Review of commercially available demineralized bone matrix products for spinal fusions: A selection paradigm

Use of allograft bone matrix in clinical orthopedics

Clinical orthopedics continuously aims to improve methods for bone formation. Clinical applications where bone formation is necessary include critical long bone defects in orthopedic trauma or tumor patients. Though some biomaterials combined with autologous stem cells significantly improve bone repair, critical-size damages are still challenged with the suitable implantation of biomaterials and donor cell survival. Extracellular matrix (ECM) is the fundamental structure in tissues that can nest and nourish resident cells as well as support specific functions of the tissue type. ECM also plays a role in cell signaling to promote bone growth, healing and turnover. In the last decade, the use of bone-derived ECMs or ECM-similar biomaterials have been widely investigated, including decellularized and demineralized bone ECM. In this article, we reviewed the current productions and applications of decellularized and demineralized bone matrices. We also introduce the current study of whole limb decellularization and recellularization.

Osteobiologics and Value-Based Care: Challenges and Opportunities

BACKGROUND

Autologous bone grafts, sourced from the iliac crest, are the gold standard for bone substitution in spine surgery. However, harvesting autografts increases the risk of postoperative complications. Bone allografts are another popular source of graft material, but their use is rapidly surpassing their availability. There has been considerable interest in manufactured bone graft substitutes, commonly referred to as osteobiologics, which mimic the properties of autologous bone and may be osteoconductive, osteoinductive, osteogenic, or a combination.

OBJECTIVE

Osteobiologics have been developed to mimic the properties of autologous bone, but their high cost and variable effectiveness raise questions about their value. This article explores the challenges and opportunities associated with the use of osteobiologics used to aid in bone healing in spinal fusion surgery within a value-based care framework. Spinal fusion treatments such as bone morphogenetic proteins, platelet-rich plasma, autologous conditioned serum, demineralized bone matrix, biomaterial scaffolds, stem cells, and cellular bone matrices are compared.

SUMMARY

Bone morphogenetic proteins are highly effective but often associated with serious risks; platelet-rich plasma shows promising results but lacks standardization in research protocols. Autologous conditioned serum is inconclusive and cost-effective, while demineralized bone matrix has variable effectiveness and limited data to use in anterior spinal fusions. Biomaterial scaffolds have limited application in the anterior spine but demonstrate high efficacy when it comes to spinal fusion. Stem cells demonstrate improved postsurgical outcomes but have low yield from bone marrow and potential risks associated with genetic engineering and cell therapy. Cellular bone matrices show promising results and have high fusion rates, yet there is currently no US Food and Drug Adminstration requirement for preclinical or clinical data before commercial usage. Although osteobiologics have considerable potential, their high price and uncertain efficiency raise questions concerning their usefulness in spinal fusion surgery. To ensure better patient outcomes, extensive research is needed to explore their utilization within a value-based care framework.

Nonoperative and Operative Soft-Tissue and Cartilage Regeneration and Orthopaedic Biologics of the Foot and Ankle: An Orthoregeneration Network Foundation Review

Orthoregeneration is defined as a solution for orthopaedic conditions that harnesses the benefits of biology to improve healing, reduce pain, improve function, and optimally, provide an environment for tissue regeneration. Options include drugs, surgical intervention, scaffolds, biologics as a product of cells, and physical and electromagnetic stimuli. The goal of regenerative medicine is to enhance the healing of tissue after musculoskeletal injuries as both isolated treatment and adjunct to surgical management, using novel therapies to improve recovery and outcomes. Various orthopaedic biologics (orthobiologics) have been investigated for the treatment of pathology involving the foot and ankle (including acute traumatic injuries and fractures, tumor, infection, osteochondral lesions, arthritis, and tendinopathy) and procedures, including osteotomy or fusion. Promising and established treatment modalities include 1) bone-based therapies (such as cancellous or cortical autograft from the iliac crest, proximal tibia, and/or calcaneus, fresh-frozen or freeze-dried cortical or cancellous allograft, including demineralized bone matrix putty or powder combined with growth factors, and synthetic bone graft substitutes, such as calcium sulfate, calcium phosphate, tricalcium phosphate, bioactive glasses (often in combination with bone marrow aspirate), and polymers; proteins such as bone morphogenic proteins; and platelet-derived growth factors; 2) cartilage-based therapies such as debridement, bone marrow stimulation (such as microfracture or drilling), scaffold-based techniques (such as autologous chondrocyte implantation [ACI] and matrix-induced ACI, autologous matrix-induced chondrogenesis, matrix-associated stem cell transplantation, particulated juvenile cartilage allograft transplantation, and minced local cartilage cells mixed with fibrin and platelet rich plasma [PRP]); and 3) blood, cell-based, and injectable therapies such as PRP, platelet-poor plasma biomatrix loaded with mesenchymal stromal cells, concentrated bone marrow aspirate, hyaluronic acid, and stem or stromal cell therapy, including mesenchymal stem cell allografts, and adipose tissue-derived stem cells, and micronized adipose tissue injections. LEVEL OF EVIDENCE: Level V, expert opinion.

Manufacturing artificial bone allografts: a perspective

Bone grafts have traditionally come from four sources: the patients' own tissue (autograft), tissue from a living or cadaveric human donor (allograft), animal donors (xenograft) and synthetic artificial biomaterials (ceramics, cement, polymers, and metal). However, all of these have advantages and drawbacks. The most commercially successful bone grafts so far are allografts, which hold 57% of the current bone graft market; however, disease transmission and scarcity are still significant drawbacks limiting their use. Tissue-engineered grafts have great potential, in which human stem cells and synthetical biomaterials are combined to produce bone-like tissue in vitro, but this is yet to be approved for widespread clinical practice. It is hypothesised that artificial bone allografts can be mass-manufactured to replace conventional bone allografts through refined bone tissue engineering prior to decellularisation. This review article aims to review current literature on (1) conventional bone allograft preparation; (2) bone tissue engineering including the use of synthetic biomaterials as bone graft substitute scaffolds, combined with osteogenic stem cells in vitro; (3) potential artificial allograft manufacturing processes, including mass production of engineered bone tissue, osteogenic enhancement, decellularisation, sterilisation and safety assurance for regulatory approval. From these assessments, a practical route map for mass production of artificial allografts for clinical use is proposed.

Sulfonate Hydrogel-siRNA Conjugate Facilitates Osteogenic Differentiation of Mesenchymal Stem Cells by Controlled Gene Silencing and Activation of BMP Signaling

Hydrogels have been widely used in bone tissue engineering due to their tunable characteristics that allow facile modifications with various biochemical properties to support cell growth and guide proper cell functions. Herein, we report a design of hydrogel-siRNA conjugate that facilitates osteogenesis via gene silencing and activation of bone morphogenetic protein (BMP) signaling. A sulfonate hydrogel is prepared by modifying chitosan with sulfoacetic acid to mimic a natural sulfated polysaccharide and to provide a hydrogel surface that enables BMP binding. Then, siRNA targeting noggin, an endogenous extracellular antagonist of BMP signaling, is covalently conjugated to the sulfonate hydrogel by visible blue light crosslinking. The sulfonate hydrogel-siRNA conjugate is efficient to bind BMPs and also successfully prolongs the release of siRNA for sustained noggin suppression, thereby resulting in significantly increased osteogenic differentiation. Lastly, demineralized bone matrix (DBM) is incorporated into the sulfonate hydrogel-siRNA conjugate, wherein the DBM incorporation induces noggin expression via a negative feedback mechanism that regulates BMP signaling in DBM. However, simultaneous delivery of siRNA downregulates noggin thus facilitating endogenous BMP activity and enhancing the osteogenic efficacy of DBM. These findings support a promising hydrogel RNA silencing platform for bone tissue engineering applications.

Trends in Spinal Surgery Performed by American Board of Orthopaedic Surgery Part II Candidates (2008 to 2017)

INTRODUCTION

The American Board of Orthopaedic Surgery (ABOS) Part II Oral Examination is typically taken two calendar years after fellowship completion. Despite previous studies using ABOS Part II Oral Examination data in other subspecialties, types of cases performed by spine surgeons in initial independent practice have not been well-studied. Such data may help trainees anticipate case composition observed in early practice and allow spine fellowship programs to understand emerging trends.

METHODS

We retrospectively reviewed surgical cases submitted to the ABOS by candidates taking the Part II Oral Examination between 2008 and 2017 whose designated subspecialty was spine. A hierarchical, restrictive algorithm was used to determine procedures based on candidate-reported International Classification of Diseases 9th/10th Revision and Current Procedural Terminology codes. Adjusted multivariable Poisson regression analyses were used to assess changes in procedure incidence rates over time.

RESULTS

We identified 37,539 cases, averaging 3,754 cases/yr, and an average of 49 cases per candidate per 6-month collection period. The most common procedures were lumbar diskectomy (22% of all procedures), posterolateral spinal fusion (PSF) (19%), and anterior cervical diskectomy and fusion (ACDF) (17%). Rates of ACDF and cervical disk arthroplasty significantly increased over time (incidence rate ratios of 1.41 and 23.3 times higher, respectively, at the end of the study period), whereas rates of cervical foraminotomy, lumbar diskectomy, PSF, and structural autograft use decreased (incidence rate ratios of 0.35, 0.84, 0.55, and 0.30). Rates of anterior lumbar interbody fusion/lateral lumbar interbody fusion and transforaminal lumbar interbody fusion did not significantly change over the study period.

DISCUSSION

Recent spine fellowship graduates are performing more cervical disk arthroplasties and ACDFs while decreasingly using structural autograft as well as performing fewer PSFs and lumbar diskectomies. Techniques such as anterior lumbar interbody fusion/lateral lumbar interbody fusions and transforaminal lumbar interbody fusions have not changed significantly over the last decade.

LEVEL OF EVIDENCE

Level IV (retrospective case series study).

Osteoformation potential of an allogenic partially demineralized bone matrix in critical-size defects in the rat calvarium

Allogenic demineralized bone matrix has been developed as a reliable alternative to the autologous bone graft. In the present study, we assessed the osteoformation potential of a partially demineralized bone matrix (PDBM) in a paste form obtained without an added carrier. This formulation included the preparation of cancelous bone from femoral heads after decellularision, delipidation, demineralization in HCl and autoclaving at 121 °C. Structural and biochemical characteristics of PDBM were determined using FTIR (Fourier transform infrared spectroscopy), hydroxyproline, DNA content assays, and optical ellipsometry. The osteoformation potential was evaluated in 8-, 6-, and 4-mm-diameter rat-calvarial bone defects by in vivo micro-CT analysis, performed immediately after surgery on days 0, 15, 30, 45, and 60. Moreover, histological and histomorphometric analyses were done on day 60. PDBM was compared to cancelous bone powder (BP) before its partial demineralization. The expression levels of selected inflammation-, angiogenesis-, and bone-related genes were also investigated by RT-PCR, 3, 7, and 14 days after surgery. Compared to the control group, the PDBM group exhibited a significant increase (p < 0.05) in radiopacity in 8-mm- and 6-mm-diameter defects at all time points tested. On day 60, the amount of newly-formed bone was greater (16 and 1.6 folds; p < 0.001; respectively) compared to that in control defects. No bone formation was observed in defects filled with BP regardeless of the size. In 8-mm-diameter defect, PDBM was effective enough to induce the upregulation of genes pertinent to inflammation (i.e., TNFα, IL-6, and IL-8), angiogenesis (i.e., VEGF, VWF), and osteogenesis (ALP, RUNX2, BGLAP, SP7) by day 3 after surgery. This study showed that the tested PDBM deeply influences the early critical events involved in bone regeneration and exhibits efficient osteoformation capacity, making it an attractive graft option for treating defects in periodontal and maxillofacial areas.

Allografts and Spinal Fusion

BACKGROUND

Back pain is a common chief complaint within the United States and is caused by a multitude of etiologies. There are many different treatment modalities for back pain, with a frequent option being spinal fusion procedures. The success of spinal fusion greatly depends on instrumentation, construct design, and bone grafts used in surgery. Bone allografts are important for both structural integrity and providing a scaffold for bone fusion to occur.

METHOD

Searches were performed using terms "allografts" and "bone" as well as product names in peer reviewed literature Pubmed, Google Scholar, FDA-510k approvals, and clinicaltrials.gov.

RESULTS

This study is a review of allografts and focuses on currently available products and their success in both animal and clinical studies.

CONCLUSION

Bone grafts used in surgery are generally categorized into 3 main types: autogenous (from patient's own body), allograft (from cadaveric or living donor), and synthetic. This paper focuses on allografts and provides an overview on the different subtypes with an emphasis on recent product development and uses in spinal fusion surgery.

Enhanced Osteoinductivity of Demineralized Bone Matrix with Noggin Suppression in Polymer Matrix

Demineralized bone matrix (DBM), a potential alternative to autologous bone-graft, has been increasingly used for clinical bone repair; however, its application in larger defects isn't successful partly due to the rapid dispersion of DBM particles and relatively lower osteoinductivity. Here, a novel strategy is created to complement the osteoinductivity of DBM by incorporating DBM in biopolymer hydrogel combined with the abrogation of BMP antagonism. Combined treatment of DBM + noggin-suppression displays increased osteogenic potency of human bone marrow mesenchymal stem cells (hBMSCs) in vitro. Injectable chitosan (MeGC)-based hydrogel with heparinization (Hep-MeGC) is further developed to localize and stabilize DBM. Noggin-suppression reveals the significant increase in osteogenesis of hBMSCs in the photopolymerizable Hep-MeGC hydrogels with the encapsulation of DBM. Moreover, the combination of DBM + noggin-suppression in the injectable Hep-MeGC hydrogel displays a robust bone healing in mouse critical-sized calvarial defects in vivo. The mechanistic analysis demonstrates that noggin-suppression increased DBM osteoinductivity by stimulating endogenous BMP/Smad signals. These results have shown promise in DBM's ability as a prominent bone grafting material while being coupled with gene editing mechanism and a localizing three-dimensional scaffold. Together, this approach poses a significant increase in the efficiency of DBM-mediated craniofacial bone repair and dental osteointegration.

Pro-angiogenic and osteogenic composite scaffolds of fibrin, alginate and calcium phosphate for bone tissue engineering

Due to the limitations of bone autografts, we aimed to develop new composite biomaterials with pro-angiogenic and osteogenic properties to be used as scaffolds in bone tissue engineering applications. We used a porous, cross-linked and slowly biodegradable fibrin/alginate scaffold originally developed in our laboratory for wound healing, throughout which deposits of calcium phosphate (CaP) were evenly incorporated using an established biomimetic method. Material characterisation revealed the porous nature and confirmed the deposition of CaP precursor phases throughout the scaffolds. MC3T3-E1 cells adhered to the scaffolds, proliferated, migrated and differentiated down the osteogenic pathway during the culture period. Chick chorioallantoic membrane (CAM) assay results showed that the scaffolds were pro-angiogenic and biocompatible. The work presented here gave useful insights into the potential of these pro-angiogenic and osteogenic scaffolds for bone tissue engineering and merits further research in a pre-clinical model prior to its clinical translation.

PEGylated Coating Affects DBM Osteoinductivity In Vivo by Changing Inflammatory Responses

PEGylation is a widely used modification in device coating or drug delivery by combing materials with poly(ethylene glycol) (PEG). In the present study, a well-established rat ectopic bone formation model was used to elucidate how PEGylated coating affects demineralized bone matrix (DBM) osteoinductivity in vivo by changing the inflammation events at the early phase of implantation. A range of cell-matrix interactions was characterized at the cellular and functional levels, including growth factor activity and kinetics, immune cell migration and activation, and bone formation in vivo. After 28 days, DBM's bone formation potential decreased in groups with increasing PEG concentration in the gelatin carrier. The increasing PEG concentration did not affect DBM's osteoinductive growth factor release or activity. However, increasing PEG cross-linking concentration resulted in decreased DBM-related early phase inflammatory reactions, reduced neutrophil infiltration, decreased coating material degradation, lowered the total number and active mast cells, and decreased CD80+ macrophage expression. Understanding and controlling cell-material responses may improve the design and development of functional medical devices.

Rational design of hydrogels to enhance osteogenic potential

Bone tissue engineering (BTE) encompasses the field of biomaterials, cells, and bioactive molecules to successfully guide the growth and repair of bone tissue. Current BTE strategies rely on delivering osteogenic molecules or cells via scaffolding materials. However, growth factor- and stem cell-based treatments have several limitations, such as source restriction, low stability, difficulties in predicting long-term efficacy, and high costs, among others. These issues have promoted the development of material-based therapy with properties of accessibility, high stability, tunable efficacy, and low-cost production. Hydrogels are widely used in BTE applications because of their unique hydrophilic nature and tunable physicochemical properties to mimic the native bone environment. However, current hydrogel materials are not ideal candidates due to minimal osteogenic capability on their own. Therefore, recent studies of BTE hydrogels attempt to counterbalance these issues by modifying their biophysical properties. In this article, we review recent progress in the design of hydrogels to instruct osteogenic potential, and present strategies developed to precisely control its bone healing properties.

Application of Cytokines of the Bone Morphogenetic Protein (BMP) Family in Spinal Fusion - Effects on the Bone, Intervertebral Disc and Mesenchymal Stromal Cells

Low back pain is a prevalent socio-economic burden and is often associated with damaged or degenerated intervertebral discs (IVDs). When conservative therapy fails, removal of the IVD (discectomy), followed by intersomatic spinal fusion, is currently the standard practice in clinics. The remaining space is filled with an intersomatic device (cage) and with bone substitutes to achieve disc height compensation and bone fusion. As a complication, in up to 30% of cases, spinal non-fusions result in a painful pseudoarthrosis. Bone morphogenetic proteins (BMPs) have been clinically applied with varied outcomes. Several members of the BMP family, such as BMP2, BMP4, BMP6, BMP7, and BMP9, are known to induce osteogenesis. Questions remain on why hyper-physiological doses of BMPs do not show beneficial effects in certain patients. In this respect, BMP antagonists secreted by mesenchymal cells, which might interfere with or block the action of BMPs, have drawn research attention as possible targets for the enhancement of spinal fusion or the prevention of non-unions. Examples of these antagonists are noggin, gremlin1 and 2, chordin, follistatin, BMP3, and twisted gastrulation. In this review, we discuss current evidence of the osteogenic effects of several members of the BMP family on osteoblasts, IVD cells, and mesenchymal stromal cells. We consider in vitro and in vivo studies performed in human, mouse, rat, and rabbit related to BMP and BMP antagonists in the last two decades. We give insights into the effects that BMP have on the ossification of the spine. Furthermore, the benefits, pitfalls, and possible safety concerns using these cytokines for the improvement of spinal fusion are discussed.

Heparinized chitosan stabilizes the bioactivity of BMP-2 and potentiates the osteogenic efficacy of demineralized bone matrix

Background

Demineralized bone matrix (DBM), an allograft bone processed to better expose osteoinductive factors such as bone morphogenetic proteins (BMPs), is increasingly used for clinical bone repair. However, more extensive use of DBM is limited by its unpredictable osteoinductivity and low bone formation capacity. Commercial DBM products often employ polymeric carriers to enhance handling properties but such carriers generally do not possess bioactive functions. Heparin is a highly sulfated polysaccharide and is shown to form a stable complex with growth factors to enhance their bioactivities. In this study, a new heparinized synthetic carrier for DBM is developed based on photocrosslinking of methacrylated glycol chitosan and heparin conjugation.

Results

Heparinized chitosan exerts protective effects on BMP bioactivity against physiological stressors related to bone fracture healing. It also enhances the potency of BMPs by inhibiting the activity of BMP antagonist, noggin. Moreover, heparinized chitosan is effective to deliver bone marrow stromal cells and DBM for enhanced osteogenesis by sequestering and localizing the cell-produced or DBM-released BMPs.

Conclusions

This research suggests an essential approach of developing a new hydrogel carrier to stabilize the bioactivity of BMPs and improve the clinical efficacy of current bone graft therapeutics for accelerated bone repair.

The use of demineralised bone fibres (DBF) in conjunction with supercritical carbon dioxide (SCCO2) treated allograft in anterior lumbar interbody fusion (ALIF)

Spinal fusion is a common procedure for the treatment of various spinal pathologies. Since the early days, spinal fusion has been carried out with the use of bone grafts as interbody spacers. With the development of synthetic interbody implants, bone grafts were used to facilitate fusion. Although autograft provides the best outcomes for fusion, allografts have been sought after due to donor site morbidity and other shortcomings. Currently, a vast variety of demineralised bone matrix (DBM) products are available with their methods of processing and preparation impacting their properties and clinical outcomes. Demineralised bone fibres (DBF), a form a DBM can be easily packed into implants when mixed with other substances such as allograft bone and patient's blood providing a scaffold for the mixture. We report two cases of anterior lumbar interbody fusion (ALIF) utilising a titanium-polyetheretherketone (PEEK) interbody cage filled with DBF, allograft and patient's blood with a maximum of 12 months follow-up outcome.

The Development of Gelatin/Hyaluronate Copolymer Mixed with Calcium Sulfate, Hydroxyapatite, and Stromal-Cell-Derived Factor-1 for Bone Regeneration Enhancement

In clinical practice, bone defects still remain a challenge. In recent years, apart from the osteoconductivity that most bone void fillers already provide, osteoinductivity has also been emphasized to promote bone healing. Stromal-cell-derived factor-1 (SDF-1) has been shown to have the ability to recruit mesenchymal stem cells (MSCs), which play an important role in the bone regeneration process. In this study, we developed a gelatin–hyaluronate (Gel-HA) copolymer mixed with calcium sulfate (CS), hydroxyapatite (HAP), and SDF-1 in order to enhance bone regeneration in a bone defect model. The composites were tested in vitro for biocompatibility and their ability to recruit MSCs after material characterization. For the in vivo test, a rat femoral condyle bone defect model was used. Micro computed tomography (Micro-CT), two-photon excitation microscopy, and histology analysis were performed to assess bone regeneration. As expected, enhanced bone regeneration was well observed in the group filled with Gel-HA/CS/HAP/SDF-1 composites compared with the control group in our animal model. Furthermore, detailed blood analysis of rats showed no obvious systemic toxicity or side effects after material implantation. In conclusion, the Gel-HA/CS/HAP/SDF-1 composite may be a safe and applicable material to enhance bone regeneration in bone defects.

Current Stage of Marine Ceramic Grafts for 3D Bone Tissue Regeneration

Bioceramic scaffolds are crucial in tissue engineering for bone regeneration. They usually provide hierarchical porosity, bioactivity, and mechanical support supplying osteoconductive properties and allowing for 3D cell culture. In the case of age-related diseases such as osteoarthritis and osteoporosis, or other bone alterations as alveolar bone resorption or spinal fractures, functional tissue recovery usually requires the use of grafts. These bone grafts or bone void fillers are usually based on porous calcium phosphate grains which, once disposed into the bone defect, act as scaffolds by incorporating, to their own porosity, the intergranular one. Despite their routine use in traumatology and dental applications, specific graft requirements such as osteoinductivity or balanced dissolution rate are still not completely fulfilled. Marine origin bioceramics research opens the possibility to find new sources of bone grafts given the wide diversity of marine materials still largely unexplored. The interest in this field has also been urged by the limitations of synthetic or mammalian-derived grafts already in use and broadly investigated. The present review covers the current stage of major marine origin bioceramic grafts for bone tissue regeneration and their promising properties. Both products already available on the market and those in preclinical phases are included. To understand their clear contribution to the field, the main clinical requirements and the current available biological-derived ceramic grafts with their advantages and limitations have been collected.

Escherichia coli BMP-2 showed comparable osteoinductivity with Chinese hamster ovary derived BMP-2 with demineralized bone matrix as carrier

Escherichia coli bone morphogenetic protein-2 (ErhBMP-2) had a larger yield but less osteoinductivity than Chinese hamster ovary cell bone morphogenetic protein-2 (CrhBMP-2). Since the release profile of rhBMP-2 affects its osteoinductivity, an appropriate carrier could improve the effect of ErhBMP-2. Demineralized bone matrix (DBM) was one of the most widely used bone substitutes, but few studies evaluated the osteoinductivity of ErhBMP-2 while it was carried by DBM. Therefore, we compared the osteoinductivity of ErhBMP-2 with CrhBMP-2 with DBM as the carrier of each. In vitro results showed ErhBMP-2 had slightly less osteoinductivity than CrhBMP-2. However, with DBM as the carrier, ErhBMP-2 induced significantly more bone regeneration in rat calvaria defects. Therefore, ErhBMP-2 might have comparable osteoinductivity with CrhBMP-2 while carried by DBM.

Regenerative medicine in lower limb reconstruction

Bone is a highly specialized connective tissue and has a rare quality as one of the few tissues that can repair without a scar to regain pre-injury structure and function. Despite the excellent healing capacity of bone, tumor, infection, trauma and surgery can lead to significant bone loss requiring skeletal augmentation. Bone loss in the lower limb poses a complex clinical problem, requiring reconstructive techniques to restore form and function. In the past, amputation may have been the only option; however, there is now an array of reconstructive possibilities and cellular therapies available to salvage a limb. In this review, we will evaluate current applications of bone tissue engineering techniques in limb reconstruction and identify potential strategies for future work.