Experimental and Numerical Models of Complex Clinical Scenarios; Strategies to Improve Relevance and Reproducibility of Joint Replacement Research

This research review aims to focus attention on the effect of specific surgical and host factors on implant fixation, and the importance of accounting for them in experimental and numerical models. These factors affect (a) eventual clinical applicability and (b) reproducibility of findings across research groups. Proper function and longevity for orthopedic joint replacement implants relies on secure fixation to the surrounding bone. Technology and surgical technique has improved over the last 50 years, and robust ingrowth and decades of implant survival is now routinely achieved for healthy patients and first-time (primary) implantation. Second-time (revision) implantation presents with bone loss with interfacial bone gaps in areas vital for secure mechanical fixation. Patients with medical comorbidities such as infection, smoking, congestive heart failure, kidney disease, and diabetes have a diminished healing response, poorer implant fixation, and greater revision risk. It is these more difficult clinical scenarios that require research to evaluate more advanced treatment approaches. Such treatments can include osteogenic or antimicrobial implant coatings, allo- or autogenous cellular or tissue-based approaches, local and systemic drug delivery, surgical approaches. Regarding implant-related approaches, most experimental and numerical models do not generally impose conditions that represent mechanical instability at the implant interface, or recalcitrant healing. Many treatments will work well in forgiving settings, but fail in complex human settings with disease, bone loss, or previous surgery. Ethical considerations mandate that we justify and limit the number of animals tested, which restricts experimental permutations of treatments. Numerical models provide flexibility to evaluate multiple parameters and combinations, but generally need to employ simplifying assumptions. The objectives of this paper are to (a) to highlight the importance of mechanical, material, and surgical features to influence implant-bone healing, using a selection of results from two decades of coordinated experimental and numerical work and (b) discuss limitations of such models and the implications for research reproducibility. Focusing model conditions toward the clinical scenario to be studied, and limiting conclusions to the conditions of a particular model can increase clinical relevance and research reproducibility

Sensitivity analysis of periprosthetic healing to cell migration, growth factor and post-operative gap using a mechanobiological model

A theoretical rationale, which could help in the investigation of mechanobiological factors affecting periprosthetic tissue healing, is still an open problem. We used a parametric sensitivity analysis to extend a theoretical model based on reactive transport and computational cell biology. The numerical experimentation involved the drill hole, the haptotactic and chemotactic migrations, and the initial concentration of an anabolic growth factor. Output measure was the mineral fraction in tissue surrounding a polymethymethacrylate (PMMA) canine implant (stable loaded implant, non-critical gap). Increasing growth factor concentration increased structural matrix synthesis. A cell adhesion gradient resulted in heterogeneous bone distribution and a growth factor gradient resulted in homogeneous bone distribution in the gap. This could explain the radial variation of bone density from the implant surface to the drill hole, indicating less secure fixation. This study helps to understand the relative importance of various host and clinical factors influencing bone distribution and resulting implant fixation

Augmentation of implant surfaces with BMP-2 in a revision setting:effects of local and systemic bisphosphonate

AIMS: We wanted to evaluate the effects of a bone anabolic agent (bone morphogenetic protein 2 (BMP-2)) on an anti-catabolic background (systemic or local zoledronate) on fixation of allografted revision implants. METHODS: An established allografted revision protocol was implemented bilaterally into the stifle joints of 24 canines. At revision surgery, each animal received one BMP-2 (5 µg) functionalized implant, and one raw implant. One group (12 animals) received bone graft impregnated with zoledronate (0.005 mg/ml) before impaction. The other group (12 animals) received untreated bone graft and systemic zoledronate (0.1 mg/kg) ten and 20 days after revision surgery. Animals were observed for an additional four weeks before euthanasia. RESULTS: No difference was detected on mechanical implant fixation (load to failure, stiffness, energy) between local or systemic zoledronate. Addition of BMP-2 had no effect on implant fixation. In the histomorphometric evaluation, implants with local zoledronate had more area of new bone on the implant surface (53%, p = 0.025) and higher volume of allograft (65%, p = 0.007), whereas implants in animals with systemic zoledronate had the highest volume of new bone (34%, p = 0.003). Systemic zoledronate with BMP-2 decreased volume of allograft by 47% (p = 0.017). CONCLUSION: Local and systemic zoledronate treatment protects bone at different stages of maturity; local zoledronate protects the allograft from resorption and systemic zoledronate protects newly formed bone from resorption. BMP-2 in the dose evaluated with experimental revision implants was not beneficial, since it significantly increased allograft resorption without a significant compensating anabolic effect. Cite this article: Bone Joint Res 2021;10(8):488–497

The effect of chicken, pigeon, and turkey demineralized bone matrix (DBM) implanted in ulnar defects fixed with the intramedullary-external skeletal fixator (IM-ESF) tie-in in pigeons (Columba livia): histological evaluations

This study was conducted to evaluate the efficacy of chicken, pigeon and turkey demineralized bone matrix (DBM) powder in stimulating the healing process in 1-cm ulna defects in pigeons. A total of 9, 11 and 9 pigeon ulnas with 1-cm defect were treated with chicken, pigeon and turkey DBM, respectively. Avian DBM prepared from chicken, pigeon and turkey sources induced bone formation via endochondral and intramembranous processes, as in mammalian studies. No significant differences were observed in the percentage of new bone, percentage of cartilage, surface-forming osteoblast area, or osteoclast count between gaps treated with chicken, pigeon, and turkey DBM. However, a significantly (p<0.05) higher percentage of inflammatory area was observed in gaps treated with chicken DBM than in gaps treated with pigeon DBM

Understanding the Virginia Literacy Act

This research and policy brief from the Metropolitan Educational Research Consortium (MERC) offers an overview of the Virginia Literacy Act. It is structured to explore the following questions: 1) What are the recent trends in reading achievement in Virginia? 2) What are the policy implications of the VLA for Virginia school divisions? 3) What does the research say about Science of Reading (SoR)? 4) What core instructional programs are approved to meet the VLA? It concludes with a series of key takeaways and recommendations

Effect of local TGF-β1 and IGF-1 release on implant fixation: comparison with hydroxyapatite coating: A paired study in dogs

Background and purpose Hydroxyapatite (HA) coating stimulates the osseointegration of cementless orthopedic implants. Recently, locally released osteogenic growth factors have also been shown experimentally to stimulate osseointegration so that bone fills gaps around orthopedic implants. Here, we have compared the effect of local release of TGF-β 1 and IGF-1 with that of hydroxyapatite coating on implant fixation

Parathyroid Hormone Treatment Increases Fixation of Orthopedic Implants with Gap Healing: A Biomechanical and Histomorphometric Canine Study of Porous Coated Titanium Alloy Implants in Cancellous Bone

Parathyroid hormone (PTH) administered intermittently is a bone-building peptide. In joint replacements, implants are unavoidably surrounded by gaps despite meticulous surgical technique and osseointegration is challenging. We examined the effect of human PTH(1–34) on implant fixation in an experimental gap model. We inserted cylindrical (10 × 6 mm) porous coated titanium alloy implants in a concentric 1-mm gap in normal cancellous bone of proximal tibia in 20 canines. Animals were randomized to treatment with PTH(1–34) 5 μg/kg daily. After 4 weeks, fixation was evaluated by histomorphometry and push-out test. Bone volume was increased significantly in the gap. In the outer gap (500 μm), the bone volume fraction median (interquartile range) was 27% (20–37%) for PTH and 10% (6–14%) for control. In the inner gap, the bone volume fraction was 33% (26–36%) for PTH and 13% (11–18%) for control. At the implant interface, the bone fraction improved with 16% (11–20%) for PTH and 10% (7–12%) (P = 0.07) for control. Mechanical implant fixation was improved for implants exposed to PTH. For PTH, median (interquartile range) shear stiffness was significantly higher (PTH 17.4 [12.7–39.7] MPa/mm and control 8.8 [3.3–12.4] MPa/mm) (P < 0.05). Energy absorption was significantly enhanced for PTH (PTH 781 [595–1,198.5] J/m2 and control 470 [189–596] J/m2). Increased shear strength was observed but was not significant (PTH 3.0 [2.6–4.9] and control 2.0 [0.9–3.0] MPa) (P = 0.08). Results show that PTH has a positive effect on implant fixation in regions where gaps exist in the surrounding bone. With further studies, PTH may potentially be used clinically to enhance tissue integration in these challenging environments

Feminist Economics, Setting out the Parameters

___Introduction___ Feminist economics has developed its position over the past decade, towards a firmer embeddedness in economic science and a source of inspiration for activists, policy makers, and social science researchers in a wide variety of fields of research. This development has come about in a relatively short period of time, as is reflected, for example, in the follow-up book of the feminist economic primer Beyond Economic Man (Ferber/Nelson 1993), published ten years later: Feminist Economics Today (Ferber/Nelson, 2003) The strengthened position of feminist economics also shows in the 10-year anniversary of the prize-winning journal Feminist Economics, the flourishing of the International Association for Feminist Economics (IAFFE), as well as the more regular demand for feminist economic policy advise by institutions like the UN, OECD and governments in developed and developing countries, and in well-established training courses in feminist economics, such as at the Institute of Social Studies and University of Utah . It is impossible to give a fair overview of the state of the art of feminist economics in the number of pages available, even when limited to issues pertaining to development and macroeconomics . As a consequence, this is a very sketchy and subjective overview of what I perceive to be recent developments in feminist economics that have relevance for feminist development analysis and policy. The next section recognizes three trends in feminist economics, in particular the engagement of feminist economists with heterodox schools of economics. The following sections will briefly review developments in methodology and methods in feminist economics. These will be followed by three sections on topics that have recently become key themes or areas of research in feminist economics, in particular in the area of development economics: unpaid labour and the care economy; the two-way relationship between gender and trade; and gender, efficiency and growth. Each of these topics will be introduced, with references to the main literature, and some links to policy recommendations. The paper will end with a conclusion