Managing atrophic nonunion in the geriatric population: incidence, distribution, and causes

Mesenchymal stem cells derived from the fibrotic tissue of atrophic nonunion or the bone marrow of iliac crest: A donor-matched comparison

Purpose

Atrophic nonunion is one of the most difficult complications of fracture. The cellular factors that contribute to atrophic nonunion are poorly understood, and mesenchymal stem cells (MSCs) are recognized as the key contributor to bone formation. This study aimed to characterize the MSCs isolated from the fibrotic tissue of atrophic nonunion (AN-MSCs) from the perspective of proliferation, differentiation potential, senescence, and paracrine function.

Methods

Human atrophic fibrotic tissue was obtained from four donors aged 29-37 for isolating AN-MSCs, and donor-matched bone marrow acquired from the iliac crest for isolating MSCs (IC-MSCs) as control. The AN-MSCs or IC-MSCs in passage 3 were applied for the following evaluations. The surface markers expressed on the two cells were evaluated using flow cytometry. The proliferation of the two cells for up to 11 days was comparatively investigated. After osteogenic, chondrogenic, or adipogenic induction, multi-lineage differentiation of AN-MSCs or IC-MSCs was comparatively evaluated using lineage-specific stains and lineage-specific gene expression. Enzyme-linked immunosorbent assay (ELISA) assessment was applied to evaluate the paracrine function of AN-MSCs or IC-MSCs. Cellular senescence of AN-MSCs or IC-MSCs was evaluated using senescence-associated β-galactosidase (SA-β-gal) staining.

Results

AN-MSCs or IC-MSCs from the four donors showed morphologic and immunophenotypic characteristics of MSCs, with the expression of MSCs markers and negative expression of hematopoietic markers. In general, AN-MSCs showed similar proliferation and adipogenic capacity with IC-MSCs. In contrast, IC-MSCs showed significantly higher osteogenic and chondrogenic capacity compared to AN-MSCs. Moreover, the culture medium of IC-MSCs contains significantly higher levels of VEGF, TGF-β1, PDGF-BB, and IGF-1 than the culture medium of AN-MSCs. Lastly, the AN-MSCs are more prone to cellular senescence than the IC-MSCs.

Conclusions

In-vitro, AN-MSCs were similar to IC-MSCs in proliferation and adipogenic capacity, but inferior to IC-MSCs in osteogenic and chondrogenic capacity, paracrine function, and anti-senescence.

Operative treatment of nonunions in the elderly: Clinical and radiographic outcomes in patients at minimum 75 years of age

BACKGROUND

Limited information exists on nonunion treatment in the elderly. This retrospective study evaluates whether results of operative treatment of nonunion of the humerus or femur in patients aged ≥ 75 years are comparable to those in younger patients.

METHODS

We identified patients age ≥ 75 years with a nonunion of humerus or femur treated with open reduction and internal fixation. The Non-Union Scoring System was calculated. Complications, clinical outcome, and radiographic findings were assessed. Primary endpoint was nonunion healing. A literature review compared time to healing of humeral and femoral nonunion in younger populations.

RESULTS

We identified 45 patients treated for a nonunion of humerus or femur with > 12 months follow-up. Median age was 79 years (range 75-96). Median time to presentation was 12 months (range 4-127) after injury, median number of prior surgeries was 1 (range 0-4). Union rate was 100%, with median time to union 6 months (range 2-42). Six patients underwent revision for persistent nonunion and healed without further complications.

CONCLUSIONS

Using a protocol of debridement, alignment, compression, stable fixation, bone grafting and early motion, patients aged 75 years or older can reliably achieve healing when faced with a nonunion of the humerus or femur.

LEVEL OF EVIDENCE

IV.

Drill-Hole Bone Defects in Animal Models of Bone Healing: Protocol for a Systematic Review

Background

Bone fractures are common conditions of the musculoskeletal system. Several animal models of bone fractures have been established to help elucidate the complex process of bone healing. In the last decades, drill-hole bone defects have emerged as a method to study bone healing. Animal models of drill-hole defects are easy to standardize and do not require external fixation of the bone. However, current studies of drill-hole bone defects lack detailed descriptions of techniques and interstudy standardization.

Objective

This systematic review aims to present a detailed description of the different methods used to induce drill-hole bone defects in long bones of laboratory animals and to provide a comprehensive overview of their methodology and potential for investigation of bone healing.

Methods

A systematic search of PubMed and Embase will be performed of abstracts containing variations of the following four keywords: “long bone,” “drill-hole,” “regeneration,” and “animal model.” Abstract screening and full-text screening will be performed independently by 2 reviewers, and data will be extracted to a predesigned extraction protocol. The primary outcome of the included studies is the technique used to create the drill-hole bone defect, and secondary outcomes are any measurements or analyses of bone defect and regeneration. A narrative synthesis will be used to present the primary outcome, while information on secondary outcomes will be displayed graphically. The study protocol follows the PRISMA-P (Preferred Reporting Items for Systematic Review and Meta-analysis Protocols) guidelines.

Results

Abstract and full-text screening is ongoing and is expected to be completed by October 2022. Data extraction will commence immediately after, and the manuscript is expected to be completed by December 2023. The systematic review will follow the PRISMA statement.

Conclusions

The strength of this systematic review is that it provides a comprehensive methodological overview of the different drill-hole methods and their advantages and disadvantages. This will assist researchers in choosing which model to use when studying different aspects of bone healing.

Trial Registration

International Prospective Register of Systematic Reviews CRD42020213076; https://tinyurl.com/bp56wdwe

International Registered Report Identifier (IRRID)

PRR1-10.2196/34887

Modifying MSC Phenotype to Facilitate Bone Healing: Biological Approaches

Healing of fractures and bone defects normally follows an orderly series of events including formation of a hematoma and an initial stage of inflammation, development of soft callus, formation of hard callus, and finally the stage of bone remodeling. In cases of severe musculoskeletal injury due to trauma, infection, irradiation and other adverse stimuli, deficient healing may lead to delayed or non-union; this results in a residual bone defect with instability, pain and loss of function. Modern methods of mechanical stabilization and autologous bone grafting are often successful in achieving fracture union and healing of bone defects; however, in some cases, this treatment is unsuccessful because of inadequate biological factors. Specifically, the systemic and local microenvironment may not be conducive to bone healing because of a loss of the progenitor cell population for bone and vascular lineage cells. Autologous bone grafting can provide the necessary scaffold, progenitor and differentiated lineage cells, and biological cues for bone reconstruction, however, autologous bone graft may be limited in quantity or quality. These unfavorable circumstances are magnified in systemic conditions with chronic inflammation, including obesity, diabetes, chronic renal disease, aging and others. Recently, strategies have been devised to both mitigate the necessity for, and complications from, open procedures for harvesting of autologous bone by using minimally invasive aspiration techniques and concentration of iliac crest bone cells, followed by local injection into the defect site. More elaborate strategies (not yet approved by the U.S. Food and Drug Administration-FDA) include isolation and expansion of subpopulations of the harvested cells, preconditioning of these cells or inserting specific genes to modulate or facilitate bone healing. We review the literature pertinent to the subject of modifying autologous harvested cells including MSCs to facilitate bone healing. Although many of these techniques and technologies are still in the preclinical stage and not yet approved for use in humans by the FDA, novel approaches to accelerate bone healing by modifying cells has great potential to mitigate the physical, economic and social burden of non-healing fractures and bone defects.

Suppression of Notch Signaling in Osteoclasts Improves Bone Regeneration and Healing

Owing to the central role of osteoclasts in bone physiology and remodeling, manipulation of their maturation process provides a potential therapeutic strategy for treating bone diseases. To investigate this, we genetically inhibited the Notch signaling pathway in the myeloid lineage, which includes osteoclast precursors, using a dominant negative form of MAML (dnMAML) that inhibits the transcriptional complex required for downstream Notch signaling. Osteoclasts derived from dnMAML mice showed no significant differences in early osteoclastic gene expression compared to the wild type. Further, these demonstrated significantly lowered resorption activity using bone surfaces while retaining their osteoblast stimulating ability using ex vivo techniques. Using in vivo approaches, we detected significantly higher bone formation rates and osteoblast gene expression in dnMAML cohorts. Further, these mice exhibited increased bone/tissue mineral density compared to wild type and larger bony calluses in later stages of fracture healing. These observations suggest that therapeutic suppression of osteoclast Notch signaling could reduce, but not eliminate, osteoclastic resorption without suppression of restorative bone remodeling and, therefore, presents a balanced paradigm for increasing bone formation, regeneration, and healing. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:2089-2103, 2019.

Nonunion fractures, mesenchymal stem cells and bone tissue engineering

Depending on the duration of healing process, 5-10% of bone fractures may result in either nonunion or delayed union. Because nonunions remain a clinically important problem, there is interest in the utilization of tissue engineering strategies to augment bone fracture repair. Three basic biologic elements that are required for bone regeneration include cells, extracellular matrix scaffolds and biological adjuvants for growth, differentiation and angiogenesis. Mesenchymal stem cells (MSCs) are capable to differentiate into various types of the cells including chondrocytes, myoblasts, osteoblasts, and adipocytes. Due to their potential for multilineage differentiation, MSCs are considered important contributors in bone tissue engineering research. In this review we highlight the progress in the application of biomaterials, stem cells and tissue engineering in promoting nonunion bone fracture healing. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A:2551-2561, 2018.

Bone intramedullary reaming grafts the fracture site with CD146+ skeletal progenitors and downmodulates the inflammatory environment

INTRODUCTION

Femoral shaft fractures generally occur in young adults following a high-energy trauma and are prone to delayed union/non-union. Novel therapies to stimulate bone regeneration will have to mimic some of the aspects of the biology of fracture healing; however, which are these aspects is unclear. Locked intramedullary nailing is the current treatment of choice for the stabilisation of femur shaft fractures, and it is associated with accelerated healing and increased union rates. These benefits were partially attributed to the reaming procedure, which, regardless of significantly destroying the haematoma, stimulates the healing response. To better understand how reaming influences healing, we evaluated the viability of the nucleated cell fraction and the frequency of CD146⁺ skeletal progenitors, which contain multipotent cells, in the post-reaming haematoma. We also screened the concentrations of inflammatory mediators and growth factors in the fracture site after reaming compared with those in the original haematoma.

METHODS

Pre- and post-reaming haematomas were percutaneously aspirated from the fracture site of 15 patients with closed femoral shaft fractures. Cellular viability and the percentage of CD146+ progenitors were analysed by flow cytometry. The concentrations of cytokines and growth factors were determined by ELISA.

RESULTS

AnnexinV/Pi analysis showed that the viability of the total nucleated cell fraction was decreased in the post-reaming haematoma. However, the procedure increased the percentage of CD146+ skeletal progenitors in the fracture site. Analysis of cytokines and growth factors in supernatants showed a decreased concentration of the inflammatory mediators IL-6, CCL-4, and MCP-1, along with an increase of anti-inflammatory IL-10, and the growth factors bFGF and PDGF-AB.

CONCLUSION

These findings support the view that the positive effects of reaming on fracture healing might result from mechanically grafting the fracture site with a population of skeletal progenitors that contain multipotent cells; transitioning the signalling environment to a less inflammatory state, and enhancing the availability of specific osteogenic and angiogenic factors. A better understanding of the requisite stimuli for optimal bone repair, considering the disturbances made by orthopaedic treatments, will be determinant for the development of innovative treatments for bone repair.

Surgically‑induced mouse models in the study of bone regeneration: Current models and future directions (Review)

Bone regeneration has been extensively studied over the past several decades. The surgically‑induced mouse model is the key animal model for studying bone regeneration, of the various research strategies used. These mouse models mimic the trauma and recovery processes in vivo and serve as carriers for tissue engineering and gene modification to test various therapies or associated genes in bone regeneration. The present review introduces a classification of surgically induced mouse models in bone regeneration, evaluates the application and value of these models and discusses the potential development of further innovations in this field in the future.

Bone fracture healing: cell therapy in delayed unions and nonunions

Bone fracture healing impairment related to mechanical problems has been largely corrected by advances in fracture management. Better protocols, more strict controls of time and function, and hardware and surgical technique evolution have contributed to better prognosis, even in complex fractures. However, atrophic nonunion persists in clinical cases where, for different reasons, the osteogenic capability is impaired. When this is the case, a better understanding of the basic mechanisms under bone repair and augmentation techniques may put in perspective the current possibilities and future opportunities. Among those, cell therapy particularly aims to correct this insufficient osteogenesis. However, the launching of safe and efficacious cell therapies still requires substantial amount of research, especially clinical trials. This review will envisage the current clinical trials on bone healing augmentation based on cell therapy, with the experience provided by the REBORNE Project, and the insight from investigator-driven clinical trials on advanced therapies towards the future. This article is part of a Special Issue entitled Stem Cells and Bone.

Vitamin D and bone fracture healing

AIM: To examine whether vitamin D is of potential relevance in the healing process of fractures.

METHODS: The present narrative review examined the bulk of the evidence based literature on the topic of vitamin D and bone healing in key electronic data bases from 1980 onwards using the terms vitamin D and bone healing, callus, fracture healing. All data were examined carefully and categorized according to type of study. A summary of the diverse terms and approaches employed in the research, as well as the rationale for hypothesizing vitamin D has a role in fracture healing was detailed.

RESULTS: The results show very few human studies have been conducted to examine if vitamin D is effective at promoting post fracture healing, and the different animal models that have been studied provide no consensus on this topic. The terms used in the related literature, as well as the methods used to arrive at conclusions on this clinical issue are highly diverse, there is no standardization of either of these important terms and methodologies, hence no conclusive statements or clinical guidelines can be forthcoming. There is a strong rational for continuing to examine if vitamin D supplements should be administered post-fracture, and ample evidence vitamin D is an essential hormone for functioning in general, as well as bone health and muscle as this relates to bone density.

CONCLUSION: Whether those with low vitamin D levels can benefit from supplements if their nutritional practices do not cover recommended daily amounts, remains in question.