Adhesion of Staphylococcus to orthopaedic metals, an in vivo study

Does Using Highly Porous Tantalum in Revision Total Hip Arthroplasty Reduce the Rate of Periprosthetic Joint Infection? A Systematic Review and Meta-Analysis

Background

Studies suggest tantalum (Ta) implants may have inherent antibacterial properties. However, there is no consensus regarding the effectiveness of Ta in preventing periprosthetic joint infection (PJI) after revision total hip arthroplasty (rTHA).

Methods

We searched 5 main databases for articles reporting the rate of PJI following rTHA using Ta implants from inception to February 2022. The PJI rates of the Ta group were meta-analyzed, compared with the control group, and represented as relative risks (RRs) in forest plots.

Results

We identified 67 eligible studies (28,414 joints) for assessing the prevalence of PJI following rTHA using Ta implants. Among these studies, only 9 compared the Ta implant group with a control group. The overall PJI rate following rTHA using Ta implants was 2.9% (95% confidence interval [CI]: 2.2%-3.8%), while it was 5.7% (95% CI = 4.1%-7.8%) if only septic revisions were considered. Comparing the Ta and control groups showed a significantly lower PJI rate following all-cause rTHA with an RR = 0.80 (95% CI = 0.65-0.98, P < .05). There was a trend toward lower reinfection rates in the Ta group after rTHA in septic cases, although the difference was not statistically significant (RR = 0.75, 95% CI = 0.44-1.29, P = .30).

Conclusions

Ta implants are associated with a lower PJI rate following all-cause rTHA but not after septic causes. Despite positive results, the clinical significance of Ta still remains unclear since the PJI rate was only reduced by 20%.

Level of Evidence

IV.

In Vivo Prevention of Implant-Associated Infections Caused by Antibiotic-Resistant Bacteria through Biofunctionalization of Additively Manufactured Porous Titanium

Additively manufactured (AM) porous titanium implants may have an increased risk of implant-associated infection (IAI) due to their huge internal surfaces. However, the same surface, when biofunctionalized, can be used to prevent IAI. Here, we used a rat implant infection model to evaluate the biocompatibility and infection prevention performance of AM porous titanium against bioluminescent methicillin-resistant Staphylococcus aureus (MRSA). The specimens were biofunctionalized with Ag nanoparticles (NPs) using plasma electrolytic oxidation (PEO). Infection was initiated using either intramedullary injection in vivo or with in vitro inoculation of the implant prior to implantation. Nontreated (NT) implants were compared with PEO-treated implants with Ag NPs (PT-Ag), without Ag NPs (PT) and infection without an implant. After 7 days, the bacterial load and bone morphological changes were evaluated. When infection was initiated through in vivo injection, the presence of the implant did not enhance the infection, indicating that this technique may not assess the prevention but rather the treatment of IAIs. Following in vitro inoculation, the bacterial load on the implant and in the peri-implant bony tissue was reduced by over 90% for the PT-Ag implants compared to the PT and NT implants. All infected groups had enhanced osteomyelitis scores compared to the noninfected controls.

Are Absorbable Plates More Resistant to Infection Than Titanium Implants? An Experimental Pre-Clinical Trial in Rabbits

Background: Infection of orthopaedic implants after internal fixation of bone fractures remains a major complication with occasionally devastating consequences. Recent studies have reported that the use of absorbable materials, instead of metallic ones, may lead to a lower incidence of postoperative infection. In this experimental pre-clinical animal study, we compared the infection rate between absorbable implants consisting of copolymers composed from trimethylene carbonate, L-polylactic acid, and D, L-polylactic acid monomers, and titanium implants after the inoculation of a pathogenic microorganism. Material and Methods: We used an experimental implant-related infection model in rabbits. Sixty animals were randomly and equally divided into two groups. In all animals, the right femur was exposed via a lateral approach and a 2.5 mm two-hole titanium plate with screws (Group A), or a two-hole absorbable plate and screws (Group B), were applied in the femoral shaft. Afterwards, the implant surface was inoculated with Pseudomonas Aeruginosa at a concentration of 2 × 108 CFU/mL. The primary outcome was the comparison of the incidence of developed infection between the two groups. The wound condition was monitored on a daily basis and radiographies were obtained at 12 weeks postoperatively. Infection-related laboratory markers (white blood cell count, erythrocyte sedimentation rate, and C-reactive protein values) were assessed at 3, 6, and 16 weeks postoperatively. Histologic analysis and cultures of tissue samples were also performed to evaluate the presence of infection. Results: Clinical and laboratory signs of infection were evident in 11 rabbits in Group A (36.7%), and 4 in Group B (13.3%). The difference between the groups was statistically significant (p = 0.04). Five animals in Group B (16.7%) had clinical and histologic signs of a foreign-body reaction with significantly elevated CRP and ESR values but no simultaneous presence of infection was identified (p = 0.04). Bone remodelling with thickening of the periosteum and surrounding sclerosis was demonstrated radiologically in animals developing infection or foreign-body reactions. Conclusions: Absorbable plates and screws show lower susceptibility to infection compared to titanium ones. However, their application is associated with foreign-body reaction and the potential need for a second surgical intervention.

Protective effect of additional cathelicidin antimicrobial peptide PR-39 on prosthetic-joint infections

BACKGROUND

Prosthetic-joint infection (PJI) is one of the severest complications after arthroplasty. However, antibiotics are not effective in the bacteria in biofilm outside the prosthetic-joint. Antimicrobial peptides have an efficient antimicrobial activity in staphylococcus aureus compared with conventional antibiotics.

METHODS

Bone marrow stem cells (BMSCs) were isolated, cultured and transfected with cathelicidins antimicrobial peptides proline-arginine-rich 39 amino acid peptide (PR-39) lentivirus. The expression of PR-39 gene in BMSCs was detected by RT-PCR, and the antibacterial activity of PR-39 was measured by agar diffusion method. The transfection efficiency was detected by fluorescence microscopy. The infection model of artificial knee joint in rabbits were established. Kirschner wire was used as the knee joint implant to implant the distal femur through the femoral intercondylar fossa of rabbits. 24 rabbits were randomly divided into 2 groups for the above operations: group A was inoculated 0.5 mL into the joint cavity immediately after the incision was sutured 1 × 10⁷ Staphylococcus aureus of colony forming unit (CFU), group B was inoculated with Staphylococcus aureus and PR-39. After operation, the wound conditions and histological changes were observed by X-ray and optical microscope respectively, CRP and erythrocyte sedimentation rate were measured by test assay.

RESULTS

The transfection efficiency of lentivirus vectortransfected BMSCs was 74.09%. The supernatant of lentivirus vector had obvious inhibitory effect on Staphylococcus aureus, and the antibacterial rate was 98.43%. 100% infection observed in group A while few infection observed in group B; serum CRP and ESR at a high level in group A while decreased in group B after operation. There were no significant difference in CRP and ESR between the pLV/PR-39 group and pLV/EGFP group at day 1 and 3 respectively after surgery. However, CRP and ESR in the pLV/PR-39 groupwere significantly lower than the pLV/EGFP group at day 7 and 14 respectively after operation.

CONCLUSIONS

Rabbits planted BMSCs expressing PR-39 were significantly increased resistance to Staphylococcus aureus in PJI than control group thus showing great potential for preventing implant-associated infection. It will provide a potential new therapeutic agent for implant-associated infection.

Preventing Antibiotic-Resistant Infections: Additively Manufactured Porous Ti6Al4V Biofunctionalized with Ag and Fe Nanoparticles

Implant-associated infections are highly challenging to treat, particularly with the emergence of multidrug-resistant microbials. Effective preventive action is desired to be at the implant site. Surface biofunctionalization of implants through Ag-doping has demonstrated potent antibacterial results. However, it may adversely affect bone regeneration at high doses. Benefiting from the potential synergistic effects, combining Ag with other antibacterial agents can substantially decrease the required Ag concentration. To date, no study has been performed on immobilizing both Ag and Fe nanoparticles (NPs) on the surface of additively manufactured porous titanium. We additively manufactured porous titanium and biofunctionalized its surface with plasma electrolytic oxidation using a Ca/P-based electrolyte containing Fe NPs, Ag NPs, and the combinations. The specimen's surface morphology featured porous TiO2 bearing Ag and Fe NPs. During immersion, Ag and Fe ions were released for up to 28 days. Antibacterial assays against methicillin-resistant Staphylococcus aureus and Pseudomonas aeruginosa showed that the specimens containing Ag NPs and Ag/Fe NPs exhibit bactericidal activity. The Ag and Fe NPs worked synergistically, even when Ag was reduced by up to three times. The biofunctionalized scaffold reduced Ag and Fe NPs, improving preosteoblasts proliferation and Ca-sensing receptor activation. In conclusion, surface biofunctionalization of porous titanium with Ag and Fe NPs is a promising strategy to prevent implant-associated infections and allow bone regeneration and, therefore, should be developed for clinical application.

A concise review on implications of silver nanoparticles in bone tissue engineering

Skeletal disorders represent a variety of degenerative diseases that affect bone and cartilage homeostasis. The regenerative capacity of bone is affected in osteoporosis, osteoarthritis, rheumatoid arthritis, bone fractures, congenital defects, and bone cancers. There is no viable, non-invasive treatment option and bone regeneration requires surgical intervention with the implantation of bone grafts. Incorporating nanoparticles in bone grafts have improved fracture healing by providing fine structures for bone tissue engineering. It is currently a revolutionary finding in the field of regenerative medicine. Silver nanoparticles (AgNPs) have garnered particular attention due to their well-known anti-microbial and potential osteoinductive properties. In addition, AgNPs have been demonstrated to regulate the proliferation and differentiation of mesenchymal stem cells (MSCs) involved in bone regeneration. Furthermore, AgNPs have shown toxicity towards cancer cells derived from bone. In the last decade, there have been multiple studies focusing on the effect of nanoparticles on the proliferation and/or differentiation of MSCs and bone cancer cells; however, the specific studies with AgNPs are limited. Although the reported investigations show promising in vitro and in vivo potential of AgNPs for application in bone regeneration, more studies are required to ensure their implications in bone tissue engineering. This review aims to highlight the current advances related to the production of AgNPs and their effect on MSCs and bone cancer cells, which will potentiate their possible implications in orthopedics. Moreover, this review article evaluates the future of AgNPs in bone tissue engineering.

Plate-associated localized osteitis in mini-pig by biofilm-forming Methicillin-resistant Staphylococcus aureus (MRSA): establishment of a novel experimental model

PURPOSE

The increasing number of implant-associated infections during trauma and orthopedic surgery caused by biofilm-forming Staphylococcus aureus in combination with an increasing resistance of conventional antibiotics requires new therapeutic strategies. One possibility could be testing for different therapeutic strategies with differently coated plates. Therefore, a clinically realistic model is required. The pig offers the best comparability to the human situation, thus it was chosen for this model. The present study characterizes a novel model of a standardized low-grade acute osteitis with bone defect in the femur in mini-pigs, which is stabilized by a titanium locking plate to enable further studies with various coatings.

METHODS

A bone defect was performed on the femur of 7 Aachen mini-pigs and infected with Methicillin-resistant S. aureus (MRSA ATCC 33592). The defect zone was stabilized with a titanium plate. After 14 days, a plate change, wound debridement and lavage were performed. Finally, after 42 days, the animals were lavaged and debrided again, followed by euthanasia. The fracture healing was evaluated radiologically and histologically.

RESULTS

A local osteitis with radiologically visible lysis of the bone could be established. The unchanged high Colony-forming Units (CFU) in lavage, the significant differences in Interleukin (IL)-6 in blood compared to lavage and the lack of increase in Alkaline Phosphates (ALP) in serum over the entire observation period show the constant local infection.

CONCLUSION

The study shows the successful induction of local osteitis with lysis of the bone and the lack of enzymatic activity to mineralize the bone. Therefore, this standardized mini-pig model can be used in further clinical studies, to investigate various coated implants, bone healing, biofilm formation and immune response in implant-associated osteitis.

Preventing Staphylococcus aureus stainless steel-associated infections in orthopedics. A systematic review and meta-analysis of animal literature

Surgical site infection in the presence of orthopedic implants poses significant healthcare and socioeconomic burden. To assess the potential of various prevention strategies against Staphylococcus-induced stainless steel-associated infections, a review of animal evidence was designed. The databases of PubMed, Embase, and CENTRAL were searched until March 10, 2020, for articles including animal models with stainless steel instrumentation and techniques to prevent Staphylococcus infection. We conducted a random-effects meta-analysis of standardized mean differences (SMD) with subgroup analysis linked to various protection strategies and we recorded complications. Quality was assessed with the SYRCLE's risk of bias tool. Twenty-five studies were included. Combined active coating (featuring organic antibacterial compound release) and degradable passive finishing (lipid- or polymer-based structure modification reducing bacterial adhesion) was favored over untreated controls (SMDs for methicillin-sensitive Staphylococcus aureus [MSSA] and methicillin-resistant Staphylococcus aureus [MRSA] were -3.46, 95% CI [-4.53 to -2.4], p < .001 [n = 4 head-to-head comparisons]; and -6.67, 95% CI [-10.53 to -3], p < .001 [n = 5 head-to-head comparisons], respectively). Systemic vitamin D supplementation and systemic antibiotic administration with or without local antibiotics demonstrated favorable outcomes against MSSA infection. On the contrary, no benefit was seen following vaccination. Of note, no side effects were documented. On the basis of data gathered from eight studies, which comprised 294 animals, a bioresorbable polymer- or lipid-based surface modification supplemented with organic coating yielded improved infection-related outcomes against MSSA and MRSA stainless steel infections, and therefore, this strategy could be further investigated in human research.

Nitinol, Stainless Steel, and Titanium Kirschner Wire Durability

Kirschner wires (K wires) are a common fixation device in foot and ankle surgery, particularly in lesser-toe fixation. Fatigue failure is a known complication of this fixation. The material properties of the K wire are a factor in the strength and durability of the wire. The purpose of this study is to compare the durability of K wires made of stainless steel, titanium, and Nitinol. Ten samples each of stainless steel, titanium. and Nitinol underwent cyclic durability testing using a rotating beam approach, and S-N curves (applied stress vs the number of cycles to failure) were generated. The results demonstrate that, generally, Nitinol K wires have a shorter life for the same applied stress than the stainless steel or titanium wires. Titanium had a longer life at low stresses compared with stainless steel, and stainless steel had a longer life at higher stresses. This study provides comparative durability data for K wires made of different metals, which have not been previously reported. Although there was a statistically significant difference in durability for wires used in K wire fixation, all 3 metal types are reasonable choices for temporary K wire fixation.Levels of Evidence: Level 5: Mechanical study.

Orthopedic Implant-Related Biofilm Pathophysiology: A Review of the Literature

Orthopedic implant-related infections remain a major problem even nowadays. Bacterial resistance through biofilm formation, in addition to the limited treatment options available, has resulted in an increased effort to better understand pathophysiology mechanisms. We performed a review of the literature in order to identify major biofilm formation pathways through which possible treatment strategies could arise.

Late spinal infections following posterior spinal fusion in pediatric deformities: treatment using single-stage titanium implant exchange

PURPOSE

Late infection following posterior spinal fusion (PSF) for deformity is a leading cause of revision. The purpose of this study is to evaluate clinical and radiographic outcomes following a single-stage debridement and exchange of spinal implants with titanium in adolescent patients with late-onset infections following PSF METHODS: A retrospective review of prospectively collected data of adolescent patients with spinal deformity, who were surgically treated with PSF was collected. Patients were included for the study if they developed late arising infection (> 1 year after index posterior fusion for the deformity) from 2006-2019. Treatment consisted of irrigation, debridement, implant exchange with titanium screws and rods, and antibiotics. Parameters evaluated include radiographic Cobb angles, operative data, and clinical data, all at minimum 2-year follow-up.

RESULTS

31 patients (29 with AIS and 2 with Scheuermann's kyphosis) developed late spinal infections. Mean age was 11.4 ± 2.3 years, 84% female, mean time from index surgery was 52.5 months. 25 had all stainless steel implants and 6 had cobalt chrome during the index procedure. Positive cultures were obtained in 5 patients (2 Staphylococcus Aureus, 1 Staphylococcus epidermidis, 1 Peptostreptococcus, 1 Pseudomonas aeruginosa) with cultures followed till 7 days post-operatively. At 2-years following the exchange, there was no change in coronal and sagittal alignment. Three (9%) patients developed subsequent infection necessitating implant removal.

CONCLUSION

A single-stage procedure consisting of implant removal, irrigation, and debridement, and replacement with all titanium implants is an effective treatment strategy in patients developing late wound infection following PSF with regards to maintenance of curve correction and minimizing recurrent infections.

Poly(methyl methacrylate) Bone Cement Composite Can Be Refilled with Antibiotics after Implantation in Femur or Soft Tissue

While periprosthetic joint infections (PJIs) result in a small percentage of patients following arthroplasties, they are challenging to treat if they spread into bone and soft tissue. Treatment involves delivering antibiotics using poly(methyl methacrylate) (PMMA) bone cement. However, antibiotic release is insufficient for prolonged infections. Previous work demonstrated efficacy of incorporating insoluble cyclodextrin (CD) microparticles into PMMA to improve antibiotic release and allow for post-implantation drug refilling to occur in a tissue-mimicking model. To simulate how antibiotic refilling may be possible in more physiologically relevant models, this work investigated development of bone and muscle refilling models. The bone refilling model involved embedding PMMA-CD into rabbit femur and administering antibiotic via intraosseous infusion. Muscle tissue refilling model involved implanting PMMA-CD beads in bovine muscle tissue and administering antibiotic via tissue injection. Duration of antimicrobial activity of refilled PMMA-CD was evaluated. PMMA-CD composite in bone and muscle tissue models was capable of being refilled with antibiotics and resulted in prolonged antimicrobial activity. PMMA-CD provided sustained and on-demand antimicrobial activity without removal of implant if infection develops. Intraosseous infusion appeared to be a viable technique to enable refilling of PMMA-CD after implantation in bone, reporting for the first time the ability to refill PMMA in bone.

Silver in biology and medicine: opportunities for metallomics researchers

The antibacterial properties of silver have been known for centuries and the threat of antibiotic-resistant bacteria has led to renewed focus on the noble metal. Silver is now commonly included in a range of household and medical items to imbue them with bactericidal properties. Despite this, the chemical fate of the metal in biological systems is poorly understood. Silver(I) is a soft metal with high affinity for soft donor atoms and displays much similarity to the chemistry of Cu(I). In bacteria, interaction of silver with the cell wall/membrane, DNA, and proteins and enzymes can lead to cell death. Additionally, the intracellular generation of reactive oxygen species by silver is posited to be a significant antimicrobial action. While the antibacterial action of silver is well known, bacteria found in silver mines display resistance against it through use of a protein ensemble thought to have been specifically developed for the metal, highlighting the need for judicious use. In mammals, ∼10-20% of ingested silver is retained by the body and thought to predominantly localize in the liver or kidneys. Chronic exposure can result in argyria, a condition characterized by blue staining of the skin, resulting from subdermal deposition of silver [as Ag(0)/sulfides], but more insidious side effects, such as inclusions in the brain, seizures, liver/kidney damage, and immunosuppression, have also been reported. Here, we hope to highlight the current understanding of the biological chemistry of silver and the necessity for continued study of these systems to fill existing gaps in knowledge.

Biomaterials against Bone Infection

Chronic bone infection is considered as one of the most problematic biofilm-related infections. Its recurrent and resistant nature, high morbidity, prolonged hospitalization, and costly medical care expenses have driven the efforts of the scientific community to develop new therapies to improve the standards used today. There is great debate on the management of this kind of infection in order to establish consistent and agreed guidelines in national health systems. The scientific research is oriented toward the design of anti-infective biomaterials both for prevention and cure. The properties of these materials must be adapted to achieve better anti-infective performance and good compatibility, which allow a good integration of the implant with the surrounding tissue. The objective of this review is to study in-depth the antibacterial biomaterials and the strategies underlying them. In this sense, this manuscript focuses on antimicrobial coatings, including the new technological advances on surface modification; scaffolding design including multifunctional scaffolds with both antimicrobial and bone regeneration properties; and nanocarriers based on mesoporous silica nanoparticles with advanced properties (targeting and stimuli-response capabilities).

Experimental reproduction of periprosthetic joint infection: Developing a representative animal model

BACKGROUND

Infection after arthroplasty (prosthetic joint infection; PJI) is a devastating complication that can lead to functional loss of the affected limb. The purpose of the present study is to develop an animal model of PJI using a three-dimensional printed species-specific implant, which is a step forward for future research to develop new therapeutic strategies.

METHODS

Fifteen New Zealand White rabbits were employed to reproduce PJI by intra-articular inoculation of 10⁵ cfu/ml of Staphylococcus aureus ATCC® 29213. Three-dimensional printing technology was used to design a species-specific four-millimeter-thick implant maintaining the anatomical irregularities of the tibial-articular surface. Response to bacterial inoculation was monitored by clinical (weight and temperature), hematological (leukocyte, lymphocyte and platelet counts) and biochemical (erythrocyte sedimentation rate) analyses at the time of inoculation and seven days thereafter, when microbiological samples for culture were also taken.

RESULTS

All animals recovered from surgery and all displayed full weight-bearing four days postoperatively. Fourteen of the 15 tested animals (93.3%) presented positive microbiological cultures. A statistically significant increase was found in the number of platelets and leukocytes, as well as a significant decrease in the percentage of lymphocytes, with P = 0.0001 in all cases.

CONCLUSIONS

An experimental model faithfully reproducing the periprosthetic infection environment and achieving a high rate of infection has been designed. The use of three-dimensional printed species-specific implants allows rapid postoperative recovery of animals and the development of a stable biofilm. These characteristics make it an interesting model to study its pathogenesis and possible therapeutic strategies.

Establishment of an in vivo rat model for chronic musculoskeletal implant infection

Background

The aim of the study was to establish an experimental chronic musculoskeletal infection model in vivo characterized by (a) a small bacterial inoculum, (b) no general or local signs of infection, (c) several parallels (implants) in each animal and finally (d) a model that is technically easy to perform.

Methods

Bone xenografts with steel plates were implanted intramuscularly in rats. To the xenografts, different inocula of Staphylococcus aureus and two strains of Staphylococcus epidermidis were added. The animals were observed for different time periods before the removal of the xenografts. The xenografts and steel plates were subjected to quantitative bacterial culture after sonication. Additional steel plates were subjected to scanning electron microscopy (SEM) for visualization of biofilm formation.

Results

Inoculation of bone grafts with S. aureus did produce a pyogenic infection in all animals. A chronic infection was established in rats where the bone grafts were inoculated with S. epidermidis. A bacterial inoculum of 100 colony-forming units (CFU) of S. epidermidis was adequate as a minimum infective dose. During a period of up until 42 days, the animals infected with S. epidermidis had no general or local signs of infection. According to the results of the quantitative bacterial culture of sonicate fluid and SEM, a biofilm was developed on all implants.

Conclusion

In the present in vivo model, a very small bacterial inoculum succeeded in establishing a chronic musculoskeletal implant infection where a biofilm was formed on the implants. The experimental model is easy to perform and allows several implants in each animal. The model could be useful for the study of biofilm formation in vivo on different implants and different surfaces.

Best Practice Guidelines for Surgical Site Infection Prevention With Surgical Treatment of Early Onset Scoliosis

BACKGROUND

Postoperative surgical site infection (SSI) is unfortunately a commonly encountered complication in the surgical treatment of children with Early Onset Scoliosis (EOS). There is documented variation in the treatment of this patient population. Previous work building consensus for the approach to high risk patients (eg, neuromuscular etiology) has been promising. The goal of the current study is to apply similar principles to develop consensus-based guidelines for the treatment of patients with EOS.

METHODS

A focus group from 2 multicenter pediatric spine deformity study groups developed a list of statements to be distributed to a larger group of EOS experts. Using the Delphi process, participants were presented with a systematic review of the literature as well as a review of current practices in growth friendly surgery. The first round was conducted using an electronic survey. Results of this survey were then discussed face-to-face and the statements were further refined. A final round was conducted using the Audience Response System, allowing participants to vote for each statement (strongly agree or agree). Agreement >80% or disagreement <20% was considered consensus.

RESULTS

A total of 29 of 57 statements reached consensus. Negative statements (statements of disagreement) were excluded, so the final consensus guidelines included 22 statements. The number of statements from the previously published Best Practice Guidelines (BPG) approved for insertion and lengthening growth friendly procedures were 12 of 14 and 11 of 14, respectively. The high risk BPG therefore does not cover all of the issues specific to the EOS population, and explains why 22 statements reached consensus in the current guideline. Upon completion of the surveys, 100% of the participants agreed to support its publication.

CONCLUSIONS

Using the Delphi process several "best practices" were developed for growth friendly surgical treatment of EOS.

LEVEL OF EVIDENCE

Level V.

Evolving concepts in bone infection: redefining "biofilm", "acute vs. chronic osteomyelitis", "the immune proteome" and "local antibiotic therapy"

Osteomyelitis is a devastating disease caused by microbial infection of bone. While the frequency of infection following elective orthopedic surgery is low, rates of reinfection are disturbingly high. Staphylococcus aureus is responsible for the majority of chronic osteomyelitis cases and is often considered to be incurable due to bacterial persistence deep within bone. Unfortunately, there is no consensus on clinical classifications of osteomyelitis and the ensuing treatment algorithm. Given the high patient morbidity, mortality, and economic burden caused by osteomyelitis, it is important to elucidate mechanisms of bone infection to inform novel strategies for prevention and curative treatment. Recent discoveries in this field have identified three distinct reservoirs of bacterial biofilm including: Staphylococcal abscess communities in the local soft tissue and bone marrow, glycocalyx formation on implant hardware and necrotic tissue, and colonization of the osteocyte-lacuno canalicular network (OLCN) of cortical bone. In contrast, S. aureus intracellular persistence in bone cells has not been substantiated in vivo, which challenges this mode of chronic osteomyelitis. There have also been major advances in our understanding of the immune proteome against S. aureus, from clinical studies of serum antibodies and media enriched for newly synthesized antibodies (MENSA), which may provide new opportunities for osteomyelitis diagnosis, prognosis, and vaccine development. Finally, novel therapies such as antimicrobial implant coatings and antibiotic impregnated 3D-printed scaffolds represent promising strategies for preventing and managing this devastating disease. Here, we review these recent advances and highlight translational opportunities towards a cure.

Disseminated Coccidioidomycosis to the Spine-Case Series and Review of Literature

Coccidioidomycosis is a fungal infectious disease caused by the Coccidioides species endemic to Southwestern United States. Symptomatic patients typically present as community-acquired pneumonia. Uncommonly, in about 1% of infections, hematogenous extra pulmonary systemic dissemination involving skin, musculoskeletal system, and meninges occur. Disseminated spinal infection is treated with antifungal drugs and/or surgical treatment. A retrospective review of medical records at our institution was done between January 2009 to December 2018 and we present three cases of spinal coccidioidomycosis and review the current literature. Disseminated coccidioidomycosis can lead to spondylitis that can present as discitis or a localized spinal or paraspinal abscess. Spinal coccidioidomycosis is typically managed with antifungal treatments but can include surgical treatment in the setting poor response to medical therapy, intractable pain, presence of neurological deficits due to compression, or structural spinal instability.

Efficacy of eluted antibiotics through 3D printed femoral implants

Costs associated with musculoskeletal diseases in the United States account for 5.7% of the Gross Domestic Product (GDP) (Weinstein et al. 2018). As such, there is a need to pursue new ideas in orthopaedic implants that can decrease cost and improve patient care. In the recent years, 3D printing of polymers using Fused Deposition Modeling (FDM) and metals using Direct Metal Laser Sintering (DMLS) has opened several exciting possibilities to create customized orthopaedic implants. Such implants can be engineered to release antibiotics in a controlled manner by infusing the drug into the material during manufacturing stage. However, the prevalence of high temperature could impact the anti-bacterial effectiveness of the eluted antibiotics in such implants. An alternative approach to circumvent this issue would be to modify the implant geometry to incorporate built-in design features such as micro-channels and reservoirs in which antibiotics can be introduced prior to the surgical procedure. Irrespective of the approach used, the ability of 3D printed orthopaedic implants to elute antibiotics, and the rate of elution are not well understood. The purpose of this article is to study the elution of doxycycline through 3D printed femoral implants using three different materials: Poly-Lactic Acid (PLA), Poly-Caprolactone (PCL) and Titanium grade Ti-6Al-4V. The PLA and Ti-6Al-4V implants were designed with built-in reservoirs and micro-channels in which doxycycline was introduced post the manufacturing stage. However, the PCL implants were printed from a PCL spool that was infused with doxycycline using an extruder. The PLA and Ti-6Al-4V experiments were run for a period of 31 days and the PCL experiment for one day. The antibacterial ability of eluted doxycycline from all implants were examined using Kirby-Bauer test on the bacteria E.coli k-12. The results show that most of doxycycline eluted through the three materials in the first 24 hours. After the initial spike, a steady release was achieved for the PLA and Ti-6Al-4V implants for 30 days. During this timeframe, Ti-6Al-4V implants released more doxycycline than the PLA implant. The eluted antibiotics through all the implants demonstrated the ability to kill bacteria in the subsequent Kirby-Bauer test. These outcomes show that irrespective of how the antibiotics were introduced, 3D printed polymeric and metallic implants have great potential in orthopaedic applications.

The use of silver coating in hip megaprostheses: a systematic review

Retrospective studies of silver-coated hip implants have demonstrated promising results and safety profile, however, the potential benefits are so far unproven in prospective studies. Silver-coated implants may have a role in patients undergoing revision or primary surgery with a high risk of infection but as yet there are no human studies investigating silver in primary hip arthroplasty. Adequately powered robust prospective studies are needed in this area to determine if silver-coated implants would be efficacious and cost-effective. The purpose of this systematic review article is to review the current literature regarding the use of silver in hip arthroplasty. Our review showed that there is some encouraging evidence that silver coatings can reduce infection.

Antibacterial and immunogenic behavior of silver coatings on additively manufactured porous titanium

Implant-associated infections (IAI) are often recurrent, expensive to treat, and associated with high rates of morbidity, if not mortality. We biofunctionalized the surface of additively manufactured volume-porous titanium implants using electrophoretic deposition (EPD) as a way to eliminate the peri-operative bacterial load and prevent IAI. Chitosan-based (Ch) coatings were incorporated with different concentrations of silver (Ag) nanoparticles or vancomycin. A full-scale in vitro and in vivo study was then performed to evaluate the antibacterial, immunogenic, and osteogenic activity of the developed implants. In vitro, Ch + vancomycin or Ch + Ag coatings completely eliminated, or reduced the number of planktonic and adherent Staphylococcus aureus by up to 4 orders of magnitude, respectively. In an in vivo tibia intramedullary implant model, Ch + Ag coatings caused no adverse immune or bone response under aseptic conditions. Following Staphylococcus aureus inoculation, Ch + vancomycin coatings reduced the implant infection rate as compared to chitosan-only coatings. Ch + Ag implants did not demonstrate antibacterial effects in vivo and even aggravated infection-mediated bone remodeling including increased osteoclast formation and inflammation-induced new bone formation. As an explanation for the poor antibacterial activity of Ch + Ag implants, it was found that antibacterial Ag concentrations were cytotoxic for neutrophils, and that non-toxic Ag concentrations diminished their phagocytic activity. This study shows the potential of EPD coating to biofunctionalize porous titanium implants with different antibacterial agents. Using this method, Ag-based coatings seem inferior to antibiotic coatings, as their adverse effects on the normal immune response could cancel the direct antibacterial effects of Ag nanoparticles. STATEMENT OF SIGNIFICANCE: Implant-associated infections (IAI) are a clinical, societal, and economical burden. Surface biofunctionalization approaches can render complex metal implants with strong local antibacterial action. The antibacterial effects of inorganic materials such as silver nanoparticles (Ag NPs) are often highlighted under very confined conditions in vitro. As a novelty, this study also reports the antibacterial, immunogenic, and osteogenic activity of Ag NP-coated additively-manufactured titanium in vivo. Importantly, it was found that the developed coatings could impair the normal function of neutrophils, the most important phagocytic cells protecting us from IAI. Not surprisingly, the Ag NP-based coatings were outperformed by an antibiotic-based coating. This emphasizes the importance of also targeting implant immune-modulatory functions in future coating strategies against IAI.

Microcalorimetric detection of staphylococcal biofilm growth on various prosthetic biomaterials after exposure to daptomycin

Primary aim of this in vitro study was to test the efficacy of daptomycin to eradicate staphylococcal biofilms on various orthopedic implant materials. Secondary aim was to quantitatively estimate the formation of staphylococcal biofilm. We tested six clinically important biomaterials: Cobalt chrome, pure titanium, grid-blasted titanium, porous plasma-coated titanium with/without hydroxyapatite, and polyethylene. Biofilms of S. aureus and S. epidermidis were formed on the samples and thereafter exposed to daptomycin. Samples were subsequently sonicated in order to detect dislodged biofilm bacteria and transferred to a microcalorimeter for real-time measurement of growth-related heat flow. Minimal biofilm eradication concentration (MBEC) was determined as the lowest concentration of daptomycin required to eradicate biofilm bacteria on the sample. Median MBEC of S. aureus biofilm on smooth metallic surfaces was lower than the rough metallic surfaces. In experiments with S. epidermidis, no pattern was seen in relation to the surface roughness. Regarding the quantitative estimation of staphylococcal biofilm formation on the sample, we found a significantly higher amount of biofilm growth on the rough surfaces than the smooth samples and polyethylene. In conclusion, the presented study showed that daptomycin could eradicate S. aureus biofilm at lower concentrations on the smooth surfaces compared to the rough surfaces, as well as polyethylene. In experiments with daptomycin against S. epidermidis biofilms, no pattern was seen in relation to the surface roughness. Furthermore, we demonstrated a faster detection of staphylococcal heat flow due to higher biofilm quantity on the rough surfaces compared to smooth samples and polyethylene. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2809-2816, 2018.

The effect of cell density, proximity, and time on the cytotoxicity of magnesium and galvanically coupled magnesium-titanium particles in vitro

Magnesium (Mg) and galvanically coupled magnesium-titanium (Mg-Ti) particles in vitro have been reported previously to kill cells in a dosage-dependent manner. Mg-Ti particles kill cells more effectively than Mg alone, due to the galvanic effect of Mg and Ti. This study further investigated the in vitro cytotoxicity of Mg and Mg-Ti in terms of particle concentration, cell density, time, and proximity. Cell density has an effect on cell viability only at low particle concentrations (below 250 µg/mL), where cell viability dropped only for lower cell densities (5000-10,000 cells/cm² ) and not for higher cell densities (20,000-30,000 cells/cm² ), showing that the particles cannot kill if there are more cells present. Cytotoxicity of Mg and Mg-Ti particles is quick and temporary, where the particles kill cells only during particle corrosion (first 24 h). Depending on the percentage of surviving cells, particle concentrations, and ongoing corrosion activity, the remaining live cells either proliferated and recovered, or just remained viable and quiescent. The particle killing is also proximity-dependent, where cell viability was significantly higher for cells far away from the particles (greater than ∼1 mm) compared to those close to the particles (less than ∼1 mm). Although the increase of pH does affect cell viability negatively, it is not the sole killing factor since cell viability is significantly dependent on particle type and proximity but not pH. Mg and Mg-Ti particles used in this study are large enough to prevent direct cell phagocytosis so that the cell killing effect may be attributed to solely electrochemical reactions. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 1428-1439, 2018.

Advances in in Vitro and in Vivo Models for Studying the Staphylococcal Factors Involved in Implant Infections

Implant infections due to staphylococci are one of the greatest threats facing patients receiving implant devices. For many years researchers have sought to understand the mechanisms involved in the adherence of the bacterium to the implanted device and the formation of the unique structure, the biofilm, which protects the indwelling bacteria from the host defence and renders them resistant to antibiotic treatment. A major goal has been to develop in vitro and in vivo models that adequately reflect the real-life situation. From the simple microtiter plate assay and scanning electron microscopy, tools for studying adherence and biofilm formation have since evolved to include specialised equipment for studying adherence, flow cell systems, real-time analysis of biofilm formation using reporter gene assays both in vitro and in vivo, and a wide variety of animal models. In this article, we discuss advances in the last few years in selected in vitro and in vivo models as well as future developments in the study of adherence and biofilm formation by the staphylococci.

Bacterial recovery using sonication versus swabbing of titanium and stainless steel implants inoculated with Staphylococcus pseudintermedius or Pseudomonas aeruginosa

Objective: To evaluate the use of sonication to improve recovery of bacteria from metal discs infected with bacteria commonly associated with implant infections in veterinary medicine.

Methods: In vitro study in which sterile titanium (Ti6Al4V) and stainless steel (AIS1316-L) discs were incubated with either Staphylococcus pseudintermedius or Pseudomonas aeruginosa for 24 hours. The following three groups were compared: 1) the sonication group involved immersing the discs in sterile saline and sonicating for five minutes; 2) the sham group was considered a negative control in which the discs were immersed in saline for five minutes without sonication; and 3) the swab group involved systematically swabbing the implant with a sterile culturette. All samples were plated on blood agar and incubated for 24 hours. Colonies were then counted and compared.

Results: For both species of bacteria, there was a significant increase in bacterial colonies isolated using sonication compared to the other two study groups (p = 0.0001). No differences in bacterial growth were found between the two types of metal implants. There was a significant increase in bacterial colony counts for S. pseudintermedius when comparing the swab group versus the sham group, but this was not significant for P. aeruginosa.

Clinical significance: Sonication significantly improves recovery of bacteria commonly associated with veterinary implant-associated surgical site infections compared to swabbing of implants in vitro. A prospective clinical evaluation is indicated to determine the in vivo efficacy of sonication in veterinary patients.

A review of local antibiotic implants and applications to veterinary orthopaedic surgery

In the face of increasing incidence of multidrug resistant implant infections, local antibiotic modalities are receiving increased attention for both infection prophylaxis and treatment. Local antibiotic therapy that achieves very high antibiotic drug concentrations at the site of the implant may represent an avenue for treatment of biofilmforming bacterial pathogens. Randomized controlled trials in human patients have demonstrated an infection risk reduction when antibiotic-impregnated cement is used for infection prophylaxis in implanted joint prostheses, and when a gentamicin-impregnated collagen sponge is used for infection prophylaxis in midline sternotomy. The other modalities discussed have for the most part yet to be evaluated in randomized controlled trials in veterinary or human patients. In general, the in vivo pharmacokinetics and appropriate dosing profiles for local antibiotic modalities have yet to be elucidated. Toxicity is possible, and attention to the dose applied is warranted.

Complications following spine fusion for adolescent idiopathic scoliosis

Complications following spine fusion for adolescent idiopathic scoliosis can be characterized as either intra-operative or post-operative. The most serious and feared complication is neurologic injury, both in the intra- and post-operative period. Other intra-operative complications include dural tears and ophthalmologic or peripheral nerve deficits, which may be related to positioning. Among the most common post-operative complications are surgical site infection, venous thromboembolism, gastrointestinal complications, and implant-related complications. Significant blood loss requiring transfusion, traditionally considered a known sequelae of spine fusion, is now being recognized as a "complication" in large national databases. Pediatric spine surgeons who care for patients with AIS must be thoroughly familiar with all potential complications and their management.

Fosfomycin Addition to Poly(D,L-Lactide) Coating Does Not Affect Prophylaxis Efficacy in Rat Implant-Related Infection Model, But That of Gentamicin Does

Gentamicin is the preferred antimicrobial agent used in implant coating for the prevention of implant-related infections (IRI). However, the present heavy local and systemic administration of gentamicin can lead to increased resistance, which has made its future use uncertain, together with related preventive technologies. Fosfomycin is an alternative antimicrobial agent that lacks the cross-resistance presented by other classes of antibiotics. We evaluated the efficacy of prophylaxis of 10% fosfomycin-containing poly(D,L-lactide) (PDL) coated K-wires in a rat IRI model and compared it with uncoated (Control 1), PDL-coated (Control 2), and 10% gentamicin-containing PDL-coated groups with a single layer of coating. Stainless steel K-wires were implanted and methicillin-resistant Staphylococcus aureus (ATCC 43300) suspensions (103 CFU/10 μl) were injected into a cavity in the left tibiae. Thereafter, K-wires were removed and cultured in tryptic soy broth and then 5% sheep blood agar mediums. Sliced sections were removed from the tibiae, stained with hematoxylin-eosin, and semi-quantitatively evaluated with X-rays. The addition of fosfomycin into PDL did not affect the X-ray and histopathological evaluation scores; however, the addition of gentamicin lowered them. The addition of gentamicin showed a protective effect after the 28th day of X-ray evaluations. PDL-only coating provided no protection, while adding fosfomycin to PDL offered a 20% level protection and adding gentamicin offered 80%. Furthermore, there were 103 CFU level growths in the gentamicin-added group, while the other groups had 105. Thus, the addition of fosfomycin to PDL does not affect the efficacy of prophylaxis, but the addition of gentamicin does. We therefore do not advise the use of fosfomycin as a single antimicrobial agent in coating for IRI prophylaxis.

Infective complications in tumour endoprostheses implanted after pathological fracture of the limbs

INTRODUCTION

Pathological fractures represent an adverse prognostic factor in primary and metastatic bone tumours. The purpose of this study was to evaluate the results of tumour silver-coated prosthesis implanted after pathological fractures.

MATERIALS AND METHODS

A retrospective analysis was conducted on 30 patients with pathological limb fracture after primary or metastatic bone tumours treated by the same surgeon with wide margin resection and tumour prosthesis implant between 2005 and 2015. Silver-coated prostheses were implanted in 17 patients and uncoated prostheses were implanted in 13 patients. The primary outcome of the study was to evaluate the infective risk, the secondary outcomes were survival and functional level (visual analogue scale [VAS], 36-Item Short Form Health Survey [SF 36], and Musculoskeletal Tumour Society [MSTS] score) obtained at the longest follow-up available. A multivariate analysis was performed considering age, sex, tumour histology, grading and location, resection size, concomitant radiotherapy/chemotherapy, use of mesh for soft tissue reconstruction and local complications (dislocation, relapse, implant breakage). Scanning electron microscopy (SEM) analysis of explanted prosthesis was performed to study the residual silver-coating.

RESULTS

The average age of patients in the study was 56.2 years (range 12-78 years). Silver-coated prostheses were implanted in 56.7% of patients, and uncoated tumour prostheses were used in the remaining 43.3%. The mean follow-up was 40.7 months. A total of 26.7% of patients died at a median time of 28.6 months after surgery. The overall rate of complications was 30%, with 16.7% due to infection. A total of 11.8% of the patients treated with silver-coated implants developed infection compared with 23.1% of the patients treated with uncoated tumour prostheses. There were no cases of early infection in the silver-coated prosthesis group, whereas early infection occurred in 66.7% of patients in the uncoated prosthesis group. All the functional outcomes were significantly improved after surgery. None of the other parameters analysed can be considered a significant negative prognostic factor for infection. The SEM analyses showed severe silver-coating degradation 2 years after first implant. No case of silver toxicity was demonstrated.

DISCUSSION

There are few papers in the literature about infective complications in tumour prosthesis after pathological fracture. Silver-coated implants showed a protective action against early infection. Late infection rate was similar between the groups, thereby indicating a reduction of antimicrobial activity for the silver-coating over time.

CONCLUSIONS

Silver-coated prostheses are a protective factor against early infections in limb salvage surgery after pathological fractures, so may represent the first-choice of implants in this type of surgery.

Silver-Coated Hip Megaprosthesis in Oncological Limb Savage Surgery

Silver coating has demonstrated good antimicrobial activity and low toxicity. Silver-coated megaprostheses have been introduced in oncological musculoskeletal surgery considering the high rate of infection. We conducted a retrospective analysis on 68 cases of primary or metastatic bone tumors, affecting the proximal femur, treated between 2005 and 2016 with wide margins resection and tumor implants reconstruction. All patients were treated by the same surgeon, with antibiotic prophylaxis according to a standard protocol. In 55.9% of patients silver-coated hip hemiarthroplasty was implanted; in the remaining 44.1% uncoated megaprostheses were implanted. Patients were reevaluated recording the complications and focusing the analysis on infective complications. The average follow-up was 46.5 months. No patient has shown any sign of local or general silver toxicity. A SEM analysis was conducted on the 3-silver-coated hip hemiarthroplasty explanted confirming a severe degradation with a small amount of residual silver on the coating surface. Silver-coated hip prostheses have a lower rate of early infection than traditional implants but showed a reduction of antimicrobial activity for silver coating wear. We recommend using silver-coated prosthesis as primary implants for limb salvage surgery, in primary or metastatic bone tumors affecting the proximal femur, considering the absence of signs of toxicity and the lower rate of early infection.

In Vivo Efficacy of a "Smart" Antimicrobial Implant Coating

BACKGROUND

Postoperative infection is a devastating complication following arthroplasty. The goals of this study were to introduce a "smart" implant coating that combines passive elution of antibiotic with an active-release mechanism that "targets" bacteria, and to use an established in vivo mouse model of post-arthroplasty infection to longitudinally evaluate the efficacy of this polymer implant coating in decreasing bacterial burden.

METHODS

A novel, biodegradable coating using branched poly(ethylene glycol)-poly(propylene sulfide) (PEG-PPS) polymer was designed to deliver antibiotics both passively and actively. In vitro-release kinetics were studied using high-performance liquid chromatography (HPLC) quantification in conditions representing both the physiologic environment and the more oxidative, hyperinflammatory environment of periprosthetic infection. The in vivo efficacy of the PEG-PPS coating delivering vancomycin and tigecycline was tested using an established mouse model of post-arthroplasty infection. Noninvasive bioluminescence imaging was used to quantify the bacterial burden; radiography, to assess osseointegration and bone resorption; and implant sonication, for colony counts.

RESULTS

In vitro-release kinetics confirmed passive elution above the minimum inhibitory concentration (MIC). A rapid release of antibiotic was noted when challenged with an oxidative environment (p < 0.05), confirming a "smart" active-release mechanism. The PEG-PPS coating with tigecycline significantly lowered the infection burden on all days, whereas PEG-PPS-vancomycin decreased infection on postoperative day (POD) 1, 3, 5, and 7 (p < 0.05). A mean of 0, 9, and 2.6 × 10(2) colony-forming units (CFUs) grew on culture from the implants treated with tigecycline, vancomycin, and PEG-PPS alone, respectively, and a mean of 1.2 × 10(2), 4.3 × 10(3), and 5.9 × 10(4) CFUs, respectively, on culture of the surrounding tissue (p < 0.05).

CONCLUSIONS

The PEG-PPS coating provides a promising approach to preventing periprosthetic infection. This polymer is novel in that it combines both passive and active antibiotic-release mechanisms. The tigecycline-based coating outperformed the vancomycin-based coating in this study.

CLINICAL RELEVANCE

PEG-PPS polymer provides a controlled, "smart" local delivery of antibiotics that could be used to prevent postoperative implant-related infections.

A novel co-culture model of murine K12 osteosarcoma cells and S. aureus on common orthopedic implant materials: 'the race to the surface' studied in vitro

Infection is a major cause of orthopedic implant failure. There are few studies assessing both tissue cell and bacterial adherence on common orthopedic implant materials in a co-culture environment. An in vitro co-culture model was created using K12 osteosarcoma cells and Staphylococcus aureus in a medium incubated over metal disks for 48 h. The results showed that, in the presence of S. aureus, there were fewer osteosarcoma cells attached to the disks for all substrata tested. There were significantly more osteosarcoma cells adhering to the cobalt chrome than the stainless steel and titanium disks. Overall, in the presence of osteosarcoma cells, there were more bacteria adhering to the disks for all the substrata tested, with significantly more bacteria adhering to the stainless steel disks compared to cobalt chrome and titanium disks. Scanning electron microscopy verified that osteosarcoma cells and bacteria were adherent to the metal disks after incubation for 48 h. Furthermore, the observation that more bacteria were in the co-culture than in the control sample suggests that the osteosarcoma cells serve as a nutrient source for the bacteria. Future models assessing the interaction of osteogenic cells with bacteria on a substratum would be improved if the model accounted for the role of the immune system in secondary bone healing.

An Approach to Lumbar Revision Spine Surgery in Adults

Along with the increase in lifestyle expectations in the aging population, a dramatic rise in surgical rates has been observed over the past 2 decades. Consequently, the rate of revision spine surgery is expected to increase. A systematic approach to treatment is required for the adult patient presenting with late or chronic complications after spinal surgery. Patient assessment includes elucidating current symptoms and knowledge of the previous surgery, performing a detailed assessment, and obtaining appropriate studies. Subsequently, differential diagnoses are formulated based on whether the pathology arises from the same levels or adjacent levels of the spine and whether it relates to the previous decompression or fusion. Finally, familiarity with different surgical approaches is imperative in treating the common pathologies encountered in this patient population.

Preliminary results of a new antibiotic susceptibility test against biofilm installation in device-associated infections: the Antibiofilmogram®

Biofilms are complex communities of microorganisms embedded in an extracellular matrix and adherent to a surface. The development was described as a four-stage process leading to the formation of a mature biofilm which was resistant to immune system and antibiotic actions. In bone and joint infections (BJIs), the formation of biofilms is a leading cause of treatment failure. Here we study the capacity of 11 antibiotics commonly used in the treatment of BJIs to inhibit the biofilm formation on 29 clinical Staphylococcus aureus isolates by a new test called Antibiofilmogram(®) The minimal inhibitory concentration (MIC) and biofilm MIC (bMIC) were determined in vitro and showed similar values for clindamycin, fusidic acid, linezolid and rifampin. Reversely, daptomycin, fosfomycin, gentamicin and ofloxacin showed a bMIC distribution different from MIC with bMIC above breakpoint. Finally, cloxacillin, teicoplanin and vancomycin revealed an intermediate bMIC distribution with a strain-dependent pattern. A murine in vivo model of catheter-associated S. aureus infection was made and showed a significant reduction, but not total prevention, of catheter colonization with cloxacillin at bMIC, and no or limited reduction with cloxacillin at MIC. Antibiofilmogram(®) could be of great interest after surgical operations on contaminated prostheses and after bacteremia in order to prevent the colonization of the device.

Surgical Debridement Is Superior to Sole Antibiotic Therapy in a Novel Murine Posttraumatic Osteomyelitis Model

Introduction

Bone infections after trauma, i.e. posttraumatic osteomyelitis, pose one of the biggest problems of orthopedic surgery. Even after sufficient clinical therapy including vast debridement of infected bone and antibiotic treatment, regeneration of postinfectious bone seems to be restricted. One explanation includes the large sized defects resulting from sufficient debridement. Furthermore, it remains unclear if inflammatory processes after bone infection do affect bone regeneration. For continuing studies in this field, an animal model is needed where bone regeneration after sufficient treatment can be studied in detail.

Methods

For this purpose we created a stable infection in murine tibiae by Staphylococcus aureus inoculation. Thereafter, osteomyelitic bones were debrided thoroughly and animals were subsequently treated with antibiotics. Controls included debrided, non-infected, as well as infected animals exclusively treated with antibiotics. To verify sufficient treatment of infected bone, different assessments detecting S. aureus were utilized: agar plates, histology and RT-qPCR.

Results

All three detection methods revealed massive reduction or eradication of S. aureus within debrided bones 1 and 2 weeks postoperatively, whereas sole antibiotic therapy could not provide sufficient treatment of osteomyelitic bones. Debrided, previously infected bones showed significantly decreased bone formation, compared to debrided, non-infected controls.

Discussion

Thus, the animal model presented herein provides a reliable and fascinating tool to study posttraumatic osteomyelitis for clinical therapies.

Animal Models of Implant-Related Low-Grade Infections. A Twenty-Year Review

The demand for joint replacement and surgical treatment is continuously increasing, thus representing a clinical burden and a cost for the healthcare system. Among several pathogens involved in implant-related infections, staphylococci account for the two-thirds of clinically isolated bacteria. Despite most of them are highly virulent microorganisms (Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa), low virulent bacteria (Staphylococcus epidermidis, Propionibacterium acnes) are responsible for delayed, low-grade infections without specific clinical signs and hardly distinguishable from aseptic prosthetic failure. Therefore, there is a real need to study the pathogenesis of orthopedic infections through in vivo animal models. The present review of the literature provides a 20-year overview of animal models of acute, subclinical or chronic orthopedic infections according to the pathogen virulence and inocula. Through this analysis, a great variety of conditions in terms of bacterial strains and inocula emerged, thus encouraging the development of more reproducible in vivo studies to provide relevant information for a translational approach to humans.

Hemodialysis-Associated Spondylodiscitis of the Cervical Spine: A Case Report

CASE

A fifty-seven-year-old, hemodialysis-dependent man presented with a one-month history of progressive neck pain and paresthesias of the upper extremities. Radiographic examination demonstrated collapse of the C5 and C6 vertebrae with resultant kyphosis and spinal cord compression.

CONCLUSION

The patient underwent a staged anterior debridement with C5 and C6 corpectomies, cage placement, and plate fixation of C4 to C7, followed by a posterior arthrodesis from C4 to C7. He completed a six-week course of intravenous antibiotics for the treatment of Staphylococcus epidermidis spondylodiscitis, followed by suppressive oral antibiotics. At one year of follow-up, he had no residual neck pain or neurological signs or symptoms.

Silver nanoparticles and their orthopaedic applications

Implant-associated infection is a major source of morbidity in orthopaedic surgery. There has been extensive research into the development of materials that prevent biofilm formation, and hence, reduce the risk of infection. Silver nanoparticle technology is receiving much interest in the field of orthopaedics for its antimicrobial properties, and the results of studies to date are encouraging. Antimicrobial effects have been seen when silver nanoparticles are used in trauma implants, tumour prostheses, bone cement, and also when combined with hydroxyapatite coatings. Although there are promising results with in vitro and in vivo studies, the number of clinical studies remains small. Future studies will be required to explore further the possible side effects associated with silver nanoparticles, to ensure their use in an effective and biocompatible manner. Here we present a review of the current literature relating to the production of nanosilver for medical use, and its orthopaedic applications.

A paradigm for the evaluation and management of spinal coccidioidomycosis

Background:

Coccidioidomycosis is a fungal infection that is endemic to parts of the Southwestern United States. When infection involves the spine, the treatment strategies can be challenging. We have devised a management protocol for spinal coccidioidomycosis based on a review of the literature and our experience.

Methods:

The electronic literature search of National Library of Medicine for publications from 1964 to 2014 was performed using the following keywords: Coccidioidomycosis and spine. The search yielded 24 papers. Treatment strategies were summarized into a treatment protocol.

Results:

A total of 164 cases of spinal coccidioidomycosis were identified, ranging in age from <10 to >80 years. Males (n = 131) and African-Americans (n = 79) were strikingly over-represented. Medical therapy: Once a diagnosis of spinal coccidioidomycosis is established, antifungal therapy should always be started. Antifungal therapy with amphotericin B or azoles like fluconazole. Medical therapy needs to be continued for many years and sometimes indefinitely to reduce disease recurrence or progression. Surgical management is indicated in cases with mechanical instability, neurologic deficit, medically intractable pain, or progression of infection despite antifungal therapy.

Conclusions:

This work provides a working protocol involving assessment and reassessment for the management of spinal coccidioidomycosis. Medical management with antifungal agents in some cases can provide satisfactory disease control. However, in patients with mechanical instability, neurologic deficit, medically intractable pain or disease progression disease control may only be achieved with surgical debridement and stabilization.

Early staphylococcal biofilm formation on solid orthopaedic implant materials: in vitro study

Biofilms forming on the surface of biomaterials can cause intractable implant-related infections. Bacterial adherence and early biofilm formation are influenced by the type of biomaterial used and the physical characteristics of implant surface. In this in vitro research, we evaluated the ability of Staphylococcus epidermidis, the main pathogen in implant-related infections, to form biofilms on the surface of the solid orthopaedic biomaterials, oxidized zirconium-niobium alloy, cobalt-chromium-molybdenum alloy (Co-Cr-Mo), titanium alloy (Ti-6Al-4V), commercially pure titanium (cp-Ti) and stainless steel. A bacterial suspension of Staphylococcus epidermidis strain RP62A (ATCC35984) was added to the surface of specimens and incubated. The stained biofilms were imaged with a digital optical microscope and the biofilm coverage rate (BCR) was calculated. The total amount of biofilm was determined with the crystal violet assay and the number of viable cells in the biofilm was counted using the plate count method. The BCR of all the biomaterials rose in proportion to culture duration. After culturing for 2-4 hours, the BCR was similar for all materials. However, after culturing for 6 hours, the BCR for Co-Cr-Mo alloy was significantly lower than for Ti-6Al-4V, cp-Ti and stainless steel (P<0.05). The absorbance value determined in the crystal violet assay and the number of viable cells on Co-Cr-Mo were not significantly lower than for the other materials (P>0.05). These results suggest that surface properties, such as hydrophobicity or the low surface free energy of Co-Cr-Mo, may have some influence in inhibiting or delaying the two-dimensional expansion of biofilm on surfaces with a similar degree of smoothness.

Antibacterial properties of metal and metalloid ions in chronic periodontitis and peri-implantitis therapy

Periodontal diseases like periodontitis and peri-implantitis have been linked with Gram-negative anaerobes. The incorporation of various chemotherapeutic agents, including metal ions, into several materials and devices has been extensively studied against periodontal bacteria, and materials doped with metal ions have been proposed for the treatment of periodontal and peri-implant diseases. The aim of this review is to discuss the effectiveness of materials doped with metal and metalloid ions already used in the treatment of periodontal diseases, as well as the potential use of alternative materials that are currently available for other applications but have been proved to be cytotoxic to the specific periodontal pathogens. The sources of this review included English articles using Google Scholar™, ScienceDirect, Scopus and PubMed. Search terms included the combinations of the descriptors "disease", "ionic species" and "bacterium". Articles that discuss the biocidal properties of materials doped with metal and metalloid ions against the specific periodontal bacteria were included. The articles were independently extracted by two authors using predefined data fields. The evaluation of resources was based on the quality of the content and the relevance to the topic, which was evaluated by the ionic species and the bacteria used in the study, while the final application was not considered as relevant. The present review summarizes the extensive previous and current research efforts concerning the use of metal ions in periodontal diseases therapy, while it points out the challenges and opportunities lying ahead.

Tantalum acetabular augments in one-stage exchange of infected total hip arthroplasty: a case-control study

During the one-stage exchange procedure for periprosthetic joint infection (PJI) after total hip arthroplasty (THA), acetabular defects challenge reconstructive options. Porous tantalum augments are an established tool for addressing acetabular destruction in aseptic cases, but their utility in septic exchange is unknown. This retrospective case-control study presents the initial results of tantalum augmentation during one-stage exchange for PJI. Primary endpoints were rates of re-infection and short-term complications associated with this technique. Study patients had no higher risk of re-infection with equivalent durability at early follow-up with a re-infection rate in both groups of 4%. In conclusion, tantalum augments are a viable option for addressing acetabular defects in one-stage exchange for septic THA. Further study is necessary to assess long-term durability when compared to traditional techniques for acetabular reconstruction.

Bacteriology and Risk Factors for Development of Late (Greater Than One Year) Deep Infection Following Spinal Fusion With Instrumentation

STUDY DESIGN

Retrospective cohort review.

OBJECTIVES

To evaluate patients who underwent instrumented spinal fusion procedures and compare late (more than 1 year) and early infection (less than 1 year).

SUMMARY OF BACKGROUND DATA

Centers for Disease Control and Prevention criteria for surgical site infections with implants include infections occurring at less than 1 year postoperatively. The authors observed a high rate of deep infection at more 1 year after instrumented spinal fusion. Retrospective review was conducted to determine whether differences in bacteriology, patient demographics, or surgical factors exist between late and early infection.

METHODS

A total of 1,390 patients underwent spinal fusion with instrumentation from 2000 to 2009. Deep infection requiring operative debridement occurred in 112 patients (70 at less than 1 year and 42 at more than 1 year after the index surgery). Clinical, operative, and microbiology reports were reviewed and logistic regression was performed to evaluate the relationship between these factors and time of infection.

RESULTS

The most common organisms in the greater than 1 year group were Propionibacterium acnes, compared with Staphylococcus aureus in the less than 1 year group. The odds of late infection in the P acnes group were 15.5 (95% confidence interval [CI], 4.36-54.72) times the odds among all other organisms (p < .0001). Patient demographics and surgical factors were not different between groups. Among all patients, the infection rate was significantly higher in patients who received stainless-steel implants (11.56%) compared with those who received titanium implants (3.53%) (p < .0001). In univariate analysis, the odds of late infection in the stainless-steel group were 6.09 (95% CI, 1.62-39.88) times the odds in the titanium group (p = .0042). However, in multivariate analysis, controlling for organism type reduced the odds ratio to 4.62 (95% CI, .53-40.14), with only a trend to significance (p = .1656).

CONCLUSIONS

Propionibacterium acnes was more commonly identified in late infection. Patients with stainless-steel implants had a higher incidence of late infection than those with titanium implants, but this was not significant after controlling for organism type.

Polymeric prodrugs of ampicillin as antibacterial coatings

A novel ampicillin prodrug containing two carboxylic acid functionalities was synthesized by reacting ampicillin with acyl chloride in the presence of base. This prodrug was subsequently converted into a poly(anhydride-amide) via solution polymerization. The polymer, which chemically incorporates the ampicillin prodrug into the polymeric backbone, was developed as a film to prevent infections associated with medical devices by controlled, localized release of antimicrobials. The robust polymer coatings exhibiting strong adhesion to stainless steel were produced under elevated temperature and reduced pressure. The in vitro hydrolytic degradation of the polymer into the ampicillin prodrug was measured and the antibacterial activity of polymer-derived coatings was examined using a Gram-positive bacterium, Staphylococcus aureus. Furthermore, the polymer cytotoxicity was screened using fibroblasts. The ampicillin prodrug demonstrated antibacterial activity and the polymer demonstrated no cytotoxic effects on fibroblasts. Based on these results, the biodegradation of the antimicrobial-based poly(anhydride-amide) into the prodrug displays substantial promise as an implant or implant coating to reduce device failure resulting from bacterial infections.

A systematic review of animal models for Staphylococcus aureus osteomyelitis

Staphylococcus aureus (S. aureus) osteomyelitis is a significant complication for orthopaedic patients undergoing surgery, particularly with fracture fixation and arthroplasty. Given the difficulty in studying S. aureus infections in human subjects, animal models serve an integral role in exploring the pathogenesis of osteomyelitis, and aid in determining the efficacy of prophylactic and therapeutic treatments. Animal models should mimic the clinical scenarios seen in patients as closely as possible to permit the experimental results to be translated to the corresponding clinical care. To help understand existing animal models of S. aureus, we conducted a systematic search of PubMed and Ovid MEDLINE to identify in vivo animal experiments that have investigated the management of S. aureus osteomyelitis in the context of fractures and metallic implants. In this review, experimental studies are categorised by animal species and are further classified by the setting of the infection. Study methods are summarised and the relevant advantages and disadvantages of each species and model are discussed. While no ideal animal model exists, the understanding of a model's strengths and limitations should assist clinicians and researchers to appropriately select an animal model to translate the conclusions to the clinical setting.

Infection with spinal instrumentation: Review of pathogenesis, diagnosis, prevention, and management

Background:

Instrumentation has become an integral component in the management of various spinal pathologies. The rate of infection varies from 2% to 20% of all instrumented spinal procedures. Every occurrence produces patient morbidity, which may adversely affect long-term outcome and increases health care costs.

Methods:

A comprehensive review of the literature from 1990 to 2012 was performed utilizing PubMed and several key words: Infection, spine, instrumentation, implant, management, and biofilms. Articles that provided a current review of the pathogenesis, diagnosis, prevention, and management of instrumented spinal infections over the years were reviewed.

Results:

There are multiple risk factors for postoperative spinal infections. Infections in the setting of instrumentation are more difficult to diagnose and treat due to biofilm. Infections may be early or delayed. C Reactive Protein (CRP) and Magnetic Resonance Imaging (MRI) are important diagnostic tools. Optimal results are obtained with surgical debridement followed by parenteral antibiotics. Removal or replacement of hardware should be considered in delayed infections.

Conclusions:

An improved understanding of the role of biofilm and the development of newer spinal implants has provided insight in the pathogenesis and management of infected spinal implants. This literature review highlights the mechanism, pathogenesis, prevention, and management of infection after spinal instrumentation. It is important to accurately identify and treat postoperative spinal infections. The treatment is often multimodal and prolonged.

Prevalence of biofilm-producing Staphylococcus epidermidis in the healthy skin of individuals in Tamil Nadu, India

PURPOSE

Staphylococcus epidermidis is a major commensal bacteria. Various strains of S. epidermidis are capable of forming biofilms by attaching to several surfaces. Biofilm-forming ability of this organism is found to be associated with many hospital-acquired infections and can even impair wound healing. S. epidermidis strains producing polysaccharide-biofilms possess the intercellular adhesion (ica) operon while strains forming the protein adhesion-mediated biofilms possess the accumulation associated protein (aap) gene. We screened for biofilm-forming S. epidermidis in the skin of healthy individuals in Tamil Nadu in order to determine the risk of acquiring S. epidermidis infections in hospital settings.

MATERIALS AND METHODS

Skin swabs were taken from seventy two subjects residing in Chennai with healthy skin who showed no visible signs of skin lesions or allergies. S. epidermidis was isolated from 58 samples out of the 72 collected. The presence of ica operon in S. epidermidis isolates was determined by PCR and biofilm production was examined using quantitative tissue culture plate assay.

RESULTS

Majority of the samples (47/72; 65.3%) showed pure S. epidermidis growth, (14/72; 19.4%) showed pure Staphylococcus aureus growth and the remainder (11/72; 15.3%) showed mixed growth. Biofilm-forming S. epidermidis were found in the majority of samples (53/58; 91.4%) and ica operon was detected in 19 samples out of 58 (32.8%) which is a significantly higher percentage when compared to other studies conducted at different parts of the globe ( P = 0.0003).

CONCLUSION

We inferred that ica operon and biofilm-forming S. epidermidis are common in the healthy skin of individuals in Tamil Nadu. Measures have to be taken to reduce the risk of hospital-acquired S. epidermidis infections.