revisions

Background

Infection rates in revision total hip arthroplasty are lower when antibiotic loaded cemented stems are utilized. Inspired by this technique, a point-of-care coating of antibiotic-loaded calcium sulfate (CaSO4) was applied to cementless revision stems in aseptic revision and 2nd stage reimplantation total hip arthroplasty.

Methods

One hundred eleven consecutive femoral stems were coated. Just prior to insertion, 10 cc of CaSO4 was mixed with 1 g vancomycin and 240 mg tobramycin with the paste applied to the stem. The results were compared to a matched cohort (N = 104) performed across the previous 5 years. The surgical methods were comparable, but for the stem coating. The study group was followed for a minimum of 3 years.

Results

In the study cohort of 111 patients, there were 69 aseptic revisions with one periprosthetic joint infection (PJI) (1.4%) and 42 second-stage reimplantations with 2 PJIs (4.8%). In the control cohort of 104 patients, there were 74 aseptic revisions with one PJI (1.4%) and 30 second-stage reimplantations with 7 PJIs (23.3%). There was no significant reduction in PJI rate in the aseptic revision subgroup (1.4% study vs 1.4% control group), P = 1.000. Antibiotic stem coating reduced PJI rate in the 2nd stage reimplantation subgroup (23.3% control vs 4.8% study group), P = .028. In both groups, there were no cases of aseptic stem loosening.

Conclusions

Point-of-care antibiotic coating of cementless revision femoral stems reduces PJI infection rate in 2nd stage reimplantations only. We theorize that microbes persist in the endosteal cortices after resection and may contribute to infection recurrence.

Killing of a Multispecies Biofilm Using Gram-Negative and Gram-Positive Targeted Antibiotic Released from High Purity Calcium Sulfate Beads

BACKGROUND

Multispecies biofilm orthopedic infections are more challenging to treat than mono-species infections. In this in-vitro study, we aimed to determine if a multispecies biofilm, consisting of Gram positive and negative species with different antibiotic susceptibilities could be treated more effectively using high purity antibiotic-loaded calcium sulfate beads (HP-ALCSB) containing vancomycin (VAN) and tobramycin (TOB) in combination than alone.

METHODS

Three sets of species pairs from bioluminescent strains of Pseudomonas aeruginosa (PA) and Staphylococcus aureus (SA) and clinical isolates, Enterococcus faecalis (EF) and Enterobacter cloacae were screened for compatibility. PA + EF developed intermixed biofilms with similar cell concentrations and so were grown on 316L stainless steel coupons for 72 h or as 24 h agar lawn biofilms and then treated with HP-ALCSBs with single or combination antibiotics and assessed by viable count or bioluminescence and light imaging to distinguish each species. Replica plating was used to assess viability.

RESULTS

The VAN + TOB bead significantly reduced the PA + EF biofilm CFU and reduced the concentration of surviving antibiotic tolerant variants by 50% compared to single antibiotics.

CONCLUSIONS

The combination of Gram-negative and positive targeted antibiotics released from HP-ALCSBs may be more effective in treating multispecies biofilms than monotherapy alone.

Influence of chitosan and chitosan oligosaccharide on dual antibiotic-loaded bone cement: In vitro evaluations

BACKGROUND AND PURPOSE

The purpose of this study was to investigate the effect of incorporating chitosan (Ch) and chitosan oligosaccharides (ChO) into the commercially premixed antibiotic-loaded bone cement (ALBC). We compare antibiotic release profiles, antibacterial activity, and mechanical properties among different ALBC formulations. The hypothesis was that increasing the amount of Ch and ChO in the cement mixture would increase the antibiotics released and bacterial control. ALBC mixed with Ch or ChO may create a greater effect due to its superior dissolving property.

MATERIALS AND METHODS

The bone cement samples used in this project were made from Copal® G+V composed of vancomycin and gentamicin. To prepare the Ch and the ChO mixed bone cement samples, different amounts of Ch and ChO were added to the polymethylmethacrylate matrix with three concentrations (1%, 5%, and 10%). Drug elution assay, antimicrobial assay, in vitro cytotoxicity, and mechanical properties were conducted.

RESULTS

Bone cement samples made from Copal® G+V alone or combined with Ch or ChO can release vancomycin and gentamicin into the phosphate-buffered saline. Mixing ChO into the bone cements can increase the amount of drug released more than Ch. ChO 10% gave the highest amount of antibiotics released. All samples showed good antibacterial properties with good biocompatibility in vitro. The microhardness values of the Ch and ChO groups increased significantly compared to the control group. In all groups tested, the microhardness of bone cements was reduced after the drug eluted out. However, this reduction of the Ch and ChO groups was in line with the control.

INTERPRETATION

Various attempts have been made to improve the ALBC efficacy. In our study, the best bone cement formulation was bone cement mixed with ChO (10%), which had the highest drug release profiles, was biocompatible, and contained antibacterial properties with acceptable mechanical properties. This phenomenon could result from the superior water solubility of the ChO. When ChO leaves the bone cement specimens, it generates pores that could act as a path that exposes the bone cement matrix to the surrounding medium, increasing antibiotic elution. From all above, ChO is a promising substance that could be added to ALBC in order to increase the drug elution rate. However, more in vitro and in vivo experiments are needed before being used in the clinic.

Antibiotic Cement Utilization for the Prophylaxis and Treatment of Infections in Spine Surgery: Basic Science Principles and Rationale for Clinical Use

Antibiotic bone cement (ABC) is an effective tool for the prophylaxis and treatment of osteomyelitis due to the controlled, sustained release of local antibiotics. ABC has been proven to be effective in the orthopedic fields of arthroplasty and extremity trauma, but the adoption of ABC in spine surgery is limited. The characteristics of ABC make it an optimal solution for treating vertebral osteomyelitis (VO), a serious complication following spine surgery, typically caused by bacterial and sometimes fungal and parasitic pathogens. VO can be devastating, as infection can result in pathogenic biofilms on instrumentation that is dangerous to remove. New techniques, such as kyphoplasty and novel vertebroplasty methods, could amplify the potential of ABC in spine surgery. However, caution should be exercised when using ABC as there is some evidence of toxicity to patients and surgeons, antibiotic allergies, bone cement structural impairment, and possible development of antibiotic resistance. The purpose of this article is to describe the basic science of antibiotic cement utilization and review its usage in spine surgery.

Exploration of the Pharmacodynamics for Pseudomonas aeruginosa Biofilm Eradication by Tobramycin

Pseudomonas aeruginosa is a Gram-negative, opportunistic pathogen which is involved in numerous infections. It is of growing concern within the field of antibiotic resistant and tolerance and often exhibits multi-drug resistance. Previous studies have shown the emergence of antibiotic resistant and tolerant variants within the zone of clearance of a biofilm lawn after exposure to aminoglycosides. As concerning as the tolerant variant emergence is, there was also a zone of killing (ZOK) immediately surrounding the antibiotic source from which no detectable bacteria emerged or were cultured. In this study, the ZOK was analyzed using both in vitro and in silico methods to determine if there was a consistent antibiotic concentration versus time constraint (area under the curve, (AUC)) which is able to completely kill all bacteria in the lawn biofilms in our in vitro model. Our studies revealed that by achieving an average AUC of 4,372.5 μg*hr/mL, complete eradication of biofilms grown on both agar and hydroxyapatite was possible. These findings show that appropriate antibiotic concentrations and treatment duration may be able to treat antibiotic resistant and tolerant biofilm infections.

Effect of Local Delivery of Vancomycin and Tobramycin on Bone Regeneration

OBJECTIVE

A bone defect rat model was established to investigate the osteogenic effect of local delivery two antibiotics (vancomycin and tobramycin powder) on bone regeneration.

METHODS

Twenty-four Sprague-Dawley (SD) male rats (6 to 8 weeks, 200 to 250 g) were used in this study. All these rats were randomly divided into four groups. Based on dose conversion between rat and human via body surface area, the rat dose of two antibiotics was 88μg/g and 176 μg/g for vancomycin and tobramycin, respectively. Con group (no antibiotic), Van group (vancomycin, 88 μg/g), Tob group (tobramycin 176 μg/g), and Van+Tob group (vancomycin 88μg/g combined with tobramycin 176 μg/g). A 5.0-mm full-thickness standardized mandibular bone defect was performed with a drill in each rat and different antibiotic powders were placed over the bone defect space, respectively. All these animals were sacrificed after 12 weeks post-operation. The mandible bones were harvested for further radiographic and histologic analysis. The bone volume/total volume (BV/TV) ratio, bone volume (BV), and bone fractional area (BFA) in the defect area via micro-computed tomography (μCT scanning) were further analyzed. Then, we performed a histological assessment via hematoxylin and eosin (H&E) and Masson's trichrome staining to analyze bone regeneration and also analyze the number of osteoblasts per filed.

RESULTS

There were no postoperative deaths, signs of vancomycin-related or tobramycin-related toxicity, or signs of systemic illness in any of the four groups. All wounds healed well, and no complications or surgical site infection were observed in all rats. From the μCT scans analyses, there was less bone regeneration in the Van group than in the Con group (BV/TV: F = 64.29, R²  = 0.9602; P = 0.0052; BFA: F = 76.17, R²  = 0.9662, P = 0.0007; BV: F = 194.4, R²  = 0.9865, P = 0.0022). However, when the tobramycin and vancomycin were combined, an increase in bone defect re-ossification was found in the Van+Tob group than in the Van group (BV/TV: F = 64.29, R²  = 0.9602, P = 0.0033; BFA: F = 76.17, R²  = 0.9662, P = 0.0006; BV: F = 194.4, R²  = 0.9865, P = 0.0033). Routine H&E and Masson staining supported the finding of μCT scanning. Quantitative indices confirmed that both the bone regeneration and the number of osteoblasts per filed in the defect area was higher in the Van+Tob group than in the Van group (percentage of bone tissue: F = 145.7, R²  = 0.9562, P = 0.0008; number of osteoblasts per file; F = 67.3, R²  = 0.9098, P < 0.0001). There was no significant difference between the Con group and the Van+Tob group on the number of osteoblasts each field (F = 145.7, R²  = 0.9562, P > 0.9999).

CONCLUSION

For bone defect, local application of vancomycin combined with tobramycin was recommended over vancomycin alone. This animal study presents data suggesting that the use of local delivery of vancomycin and tobramycin should be investigated further in clinical studies.

Coated nails: is their use supported by the literature?

Antibiotic-coated intramedullary nails have been popularized in recent decades for treating long-bone infections. They are especially useful in treating diaphyseal infections requiring stability, such as those involving fractures and nonunions. The nails are made by injecting antibiotic-impregnated polymethylmethacrylate or "cement" around a metal core using a silicone tube as a mold. There are a variety of techniques that can be used to customize the nail to the affected site. Antibiotic cement has long been demonstrated as an effective local antibiotic delivery system. It is able to elute high concentrations of antibiotics while having little systemic toxicity. Several case series have reported good outcomes using this technique, defined by bone union and infection control. Further research is needed to determine the amount of weight that can safely be transferred through the nail and to optimize antibiotic elution.

Distal femoral replacement - Cemented or cementless? Current concepts and review of the literature

Distal femoral endoprosthetic replacement has been successfully used to reconstruct distal femoral defects after tumor resection for over four decades. Despite continued advances, aseptic loosening continues to be the most common failure mode after infection. Debate still exists about a variety of design features and the optimal fixation method remains controversial. To date, no large-scale study or meta-analysis has demonstrated the superiority of one fixation technique over another. While the classic dichotomy of cemented versus cementless stems is well-known, the contemporary surgeon needs to fully understand the optimal clinical setting for each type of fixation technique and additional strategies to maximize implant stability. In clinical practice, the choice of fixation must be tailored to the individual patient. The surgeon must consider whether the operation is being performed for primary sarcoma or metastatic carcinoma, the presence of distant metastases, age, comorbidities, and whether radiotherapy has been previously given or will be required at the site of fixation. The best strategy for each patient optimizes tumor control and appropriately weighs risks of fixation failure versus the expected patient survival. This review will explore cemented and uncemented distal femoral replacement and highlight modern concepts to optimize each technique.

The Osteogenic Effect of Local Delivery of Vancomycin and Tobramycin on Bone Marrow Stromal Cells

Purpose

Bone tissue infections are a difficult problem in orthopedic surgery. Topical application of vancomycin and tobramycin powder has been proved to significantly reduce infection rates. However, the osteogenic effect of the topical application of these two antibiotics is unclear. In this study, the osteogenic effect of local delivery antibiotics on bone regeneration was investigated in vitro.

Methods

Bone marrow stromal cells (BMSCs) were incubated in the presence of vancomycin (14.28μg/mL), tobramycin (28.57μg/mL), or vancomycin combined with tobramycin (vancomycin 14.28μg/mL and tobramycin 28.57μg/mL). Cell viability, proliferation, and migration were analyzed. The alizarin red staining as well as the alkaline phosphatase staining was investigated. Then, the quantitative real-time (qRT)-PCR of osteogenic mRNA expression levels were also evaluated.

Results

The results showed that vancomycin combined with tobramycin has no adverse effect on the viability and proliferation of BMSCs. The topical application of vancomycin alone may interfere with the bone regenerative processes. However, the tobramycin can promote the osteogenic differentiation of BMSCs and also rescue the osteogenic potential of BMSCs inhibited by vancomycin both in vitro.

Conclusion

From this in vitro study, local application of vancomycin combined with tobramycin does not affect the osteogenic potential of BMSCs.

Antimicrobial properties of antibiotic-loaded implants

AIMS

The aim of this study was to compare the ability of tantalum, 3D porous titanium, antibiotic-loaded bone cement, and smooth titanium alloy to inhibit staphylococci in an in vitro environment, based on the evaluation of the zone of inhibition (ZOI). The hypothesis was that there would be no significant difference in the inhibition of methicillin-sensitive or methicillin-resistant Staphylococcus aureus (MSSA/MRSA) between the two groups.

METHODS

A total of 30 beads made of three different materials (tantalum/3D porous titanium and smooth titanium alloy) were bathed for one hour in a solution of 1 g vancomycin in 20 ml of sterile water for injection (bath concentration: 50 mg/mL). Ten 1 cm³ cylinders of antibiotic-loaded cement were also created by mixing standard surgical cement with 1 g of vancomycin in standardized sterile moulds. The cylinders were then placed on agar plates inoculated with MSSA and MRSA. The ZOIs were measured each day and the cylinders were transferred onto a new inoculated plate.

RESULTS

For MSSA and MRSA, no inhibitory effect was found in the control group, and antibiotic-loaded smooth titanium alloy beads showed a short inhibitory effect until day 2. For MSSA, both tantalum and 3D porous titanium beads showed significantly larger mean ZOIs than cement beads (all p < 0.01) each day until day 7 for tantalum and until day 3 for 3D porous titanium. After six days, antibiotic-loaded cement had significantly larger mean ZOIs than the 3D porous titanium (p = 0.027), but no significant difference was found with tantalum (p = 0.082). For MRSA, both tantalum and 3D porous titanium beads had significantly larger mean ZOIs than antibiotic-loaded cement each day until day 6 for tantalum (all p < 0.01) and until day 3 for 3D porous titanium (all p < 0.04). Antibiotic-loaded cement had significantly larger mean ZOIs than tantalum and 3D porous titanium from day 7 to 9 (all p < 0.042).

CONCLUSION

These results show that porous metal implants can deliver local antibiotics over slightly varying time frames based on in vitro analysis. Cite this article: Bone Joint J 2020;102-B(6 Supple A):158-162.

Does the Effectiveness and Mechanical Strength of Kanamycin-Loaded Bone Cement in Musculoskeletal Tuberculosis Compare to Vancomycin-Loaded Bone Cement

BACKGROUND

Antibiotic-loaded bone cement (ALBC) is used to deliver antimycobacterial agents into the focal lesion of musculoskeletal tuberculosis. Although kanamycin is currently used as an antimycobacterial agent for the treatment of multidrug-resistant tuberculosis, there is no information about its suitability in ALBC.

METHODS

An in vitro experiment was conducted with cylindrical shape of 40 g of bone cement with 1, 2, and 3 g of kanamycin. Eluate (1 mL) was extracted from each specimen to measure the level of elution and antimycobacterial activity on days 1, 4, 7, 14, and 30. The quantity of kanamycin in eluates was evaluated by a liquid chromatography-mass spectrometry system, and the antimycobacterial activity of eluates against Mycobacterium tuberculosis H37Rv was calculated by comparing the minimal inhibitory concentration. The ultimate compression strength was conducted using a material testing system machine (Instron 3366; Instron, Norwood, MA) before and after elution.

RESULTS

Eluates from ALBC containing 2 and 3 g of kanamycin had effective antimycobacterial activity for 30 days, whereas eluates from ALBC containing 1 g of kanamycin were partially active until day 30. The pre-eluted compression strength of kanamycin-loaded cement and vancomycin-loaded cement was weaker as they contained a larger amount of antibiotics. There was no statistical difference between the strength of all kanamycin regimens and 1 g of vancomycin in the ultimate compression test. After 30 days of elution, the strength of all kanamycin-loaded cement and vancomycin-loaded cement cylinders was significantly lower than that of initial specimens (P < .05).

CONCLUSION

The antimycobacterial activity of ALBC containing more than 2 g of kanamycin was effective during a 30-day period. The ultimate compression strength of bone cement loaded with 1-3 g of kanamycin was comparable with 1 g of vancomycin while maintaining effective elution until day 30.

Short or Long Antibiotic Regimes in Orthopaedics (SOLARIO): a randomised controlled open-label non-inferiority trial of duration of systemic antibiotics in adults with orthopaedic infection treated operatively with local antibiotic therapy

BACKGROUND

Orthopaedic infections, such as osteomyelitis, diabetic foot infection and prosthetic joint infection, are most commonly treated by a combination of surgical debridement and a prolonged course of systemic antibiotics, usually for at least 4-6 weeks. Use of local antibiotics, implanted directly into the site of infection at the time of surgery, may improve antibiotic delivery and allow us to shorten the duration of systemic antibiotic therapy, thereby limiting the frequency of side effects, cost and selection pressure for antimicrobial resistance.

METHODS

SOLARIO is a multicentre open-label randomised controlled non-inferiority trial comparing short and long systemic antibiotic therapy alongside local antibiotic therapy. Adult patients with orthopaedic infection, who have given informed consent, will be eligible to participate in the study provided that no micro-organisms identified from deep tissue samples are resistant to locally implanted antibiotics. Participants will be randomised in a 1:1 ratio to receive either a short course (≤ 7 days) or currently recommended long course (≥ 4 weeks) of systemic antibiotics. The primary outcome will be treatment failure by 12 months after surgery, as ascertained by an independent Endpoint Committee blinded to treatment allocation. An absolute non-inferiority margin of 10% will be used for both per-protocol and intention-to-treat populations. Secondary outcomes will include probable and definite treatment failure, serious adverse events, treatment side effects, quality of life scores and cost analysis.

DISCUSSION

This study aims to assess a treatment strategy that may enable the reduction of systemic antibiotic use for patients with orthopaedic infection. If this strategy is non-inferior, this will be to the advantage of patients and contribute to antimicrobial stewardship.

TRIAL REGISTRATION

Clinicaltrials.gov, NCT03806166. Registered on 11 November 2019.

Effects of Intraoperative Intrawound Antibiotic Administration on Spinal Fusion: A Comparison of Vancomycin and Tobramycin in a Rat Model

BACKGROUND

Local, intrawound use of antibiotic powder, such as vancomycin and tobramycin, in spinal fusion surgery has become an increasingly common prophylactic measure in an attempt to reduce rates of postsurgical infection. However, the effects of localized antibiotic delivery on fusion remain unclear. The objective of this study was to examine the in vivo effects of intraoperative local delivery of 2 antibiotics commonly used in bone-grafting surgery on spinal fusion outcomes in a rat model.

METHODS

Single-level (L4-L5), bilateral posterolateral intertransverse process lumbar fusion surgery was performed on 60 female Lewis rats (6 to 8 weeks of age) using syngeneic iliac crest allograft mixed with clinical bone-graft substitute and varying concentrations of antibiotics (n = 12 each): (1) control without any antibiotics, (2) low-dose vancomycin (14.3 mg/kg), (3) high-dose vancomycin (71.5 mg/kg), (4) low-dose tobramycin (28.6 mg/kg), and (5) high-dose tobramycin (143 mg/kg). Eight weeks postoperatively, fusion was evaluated via micro-computed tomography (µCT), manual palpation, and histological analysis, with blinding to treatment group. In the µCT analysis, fusion-mass volumes were measured for each rat. Each spine specimen (L4-L5) was rated (manual palpation score) on a scale of 2 to 0 (2 = fused, 1 = partially fused, and 0 = non-fused).

RESULTS

The mean fusion-mass volume on µCT (mm) was as follows: control, 29.3 ± 6.2; low-dose vancomycin, 26.3 ± 8.9; high-dose vancomycin, 18.8 ± 7.9; low-dose tobramycin, 32.7 ± 9.0; and high-dose tobramycin, 43.8 ± 11.9 (control versus high-dose vancomycin, p < 0.05; and control versus high-dose tobramycin, p < 0.05). The mean manual palpation score for each group was as follows: control, 1.46 ± 0.58; low-dose vancomycin, 0.86 ± 0.87; high-dose vancomycin, 0.68 ± 0.62; low-dose tobramycin, 1.25 ± 0.71; and high-dose tobramycin, 1.32 ± 0.72 (control versus high-dose vancomycin, p < 0.05). The histological analyses demonstrated a similar trend with regard to spinal fusion volume.

CONCLUSIONS

Intraoperative local application of vancomycin, particularly at a supraphysiological dosage, may have detrimental effects on fusion-mass formation. No inhibitory effect of tobramycin on fusion-mass formation was observed.

CLINICAL RELEVANCE

When spine surgeons decide to use intraoperative intrawound antibiotics in spinal fusion surgery, they should weigh the reduction in surgical site infection against a possible inhibitory effect on fusion.

Antibiotic-loaded tantalum may serve as an antimicrobial delivery agent

Aims

The aims of this study were to compare the mean duration of antibiotic release and the mean zone of inhibition between vancomycin-loaded porous tantalum cylinders and antibiotic-loaded bone cement at intervals, and to evaluate potential intrinsic antimicrobial properties of tantalum in an in vitro medium environment against methicillin-sensitive Staphylococcus aureus (MSSA).

Materials and Methods

Ten porous tantalum cylinders and ten cylinders of cement were used. The tantalum cylinders were impregnated with vancomycin, which was also added during preparation of the cylinders of cement. The cylinders were then placed on agar plates inoculated with MSSA. The diameter of the inhibition zone was measured each day, and the cylinders were transferred to a new inoculated plate. Inhibition zones were measured with a Vernier caliper and using an automated computed evaluation, and the intra- and interobserver reproducibility were measured. The mean inhibition zones between the two groups were compared with Wilcoxon’s test.

Results

MSSA was inhibited for 12 days by the tantalum cylinders and for nine days by the cement cylinders. At day one, the mean zone of inhibition was 28.6 mm for the tantalum and 19.8 mm for the cement group (p < 0.001). At day ten, the mean zone of inhibition was 3.8 mm for the tantalum and 0 mm for the cement group (p < 0.001). The porous tantalum cylinders soaked only with phosphate buffered solution showed no zone of inhibition.

Conclusion

Compared with cement, tantalum could release antibiotics for longer. Further studies should assess the advantages of using antibiotic-loaded porous tantalum implants at revision arthroplasty. Cite this article: Bone Joint J 2019;101-B:848–851.

Vancomycin elution kinetics from porous tantalum metal

Revisions TKAs are being completed with uncemented constructs more frequently. We hypothesized that tantalum cones could be an efficient carrier of antibiotics in uncemented procedures. We aimed to compare the release of vancomycin between (i) tantalum and smooth stainless cylinders; (ii) different concentrations of vancomycin; and (iii) different durations of bathing. Specifically designed tantalum cylinders were bathed in a vancomycin solution with various durations of baths. We investigated rinses between each interval as well as the dose of vancomycin. Vancomycin concentrations were determined in each group by fluorescence polarization immunoassay at different intervals (1 h, days 1, 2, 3, 5). At 1 h, the mean vancomycin concentration for the 1-hour soaking group was 3,172 μg/ml, whereas mean concentration for the smooth stainless steel group was 39.37 μg/ml (p < 0.001). The rinsing group showed a significantly lower concentration at 1 h and 1 day (p < 0.05). The 2-gram vancomycin group showed no difference at days 1, 2, and 3 compared to the 1-hour group. The 5, 15, and 30-minute bathing groups showed significantly lower vancomycin concentrations at all-time points. All vancomycin concentrations at day 3 were superior to the minimal inhibitory concentration of Staphyloccocus aureus. The mean concentration of vancomycin depends on the material, duration of bathing, the rinsing effect, and the drug dose. Our in-vitro study is the first to show that porous tantalum cylinders allow antibiotic carriage and progressive release. If appearing in vivo, in a similar extent, this intrinsic property might be useful to prevent and/or treat peri-prosthetic joint infection. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:308-312, 2019.

In vivo efficacy of tobramycin-loaded synthetic calcium phosphate beads in a rabbit model of staphylococcal osteomyelitis

Background

Osteomyelitis is an acute or chronic inflammatory process of the bone following infection with pyogenic organisms like Staphylococcus aureus. Tobramycin (TOB) is a promising aminoglycoside antibiotic used to treat various bacterial infections, including S. aureus. The aim of this study was to investigate the efficacy of tobramycin-loaded calcium phosphate beads (CPB) in a rabbit osteomyelitis model.

Methods

Tobramycin (30 mg/mL) was incorporated into CPB by dipping method and the efficacy of TOB-loaded CPB was studied in a rabbit osteomyelitis model. For juxtaposition, CPB with and without TOB were prepared. Twenty-five New Zealand white rabbits were grouped (n = 5) as sham (group 1), TOB-loaded CPB without S. aureus (group 2), S. aureus only (group 3), S. aureus + CPB (group 4), and S. aureus + TOB-loaded CPB (group 5). Groups infected with S. aureus followed by CPB implantation were immediately subjected to surgery at the mid-shaft of the tibia. After 28 days post-surgery, all rabbits were euthanized and the presence or absence of chronic osteomyelitis and the extent of architectural destruction of the bone were assessed by radiology, bacteriology and histological studies.

Results

Tobramycin-loaded CPB group potentially inhibited the growth of S. aureus causing 3.2 to 3.4 log₁₀ reductions in CFU/g of bone tissue compared to the controls. Untreated groups infected with S. aureus showed signs of chronic osteomyelitis with abundant bacterial growth and alterations in bone architecture. The sham group and TOB-loaded CPB group showed no evidence of bacterial growth.

Conclusions

TOB-incorporated into CPB for local bone administration was proven to be more successful in increasing the efficacy of TOB in this rabbit osteomyelitis model and hence could represent a good alternative to other formulations used in the treatment of osteomyelitis.

Electronic supplementary material

The online version of this article (10.1186/s12941-018-0296-3) contains supplementary material, which is available to authorized users.

Nephrotoxicity After the Treatment of Periprosthetic Joint Infection With Antibiotic-Loaded Cement Spacers

BACKGROUND

Treatment of periprosthetic joint infections commonly involves insertion of an antibiotic-loaded cement spacer (ACS). The risk for acute kidney injury (AKI) related to use of antibiotic spacers has not been well defined. We aimed to identify the incidence of and risk factors for AKI after placement of an ACS.

METHODS

We performed a prospective cohort study of patients with an infected primary total hip or knee arthroplasty treated with ACSs with vancomycin, gentamicin, and tobramycin. Serum creatinine and glomerular filtration rate data were collected at baseline and weekly intervals for 8 weeks. Patients were classified into Risk, Injury, Failure, Loss of kidney function, and End-stage kidney disease (RIFLE) stages to determine incidence of AKI. Risk factors for kidney injury were identified via regression analysis.

RESULTS

A total of 37 patients (20 total knee arthroplasty and 17 total hip arthroplasty) were included. During the 8 weeks after ACS placement, 10 patients (27%) fit RIFLE criteria for kidney injury and 2 patients (5%) fit RIFLE criteria for kidney failure. No baseline patient characteristics were associated with development of AKI.

CONCLUSION

Patients should be monitored closely for development of AKI after placement of ACSs for the treatment of periprosthetic joint infection. Further research into minimizing risk for AKI is warranted.

Short-term Follow-up of Antibiotic-loaded Articulating Cement Spacers in Two-stage Revision of Infected Total Knee Arthroplasty: A Case Series

OBJECTIVE

Infection of total knee arthroplasty (TKA) is a rare but devastating complication. Two-stage revision is an effective treatment for late infected TKA. This study aimed to assess the short-term results of two-stage revision using articulating antibiotic-loaded spacers.

METHODS

Twenty-five patients (10 men and 15 women) were diagnosed with late infections after TKA and treated with two-stage revision from April 2006 to August 2010; 19 of these patients had TKA for osteoarthritis and 6 for rheumatoid arthritis. Median age was 64.9 (range, 56-83) years. In the first-stage surgery, the prosthesis and all bone cement was removed. After thorough debridement, bone cement with vancomycin and tobramycin was put into a die cavity and made into temporary femoral and tibial spacers, respectively. In the cases of good knee range of motion, the temporary spacers were affixed to the bone surface using the same antibiotic bone cement. In the second surgery, gentamycin Refobacin Bone Cement with vancomycin was used to fix the prosthesis. After two-stage revision, patients were followed up clinically and radiologically at 1, 3, and 6 months, and then annually. Knee Society Score (KSS), knee function score, knee pain score, and knee range of motion (ROM) were assessed.

RESULTS

Among the group, all spacers were easily removed, and bone defect degree showed no obvious change compared with pre-implant, 24 (96%) patients had been debrided once, and 1 patient had been debrided twice before reimplant prosthesis. Mean follow-up was 64.2 (range, 52-89) months. There was no infection recurrence at final follow-up. Compared with preoperative data, the KSS (66 [59, 71], 83 [80, 88] vs 46 [43, 57], P < 0.01), knee function score (43 [42, 49], 78 [73, 82] vs 32 [25, 37], P < 0.01), knee pain score (34 [33, 37], 42 [40, 45] vs 18 [16, 23], P < 0.01), and knee ROM (92° [86°, 96°], 94° [90°, 98°] vs 78° [67°, 86°], P < 0.01) were all improved during follow-up and at final visit. Three patients experienced complications in the interval period: one case had knee dislocation, one had knee instability, and one had a chip in the femoral component of the spacer.

CONCLUSION

Using articulating antibiotic-loaded spacers showed benefits for treating infected TKA in selected patients. No infection recurrence was observed during follow-up.

Systemic Absorption of Antibiotics From Antibiotic-Loaded Cement Spacers for the Treatment of Periprosthetic Joint Infection

BACKGROUND

Two-stage treatment of periprosthetic joint infections involves placement of high-dose antibiotic-loaded cement spacers (ACSs). Reports of ACS-induced nephrotoxicity have raised concern regarding systemic absorption of antibiotics after ACS placement. We sought to characterize the serum concentrations of antibiotics that occur after ACS placement.

METHODS

We performed a prospective study of patients with an infected primary total hip (THA) or knee arthroplasty (TKA) treated with standardized ACSs with vancomycin, gentamicin, and tobramycin. Serum antibiotic levels were collected weekly for 8 weeks.

RESULTS

Twenty-one patients (10 THA, 11 TKA) were included. Mean serum gentamicin levels ranged between 0.275±0.046 and 0.364±0.163 mg/L; mean serum tobramycin levels ranged from 0.313±0.207 to 0.527±0.424 mg/L; and mean serum vancomycin levels ranged from 5.46±6.6 to 15.34±9.6 mg/L. Serum antibiotic levels were detectable throughout the 8-week duration of ACS treatment. Regression analysis found that diabetes (coefficient 6.73, 95% CI 0.92-12.54, P < .05), blood urea nitrogen (coefficient 0.83, 95% CI 0.45-1.22, P < .001), number of cement doses (coefficient 3.71, 95% CI 0.76-6.66, P < .05), and use of systemic vancomycin (coefficient 6.24, 95% CI 2.72-9.75, P < .001) correlated with serum vancomycin levels. Patient age (coefficient -0.01, 95% CI -0.02 to 0, P < .01) and male sex (coefficient 0.20, 95% CI 0-0.41, P < .05) correlated with serum aminoglycoside level.

CONCLUSION

Systemic absorption of antibiotics from high-dose ACS persists for at least 8 weeks. Patients should be monitored closely for complications related to systemic absorption of antibiotics from ACS treatment.

Topical vancomycin and its effect on survival and migration of osteoblasts, fibroblasts, and myoblasts: An in vitro study

The purpose of this study was to examine the influence of topical vancomycin on cell migration and survival of tissue healing cells. Human osteoblasts, myoblasts and fibroblasts were exposed to vancomycin at concentrations of 1, 3, 6, or 12 mg/cm² for either a 1-h or 48-h (continuous) duration. Continuous exposure to all vancomycin concentrations significantly reduced cell survival (<22% cells survived) and migration in osteoblasts and myoblasts (P < 0.001). 1-h vancomycin exposure reduced osteoblast and myoblast survival and migration only at 12 mg/cm² (P < 0.001). Further in vivo studies are warranted to optimize the dosage of intrawound vancomycin.

Release of vancomycin and tobramycin from polymethylmethacrylate cements impregnated with calcium polyphosphate hydrogel

The influence of calcium polyphosphate (CPP) gel incorporation on the release of vancomycin and tobramycin from polymethyl methacrylate (PMMA) cement (Simplex P, SP) has been studied. Adding 10% CPP gel to SP led to a much lower burst release of vancomycin and considerably extended release of both vancomycin and tobramycin up to 24 weeks. Antibiotics released from this new material retain their bactericidal activity for up to 15 weeks. The improvement in the antibiotic release is mainly due to the molecular interactions of antibiotics with embedded CPP polyphosphate chains as confirmed by Raman spectroscopy analysis. The inclusion of CPP hydrogel also increased the SP surface roughness and pore sizes, leading to a higher release rate of antibiotics. The new material is biocompatible and has similar handling properties and mechanical strength as compared to SP cements. We believe that incorporating CPP gel provides a better and usable drug carrier for PMMA cement. © 2017 The Authors Journal of Biomedical Materials Research Part B: Applied Biomaterials Published by Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 2827-2840, 2018.

"Iatrogenic" Segmental Defect: How I Debride High-Energy Open Tibial Fractures

High-energy, open tibial shaft fractures may result in significant comminution, bone loss, and soft tissue injuries. Early, thorough debridement of all nonviable tissue is of critical importance in treating these fractures as an inadequate initial debridement increases the risk of infection and nonunion. Large iatrogenic bone and soft tissue defects can result from debridement and will require subsequent reconstruction by both orthopaedic and plastic surgeons. Although a variety of approaches exist to address these reconstructions, successful management of bone defects remains a considerable challenge. In this article, we detail our approach to debridement and reconstruction of segmental tibial defects and provide a review on the literature on this topic.

Success rates, characteristics, and costs of articulating antibiotic spacers for total knee periprosthetic joint infection

BACKGROUND

The optimal type, characteristics, and success rates of articulating antibiotic spacers used during total knee arthroplasty (TKA) periprosthetic joint infection (PJI) have not been well defined in a single series. We sought to (1) determine the success rate for three unique spacer constructs and (2) evaluate any microbiological, surgical, or patient characteristics that would influence the success rate.

METHODS

We retrospectively reviewed patients who underwent a two-stage exchange for a TKA PJI with a prefabricated spacer (PREFAB), home-made mold (MOLD), or autoclaved femoral component (AUTOCL). Patient demographics, microbiology data, amount of antibiotic in each spacer construct, postoperative course, and infection cure outcomes were evaluated.

RESULTS

The success rate for being infection free at final follow-up without the need for further reoperation for infection was 82.7% in the PREFAB group, 88.4% in the MOLD group, and 79.4% in the AUTOCL group (p=0.54). There was no clear statistical link between raw quantities of vancomycin and aminoglycoside in the spacer and a successful outcome. The surgeon's own intraoperatively created mold group had the lowest construct cost at a mean $1341.00±889.10 (p<0.0001) per construct, while the commercial cement molds had the highest mean cost at $5439.00±657.80 (p<0.0001).

CONCLUSIONS

There was no statistically significant difference in the success rates between the antibiotic spacer types. The surgeon's own intraoperative mold had the least overall associated cost.

The Influence of a Failed Irrigation and Debridement on the Outcomes of a Subsequent 2-Stage Revision Knee Arthroplasty

BACKGROUND

Previous work has suggested a failed irrigation and debridement (I&D) before a 2-stage exchange negatively impacts the outcome of the subsequent 2-stage revision.

METHODS

This was a retrospective review of 132 patients who underwent a 2-stage exchange without prior I&D (2-Stage), and 45 patients had a failed I&D before their 2-stage exchange (I&D+2Stage) between April 2009 and April 2015. Charts were reviewed for patient demographics, presenting inflammatory laboratory values, type of antibiotic spacer used, surgical details, microbiology data, length of postoperative antibiotic treatment, and reoperation. A logistic regression was used to assess the association between I&D and reoperation.

RESULTS

The I&D+2Stage group had an 82.2% success rate, and the 2-Stage group had an 82.5% success rate (P = .95). The odds of reoperation for infection with the use of greater than 2 grams of vancomycin was 0.33 (P = .01, 95% confidence interval 0.14-0.79) as compared with having less than 2 grams of vancomycin in the construct. Spacer type, having a prior I&D to the 2-stage procedure, being infected with an antibiotic resistant organism, total grams of aminoglycoside were not associated with a risk of failure.

CONCLUSION

Success rates between the I&D+2Stage group and the 2-Stage group were similar. The use of greater than 2 grams of vancomycin in the spacer construct decreased the odds of reoperation. I&D before a 2-stage exchange may not negatively influence the outcomes of a subsequent 2-stage revision procedure and requires further investigation.

Treatment of chronic orthopaedic infection

Chronic infections are one of the major challenges in orthopaedic surgery, both for surgeons and patients. They are characterised by obstinate persistency of the causing microorganisms and resulting long-term disablement of the patients, associated with remarkable costs for the health care system.

Difficulties derive from the biofilm-mode of living of pathogens with resistances against immunological defence and antimicrobial substances, and osseous defects resulting from the disease itself and surgical interventions.

Established techniques usually require multiple costly operations with extended periods of disablement and impairment of the patients, sometimes making the therapy worse than the disease.

Better understanding of the backgrounds of the conditions has led to new surgical techniques and differentiated application of antibiotics, aiming in improved quality of life for our patients.

Cite this article: EFORT Open Rev 2017;2. DOI: 10.1302/2058-5241.2.160063. Originally published online at www.efortopenreviews.org

Allograft Bone as Antibiotic Carrier

The treatment of chronic bone and joint infections is characterized by obstinate persistency of the causing microorganisms and resulting long term disability to patients, associated with remarkable costs for the health care system. Difficulties derive from biofilm formed on dead bone and eventual implants, with resistance against immunological defences and antimicrobial substances. Biofilm embedded bacteria require up to 1000 times the antibiotic concentration of planktonic bacteria for elimination. Systemic antibiotic treatment alone cannot provide the concentrations required and surgical intervention is always prerequisite for potentially providing a cure. A second issue is that osseous defects are almost always present after surgical debridement, and it is difficult to address their reconstruction. One option is to use bone grafts, either from the patient´s own body or from foreign donors (allografts). Grafts are usually unvascularized and are prone to colonization with bacteria. Loading of allografts with antibiotics may not only protect grafts from bacterial adhesion but, using appropriate processing methods, may also provide high local antibiotic concentrations that may eliminate remaining sessile pathogens. For efficient action as antibiotic carriers, the release of antibiotics should be above the minimum biofilm eradication concentration (MBEC) for a prolonged period of time. Cleaning the bone from bone marrow opens a large reservoir for storage of antimicrobial substances that, after implantation, may be released to the surrounding in a sustained mode, possibly eliminating remaining biofilm remnants. Removal of bone marrow, leaving a pure matrix, provides increased safety and improved revascularization of the graft. Local provision of antibiotic concentrations above the MBEC may enable simultaneous internal fixation with osteosynthetic material and single stage exchange of infected endoprostheses, resulting in shorter hospital stays with reduced pain and faster rehabilitation of patients.

What is the Intraarticular Concentration of Tobramycin Using Low-dose Tobramycin Bone Cement in TKA: An In Vivo Analysis?

BACKGROUND

Antibiotic-impregnated bone cement has increased in popularity as an effort to reduce the risk of infection in high-risk TKAs. However, limited data has been reported regarding antibiotic levels achieved when using tobramycin-impregnated bone cement after implanting total knee components.

QUESTIONS/PURPOSES

We asked: (1) What is the tobramycin serum and knee intraarticular levels in patients undergoing primary TKA using tobramycin cement? (2) What is the intraarticular tobramycin level for patients receiving only intravenous tobramycin?

METHODS

All patients undergoing primary TKA by one of the two study surgeons (GV, JP) during a 6-month period were evaluated for inclusion and invited to participate. The study enrolled 15 patients undergoing primary TKA by one of two surgeons (GV, JP) who met inclusion criteria; treatment allocation was assigned randomly through blinded envelope. The study group consisted of 10 patients whose components were implanted using a commercially prepared low-dose tobramycin bone cement mixture (1 g/40 g). The control group consisted of five patients who received standard weight-based dose intravenous tobramycin. Samples of serum and Hemovac^® drain-collected intraarticular hematoma were analyzed at 6, 24, and 48 hours postoperatively. Tobramycin levels were measured using an immunoassay technique with a low-end sensitivity of 0.28 μg/mL. Mann-Whitney U tests were performed to compare the serum and intraarticular tobramycin concentrations at each time in the independent variable of group (Control and Study).

RESULTS

The median (interquartile range [IQR]) intraarticular tobramycin concentrations for the study group, with tobramycin-impregnated bone cement, was 31.8 (29.0) μg/mL at 6 hours, 17.1 (13.1) μg/mL at 24 hours, and 6.8 (6.8) μg/mL at 48 hours. The intraarticular tobramycin concentrations of this study group were larger than those for the control group at 6 hours (median = 1.3; IQR = 0.7; p = 0.002), 24 hours (median = 1.3, IQR = 1.0; p = 0.002), and 48 hours (median = 1.4; IQR = 1.0; p = 0.02). The serum concentrations for the tobramycin-impregnated bone cement group were 0.3 μg/mL or less for all samples whereas serum concentrations and median (IQR) for the control group were 1.2 (2.6) μg/mL, 1.6 (4.4) μg/mL, and 2.0 (3.3) μg/mL at 6, 24, and 48 hours respectively. The serum levels for the tobramycin-impregnated cement group were less than those for the control group at 6 hours (p = 0.001), 24 (p = 0.001), and 48 hours (p < 0.001).

CONCLUSIONS

Tobramycin-impregnated bone cement provides a way to deliver antibiotics in patients undergoing TKA. This supratherapeutic short-term prophylactic perioperative antibiotic local delivery can be achieved with limited systemic absorption, whereas joint tobramycin levels were less than therapeutic levels when given intravenously alone. In the control group, with only intravenous tobramycin, a subtherapeutic (< 2.0 μg/mL) level of tobramycin was found in all the intraarticular samples at 6, 24, and 48 hours. Based on the evidence obtained in this study, commercially prepared low-dose tobramycin bone cement can be used to obtain short-term supratherapeutic local concentrations in the knee while maintaining serum tobramycin levels at a minimum.

LEVEL OF EVIDENCE

Level II, therapeutic study.

Concomitant Suppurative Parotitis and Condylar Osteomyelitis

Parotitis is a common occurrence in the immunocompromised, dehydrated, and malnourished patient as a result of dysfunctional ductal and parotid cells. Inflammation can be acute or chronic based on clinical history, and it can be suppurative based on the presence of micro or macro abscess formation within the substance of the gland. This report presents a case of concomitant condylar osteomyelitis and chronic suppurative parotitis in the setting of previous methicillin-susceptible Staphylococcus aureus foot infection. Ultimately, resection of osteomyelitis, drainage of parotid infection, and intravenous antibiotic therapy led to full resolution of the infection and symptoms. The final pathology of osteomyelitis of the temporomandibular joint and methicillin-resistant S aureus infection is an unusual consequence of chronic parotitis. The patient was restored with a total joint replacement approximately 3 months after resection with no recurrence of infection after 24 months.

An Osteoconductive Antibiotic Bone Eluting Putty with a Custom Polymer Matrix

With the rising tide of antibiotic resistant bacteria, extending the longevity of the current antibiotic arsenal is becoming a necessity. Developing local, controlled release antibiotic strategies, particularly for difficult to penetrate tissues such as bone, may prove to be a better alternative. Previous efforts to develop an osteoconductive local antibiotic release device for bone were created as solid molded composites; however, intimate contact with host bone was found to be critical to support host bone regrowth; thus, an osteocondconductive antibiotic releasing bone void filling putty was developed. Furthermore, a controlled releasing polymer matrix was refined using pendant-functionalized diols to provide tailorable pharmacokinetics. In vitro pharmacokinetic and bioactivity profiles were compared for a putty formulation with an analogous composition as its molded counterpart as well as four new pendant-functionalized polymers. A best-fit analysis of polymer composition in either small cylindrical disks or larger spheres revealed that the new pendant-functionalized polymers appear to release vancomycin via both diffusion and erosion regardless of the geometry of the putty. In silico simulations, a valuable technique for diffusion mediated controlled release models, will be used to confirm and optimize this property.

Enhancing Drug Release From Antibiotic-loaded Bone Cement Using Porogens

OBJECTIVE

To evaluate whether the addition of porogens to polymethyl methacrylate (PMMA) enhances the antibiotic elution rate from antibiotic-loaded bone cement.

METHODS

Two porogens, gelatin sponge (Spongostan, Ferrosan Medical Devices) and ceramic granules (Bicera, Wiltrom), were added to liquid gentamicin-loaded PMMA at increasing concentrations. Porosity was analyzed using Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy. Young's modulus and drug elution were also measured. The gentamicin content of the eluents was evaluated by o-phthaldialdehyde (OPA) assay on days 1, 2, 5, 7, 10, and 14.

RESULTS

After day 5, the drug-releasing rate of Spongostan was significantly higher than that of Bicera in the order G3 > G2 > T3 > G1 > T2 > T1 > bone cement, where G represents the concentration of Spongostan and T represents the concentration of Bicera. The addition of Bicera and Spongostan increased the drug-releasing efficiency of PMMA by 3.75-fold and 5.65-fold, respectively. Spongostan also resulted in larger pores (ie, 70 to approximately 200 μm) compared with Bicera (5 to 10 μm) but reduced biomechanical strength.

CONCLUSION

Both gelatin sponge and ceramic granules improved the local antibiotic elution rate, although the drug-releasing rate of Spongostan was significantly higher than that of Bicera.

A simple method for fashioning an antibiotic impregnated cemented rod for intramedullary placement in infected non-union of long bones

The intramedullary insertion of antibiotic impregnated PMMA rods, beads or nails are widely used and accepted modality of treatment for chronic osteomyelitis of long bones. But at times it becomes difficult to insert and remove these antibiotic delivery systems owing to narrowed medullary canals. Here we present a technique for preparing PMMA rods with diameter ranging from 6 mm to 3 mm. These rods could easily be placed in narrow intramedullary canal of long bones with chronic osteomyelitis or infected non-union. We have used high viscosity bone cement (Simplex P) along with two antibiotics (cefuroxime and vancomycin) for preparing cement rods. Food grade straw and low profile teflon tube guide wire exchanger used in IM nailing were used as mold. Ilizarov wire, 1 mm K wire and 24 gauge stainless steel wire were used as internal support core material for imparting strength. We used this technique in seven cases and were successful in treating infection of long bones of upper and lower limbs (femur). With average follow up of 7.28 months rate of union in our series was 71% (five cases). Four cases (57%) had no evidence of infection and two cases (29%) had control of infection and in one case (14%) infection was still there but union was achieved.

Development of a Novel Model for the Assessment of Dead-Space Management in Soft Tissue

Following extensive surgical debridement in the treatment of infection, a “dead space” can result following surgical closure that can fill with hematoma, an environment conducive to bacterial growth. The eradication of dead space is essential in order to prevent recurrent infection. This study describes a novel small animal model to investigate dead-space management in muscle tissue. Two absorbable test materials were implanted in each animal; beads of calcium sulfate alone, and beads loaded with vancomycin and tobramycin. In-life blood samples and radiographs were taken from each animal following implantation. Animals were sacrificed at 1, 7, 21, 42, and 63 days post-operatively (n = 4), and implant sites were analysed by micro-computed tomography, histology and immunohistochemistry. Complete resorption was confirmed radiographically at 3 weeks post-implantation. Histologically, the host tissue response to both materials was identical, and subsequent healing at the implant sites was observed with no dead space remaining. Vancomycin was not detected in blood serum. However, peak tobramycin levels were detected in all animals at 6 hours post-implantation with no detectable levels in any animals at 72 hours post implantation. Serological inflammatory cytokine expression for IL-6, TNF-α and IL-1β indicated no unusual inflammatory response to the implanted materials or surgical procedure. The model was found to be convenient and effective for the assessment of implant materials for management of dead space in muscle tissue. The two materials tested were effective in resolving the surgically created dead space, and did not elicit any unexpected adverse host response.

Local antibiotic therapy strategies in orthopaedic trauma: Practical tips and tricks and review of the literature

The use of local antibiotics for the prevention of infection in the setting of open fractures and as part of the treatment of osteomyelitis is well established. Antibiotics are most commonly incorporated into polymethylmethacrylate (PMMA) cement, which can then be formed into beads, moulded to fit a bone defect or used to coat a guide wire or IM nail. Newer delivery vehicles and techniques are being evaluated to improve upon these methods. Many factors influence how local antibiotics are applied. Treatment strategies are challenging to standardise due to the variability of clinical presentations. The presence of hardware, upper versus lower extremity, healed versus non-healed fracture and quality of soft tissues overlying the affected bone, as well as patients' comorbidities all need to be considered. Despite the accepted use of local antibiotic therapy in orthopaedic trauma, high-quality evidence regarding the use of local antibiotics is lacking. Indications, techniques, dosages, types of antibiotics, elution properties and pharmacokinetics are poorly defined in the clinical setting. The purpose of our manuscript is to review current strategies and provide practical tips for local application of antibiotics in orthopaedic trauma. We focus on delivery vehicles, types of antibiotics, dosage recommendations when mixed with PMMA and indications.

A resorbable antibiotic-eluting polymer composite bone void filler for perioperative infection prevention in a rabbit radial defect model

Nearly 1.3 million total joint replacement procedures are performed in the United States annually, with numbers projected to rise exponentially in the coming decades. Although finite infection rates for these procedures remain consistently low, device-related infections represent a significant cause of implant failure, requiring secondary or revision procedures. Revision procedures manifest several-fold higher infection recurrence rates. Importantly, many revision surgeries, infected or not, require bone void fillers to support the host bone and provide a sufficient tissue bed for new hardware placement. Antibiotic-eluting bone void fillers (ABVF), providing both osteoconductive and antimicrobial properties, represent one approach for reducing rates of orthopedic device-related infections. Using a solvent-free, molten-cast process, a polymer-controlled antibiotic-eluting calcium carbonate hydroxyapatite (HAP) ceramic composite BVF (ABVF) was fabricated, characterized, and evaluated in vivo using a bacterial challenge in a rabbit radial defect window model. ABVF loaded with tobramycin eliminated the infectious burden in rabbits challenged with a clinically relevant strain of Staphylococcus aureus (inoculum as high as 10⁷ CFU). Histological, microbiological, and radiographic methods were used to detail the effects of ABVF on microbial challenge to host bone after 8 weeks in vivo. In contrast to the HAP/BVF controls, which provided no antibiotic protection and required euthanasia 3 weeks post-operatively, tobramycin-releasing ABVF animals showed no signs of infection (clinical, microbiological, or radiographic) when euthanized at the 8-week study endpoint. ABVF sites did exhibit fibrous encapsulation around the implant at 8 weeks. Local antibiotic release from ABVF to orthopedic sites requiring bone void fillers eliminated the periprosthetic bacterial challenge in this 8-week in vivo study, confirming previous in vitro results.

Nephrotoxicity Risk Factors and Intravenous Vancomycin Dosing in the Immediate Postoperative Period Following Antibiotic-Impregnated Cement Spacer Placement

BACKGROUND

Several case reports have documented acute kidney injury (AKI) attributable to antibiotic-impregnated cement (AIC) spacers.

OBJECTIVES

To identify AKI risk factors among patients who underwent AIC placement and determine whether vancomycin-AIC placement affects systemic vancomycin dosing.

METHODS

Phase 1 was a case-control study to identify AKI risk factors among patients who underwent AIC placement. Cases experienced AKI; controls had unchanged renal function. Phase 2 was a retrospective cohort study. Patients who received ≥72 hours of intravenous (IV) vancomycin were divided into 2 groups according to whether they underwent vancomycin-AIC placement. Primary outcome was number of vancomycin dosing changes.

RESULTS

Phase 1: Among 26 cases and 74 controls AKI risk factors on univariate and multivariable analysis included exposure to angiotensin-converting-enzyme (ACE) inhibitor exposure within 7 days of AIC placement (42% vs 20%, P = 0.03) and piperacillin-tazobactam within 7 days following AIC placement (31% vs 12%, P = 0.03). Phase 2: Among 53 patients who underwent vancomycin-AIC placement and 104 who underwent another surgery type, vancomycin was adjusted more frequently in patients who underwent vancomycin-AIC placement (28% vs 15%, P = 0.06).

CONCLUSIONS

Among patients who undergo AIC placement with vancomycin and/or tobramycin, exposure to ACE inhibitors and piperacillin-tazobactam are associated with increased risk of AKI in the immediate postoperative period. No empirical adjustments to IV vancomycin dosing are necessary in patients undergoing vancomycin-AIC placement.

Evidence of MRSE on a gentamicin and vancomycin impregnated polymethyl-methacrylate (PMMA) bone cement spacer after two-stage exchange arthroplasty due to periprosthetic joint infection of the knee

BACKGROUND

Periprosthetic joint infections (PJI) are often treated by two stage exchange with the use of an antibiotic impregnated spacer. Most of the two-stage exchange algorithms recommend the implantation of an antibiotic-impregnated spacer during the first stage for a period of 2-24 weeks before reimplantation of the new prosthesis. For the spacer to have a therapeutic effect, the local antibiotic concentration must be greater than the minimal inhibition concentration (MIC) against the pathogens causing the PJI. It must remain so for the entire spacer period, otherwise recurrence of infection or resistances might occur. The question as to whether a sufficient concentration of antibiotics in vivo is reached for the entire spacer period has not been answered satisfactorily.

CASE PRESENTATION

We here present a case of a histologically confirmed chronic PJI 20 month after primary arthroplasty. The primary knee arthroplasty was performed due to osteoarthritis of the joint. Initial assessment did not detect a causative pathogen, and two stage exchange with a vancomycin-gentamycin impregnated spacer was performed. At the time of reimplantation, sonication of the explanted spacer revealed a multi-resistant strain of staphylococcus epidermidis on the device and in the joint. Adaption of the therapy and prolonged treatment successfully eradicated the infection.

CONCLUSION

According to the authors' knowledge, the case presented here confirms for the first time the surface contamination (proven through sonication) of a vancomycin-/gentamicin- impregnated Vancogenx®-spacer with a MRSE after ten weeks of implantation.This case study demonstrates the difficulties still associated with the diagnostics of PJI and the published different two stage treatment regimes with the use of antibiotic impregnated spacers.

Antimicrobial activity of gentamicin and vancomycin combination in joint fluids after antibiotic-loaded cement spacer implantation in two-stage revision surgery

Gentamicin (G) and vancomycin (V) concentrations in joints fluids obtained from patients during the first 24 hours after implantation of antibiotic-loaded polymethylmethacrylate (PMMA) spacers in two-stage revision for infected arthroplasty, and the inhibitory activity of joint fluids against different multiresistant clinical isolates were studied. A total of 12 patients undergoing two-stage revision surgery with implantation of industrial G spacers added with different amounts of V was studied. Serum and joint fluid samples were collected 1, 4, and 24 hours after spacer implantation. Antibiotics concentrations and joint bactericidal titer (JBT) of combination were determined against multiresistant staphylococcal strains. The local release of G and V from PMMA cement seemed prompt and effective. Serum levels were below the limit of detection. The same joint fluid showed different activity according to the susceptibility of the pathogens tested. Gentamicin and V were released from spacers at bactericidal concentrations exerting a strong inhibition against methicillin-resistant Staphylococcus aureus (MRSA) and coagulase-negative staphylococci (CoNS) strains.

Release of gentamicin and vancomycin from preformed spacers in infected total hip arthroplasties: measurement of concentrations and inhibitory activity in patients' drainage fluids and serum

Gentamicin (G) and vancomycin (V) concentrations in drainage fluids obtained from patients during the first 24 hours after implantation of antibiotic-loaded polymethylmethacrylate (PMMA) spacers in two-stage revision of infected total hip arthroplasty were studied. The inhibitory activity of drainage fluids against different multiresistant clinical isolates was investigated as well. Seven hips were treated by implantation of industrial G-loaded spacers. Vancomycin was added by manually mixing with PMMA bone cement. Serum and drainage fluid samples were collected 1, 4, and 24 hours after spacer implantation. Antibiotics concentrations and drains bactericidal titer of combination were determined against multiresistant staphylococcal strains. The release of G and V from PMMA cement at the site of infection was prompt and effective. Serum levels were below the limit of detection. The local release kinetics of G and V from PMMA cement was similar, exerting a pronounced, combined inhibitory effect in the implant site. The inhibitory activity of drainage fluids showed substantial intersubject variability related to antibiotic concentrations and differed according to the pathogens tested. Gentamicin and vancomycin were released from temporary hip spacers at bactericidal concentrations, and their use in combination exerted strong inhibition against methicillin-resistant S. aureus and Coagulase Negative Staphylococci strains.

Polymethylmethacrylate bone cements and additives: A review of the literature

Polymethylmethacrylate (PMMA) bone cement technology has progressed from industrial Plexiglass administration in the 1950s to the recent advent of nanoparticle additives. Additives have been trialed to address problems with modern bone cements such as the loosening of prosthesis, high post-operative infection rates, and inflammatory reduction in interface integrity. This review aims to assess current additives used in PMMA bone cements and offer an insight regarding future directions for this biomaterial. Low index (< 15%) vitamin E and low index (< 5 g) antibiotic impregnated additives significantly address infection and inflammatory problems, with only modest reductions in mechanical strength. Chitosan (15% w/w PMMA) and silver (1% w/w PMMA) nanoparticles have strong antibacterial activity with no significant reduction in mechanical strength. Future work on PMMA bone cements should focus on trialing combinations of these additives as this may enhance favourable properties.

Effect of negative pressure wound therapy on the elution of antibiotics from polymethylmethacrylate beads in a porcine simulated open femur fracture model

OBJECTIVES

To determine whether negative pressure wound therapy (NPWT) affects antibiotic elution in simulated femur fractures treated with antibiotic impregnated polymethylmethacrylate (PMMA) beads and whether fascial closure between beads and sponge affects the outcome.

METHODS

PMMA beads containing vancomycin and tobramycin were placed adjacent to bilateral corticotomies created in 20 anesthetized pigs. In 1 leg, NPWT was applied with the sponge either in direct contact with the beads or superficial to reapproximated fascia lata. The contralateral wound was conventionally closed. Vancomycin and tobramycin concentrations in wound drainage were measured every 12 hours for 72 hours, and tobramycin levels were measured in periosteal tissue obtained at 72 hours.

RESULTS

Drainage vancomycin and tobramycin concentrations were highest at 12 hours and fell rapidly by 24 hours but remained steady thereafter. At each 12-hour interval, there were no significant differences in the vancomycin and tobramycin concentrations between NPWT and control wound drainage, although whether the fascia was closed or left open had an influence on vancomycin levels. The total vancomycin and tobramycin eluted into the drains was significantly less in the NPWT group with open fascia. The antibiotic levels measured in wound drainage remained above the minimum inhibitory concentration for common wound organisms throughout the study period. Neither NPWT nor fascial closure had a significant effect on tobramycin periosteal tissue concentrations.

CONCLUSIONS

Concurrent application of NPWT with antibiotic impregnated PMMA beads to simulated open femur fractures in pigs did not decrease local antibiotic concentrations but did decrease the total amount of eluted vancomycin and tobramycin locally available when the fascia was left open.

Sufficient release of antibiotic by a spacer 6 weeks after implantation in two-stage revision of infected hip prostheses

BACKGROUND

Although antibiotic-loaded spacers are commonly used to treat periprosthetic infections, it is unclear whether spacers continue to release bactericidal levels of antibiotic 6 weeks after implantation.

QUESTIONS/PURPOSES

We asked whether an antibiotic can be detected in the tissue surrounding the spacer 6 weeks after implantation and whether the concentration is higher than the minimal inhibition concentration (MIC) previously determined for pathogens that are responsible for most periprosthetic infections.

METHODS

We removed 14 spacers used in two-stage septic revisions of infected hip prostheses 6 weeks after the primary implantations and determined the concentration of the antibiotics in the membrane formed between the spacer and the neighboring bone on the acetabular and the femoral sides. In seven cases Copal cement with gentamicin and clindamycin were used, and in seven other cases vancomycin was added to the Copal cement. Concentrations of the spacer antibiotics in the neighboring tissue were determined by tandem mass spectroscopy.

RESULTS

All three antibiotics were detected in concentrations higher than their MIC. There were no differences between the groups regardless whether vancomycin was added to the cement, or whether the cement was applied with the acetabular cup spacer or with the stem spacer.

CONCLUSIONS

We concluded that, using the spacer technique described in this study, 6 weeks after spacer implantation, the concentrations of antibiotic are sufficient to treat a periprosthetic infection.

Antibiotic-loaded cement in orthopedic surgery: a review

Infections in orthopaedic surgery are a serious issue. Antibiotic-loaded bone cement was developed for the treatment of infected joint arthroplasties and for prophylaxes in total joint replacement in selected cases. Despite the widespread use of the antibiotic-loaded bone cement in orthopedics, many issues are still unclear or controversial: bacterial adhesion and antibiotic resistance, modification of mechanical properties which follows the addition of the antibiotic, factors influencing the release of the antibiotic from the cement and the role of the surface, the method for mixing the cement and the antibiotic, the choice and the effectiveness of the antibiotic, the combination of two or more antibiotics, and the toxicity. This review discusses all these topics, focusing on properties, merits, and defects of the antibiotic loaded cement. The final objective is to provide the orthopaedic surgeons clear and concise information for the correct choice of cement in their clinical practice.

Chitosan-vancomysin composite biomaterial as a laser activated surgical adhesive with regional antimicrobial activity

We have used laser irradiation to enhance the natural adhesiveness of chitosan to form a thin film surgical adhesive. Prevention of infection at surgical sites often utilizes systemic provision of antibiotics with reduced local efficacy and potential side effects. In the work reported here, we investigate the bactericidal properties of laser-irradiated chitosan films and their impregnation with the antibiotic vancomycin. Despite strong efficacy in solution, chitosan films showed no antimicrobial activity against representatives of common pathogens Escherichia coli , Staphylococcus aureus , and S. epidermidis . In contrast, a composite of chitosan adhesive and the antibiotic vancomycin showed therapeutically significant release profiles greater that the Minimum Bactericidal Concentrations (MBCs) for the Staphylococci over a 28 day period. These composite films had greater crystallinity, up to 28 ± 3 compared to 8.9 ± 2%, for its unblended counterpart. Despite a significant increase in material strength from 31.4 ± 4 to 77.5 ± 5 MPa, flexibility was still maintained with an elongation to break around 5 ± 2% and fold endurance of approximately 30 ± 3-folds. Laser irradiation had no apparent effect on the release or activity of the antibiotic which survived transient temperatures at the film-tissue interface during infrared irradiation of around 54 °C. Furthermore, significant adhesive strength was still apparent, 15.6 ± 2 KPa. Thus, we have developed a laser-activated bioadhesive with the potential to close wounds while facilitating the prevention of microbial infection through local release of antibiotic targeted to the site of potential infection.

Polymethylmethacrylate: properties and contemporary uses in orthopaedics

Polymethylmethacrylate (PMMA) has been used in orthopaedics since the 1940s. Despite the development and popularity of new biomaterials, PMMA remains popular. Although its basic components remain the same, small proprietary and environmental changes create variations in its properties. PMMA can serve as a spacer and as a delivery vehicle for antibiotics, and it can be placed to eliminate dead space. Endogenous and exogenous variables that affect its performance include component variables, air, temperature, and handling and mixing. PMMA is used in hip arthroplasty and vertebral augmentation, notably, vertebroplasty and kyphoplasty. Cardiopulmonary complications have been reported.

Treatment of infected hip arthroplasty

The clinical outcomes of a consecutive series of deep total joint infections treated with a prosthesis retaining protocol were reviewed. The treatment of deep periprosthetic joint infections is challenging. In recent years, two-stage exchange arthroplasty has emerged as the gold standard for successful elimination of infection. With success rates averaging 82% to 96%, this treatment method has both the highest and most consistent rate of infection eradication. Another alternative in the treatment of the deep periprosthetic infection is the single-stage exchange arthroplasty. Successful eradication of infection after single-stage exchange arthroplasty has been reported to average from 60% to 83% after total hip infections. While both the single and two-stage exchange arthroplasty are viable treatment options, they are associated with negative factors such as they are time consuming, expensive, and may entail a 6- to 12-week period with a minimally functioning extremity after prosthesis removal. This paper reports the general principles of management, the treatment of acute infection occurring in the postoperative period or later, and the treatment of chronic infection by exchange arthroplasty or resection arthroplasty.

Rationale for one stage exchange of infected hip replacement using uncemented implants and antibiotic impregnated bone graft

Infection of a total hip replacement (THR) is considered a devastating complication, necessitating its complete removal and thorough debridement of the site. It is undoubted that one stage exchange, if successful, would provide the best benefit both for the patient and the society. Still the fear of re-infection dominates the surgeons decisions and in the majority of cases directs them to multiple stage protocols. However, there is no scientifically based argument for that practice. Successful eradication of infection with two stage procedures is reported to average 80% to 98%. On the other hand a literature review of Jackson and Schmalzried (CORR 2000) summarizing the results of 1,299 infected hip replacements treated with direct exchange (almost exclusively using antibiotic loaded cement), reports of 1,077 (83%) having been successful. The comparable results suggest, that the major factor for a successful outcome with traditional approaches may be found in the quality of surgical debridement and dead space management. Failures in all protocols seem to be caused by small fragments of bacterial colonies remaining after debridement, whereas neither systemic antibiotics nor antibiotic loaded bone cement (PMMA) have been able to improve the situation significantly. Reasons for failure may be found in the limited sensitivity of traditional bacterial culturing and reduced antibiotic susceptibility of involved pathogens, especially considering biofilm formation. Whenever a new prosthesis is implanted into a previously infected site the surgeon must be aware of increased risk of failure, both in single or two stage revisions. Eventual removal therefore should be easy with low risk of additional damage to the bony substance. On the other hand it should also have potential of a good long term result in case of success. Cemented revisions generally show inferior long term results compared to uncemented techniques; the addition of antibiotics to cement reduces its biomechanical properties. Efficient cementing techniques will result in tight bonding with the underlying bone, making eventual removal time consuming and possibly associated with further damage to the osseous structures. All these issues are likely to make uncemented revisions more desirable. Allograft bone may be impregnated with high loads of antibiotics using special incubation techniques. The storage capacities and pharmacological kinetics of the resulting antibiotic bone compound (ABC) are more advantageous than the ones of antibiotic loaded cement. ABC provides local concentrations exceeding those of cement by more than a 100fold and efficient release is prolonged for several weeks. The same time they are likely to restore bone stock, which usually is compromised after removal of an infected endoprosthesis. ABC may be combined with uncemented implants for improved long term results and easy removal in case of a failure. Specifications of appropriate designs are outlined. Based on these considerations new protocols for one stage exchange of infected TJR have been established. Bone voids surrounding the implants may be filled with antibiotic impregnated bone graft; uncemented implants may be fixed in original bone. Recent studies indicate an overall success rate of more than 90% without any adverse side effects. Incorporation of allografts appears as after grafting with unimpregnated bone grafts. Antibiotic loaded bone graft seems to provide sufficient local antibiosis for protection against colonisation of uncemented implants, the eluted amounts of antibiotics are likely to eliminate biofilm remnants, dead space management is more complete and defects may be reconstructed efficiently. Uncemented implants provide improved long term results in case of success and facilitated re-revision in case of failure. One stage revision using ABC together with uncemented implants such should be at least comparably save as multiple stage procedures, taking advantage of the obvious benefits for patients and economy.

Antibiotic delivery system using nano-hydroxyapatite/chitosan bone cement consisting of berberine

Different concentrations of berberine were mixed with nano-hydroxyapatite/chitosan (n-HA/CS) bone cement to generate an antibiotic drug delivery system for treatment of bone defects. Properties of the system such as setting time, compressive strength, surface morphology, phase compositions, drug release profiles and antimicrobial activity were also characterized. It was shown that the setting time of the cement ranged from 17.03 +/- 0.50 min to 28.47 +/- 0.96 min and the compressive strength changed from 184.00 +/- 7.94 MPa to 120.33 +/- 9.02 MPa with the increase of berberine. The XRD, IR, and SEM analyses suggested that berberine powders were stable in the bone cement in simulated body fluid (SBF). In vitro release of berberine from the bioactive bone cement pellets in SBF could last more than 4 weeks. The release profiles of 1.0 wt % berberine loaded bone cement followed the Higuchi equation at the infusion stage. The drug loaded pellets can inhibit bacterial growth (Staphylococcus aureus) at the standardized berberine minimum inhibitory concentration of 0.02 mg/mL during berberine release from 1 to 28 days. The n-HA/CS bone cement only with 1.0 wt % berberine proved to be an efficient antibiotic drug delivery system.