Concentrated autologous bone marrow aspirate is not "stem cell" therapy in the repair of nonunions and bone defects

Research Progress of Bone Grafting: A Comprehensive Review

Bone tissue, the second most transplanted tissue after blood, is utilized in over 2.2 million bone grafts annually to address various bone-related conditions including fractures, tumors, bone infections, scoliosis, congenital defects, osteoporosis, osteoarthritis, and osteogenesis imperfecta. According to incomplete statistics, $4.3 billion was spent on bone graft materials in 2015 alone, with projections suggesting this figure may reach $66 billion by 2026. The limited availability of autogenous bone graft considered the gold standard due to their three critical biological properties: osteoconduction, osteoinduction, and osteogenesis-alongside the increasing global aging population, may be contributing to this rising expenditure. Furthermore, advancements in biomaterials and engineering technologies have created opportunities for the exploration of new bone graft substitutes. In this review, we will examine the fundamental structure of natural bone and the characteristics of ideal bone graft, highlighting common bone graft materials currently available, such as true bone ceramics, decalcified bone matrix, freeze-dried bone and demineralized freeze-dried bone, bioactive glasses, bone marrow aspirate concentrate, polymer nanocomposites, which have different characteristics in osteogenic, osteoconductivity, osteoinductivity, biocompatibility, mechanical properties, and resorption. How to utilize its advantages to maximize the osteogenic effect will be the focus of this review, and some of the current challenges in the field of bone grafting will be identified, outlining potential directions for future development. In conclusion, the choice of bone graft is critical to bone repair and regeneration, and a comprehensive understanding of the advantages and disadvantages of bone graft materials can improve the effectiveness of related surgical interventions.

The Advantages and Shortcomings of Stem Cell Therapy for Enhanced Bone Healing

This review explores the regenerative potential of key progenitor cell types and therapeutic strategies to improve healing of complex fractures and bone defects. We define, summarize, and discuss the differentiation potential of totipotent, pluripotent, and multipotent stem cells, emphasizing the advantages and shortcomings of cell therapy for bone repair and regeneration. The fundamental role of mesenchymal stem cells is highlighted due to their multipotency to differentiate into the key lineage cells including osteoblasts, osteocytes, and chondrocytes, which are crucial for bone formation and remodeling. Hematopoietic stem cells (HSCs) also play a significant role; immune cells such as macrophages and T-cells modulate inflammation and tissue repair. Osteoclasts are multinucleated cells that are important to bone remodeling. Vascular progenitor (VP) cells are critical to oxygen and nutrient supply. The dynamic interplay among these lineages and their microenvironment is essential for effective bone restoration. Therapies involving cells that are more than "minimally manipulated" are controversial and include embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs). ESCs, derived from early-stage embryos, possess pluripotent capabilities and have shown promise in preclinical studies for bone healing. iPSCs, reprogrammed from somatic cells, offer personalized medicine applications and can differentiate into various tissue-specific cell lines. Minimally manipulative cell therapy approaches such as the use of bone marrow aspirate concentrate (BMAC), exosomes, and various biomaterials for local delivery are explored for their effectiveness in bone regeneration. BMAC, which contains mostly immune cells but few mesenchymal and VPs, probably improves bone healing by facilitating paracrine-mediated intercellular communication. Exosome isolation harnesses the biological signals and cellular by-products that are a primary source for cell crosstalk and activation. Safe, efficacious, and cost-effective strategies to enhance bone healing using novel cellular therapies are part of a changing paradigm to modulate the inflammatory, repair, and regenerative pathways to achieve earlier more robust tissue healing and improved physical function. Impact Statement Stem cell therapy holds immense potential for bone healing due to its ability to regenerate damaged tissue. Nonmanipulated bone marrow aspirate contains mesenchymal stem cells that promote bone repair and reduce healing time. Induced pluripotent stem cells offer the advantage of creating patient-specific cells that can differentiate into osteoblasts, aiding in bone regeneration. Other delivery methods, such as scaffold-based techniques, enhance stem cell integration and function. Collectively, these approaches can improve treatment outcomes, reduce recovery periods, and advance our understanding of bone healing mechanisms, making them pivotal in orthopedic research and regenerative medicine.

The interactions of macrophages, lymphocytes, and mesenchymal stem cells during bone regeneration

Bone regeneration and repair are crucial to ambulation and quality of life. Factors such as poor general health, serious medical comorbidities, chronic inflammation, and ageing can lead to delayed healing and nonunion of fractures, and persistent bone defects. Bioengineering strategies to heal bone often involve grafting of autologous bone marrow aspirate concentrate (BMAC) or mesenchymal stem cells (MSCs) with biocompatible scaffolds. While BMAC shows promise, variability in its efficacy exists due to discrepancies in MSC concentration and robustness, and immune cell composition. Understanding the mechanisms by which macrophages and lymphocytes - the main cellular components in BMAC - interact with MSCs could suggest novel strategies to enhance bone healing. Macrophages are polarized into pro-inflammatory (M1) or anti-inflammatory (M2) phenotypes, and influence cell metabolism and tissue regeneration via the secretion of cytokines and other factors. T cells, especially helper T1 (Th1) and Th17, promote inflammation and osteoclastogenesis, whereas Th2 and regulatory T (Treg) cells have anti-inflammatory pro-reconstructive effects, thereby supporting osteogenesis. Crosstalk among macrophages, T cells, and MSCs affects the bone microenvironment and regulates the local immune response. Manipulating the proportion and interactions of these cells presents an opportunity to alter the local regenerative capacity of bone, which potentially could enhance clinical outcomes.

Bone marrow aspirate and bone marrow aspirate concentrate: Does the literature support use in long-bone nonunion and provide new insights into mechanism of action?

PURPOSE

To assess the use of bone marrow aspirate (BM) and bone marrow aspirate concentrate (BMAC) in the treatment of long-bone nonunion and to understand mechanism of action.

METHODS

A systematic review of PubMed and EBSCOHost was completed to identify studies that investigated the use of BM or BMAC for the diagnosis of delayed union and/or nonunion of long-bone fractures. Studies of isolated bone marrow-mesenchymal stem cells (BM-MSCs) and use in non-long-bone fractures were excluded. Statistical analysis was confounded by heterogeneous fracture fixation methods, treatment history, and scaffold use.

RESULTS

Our initial search yielded 430 publications, which was screened down to 25 studies. Successful treatment in aseptic nonunion was reported at 79-100% (BM) and 50-100% (BMAC). Septic nonunion rates were slightly better at 73-100% (BM) and 83.3-100% (BMAC). 18/24 studies report union rates > 80%. One study reports successful treatment of septic nonunion with BMAC and no antibiotics. A separate study reported a significant reduction in autograft reinfection rate when combined with BMAC (P = 0.009). Major adverse events include two deep infections at injection site and one case of heterotopic ossification. Most studies note transient mild donor site discomfort and potential injection site discomfort attributed to needle size.

CONCLUSION

The current literature pertaining to use of BM/BMAC for nonunion is extremely heterogeneous in terms of patient population and concomitant treatment modalities. While results are promising for use of BM/BMAC with other gold standard treatment methodologies, the literature requires additional Level I data to clarify the impact of role BM/BMAC in treating nonunion when used alone and in combination with other modalities.

LEVEL OF EVIDENCE

Level III.

Bone Marrow Aspirate Concentrate for Treatment of Primary Knee Osteoarthritis: A Prospective, Single-Center, Non-randomized Study with 2-Year Follow-Up

Introduction

Knee osteoarthritis (OA) is a widespread, disabling condition with no intervention to fully restore cartilage or halt progression. Bone marrow aspirate concentrate (BMAC), an autologous product from bone marrow aspiration, has shown promise as a regenerative therapy due to its cell composition and chondrogenic effects. Our study aims to assess the functional outcomes, including pain, function, satisfaction, and complications post-BMAC injection in knee OA patients.

Materials and Methods

In this prospective, single-center study, 63 patients with grade II-III knee OA (Kellgren-Lawrence (K-L) scale) unresponsive to conservative management underwent BMAC injection. The procedure involved bone marrow aspiration from the anterior iliac crest, processing to obtain a concentrate, followed by intra-articular injection. Patients were followed for 24 months, assessing outcomes using the Visual Analog Scale (VAS), International Knee Documentation Committee (IKDC) score, and MOCART 2.0 score.

Results

The cohort, with a slight female predominance and predominantly aged 41-50 years, majorly comprised K-L grade III OA patients. BMAC treatment resulted in significant improvements in VAS pain scores, IKDC functional scores, and MOCART 2.0 scores over the 24-month follow-up.

Conclusion

BMAC injection provides significant improvement in both pain and functional outcomes at mid-term follow-up in patients with mild-to-moderate OA of the knee. Further high-quality, adequately powered, multi-center, prospective, double-blinded, randomized controlled trials with longer follow-up are necessary to justify the routine clinical use of BMAC for treatment of patients suffering with knee OA.

Graphical Abstract

Skin and Bone Regeneration of Solid Bone Marrow Aspirate Concentrate Versus Platelet-Rich Fibrin

Solid bone marrow aspirate concentrate (sBMAC) is harvested from bone marrow aspirate without anticoagulants by a centrifugation protocol similar to that for platelet-rich fibrin (PRF) prepared from peripheral blood. It was hypothesized that sBMAC could accelerate not only wound healing but also bone regeneration because of the abundant growth factor (GF) releases from enriched bone marrow cells. The purpose of the present study was to investigate skin wound healing and bone regenerative potential of sBMAC compared with arterial blood-derived PRF (Ar-PRF) and venous blood-derived PRF (Ve-PRF) in a skin defect and calvarial bone defect model in rabbits. GF release assays revealed significantly higher release of transforming growth factor-β (TGF-β), alkaline phosphatase (ALP), and osteocalcin (OCN) from sBMAC compared with PRFs for 24 h. In the skin defect animal model, sBMAC and PRFs promoted wound bed angiogenesis and re-epithelization in skin defect sites with higher collagen 1 synthesis, cytokeratin AE1/AE3, vascular endothelial growth factor (VEGF) expressions on week 1. Furthermore, a calvarial defect assay revealed that sBMAC promoted new bone formation with a sufficient bone marrow structure similar to that of intact bone in the bone defects. Ar-PRF achieved the second highest bone closure and new bone volume but yielded new bone that was thinner than the intact bone. In conclusion, sBMAC treatment might be a good option instead of PRF as an adjuvant therapy for both skin and bone tissue regeneration therapies in certain clinical situations. Impact statement Solid bone marrow aspirate concentrate (sBMAC) is new type of clot material prepared from bone marrow aspirate. The present study for the first time showed that sBMAC significantly accelerated both skin wound healing and bone formation in the defects, compared with conventional platelet-rich fibrin in rabbit experiment models.