Evaluation of Anterior Vertebral Interbody Fusion Using Osteogenic Mesenchymal Stem Cells Transplanted in Collagen Sponge

Animal Model for Anterior Lumbar Interbody Fusion: A Literature Review

Lumbar interbody fusion (LIF) is a surgical procedure for treating lumbar spinal stenosis and deformities. It removes a spinal disc and insert a cage or bone graft to promote solid fusion. Extensive research on LIF has been supported by numerous animal studies, which are being developed to enhance fusion rates and reduce the complications associated with the procedure. In particular, the anterior approach is significant in LIF research and regenerative medicine studies concerning intervertebral discs, as it utilizes the disc and the entire vertebral body. Several animal models have been used for anterior LIF (ALIF), each with distinct characteristics. However, a comprehensive review of ALIF models in different animals is currently lacking. Medium-sized and large animals, such as dogs and sheep, have been employed as ALIF models because of their suitable spine size for surgery. Conversely, small animals, such as rats, are rarely employed as ALIF models because of anatomical challenges. However, recent advancements in surgical implants and techniques have gradually allowed rats in ALIF models. Ambitious studies utilizing small animal ALIF models will soon be conducted. This review aims to review the advantages and disadvantages of various animal models, commonly used approaches, and bone fusion rate, to provide valuable insights to researchers studying the spine.

Development of Murine Anterior Interbody and Posterolateral Spinal Fusion Techniques

BACKGROUND

Multiple animal models have previously been utilized to investigate anterior fusion techniques, but a mouse model has yet to be developed. The purpose of this study was to develop murine anterior interbody and posterolateral fusion techniques.

METHODS

Mice underwent either anterior interbody or posterolateral spinal fusion. A protocol was developed for both procedures, including a description of the relevant anatomy. Samples were subjected to micro-computed tomography to assess fusion success and underwent biomechanical testing with use of 4-point bending. Lastly, samples were fixed and embedded for histologic evaluation.

RESULTS

Surgical techniques for anterior interbody and posterolateral fusion were developed. The fusion rate was 83.3% in the anterior interbody model and 100% in the posterolateral model. Compared with a control, the posterolateral model exhibited a greater elastic modulus. Histologic analysis demonstrated endochondral ossification between bridging segments, further confirming the fusion efficacy in both models.

CONCLUSIONS

The murine anterior interbody and posterolateral fusion models are efficacious and provide an ideal platform for studying the molecular and cellular mechanisms mediating spinal fusion.

CLINICAL RELEVANCE

Given the extensive genetic tools available in murine disease models, use of fusion models such as ours can enable determination of the underlying genetic pathways involved in spinal fusion.

Lumbar spine intervertebral disc gene delivery of BMPs induces anterior spine fusion in lewis rats

Minimally invasive techniques and biological autograft alternatives such as the bone morphogenetic proteins (BMPs) can reduce morbidity associated with spinal fusions. This study was a proof-of-concept for gene-therapy-mediated anterior spine fusion that could be adapted to percutaneous technique for clinical use. Isogeneic bone marrow stromal cells genetically programmed to express b-galactosidase (LACZ, a marker gene), BMP2, BMP7, a mixture of BMP2 and BMP7 infected cells (homodimers, HM), or BMP2/7 heterodimers (HT) were implanted into the discs between lumbar vertebrae 4 and 5 (L4/5) and L5/6 of male Lewis rats. Spine stiffening was monitored at 4, 8 and 12 weeks using noninvasive-induced angular displacement (NIAD) testing. At 12 weeks isolated spines were assessed for fusion and bone formation by palpation, biomechanical testing [four-point bending stiffness, moment to failure in extension, and in vitro angular displacement (IVAD)], faxitron x-rays, microCT, and histology. Progressive loss of NIAD occurred in only the HT group (p < 0.001), and biomechanical tests correlated with the NIAD results. Significant fusion occurred only in the HT group (94% of animals with one or both levels) as assessed by palpation (p < 0.001), which predicted HT bone production assessed by faxitron (p ≤ 0.001) or microCT (p < 0.023). Intervertebral bridging bone was consistently observed only in HT-treated specimens. Induced bone was located anterior and lateral to the disc space, with no bone formation noted within the disc. Percutaneous anterior spine fusions may be possible clinically, but induction of bone inside the disc space remains a challenge.

Osteobiologics

BACKGROUND

Osteobiologics are engineered materials that facilitate bone healing and have been increasingly used in spine surgery. Autologous iliac crest bone grafts have been used historically, but morbidity associated with graft harvesting has led surgeons to seek alternative solutions. Allograft bone, biomaterial scaffolds, growth factors, and stem cells have been explored as bone graft substitutes and supplements.

OBJECTIVE

To review current and emerging osteobiologic technologies.

METHODS

A literature review of English-language studies was performed in PubMed. Search terms included combinations of "spine," "fusion," "osteobiologics," "autologous," "allogen(e)ic," "graft," "scaffold," "bone morphogenic protein," and "stem cells."

RESULTS

Evidence supports allograft bone as an autologous bone supplement or replacement in scenarios where minimal autologous bone is available. There are promising data on ceramics and P-15; however, comparative human trials remain scarce. Growth factors, including recombinant human bone morphogenic proteins (rhBMPs) 2 and 7, have been explored in humans after successful animal trials. Evidence continues to support the use of rhBMP-2 in lumbar fusion in patient populations with poor bone quality or revision surgery, while there is limited evidence for rhBMP-7. Stem cells have been incredibly promising in promoting fusion in animal models, but human trials to this point have only involved products with questionable stem cell content, thereby limiting possible conclusions.

CONCLUSION

Engineered stem cells that overexpress osteoinductive factors are likely the future of spine fusion, but issues with applying viral vector-transduced stem cells in humans have limited progress.

The Biological Enhancement of Spinal Fusion for Spinal Degenerative Disease

In this era of aging societies, the number of elderly individuals who undergo spinal arthrodesis for various degenerative diseases is increasing. Poor bone quality and osteogenic ability in older patients, due to osteoporosis, often interfere with achieving bone fusion after spinal arthrodesis. Enhancement of bone fusion requires shifting bone homeostasis toward increased bone formation and reduced resorption. Several biological enhancement strategies of bone formation have been conducted in animal models of spinal arthrodesis and human clinical trials. Pharmacological agents for osteoporosis have also been shown to be effective in enhancing bone fusion. Cytokines, which activate bone formation, such as bone morphogenetic proteins, have already been clinically used to enhance bone fusion for spinal arthrodesis. Recently, stem cells have attracted considerable attention as a cell source of osteoblasts, promising effects in enhancing bone fusion. Drug delivery systems will also need to be further developed to assure the safe delivery of bone-enhancing agents to the site of spinal arthrodesis. Our aim in this review is to appraise the current state of knowledge and evidence regarding bone enhancement strategies for spinal fusion for degenerative spinal disorders, and to identify future directions for biological bone enhancement strategies, including pharmacological, cell and gene therapy approaches.

Regenerative Medicine Strategies in Biomedical Implants

PURPOSE OF REVIEW

Recently, significant progress has been made in the research related to regenerative medicine. At the same time, biomedical implants in orthopedics and dentistry are facing many challenges and posing clinical concerns. The purpose of this chapter is to provide an overview of the clinical applications of current regenerative strategies to the fields of dentistry and orthopedic surgery. The main research question in this review is: What are the major advancement strategies in regenerative medicine that can be used for implant research?

RECENT FINDINGS

The implant surfaces can be modified through patient-specific stem cells and plasma coatings, which may provide methods to improve osseointegration and sustainability of the implant. Overall understanding from the review suggesting that the outcome from the studies could lead to identify optimum solutions for many concerns in biomedical implants and even in drug developments as a long-term solution to orthopedic and dental patients.

Mesenchymal Stem Cells for the Treatment of Spinal Arthrodesis: From Preclinical Research to Clinical Scenario

The use of spinal fusion procedures has rapidly augmented over the last decades and although autogenous bone graft is the “gold standard” for these procedures, alternatives to its use have been investigated over many years. A number of emerging strategies as well as tissue engineering with mesenchymal stem cells (MSCs) have been planned to enhance spinal fusion rate. This descriptive systematic literature review summarizes the in vivo studies, dealing with the use of MSCs in spinal arthrodesis surgery and the state of the art in clinical applications. The review has yielded promising evidence supporting the use of MSCs as a cell-based therapy in spinal fusion procedures, thus representing a suitable biological approach able to reduce the high cost of osteoinductive factors as well as the high dose needed to induce bone formation. Nevertheless, despite the fact that MSCs therapy is an interesting and important opportunity of research, in this review it was detected that there are still doubts about the optimal cell concentration and delivery method as well as the ideal implantation techniques and the type of scaffolds for cell delivery. Thus, further inquiry is necessary to carefully evaluate the clinical safety and efficacy of MSCs use in spine fusion.

The role of stem cell therapies in degenerative lumbar spine disease: a review

Degenerative conditions of the lumbar spine are extremely common. Ninety percent of people over the age of 60 years have degenerative change on imaging; however, only a small minority of people will require spine surgery (Hicks et al. Spine (Phila Pa 1976) 34(12):1301-1306, 2009). This minority, however, constitutes a core element of spinal surgery practice. Whilst the patient outcomes from spinal surgeries have improved in recent years, some patients will remain with pain and disability despite technically successful surgery. Advances in regenerative medicine and stem cell therapies, particularly the use of mesenchymal stem cells and allogeneic mesenchymal precursor cells, have led to numerous clinical trials utilising these cell-based therapies to treat degenerative spinal conditions. Through cartilage formation and disc regeneration, fusion enhancement or via modification of pain pathways, stem cells are well suited to enhance spinal surgery practice. This review will focus on the outcomes of lumbar spinal procedures and the role of stem cells in the treatment of degenerative lumbar conditions to enhance clinical practice. The current status of clinical trials utilising stem cell therapies will be discussed, providing clinicians with an overview of the various cell-based treatments likely to be available to patients in the near future.