ObjectiveLocal antibiotic delivery systems with differing chemical and mechanical properties have been developed to assist in the management of osteomyelitis. We investigated the bone conductive and resorptive capabilities of a calcium phosphate-calcium sulfate (CaP/CaS) composite compared with commercially available polymethylmethacrylate (PMMA). In addition, we compared the in vivo preventative and treatment efficacies of both biomaterials in a proven osteomyelitis model.MethodsSixty-four, male Sprague-Dawley rats were inoculated with 10 μl of 1.5 x 108 CFU/ml of Staphylococcus aureus in a surgically drilled defect in the right proximal tibia. Infected animals were randomly allocated into prevention and treatment groups with 32 rats each. In the prevention group, the defect was filled with a plug containing either PMMA or CaP/CaS immediately after the inoculation. In the treatment group, the infected defects were irrigated, debrided, and filled with either a PMMA or CaP/CaS plug. Both CaP/CaS and PMMA were impregnated with 10% weight of vancomycin. Rats were sacrificed 6 weeks after cement insertion. Infection was detected by bacterial culture and histological analysis. Bone formation in the defect was assessed with micro-computed tomography and histology.ResultsNo bacteria were detected in any group. Both the prevention and treatment groups using CaP/CaS had significantly more bone volume fraction, bone area, and cartilage area than the PMMA groups.ConclusionsWhen loaded with 10% of vancomycin, CaP/CaS and PMMA have the same efficacy for treatment and prevention of osteomyelitis. CaP/CaS enhances bone defect healing through improved bone remodeling in our osteomyelitis rat model.

Aims Current treatments of prosthetic joint infection (PJI) are minimally effective against Staphylococcus aureus biofilm. A murine PJI model of debridement, antibiotics, and implant retention (DAIR) was used to test the hypothesis that PlySs2, a bacteriophage-derived lysin, can target S. aureus biofilm and address the unique challenges presented in this periprosthetic environment. Methods The ability of PlySs2 and vancomycin to kill biofilm and colony-forming units (CFUs) on orthopaedic implants were compared using in vitro models. An in vivo murine PJI model of DAIR was used to assess the efficacy of a combination of PlySs2 and vancomycin on periprosthetic bacterial load. Results PlySs2 treatment reduced 99% more CFUs and 75% more biofilm compared with vancomycin in vitro. A combination of PlySs2 and vancomycin in vivo reduced the number of CFUs on the surface of implants by 92% and in the periprosthetic tissue by 88%. Conclusion PlySs2 lysin was able to reduce biofilm, target planktonic bacteria, and work synergistically with vancomycin in our in vitro models. A combination of PlySs2 and vancomycin also reduced bacterial load in periprosthetic tissue and on the surface of implants in a murine model of DAIR treatment for established PJI. Cite this article: Bone Joint J 2020;102-B(7 Supple B):3–10.

Staphyloccocus aureus is one of the major pathogens in orthopedic periprosthetic joint infection (PJI), a devastating complication of total joint arthroplasty that often results in chronic and persistent infections that are refractory to antibiotics and require surgical interventions. Biofilm formation has been extensively investigated as a reason for persistent infection. The cellular composition, activation status, cytokine profile, and role of the immune response during persistent S. aureus PJI are incompletely understood. In this study, we used histology, multiparametric flow cytometry, and gene expression analysis to characterize the immune response in a clinically relevant orthopedic PJI model. We tested the hypothesis that persistent S. aureus infection induces feedback mechanisms that suppress immune cell activation, thereby affecting the course of infection. Surprisingly, persistent infection was characterized by strikingly high cytokine gene expression indicative of robust activation of multiple components of innate and adaptive immunity, along with ongoing severe neutrophil-dominated inflammation, in infected joint and bone tissues. Activation and expansion of draining lymph nodes and a bone marrow stress granulopoiesis reaction were also maintained during late phase infection. In parallel, feedback mechanisms involving T-cell inhibitory receptors and exhaustion markers, suppressive cytokines, and regulatory T cells were activated and associated with decreased T-cell proliferation and tissue infiltration during the persistent phase of infection. These results identify the cellular and molecular components of the mouse immune response to persistent S. aureus PJI and indicate that neutrophil infiltration, inflammatory cytokine responses, and ongoing lymph node and bone marrow reactions are insufficient to clear infection and that immune effector mechanisms are suppressed by feedback inhibitory pathways. These immune-suppressive mechanisms are associated with diminished T-cell proliferation and tissue infiltration and can be targeted as part of adjuvant immunotherapeutic strategies in combination with debridement of biofilm, antibiotics, and other therapeutic modalities to promote eradication of infection.

Administration of bisphosphonates following total joint arthroplasty might be beneficial to reduce aseptic loosening. However, their effects on peri-implant bone formation and bone-implant interface strength have not been investigated yet. We used a physiologically loaded mouse implant model to investigate the short-term effects of postoperative systemic alendronate on osseointegration. A titanium implant with a rough surface was inserted in the proximal tibiae of 17-week-old female C57BL/6 mice (n = 44). Postimplantation mice were given alendronate (73 μg/kg/days, n = 22) or vehicle (n = 22) 5 days/week. At 7-and 14-day postimplantation, histology and histomorphometry were conducted. At 28 days, microcomputed tomography and biomechanical testing were performed (n = 10/group). Postoperative alendronate treatment enhanced osseointegration, increasing maximum pullout load by 45% (p < .001) from 19.1 ± 4.5 N in the control mice to 27.6 ± 4.9 N in the treated mice, at day 28 postimplantation. Alendronate treatment increased the bone volume fraction by 139% (p < .001) in the region distal to the implant and 60% (p < .05) in the peri-implant region. At 14-day postimplantation, alendronate treatment decreased the number of osteoclasts per bone perimeter (p < .05) and increased bone volume fraction (p < .01) when compared with the control group. Postimplantation, short-term alendronate treatment enhanced osseointegration as demonstrated by increased bone mass, trabecular bone thickness, and maximum pullout load. Alendronate decreased peri-implant osteoclasts while preserving peri-implant osteoblasts and endothelial cells, in turn, increasing bone volume fraction. This data supports the postoperative clinical use of bisphosphonates, especially in patients with high risks of aseptic loosening.

Background:Amikacin, meropenem, minocycline, and fosfomycin have potential clinical utility for orthopaedic infections; however, their suitability for use in polymethylmethacrylate (PMMA) is poorly understood. The purpose of this study was (1) to quantify the thermal stability of these antibiotics at clinically relevant temperatures and (2) to determine the elution pharmacodynamics of these alternative antibiotics in vitro from PMMA beads of different sizes.Methods:Polymerization temperatures of 10-mm PMMA beads were measured over time to generate a simulated heating curve. Aqueous solutions of tobramycin, amikacin, meropenem, minocycline, and fosfomycin were subjected to the temperature curves, followed by incubation at 37°C. Minimum inhibitory concentrations of each antibiotic were evaluated against Staphylococcus aureus, Escherichia coli, and Acinetobacter baumannii. High-dose 4.5-mm, 6-mm, and 10-mm antibiotic-laden PMMA beads (10% antibiotic by weight) were submerged individually in a phosphate-buffered saline solution and incubated at 37°C. Antibiotic elution was determined with use of high-performance liquid chromatography with mass spectrometry.Results:Tobramycin, amikacin, and fosfomycin demonstrated thermal stability and maintained antimicrobial activity for 28 days. Minocycline and meropenem lost antimicrobial activity against all 3 organisms after 48 hours and 7 days, respectively. Elution concentrations, rates, and cumulative drug mass for tobramycin, amikacin, and meropenem were orders of magnitude higher than minocycline and fosfomycin at each time point.Conclusions:This study identified notable differences in thermal stability and elution among antibiotics used to treat infections. Amikacin exhibited activity similarly to tobramycin. Meropenem demonstrated favorable elution kinetics and thermal stability in the initial 7-day period.Clinical Relevance:Amikacin and meropenem show pharmacologic promise as potential acceptable alternatives for local delivery in PMMA for treatment of orthopaedic infections. Further work to establish clinical relevance and utility is needed.