Efficacy of minimally invasive techniques for enhancement of fracture healing: evidence today. Int Orthop. 2010;34:3-12. [PMID: 19844709 DOI: 10.1007/s00264-009-0892-0]

Comparison of mini-open reduction and autologous bone grafting with closed reduction and intramedullary device insertion for tibial shaft fractures: a retrospective study

BACKGROUND

We compared the clinical efficacy of mini-open reduction and autologous bone grafting (G_M) and closed reduction (G_C) using intramedullary nailing for the treatment of tibial shaft fractures.

METHODS

This retrospective study included 70 tibial shaft fractures treated with G_M or G_C between January 2018 and December 2021. The demographic characteristics and clinical outcomes were compared between the two treatment methods.

RESULTS

This study included 70 patients who were followed-up for 12.4 months. In total, 31 and 39 patients were treated with G_M and G_C, respectively. The operative duration was significantly shorter for G_M (95.2 ± 19.3 min) than for G_C (105.5 ± 22.2 min, p = 0.0454). The number of radiation times was significantly lower for G_M (14.7 ± 6.3) than for G_C (22.2 ± 9.2, p < 0.005). There were no statistically significant differences between the groups in terms of the wound complication or infection rates. The malunion and nonunion rates were high after G_C than after G_M, but there are no significant differences between the groups.

CONCLUSIONS

Closed reduction and intramedullary nailing remains the first choice for tibial shaft fractures. G_M is a safe and effective treatment worth considering. Future prospective randomized controlled trials are warranted.

Wnt7b: Is It an Important Factor in the Bone Formation Process after Calvarial Damage?

OBJECTIVE

Previous studies found that Wnt7b played a unique and indispensable role in the process of osteoblast differentiation and could accelerate the repair of bone loss. However, what is the role of Wnt7B in osteogenesis? Is it possible to increase the expression of Wnt7b to promote the repair of skull defects? This study intends to provide the basic data for the application of Wnt7b in the treatment of craniomaxillofacial bone repair.

METHODS

A calvarial defect mouse model that could induce Wnt7b overexpression was established. Three days after the operation, the mice in each group were intraperitoneally injected with tamoxifen (TAM) or oil eight times every other day. There were three groups. The TAMc group (R26^Wnt7b/Wnt7b) was injected with tamoxifen. The Oil group (3.2 kb Col1-Cre-ER^T2; R26^Wnt7b/Wnt7b) was injected with oil. The TAM group (3.2 kb Col1-Cre-ER^T2; R26^Wnt7b/Wnt7b) was injected with tamoxifen. Four weeks after the surgery, micro-CT scanning was utilized to observe new bone formation and compare the ability to form new bone around the defect area.

RESULTS

Four weeks after the operation, bone healing conditions were measured by using micro-CT scanning. The defect area of the TAM group was smaller than that of the other groups. Similarly, the bone volume fraction (BV/TV) significantly increased (p < 0.05), the trabecular number (Tb.N) increased, and the trabecular separation (Tb.Sp) decreased.

CONCLUSIONS

Wnt7b participates in the bone formation process after calvarial damage, indicating the important role of Wnt7b in osteogenesis.

Biological and molecular profile of fracture non-union tissue: A systematic review and an update on current insights

Fracture non‐union represents a common complication, seen in 5%–10% of all acute fractures. Despite the enhancement in scientific understanding and treatment methods, rates of fracture non‐union remain largely unchanged over the years. This systematic review investigates the biological, molecular and genetic profiles of both (i) non‐union tissue and (ii) non–union‐related tissues, and the genetic predisposition to fracture non‐union. This is crucially important as it could facilitate earlier identification and targeted treatment of high‐risk patients, along with improving our understanding on pathophysiology of fracture non‐union. Since this is an update on our previous systematic review, we searched the literature indexed in PubMed Medline; Ovid Medline; Embase; Scopus; Google Scholar; and the Cochrane Library using Medical Subject Heading (MeSH) or Title/Abstract words (non‐union(s), non‐union(s), human, tissue, bone morphogenic protein(s) (BMPs) and MSCs) from August 2014 (date of our previous publication) to 2 October 2021 for non‐union tissue studies, whereas no date restrictions imposed on non–union‐related tissue studies. Inclusion criteria of this systematic review are human studies investigating the characteristics and properties of non‐union tissue and non–union‐related tissues, available in full‐text English language. Limitations of this systematic review are exclusion of animal studies, the heterogeneity in the definition of non‐union and timing of tissue harvest seen in the included studies, and the search term MSC which may result in the exclusion of studies using historical terms such as ‘osteoprogenitors’ and ‘skeletal stem cells’. A total of 24 studies (non‐union tissue: n = 10; non–union‐related tissues: n = 14) met the inclusion criteria. Soft tissue interposition, bony sclerosis of fracture ends and complete obliteration of medullary canal are commonest macroscopic appearances of non‐unions. Non‐union tissue colour and surrounding fluid are two important characteristics that could be used clinically to distinguish between septic and aseptic non‐unions. Atrophic non‐unions had a predominance of endochondral bone formation and lower cellular density, when compared against hypertrophic non‐unions. Vascular tissues were present in both atrophic and hypertrophic non‐unions, with no difference in vessel density between the two. Studies have found non‐union tissue to contain biologically active MSCs with potential for osteoblastic, chondrogenic and adipogenic differentiation. Proliferative capacity of non‐union tissue MSCs was comparable to that of bone marrow MSCs. Rates of cell senescence of non‐union tissue remain inconclusive and require further investigation. There was a lower BMP expression in non‐union site and absent in the extracellular matrix, with no difference observed between atrophic and hypertrophic non‐unions. The reduced BMP‐7 gene expression and elevated levels of its inhibitors (Chordin, Noggin and Gremlin) could potentially explain impaired bone healing observed in non‐union MSCs. Expression of Dkk‐1 in osteogenic medium was higher in non‐union MSCs. Numerous genetic polymorphisms associated with fracture non‐union have been identified, with some involving the BMP and MMP pathways. Further research is required on determining the sensitivity and specificity of molecular and genetic profiling of relevant tissues as a potential screening biomarker for fracture non‐unions.

Minimally invasive treatment of long bone non-unions with bone marrow concentrate, demineralized bone matrix and platelet-rich fibrin in 38 patients

To determine the efficacy of percutaneous injection of autologous bone marrow concentrated (BMC), demineralized bone matrix (DBM), and platelet rich fibrin (PRF) in the treatment of long bone non-unions. From January 2011 to January 2018 patients with non-union of the lower limbs who were on the waiting list for open grafting with established tibial or femoral non-union and minimal deformity were eligible to participate in this study. Patients were treated with a single percutaneous injection of DBM, BMC and PRF. Our study group comprised 38 patients (26 males and 12 females; mean age 39, range 18 to 65). Non-unions were located in the femur (18 cases) and in the tibia (20 cases). Clinical and imaging follow-up ranged from 4 to 60 months (mean 20 months). Bone union occurred in 30 out of 38 patients (79%) in an average of 7 months (range 3 to 12) and all healed patients had full weight bearing after 9 months on average (range 6 to 12) from injection. In 19 cases the osteosynthesis was removed 12 months on average (range 3 to 36) from surgery. One patient developed infection at the non-union site after treatment. Percutaneous injection of DBM, BMC, and PRF is an effective treatment for long-bone non-unions. This technique allows the bone to heal with a minimally invasive approach and with a hospitalization of 2 days. Key elements of bone regeneration consist of a combination of biological and biomechanical therapeutic approach.

Adult mesenchymal stem cells: is there a role for purine receptors in their osteogenic differentiation?

The role played by mesenchymal stem cells (MSCs) in contributing to adult tissue homeostasis and damage repair thanks to their differentiation capabilities has raised a great interest, mainly in bone regenerative medicine. The growth/function of these undifferentiated cells of mesodermal origin, located in specialized structures (niches) of differentiated organs is influenced by substances present in this microenvironment. Among them, ancestral and ubiquitous molecules such as adenine-based purines, i.e., ATP and adenosine, may be included. Notably, extracellular purine concentrations greatly increase during tissue injury; thus, MSCs are exposed to effects mediated by these agents interacting with their own receptors when they act/migrate in vivo or are transplanted into a damaged tissue. Here, we reported that ATP modulates MSC osteogenic differentiation via different P2Y and P2X receptors, but data are often inconclusive/contradictory so that the ATP receptor importance for MSC physiology/differentiation into osteoblasts is yet undetermined. An exception is represented by P2X7 receptors, whose expression was shown at various differentiation stages of bone cells resulting essential for differentiation/survival of both osteoclasts and osteoblasts. As well, adenosine, usually derived from extracellular ATP metabolism, can promote osteogenesis, likely via A2B receptors, even though findings from human MSCs should be implemented and confirmed in preclinical models. Therefore, although many data have revealed possible effects caused by extracellular purines in bone healing/remodeling, further studies, hopefully performed in in vivo models, are necessary to identify defined roles for these compounds in favoring/increasing the pro-osteogenic properties of MSCs and thereby their usefulness in bone regenerative medicine.

Nano-scale characterization of nano-hydroxyapatite incorporated chitosan particles for bone repair

In this study, injectable porous spherical particles were fabricated using chitosan (CS) biopolymer, sodium tripolyphosphate (TPP), and nano-hydroxyapatite (nHA). TPP was primarily used as an ionic crosslinker to crosslink 2% (w/v) CS droplets. 2% (w/v) nHA was used to prepare nHA incorporated particles. The surface morphological properties and nanomechanical properties such as topography, deformation, adhesion, and dissipation of CS particles with and without nHA were studied using contact mode and peakforce quantitative nanomechanical property mapping mode in atomic force microscopy. The nHA spots have higher density than CS which leads to higher forces acting on the probe tip and higher energy dissipation to lift the tip from nHA areas. The cumulative release data showed that about 87% of total BMP-2 encapsulated within the particles was released by third week of experiment period. Degradation study was conducted to understand how the particles degradation occurs in the presence of phosphate buffered saline with continues shaking in an incubator at 37° C. In addition, BMP-2 release from the 2% nHA/CS particles was studied over a three weeks period and found that BMP-2 release was governed by the simple diffusion rather than the degradation of particles.

Percutaneous autologous bone marrow transplantation for the treatment of delayed union of limb bone in children

Background and purpose

Percutaneous autologous bone marrow transplantation (PABMT) is a minimally invasive therapeutic strategy for the treatment of delayed bone union in adults, which has been confirmed by many studies. However, there is no report on PABMT application in pediatric orthopedic surgery. The aim of this article was to analyze the therapeutic effect of PABMT in children with delayed union of limb bone and its influence in relation to delayed bone union therapy, transplantation period, patients’ sex, fracture location, and fracture fixation.

Methods

In this study, 53 patients (aged 3–16 years, with an average age of 6.7 years) with delayed union of long bone (20 femurs, 12 tibiae, 10 humeri, 5 radiuses, 5 ulnas, and 1 fibula) were treated using PABMT. Clinical examination and X-ray were integrated to evaluate the therapeutic effect.

Results

All 53 patients were followed up for 2–6 years (average time, 3.5 years). Of the 53 patients, 47 (88.7%) were healed, whereas the other 6 (11.3%) were not, and were subsequently treated by autologous bone grafting. In 30 patients who received their first PABMT treatment 6–8 months after fixation, the clinical cure rate, operation times, and healing time were 83.3%, 5.8±0.5 months, and 2.5±0.6, respectively. In the other 23 patients, whose first PABMT treatments were started within 4 to 6 months after fixation, the clinical cure rate, operation times, and healing time were 95.7% (P=0.167), 3.2±0.3 months (P=0.001), and 1.3±0.6 (P=0.001), respectively. The patients’ sex, fracture location, and fracture fixation did not have statistical influence on the clinical efficacy.

Conclusion

PABMT is a minimally invasive and effective strategy for the treatment of delayed union of limb bone in children. The early surgical treatment facilitates the fracture healing, reduces the number of transplantation, and shortens the course of treatment.

Evaluation of the Effect of Platelet-Rich Fibrin on Long Bone Healing: An Experimental Rat Model

Pseudoarthrosis, or nonunion, of the long bones is a challenging medical condition for orthopedic surgeons to treat. Therefore, healing enhancer materials are commonly used. The authors investigated whether platelet-rich fibrin accelerates long bone healing by comparing radiological and histological findings in a rat model of open femoral fracture. Platelet-rich fibrin is a current biomaterial that contains many growth factors and platelets. There are no studies in the literature investigating the effects of platelet-rich fibrin on fracture healing. Sixteen mature male rats were divided into 2 groups. In both groups, an open femoral fracture was created. The platelet-rich fibrin was obtained by centrifuging blood collected from the rats. Rats in the study group were treated with sterile platelet-rich fibrin, and those in the control group were administered saline. The rats were killed at the end of 4 weeks and examined histologically and radiologically. The radiographic and histological scores of the 2 groups differed significantly (P<.05). These results indicate that platelet-rich fibrin is an efficient biomaterial in fracture healing and that it increases the amount of osseous tissue formation. Platelet-rich fibrin does not cause an allergic reaction, is cost-effective, and is easy to obtain. Additional studies are necessary to determine whether platelet-rich fibrin accelerates the fracture healing process or induces a better quality of fracture healing. [Orthopedics. 2017; 40(3):e479-e484.].

Effect of methotrexate on bone and wound healing

INTRODUCTION

Methotrexate (MTX) is one of the most commonly used disease modifying drugs administered for wide spectrum of conditions. Through the expansion of the indications of MTX use, an increasing number of patients nowadays attend orthopaedic departments receiving this pharmacological agent. The aim of this manuscript is to present our current understanding on the effect of MTX on bone and wound healing. Areas covered: The authors offer a comprehensive review of the existing literature on the experimental and clinical studies analysing the effect of MTX on bone and wound healing. The authors also analyse the available literature and describe the incidence of complications after elective orthopaedic surgery in patients receiving MTX. Expert opinion: The available experimental data and clinical evidence are rather inadequate to allow any safe scientific conclusions on the effect of MTX on bone healing. Regarding wound healing, in vitro and experimental animal studies suggest that MTX can adversely affect wound healing, whilst the clinical studies show that lose-dose MTX is safe and does not affect the incidence of postoperative wound complications.

Changes of mineralogical characteristics and osteoblast activities of raw and processed pyrites

Pyrite, a commonly used mineral medicine in traditional Chinese medicine (TCM), is normally prescribed in the form of calcined or processed pyrite to ensure clinical safety and efficacy.

Protective effect of berberine against oxidative stress-induced apoptosis in rat bone marrow-derived mesenchymal stem cells

Bone marrow-derived mesenchymal stem cells (BMSCs) have the potential to be used for the treatment of delayed union, nonunion or persistent bone defects in MSC-based cell therapy. However, implantation of BMSCs into the fracture site is confronted with apoptosis on account of harsh conditions and oxidative stress. In the present study, the anti-apoptotic effects of berberine (BBR) on BMSCs subjected to hydrogen peroxide (H₂O₂) are investigated, and the potential underlying mechanisms are explored. Oxidative injury was induced by exposure to H₂O₂, and cell viability was assessed using a cell counting kit-8 assay. The apoptosis of BMSCs was measured by Hoechst 33258 and Annexin V-fluorescein isothiocyanate/propidium iodide assay. Reactive oxygen species staining and superoxide dismutase (SOD) assay were applied to assess the anti-oxidative effect of BBR. Finally, western blot was performed to measure the expression levels of phosphorylated (p)-Akt, B-cell lymphoma 2 (Bcl-2), Bcl-2-associated X protein (Bax) and cleaved caspase-3. In the present study, it was identified that BBR remarkably attenuated H₂O₂-induced apoptotic cell death via quenching ROS production and increasing SOD activity. Further studies indicated that BBR can reduce apoptosis by upregulating the expression level of p-Akt and Bcl-2, and downregulating the expression levels of Bax and cleaved caspase-3. Taken together, the results of the present study demonstrate that pretreatment with BBR could alleviate H₂O₂-induced apoptosis in rat BMSCs in vitro.

The role of peptides in bone healing and regeneration: a systematic review

BACKGROUND

Bone tissue engineering and the research surrounding peptides has expanded significantly over the last few decades. Several peptides have been shown to support and stimulate the bone healing response and have been proposed as therapeutic vehicles for clinical use. The aim of this comprehensive review is to present the clinical and experimental studies analysing the potential role of peptides for bone healing and bone regeneration.

METHODS

A systematic review according to PRISMA guidelines was conducted. Articles presenting peptides capable of exerting an upregulatory effect on osteoprogenitor cells and bone healing were included in the study.

RESULTS

Based on the available literature, a significant amount of experimental in vitro and in vivo evidence exists. Several peptides were found to upregulate the bone healing response in experimental models and could act as potential candidates for future clinical applications. However, from the available peptides that reached the level of clinical trials, the presented results are limited.

CONCLUSION

Further research is desirable to shed more light into the processes governing the osteoprogenitor cellular responses. With further advances in the field of biomimetic materials and scaffolds, new treatment modalities for bone repair will emerge.

The regeneration and augmentation of bone with injectable osteogenic cell sheet in a rat critical fracture healing model

Limitations in the current treatment strategies make cases with compromised bone healing challenging clinical problems. Osteogenic cell sheets (OCSs), fabricated from rat bone marrow stromal cells (BMSCs), contain enriched osteoblasts and extracellular matrix. Here, we evaluated whether the minimally invasive percutaneous injection of OCSs without a scaffold could be used as a treatment to increase bone regeneration in a critical fracture healing model. Critical fracture healing model was created in the femora of 60 male Fischer 344 inbred rats using marrow ablation and periosteal removal. The rats were then randomly divided into two groups. Six hours after fracture, one group received an injection of OCSs (OCS group), while the second group was injected with phosphate-buffered saline (PBS) (control group). Fracture healing was evaluated using radiological, histological, micro-computed tomography (CT) and biomechanical analyses. The radiological and histological evaluations demonstrated enhanced bone regeneration in the OCS group compared with that in the control group. By 12 weeks, the hard callus had been remodelled via recorticalization in the OCS group. By contrast, no fracture union was found in the rats in the control group. Biomechanical testing revealed a significantly higher maximum bending load in the OCS group compared with that in the control group. The results of the present study demonstrate that the injection of entire OCSs can enhance bone regeneration and lead to bony union in a critical fracture healing model. Therefore, this procedure offers a minimally invasive technique to promote hard tissue reconstruction and, in particular, bone repair strategies for cases with compromised bone healing.

Biological and molecular profile of fracture non-union tissue: current insights

Delayed bone healing and non-union occur in approximately 10% of long bone fractures. Despite intense investigations and progress in understanding the processes governing bone healing, the specific pathophysiological characteristics of the local microenvironment leading to non-union remain obscure. The clinical findings and radiographic features remain the two important landmarks of diagnosing non-unions and even when the diagnosis is established there is debate on the ideal timing and mode of intervention. In an attempt to understand better the pathophysiological processes involved in the development of fracture non-union, a number of studies have endeavoured to investigate the biological profile of tissue obtained from the non-union site and analyse any differences or similarities of tissue obtained from different types of non-unions. In the herein study, we present the existing evidence of the biological and molecular profile of fracture non-union tissue.

Ability of bone graft substitutes to support the osteoprogenitor cells: An in-vitro study

AIM: To compare seven commercially available bone graft substitutes (BGS) in terms of these properties and without using any additional biological growth factors.

METHODS: Porcine osteoprogenitor cells were loaded on seven commercially available BGS and allowed to proliferate for one week followed by osteogenic induction. Staining for live/dead cells as well as scanning electron microscopy (SEM) was carried out to determine viability and cellular binding. Further outcome measures included alkaline phosphatase (ALP) assays with normalisation for DNA content to quantify osteogenic potential. Negative and positive control experiments were carried out in parallel to validate the results.

RESULTS: Live/dead and SEM imaging showed higher viability and attachment with β-tricalcium phosphate (β-TCP) than with other BGS (P < 0.05). The average ALP activity in nmol/mL (normalised value for DNA content in nmol/μg DNA) per sample was 657.58 (132.03) for β-TCP, 36.22 (unable to normalise) for calcium sulphate, 19.93 (11.39) for the Hydroxyapatite/Tricalcium Phosphate composite, 14.79 (18.53) for polygraft, 13.98 (8.15) for the highly porous β-Tricalcium Phosphate, 5.56 (10.0) for polymers, and 3.82 (3.8) for Hydroxyapatite.

CONCLUSION: Under the above experimental conditions, β-TCP was able to maintain better the viability of osteoprogenitor cells and allow proliferation and differentiation (P < 0.05).

Can we enhance fracture vascularity: What is the evidence?

Angiogenesis is a vital component of bone healing. The formation of the new blood vessels at the fracture site restores the hypoxia and nutrient deprivation found at the early stages after fracture whilst at a later stage facilitates osteogenesis by the activity of the osteoprogenitor cells. Emerging evidence suggests that there are certain molecules and gene therapies that could promote new blood vessel formation and as a consequence enhance the local bone healing response. This article summarizes the current in vivo evidence on therapeutic approaches aiming at the augmentation of the angiogenic signalling during bone repair.

Percutaneous autologous concentrated bone marrow grafting in the treatment for nonunion

The purpose of this study was to evaluate the clinical and radiographic treatment effects of percutaneous autologous concentrated bone marrow grafting in nonunion cases and to evaluate the effectiveness of this grafting procedure. We enrolled 17 cases those had atrophic changes due to continuous nonunion for over 9 months after injury and had undergone low-intensity pulsed ultrasound treatment for more than 3 months. The site of nonunion was the femur in 10 cases, the tibia in 5 cases, the humerus in 1 case, and the ulna in 1 case. They underwent percutaneous autologous concentrated bone marrow grafting and continued low-intensity pulsed ultrasound stimulation treatment after grafting. Patients were evaluated using the visual analogue scale for pain at immediately before the procedure, 3, 6, and 12 months after grafting. Plain radiographs of the affected site were taken and evaluated about the healing of the nonunion site at each clinical evaluation. As quantitative assessment, CT scans were undertaken before the procedure and 6 months after grafting. The visual analogue scale pain score was reduced consistently after grafting in all patients. About the healing at the nonunion site, 11 and 13 cases of bone union were observed at 6 and 12 months after grafting. The mean volume of callus formation based on CT images was 4,147 (262-27,392) mm3 total between grafting and 6 months. Percutaneous autologous concentrated bone marrow grafting is an effective procedure for the treatment of patients with nonunion.

Release of growth factors and the effect of age, sex, and severity of injury after long bone fracture. A preliminary report

BACKGROUND AND PURPOSE

The systemic response after fracture is regulated by a complex mechanism involving numerous growth factors. In this study, we analyzed the kinetics of key growth factors following lower-limb long bone fracture.

MATERIALS AND METHODS

Human serum was isolated from 15 patients suffering from lower-limb long bone fracture (tibia/femur) requiring surgical fixation. The levels of platelet-derived growth factor (PDGF-BB), vascular edothelial growth factor (VEGF), insulin growth factor-I (IGF-I), and transforming growth factor β1 (TGF-β1) were assayed by colorimetric ELISA at different time points during the first week after fracture. 10 healthy volunteers made up the control group of the study. Serum levels of the growth factors measured were compared to age, sex, and injury severity score.

RESULTS

We found that there was a decline in the levels of PDGF-BB, IGF-I and TGF-β1 during the first 3 days after fracture. However, VEGF levels remained unchanged. The levels of all the growth factors studied then increased, with the highest concentrations noted at day 7 after surgery. No correlation was found between circulating levels of growth factors and age, injury severity score (ISS), blood loss, or fluid administration.

INTERPRETATION

There are systemic mitogenic and osteogenic signals after fracture. Important growth factors are released into the peripheral circulation, but early after surgery it appears that serum levels of key growth factors fall. By 7 days postoperatively, the levels had increased considerably. Our findings should be considered in cases where autologous serum is used for ex vivo expansion of mesenchymal stem cells. There should be further evaluation of the use of these molecules as biomarkers of bone union.

Bone graft substitutes: What are the options?

Currently, a number of bone grafting materials are available in the clinical setting to enhance bone regeneration, varying from autologous bone to several bone graft substitutes. Although autologous bone remains the "gold standard" for stimulating bone repair and regeneration, the morbidity from its harvesting and its restricted availability generated the need for the development of other materials or strategies either to substitute autologous bone graft or expand its limited supply. Bone graft substitutes can possess one or more components: an osteoconductive matrix, acting as a scaffold; osteoinductive proteins and other growth factors to induce differentiation and proliferation of bone-forming cells; and osteogenic cells for bone formation. Based on their distinct properties, all these bone grafting alternatives have specific indications, and can be used either alone or in combination. In this review, we summarise the available bone grafting materials, focussing mainly on the various bone substitutes and their characteristics, in an effort to specify the indications for their use.

Bone regeneration: current concepts and future directions

Bone regeneration is a complex, well-orchestrated physiological process of bone formation, which can be seen during normal fracture healing, and is involved in continuous remodelling throughout adult life. However, there are complex clinical conditions in which bone regeneration is required in large quantity, such as for skeletal reconstruction of large bone defects created by trauma, infection, tumour resection and skeletal abnormalities, or cases in which the regenerative process is compromised, including avascular necrosis, atrophic non-unions and osteoporosis. Currently, there is a plethora of different strategies to augment the impaired or 'insufficient' bone-regeneration process, including the 'gold standard' autologous bone graft, free fibula vascularised graft, allograft implantation, and use of growth factors, osteoconductive scaffolds, osteoprogenitor cells and distraction osteogenesis. Improved 'local' strategies in terms of tissue engineering and gene therapy, or even 'systemic' enhancement of bone repair, are under intense investigation, in an effort to overcome the limitations of the current methods, to produce bone-graft substitutes with biomechanical properties that are as identical to normal bone as possible, to accelerate the overall regeneration process, or even to address systemic conditions, such as skeletal disorders and osteoporosis.