rhBMP-2 modulation of gene expression in infected segmental bone defects

Choosing the right animal model for osteomyelitis research: Considerations and challenges

Osteomyelitis is a debilitating bone disorder characterized by an inflammatory process involving the bone marrow, bone cortex, periosteum, and surrounding soft tissue, which can ultimately result in bone destruction. The etiology of osteomyelitis can be infectious, caused by various microorganisms, or noninfectious, such as chronic nonbacterial osteomyelitis (CNO) and chronic recurrent multifocal osteomyelitis (CRMO). Researchers have turned to animal models to study the pathophysiology of osteomyelitis. However, selecting an appropriate animal model that accurately recapitulates the human pathology of osteomyelitis while controlling for multiple variables that influence different clinical presentations remains a significant challenge. In this review, we present an overview of various animal models used in osteomyelitis research, including rodent, rabbit, avian/chicken, porcine, minipig, canine, sheep, and goat models. We discuss the characteristics of each animal model and the corresponding clinical scenarios that can provide a basic rationale for experimental selection. This review highlights the importance of selecting an appropriate animal model for osteomyelitis research to improve the accuracy of the results and facilitate the development of novel treatment and management strategies.

Off-Label Use of Bone Morphogenetic Protein 2 in the Reconstructions of Mandibular Continuity Defects

This paper describes 3 patients of off-label use of bone morphogenetic protein 2 (rhBMP-2) in the reconstruction of mandibular continuity defects. In the first patient, rhBMP-2 was associated with iliac crest bone graft for late mandibular reconstruction after resection of osteosarcoma. In the 2 other patients, rhBMP-2 was used alone. In 1 patient the mandibular continuity defect was due to resection for treatment of osteomyelitis and in the other patient a continuity defect was created by unsuccessful osteogenic distraction for correction of mandibular hypoplasia. Despite the good results in those patients, the off-label use of rhBMP-2 is associated with increased rate of complications, so more studies are needed to assess the predictability of the use of rhBMP-2 in mandibular continuity defects. Therefore, at the moment the off-label use of rhBMP-2 should be restricted to complicated bone defects in which the conventional alternatives of reconstruction were unsuccessful.

Infection after fracture osteosynthesis - Part II

In the first part of this article, we have discussed the pathogenesis, clinical presentation, diagnosis and classification of infection after fracture osteosynthesis with implants, termed here as osteosynthesis-associated infection (OAI). Prolonged antibiotic treatment is usually necessary. Implant retention and maintenance of fracture stability to allow for fracture healing in spite of infection are allowed for OAI. Depending on the severity of infection, status of fracture healing and host status, the treatment follows five common pathways. These are non-operative treatment, debridement with implant retention, conversion of fixation, implant removal and suppression therapy. The decision-making process leading to each treatment pathway and challenging scenarios is discussed in detail.

Repair of a Complicated Calvarial Defect: Reconstruction of an Infected Wound With rhBMP-2

BACKGROUND

Management of the previously infected craniofacial defect remains a significant clinical challenge, posing obstacles such as wound healing complications, lack of donor site availability, and predisposition to failure of the repair. Optimal therapy would reconstruct like with like, without donor site morbidity. The purpose of this study was to compare the efficacy of recombinant human bone morphogenetic protein-2 (rhBMP-2)-mediated bone regeneration with the current standard of autologous bone graft for repair of previously infected calvarial defects.

METHODS

Nineteen adult New Zealand white rabbits underwent subtotal calvariectomy. Bone flaps were inoculated with Staphylococcus aureus and replanted. After 1 week of infection, bone flaps were removed, and wounds were debrided, followed by 10 days of antibiotic treatment. After 6 weeks, animals underwent scar debridement followed by definitive reconstruction in 1 of 4 groups: empty control (n = 3), vehicle control (buffer solution on absorbable collagen sponge [ACS], n = 3), autologous bone graft (n = 3), or rhBMP-2 repair (rhBMP-2/ACS, n = 10). Animals underwent computed tomography imaging at 0, 2, 4, and 6 weeks postoperatively, followed by euthanization and histological analysis. Percent healing was determined by 3-dimensional analysis. A (time × group) 2-way analysis of variance was performed on healing versus treatment group and postoperative time.

RESULTS

At 6 weeks postoperatively, rhBMP-2/ACS and autologous bone graft resulted in 93% and 68% healing, respectively, whereas the empty and vehicle control treatment resulted in 27% and 26% healing (P < 0.001). Histologically, compared to autologous bone graft, bone in the rhBMP-2/ACS group was more cellular and more consistently continuous with wound margins.

CONCLUSIONS

The rhBMP-2 therapy is effective in achieving radiographic coverage of previously infected calvarial defects.

Infection, inflammation, and bone regeneration: a paradoxical relationship

Various strategies have been developed to promote bone regeneration in the craniofacial region. Most of these interventions utilize implantable materials or devices. Infections resulting from colonization of these implants may result in local tissue destruction in a manner analogous to periodontitis. This destruction is mediated via the expression of various inflammatory mediators and tissue-destructive enzymes. Given the well-documented association among microbial biofilms, inflammatory mediators, and tissue destruction, it seems reasonable to assume that inflammation may interfere with bone healing and regeneration. Paradoxically, recent evidence also suggests that the presence of certain pro-inflammatory mediators is actually required for bone healing. Bone injury (e.g., subsequent to a fracture or surgical intervention) is followed by a choreographed cascade of events, some of which are dependent upon the presence of pro-inflammatory mediators. If inflammation resolves promptly, then proper bone healing may occur. However, if inflammation persists (which might occur in the presence of an infected implant or graft material), then the continued inflammatory response may result in suboptimal bone formation. Thus, the effect of a given mediator is dependent upon the temporal context in which it is expressed. Better understanding of this temporal sequence may be used to optimize regenerative outcomes.

Infection and tissue engineering in segmental bone defects--a mini review

As tissue engineering becomes more of a clinical reality through the ongoing bench to bedside transition, research in this field must focus on addressing relevant clinical situations. Although most in vivo work in the area of bone tissue engineering focuses on bone regeneration within sterile, surgically created defects, there is a growing need for the investigation of bone tissue engineering approaches within contaminated or scarred wound beds, such as those that may be encountered following traumatic injury or during delayed reconstruction/regeneration. Significant work has been performed in the area of local drug delivery via biomaterial carriers, but there is little intersection in the available literature between antibiotic delivery and tissue regeneration. In this review, we examine recent advances in segmental bone defect animal models, bone tissue engineering, and drug delivery with the goal of identifying promising approaches and areas needing further investigation towards developing both a better understanding of and new tissue engineering approaches for addressing infection control while simultaneously initiating bone regeneration.

Recent advances in the use of serological bone formation markers to monitor callus development and fracture healing

The failure of an osseous fracture to heal, or the development of a nonunion, is common; however, current diagnostic measures lack the capability of early and reliable detection of such events. Analyses of radiographic imaging and clinical examination, in combination, remain the gold standard for diagnosis; however, these methods are not reliable for early detection. Delayed diagnosis of a nonunion is costly from both the patient and treatment standpoints. In response, repeated efforts have been made to identify bone metabolic markers as diagnostic or prognostic tools for monitoring bone healing. Thus far, the evidence regarding a correlation between the kinetics of most bone metabolic markers and nonunion is very limited. With the aim of classifying the role of biological pathways of bone metabolism and of understanding bone conditions in the development of osteoporosis, advances have been made in our knowledge of the molecular basis of bone remodeling, fracture healing, and its failure. Procollagen type I amino-terminal propeptide has been shown to be a reliable bone formation marker in osteoporosis therapy and its kinetics during fracture healing has been recently described. In this article, we suggest that procollagen type I amino-terminal propeptide presents a good opportunity for early detection of nonunion. We also review the role and potential of serum PINP, as well as other markers, as indications of fracture healing.

Low-intensity pulsed ultrasound produced an increase of osteogenic genes expression during the process of bone healing in rats

The aim of this study was to measure the temporal expression of osteogenic genes during the process of bone healing in low-intensity pulsed ultrasound (LIPUS) treated bone defects by means of histopathologic and real-time polymerase chain reaction (PCR) analysis. Animals were randomly distributed into two groups (n = 30): control group (bone defect without treatment) and LIPUS treated (bone defect treated with LIPUS). On days 7, 13 and 25 postinjury, 10 rats per group were sacrificed. Rats were treated with a 30 mW/cm(2) LIPUS. The results pointed out intense new bone formation surrounded by highly vascularized connective tissue presenting a slight osteogenic activity, with primary bone deposition was observed in the group exposed to LIPUS in the intermediary (13 days) and late stages of repair (25 days) in the treated animals. In addition, quantitative real-time polymerase chain reaction (RT-qPCR) showed an upregulation of bone morphogenetic protein 4 (BMP4), osteocalcin and Runx2 genes 7 days after the surgery. In the intermediary period, there was no increase in the expression. The expression of alkaline phosphatase, BMP4 and Runx2 was significantly increased at the last period. Our results indicate that LIPUS therapy improves bone repair in rats and upregulated osteogenic genes, mainly at the late stages of recovery.

Infection

Musculoskeletal infection is a clinical problem with significant direct healthcare costs. The prevalence of infection after closed, elective surgery is frequently estimated to be less than 2%, but in severe injuries, posttraumatic infection rates have been reported as 10% or greater. Although clinical infections are found outside the realm of medical devices, it is clear that the enormous increase of infections associated with the use of implants presents a major challenge worldwide. This review summarizes recent advances in the understanding, diagnosis, and treatment of musculoskeletal infections.