Use of bone morphogenetic proteins in traumatology

Bone Substitute Options for Spine Fusion in Patients With Spine Trauma-Part II: The Role of rhBMP

In Part II, we focus on an important aspect of spine fusion in patients with spine trauma: the pivotal role of recombinant human bone morphogenetic protein-2 (rhBMP-2). Despite the influx of diverse techniques facilitated by technological advancements in spinal surgery, spinal fusion surgery remains widely used globally. The persistent challenge of spinal pseudarthrosis has driven extensive efforts to achieve clinically favorable fusion outcomes, with particular emphasis on the evolution of bone graft substitutes. Part II of this review aims to build upon the foundation laid out in Part I by providing a comprehensive summary of commonly utilized bone graft substitutes for spinal fusion in patients with spinal trauma. Additionally, it will delve into the latest advancements and insights regarding the application of rhBMP-2, offering an updated perspective on its role in enhancing the success of spinal fusion procedures.

Effect of Bone Morphogenetic Protein-2 in the Treatment of Long Bone Non-Unions

Background: Delayed fracture healing continues to cause significant patient morbidity and an economic burden to society. Biological stimulation of non-unions includes application of recombinant bone morphogenetic protein-2 (rhBMP-2). However, rhBMP-2 use continues to be a matter of controversy as literature shows scarce evidence for treatment effectiveness. Questions: The objective of this study was to evaluate the effectiveness of rhBMP-2 treatment on long bone non-unions measuring union rate and time to union. Furthermore, we assess risk factors for treatment failure. Methods and patients: A total of 91 patients with non-unions of long bones were treated with rhBMP-2 (n = 72) or standard care without BMP (n = 19) at our institution. Patient characteristics, comorbidities, nicotine consumption, and complications were recorded. Bone healing was assessed by plane X-rays and clinical examination. Patients were followed up with for 24 months. Results: Overall, there was significantly faster bone healing after rhBMP-2 application compared to the no-BMP group (p < 0.001; HR = 2.78; 95% CI 1.4–5.6). Union rates differed significantly between rhBMP-2 compared to the no-BMP group (89% vs. 47%; p < 0.001). At the humerus, there was neither a significantly higher union rate in the rhBMP-2 (83%) compared to the no-BMP group (50%) (p = 0.26; n = 12) nor a faster bone healing with a median time of 9 months in both groups (HR = 2.01; 95% CI 0.49–8.61; p = 0.315). The 33 femora treated using rhBMP-2 healed significantly faster than 9 femora in the no-BMP group (HR = 2.93; 95% CI 1.00–8.4; p = 0.023) with significant differences in union rate with 85% and 44%, respectively (p = 0.022). Regarding tibia non-unions, 25 out of 27 (93%) healed with a median of 9 months after rhBMP-2 application with no significant difference in the no-BMP group (33%) in time to union (p = 0.097) but a significantly higher union rate (p = 0.039). There was no effect of comorbidities, age, sex, soft tissue damage, or nicotine use on time to union, union rate, or secondary interventions. Conclusion: Consistent with the literature, overall, significantly higher union rates with reduced time to union were achieved after rhBMP-2 application. Femoral and tibial non-unions in particular seem to profit from rhBMP-2 application.

Vibration acceleration promotes endochondral formation during fracture healing through cellular chondrogenic differentiation

Vibration acceleration through whole body vibration has been reported to promote fracture healing. However, the mechanism responsible for this effect remains unclear. Purpose of this study was to determine whether vibration acceleration directly affects cells around the fracture site and promotes endochondral ossification. Four-week-old female Wistar Hannover rats were divided into two groups (vibration [V group] and control [C group]). The eighth ribs on both sides were cut vertically using scissors. From postoperative day 3 to 11, vibration acceleration using Power Plate^® (30 Hz, low amplitude [30-Low], 10 min/day) was applied in the V group. Mature calluses appeared earlier in the V group than in the C group by histological analysis. The GAG content in the fracture callus on day 6 was significantly higher in the V group than in the C group. The mRNA expressions of SOX-9, aggrecan, and Col-II in the fracture callus on day 6 and Col-X on day 9 were significantly higher in the V group than in the C group. For in vitro analysis, four different conditions of vibration acceleration (30 or 50 Hz with low or high amplitude [30-Low, 30-High, 50-Low, and 50-High], 10 min/day) were applied to a prechondrogenic cell (ATDC5) and an undifferentiated cell (C3H10T1/2). There was no significant difference in cell proliferation between the control and any of the four vibration conditions for both cell lines. For both cell lines, alcian blue staining was greater under 30-Low and 50-Low conditions than under control as well as 30-High and 50-High conditions on days 7 and 14. Vibration acceleration under 30-L condition upregulated chondrogenic gene expressions of SOX-9, aggrecan, Col-II, and Col-X. Low-amplitude vibration acceleration can promote endochondral ossification in the fracture healing in vivo and chondrogenic differentiation in vitro.

Safety study: is there a pathologic IGF-1, PDGF and TGF-β cytokine expression caused by adjunct BMP-7 in tibial and femoral non-union therapy?

Background

In this prospective safety study, we investigated if the characteristic cytokine expression during bone regeneration is manipulated by the local application of bone morphogenetic protein-7 (BMP-7) in non-union surgery. Therefore, the levels of insulin like growth factor 1 (IGF-1), platelet-derived growth factor AB (PDGF-AB) and transforming growth factor beta (TGF-β) were compared between patients with the gold standard use of autologous bone graft (ABG) and those with additional application of BMP-7 as part of the diamond concept.

Patients and methods

Between 2009 and 2014, of the 153 patients with tibial and femoral non-unions, a matched pair analysis was performed to compare the serological cytokine expressions. Blood samples were collected preoperatively, 1, 2 and 6 weeks as well as 3 and 6 months after non-union surgery. Matching criteria were smoking status, fracture location, gender, age and body mass index (BMI). Patients in G1 (n=10) were treated with ABG and local BMP-7 while their matching partners in G2 (n=10) received ABG only. The routine clinical and radiologic follow-up was 1 year.

Results

Although the IGF-1 quantification in G2 showed higher pre- and postoperative values compared to G1 (p<0.05), the courses of both groups were similar. Likewise, PDGF-AB and TGF-β expressions appeared similar in G1 and G2 with peaks in both groups at 2 weeks follow-up. Osseous consolidation was assessed in all operated non-unions. The adjunct application of BMP-7 did not cause any pathologic cytokine expression.

Conclusion

Similar expressions of the serum cytokines IGF-1, PDGF-AB and TGF-β were demonstrated in non-union patients treated with ABG and additional application of BMP-7 according to the diamond concept. Our findings indicate that the local application of BMP-7, which imitates the physiologic secretion of growth factors during bone regeneration, is safe and without the risk of abnormal systemic cytokine expression. Studies with higher patient numbers will have to validate these assumptions.

Formulation, Delivery and Stability of Bone Morphogenetic Proteins for Effective Bone Regeneration

Bone morphogenetic proteins (BMPs) are responsible for bone formation during embryogenesis and bone regeneration and remodeling. The osteoinductive action of BMPs, especially BMP-2 and BMP-7, has led to their use in a range of insurmountable treatments where intervention is required for effective bone regeneration. Introduction of BMP products to the market, however, was not without reports of multiple complications and side effects. Aiming for optimization of the therapeutic efficacy and safety, efforts have been focused on improving the delivery of BMPs to lower the administered dose, localize the protein, and prolong its retention time at the site of action. A major challenge with these efforts is that the protein stability should be maintained. With this review we attempt to shed light on how the stability of BMPs can be affected in the formulation and delivery processes. We first provide a short overview of the current standing of the complications experienced with BMP products. We then discuss the different delivery parameters studied in association with BMPs, and their influence on the efficacy and safety of BMP treatments. In particular, the literature addressing the stability of BMPs and their possible interactions with components of the delivery system as well as their sensitivity to conditions of the formulation process is reviewed. In summary, recent developments in the fields of bioengineering and biopharmaceuticals suggest that a good understanding of the relationship between the formulation/delivery conditions and the stability of growth factors such as BMPs is a prerequisite for a safe and effective treatment.

The role of bone marrow aspirate cells in the management of atrophic mandibular fractures by mini-invasive surgical approach: Single-institution experience

PURPOSE

The treatment of fractures involves addressing the biology of fracture repair and the mechanical stability of fracture fixation. Traditionally it has included the addition of bone graft to enhance healing. New advances in the understanding of the cellular and molecular mechanisms of fracture repair have led to the use of growth factors to accelerate bone healing. This study aimed to assess the advantages of autologous stem cell use for atrophic mandibular fracture treatment in comparison to standard technique.

MATERIALS AND METHODS

A total of 35 patients (14 male and 21 female) were treated for fractures of atrophic mandibles between January 2011 and December 2014. Surgical technique provided mini-invasive open reduction with or without immediate homologous bone graft, while selected patients received autologous bone marrow aspirate cell grafts in addition to the standard treatment. Demographic data and details of treatment and outcomes were recorded.

RESULTS

Patients were categorized according to the use of autologous stem cells, leaving 17 patients treated with standard technique and autologous stem cells (Group A) and 18 treated with standard osteosynthesis only (Group B). Of the 35 patients, 26 had bilateral fractures; most patients had significant medical co-morbidities. Immediate bone graft was used in 37.1% of patients (7 in group A and 6 in group B). Complications occurred in 5 patients (14.3%). Two patients in group B (11.1%) showed non-union of the fracture. One patient in group A (5.8%) and one patient in group B (5.5%) showed wound dehiscence and were treated conservatively; one patient in group B had a local infection (5.5%), one out of 35 (2.8%), that was managed by prolonged antibiotic treatment.

CONCLUSIONS

Despite the advanced age and medical co-morbidities of the vast majority of patients, mini-invasive open approach with autologous bone graft ensures a fast and excellent recovery. Moreover, the management of atrophic mandibular fractures by bone marrow aspirate cells is a safe and useful procedure which has a lower complication rate when compared to standard technique.

Application of calcium phosphates and fibronectin as complementary treatment for osteoporotic bone fractures

INTRODUCTION

The gradual aging of the population results in increased incidence of osteoporotic bone fractures. In a good quality bone, the fixation with the usual methods is adequate, but not in osteoporotic bone, in which consolidation delays and other complications are common, with failure rates for screws up to 25%.

OBJECTIVE

To test fibronectin loaded hydroxyapatite as a complementary treatment for osteoporotic fractures.

MATERIAL AND METHODS

This study was performed in a vivo model; 42 female osteoporotic adult rabbits 4-5kg (White New Zealand) were used. Two groups (hydroxyapatite and fibronectin loaded hydroxyapatite) and a control group were tested. 3 time points 24h, 48h and 5days were studied. Defects were created in both femurs, in one of them, a cannulated screw (4mm) and a biocompatible material were placed; in the other femur a screw was inserted without supplemented material forming the control group. Osteoporosis was induced from models already known throughout administration of steroids. Samples were analyzed histologically and through imaging (micro Ct).

RESULTS

Basal levels of BMD are observed below to normal when compared to other studies (0.25/0.3 instead of 0.4). Global and dependent of time analysis of samples, show no significant differences for samples analyzed. However, an important trend was noted for variables that define the trabecular bone microarchitecture. Indices that define trabecular microarchitecture in the comparative analysis found to have statistical differences (p<0.01).

DISCUSSION

Osteosynthesis in an osteoporotic bone is a challenge for the surgeon, due to a reduced bone mineral density and different bone architecture. The main finding was the verification of the hypothesis that the trabecular bone parameters increases with our augmentation material in weak rabbit bone quality. Also, the histological analyses of samples show an increase of non inflammatory cells in protein samples (OHAp-Fn) from the first 24hours.

CONCLUSION

An early response of rabbit osteroporotic bone to a complementary treatment with fibronectin loaded hydroxyapatite has been observed. This response is reflected in greater values for indices that define the trabecular bone microarchitecture, thickness and separation, a greater non-inflammatory cellularity after only 24hours and an increased amount of connective tissue observed at 48hours.

Bone Morphogenetic Protein for the Healing of Tibial Fracture: A Meta-Analysis of Randomized Controlled Trials

PURPOSE

To review the evidence from RCTs on clinical outcomes and benefit of acute tibial fracture and nonunion treated with and without BMPs.

MATERIAL

We searched multiple databases (MEDLINE, EMABSE, BIOSIS and Cochrane central) as well as reference lists of articles and contacted authors. Evaluated outcomes included union rate, revision rate, hardware failure and infection. The weighted and standard mean difference (WMD and SMD) or the relative risk (RR) was calculated for continuous or dichotomous data respectively. The quality of the trial was assessed, and meta-analyses were performed with the Cochrane Collaboration's REVMAN 5.0 software.

RESULTS

Eight RCTs involving 1113 patients were included. For acute tibial fracture, BMP group was associated with a higher rate of union (RR, 1.16; 95% CI, 1.04 to 1.30) and a lower rate of revision (RR, 0.68; 95% CI, 0.54 to 0.85) compared with control group. No significant differences were found in rate of hardware failure and infection. The pooled RR for achieving union for tibial fracture nonunion was 0.98 (95% CI, 0.86 to 1.13). There was no significant difference between the two groups in the rate of revision (RR, 0.48; 95% CI, 0.13 to 1.85) and infection (RR, 0.61; 95% CI, 0.37 to 1.02).

CONCLUSION

Study on acute tibial fractures suggests that BMP is more effective that controls, for bone union and for decreasing the rate of surgical revision to achieve union. For the treatment of tibial fracture nonunion, BMP leads to similar results to as autogenous bone grafting. Finally, well-designed RCTs of BMP for tibial fracture treatment are also needed.

Salvianolic acid B promotes bone formation by increasing activity of alkaline phosphatase in a rat tibia fracture model: a pilot study

BACKGROUND

Radix Salviae miltiorrhizae is a herb frequently used within traditional Chinese medicine for the treatment of cardiovascular- and trauma-related diseases. Danshen is the dried root of Salviae miltiorrhizae, from which the polyphenolic compound Salvianolic acid B (Sal B) can be obtained. Sal B is a key component of Danshen. The aim of this study was to determine the effect of Sal B on the healing of long bones following trauma in a rat tibia fracture model.

METHODS

Tibia fractures were created in 20 male Sprague Dawley rats. The animals were divided into two groups: (1) experimental group (n = 10); and (2) control group (n = 10). Rats in the experimental group were intraperitoneally administered with Sal B (40 mg/kg/d) for 3 weeks, while rats in the control group received an identical volume of physiological saline solution, administered in the same way. X-ray photographs were taken of all animals at the time points. Rats were euthanized at weeks 1, 3, 8 and 12 post-fracture. Fracture calluses were measured and callus sections were obtained and stained using hematoxylin and eosin (HE) and the calcium cobalt method. HE stained sections were observed and evaluated according to different grades of bone remodeling. Sections stained using the calcium cobalt method were analyzed with an imagine analysis system.

RESULTS

Data showed that callus growth was significantly greater in the experimental group compared with the control group (P < 0.05). Furthermore, histological scores in the Sal B-treated group were statistically higher than in the saline treated group at weeks 1, 3 and 8 post-fracture (P < 0.05). Alkaline phosphatase (ALP) activity was enhanced in the experimental group at weeks 1 and 3 post-fracture (P < 0.05).

CONCLUSIONS

Our results suggest that Sal B may accelerate early-stage fracture healing. Increased activity of ALP may be one factor which promotes the healing process. This pilot study provides brief insight into the effect of Sal B in fracture healing. These findings will contribute to the development of more and enhanced treatment options for trauma fracture patients.

Acute Intravenous Injection Toxicity Study of Escherichia coli-Derived Recombinant Human Bone Morphogenetic Protein-2 in Rat

Study Design

Prospective in vivo toxicity study.

Purpose

To evaluate the conducted acute toxicity study of Escherichia coli (E. coli)-derived recombinant human bone morphogenetic protein-2 (rhBMP-2) with 6-weeks old Sprague-Dawley rats.

Overview of Literature

rhBMP-2 has well-known osteoinductivity and it is used as a bone graft substitute. E. coli-derived rhBMP-2 can be mass-produced with relatively low costs. E. coli-derived rhBMP-2 facilitates osteoblastic differentiation and bone formation in vitro and in vivo. However, studies regarding side effects or toxicity of E. coli-derived rhBMP-2 have not been published. Thus, we conducted the acute toxicity study of E. coli-derived rhBMP-2 on 6-weeks old Sprague-Dawley rats.

Methods

One mg of BMP-2 was diluted in 0.285 mL of glycine buffer to prepare high BMP-2 concentrations (3.5 mg/mL). Intermediate (0.9 mg/mL) or low (0.35 mg/mL) concentrations of BMP-2 solution was prepared by serial dilutions. The compound was administrated at a dose of 0, 0.7, 1.8, 7 mg/kg by single intravenous injection to five of male and female rats. After the injection, the gross general observations including changes of body weight and histopathological analysis was performed for 14 days.

Results

No animal was found dead during the experiment and the body weight changes were both statistically insignificant in the control and experimental groups. No abnormal sign was shown in general observations and autopsy examinations.

Conclusions

Thus, the lethal dose of E. coli-derived rhBMP-2 should be higher than 7 mg/kg with a single intravenous injection.

Tissue engineered strategies for pseudoarthrosis

Numerous classification systems of non-union have been proposed based on: presence or absence of infection, radiographic features, clinical findings, biologic activity, location and shape. The management of pseudarthrosis is strongly related to the type of non-union (infected versus uninfected, atrophic versus hypertrophic). Surgical management of pseudarthrosis is generally effective with a success rate ranging from 75 to 100%. Nevertheless, in a relatively high number of instances several combined treatments are required for the fracture healing. The current gold standard to stimulate the bone regeneration is represented by the revision surgery with the application of autologous bone grafts. However, several approaches have been described to promote and enhance the bone tissue regeneration, including extracorporeal shock wave therapy (ESWT), ultrasound, electromagnetic, bone morphogenic proteins (BMPs) and platelet-rich-plasma (PRP).The aim of the present study was to perform a systematic review of the literature evaluating the current therapies to promote and enhance the bone tissue healing. The systematic review was performed according to PRISMA guidelines with a PRISMA checklist and algorithm.Limitations of the present systematic review are mainly related to the scanty quality of the studies available in the literature. Although the therapies previously described for the management of patients with non-unions seems to be effective, the limitations of the included studies, especially the extensive clinical heterogeneity, make not possible to provide clear recommendations regarding the application of these approaches. The problems remain the need to better understand the most effective treatment options, subject to surgical stabilization as a first step.

PEG matrix enables cell-mediated local BMP-2 gene delivery and increased bone formation in a porcine critical size defect model of craniofacial bone regeneration

PURPOSE

This study addressed the suitability of a polyethylene glycol (PEG) matrix as scaffold for cell-mediated local BMP-2 gene transfer in a calvarial critical size defect (CSD) model.

MATERIALS AND METHODS

PEG matrix (degradation time 10 days) and PEG membrane (degradation time 120 days) were used in the pig calvarial model. Cylindrical (1 × 1 cm) CSD (9 per animal; 20 animals) were filled with: (i) HA/TCP, covered by PEG membrane (group 1); (ii) HA/TCP, mixed with PEG matrix (group 2); and (iii) HA/TCP mixed with BMP-2 transfected osteoblasts and PEG matrix (group 3). BMP-2/4 gene transfer: liposomal in vitro transfection of BMP-2/V5-tag fusion-protein. Quantitative histomorphometry (toluidine blue staining) after 2, 4 and 12 weeks assessed bone formation. Semiquantitative immunohistochemistry estimated the expression of BMP-2 and V5-tag.

RESULTS

Group 3 showed significantly higher new bone formation than groups 1, 2 at 4 (P < 0.05) and 12 (P < 0.02) weeks. BMP-2-V5-tag was detected for 4 weeks. BMP-2 expression in group 3 was higher compared to all other groups after 2 and 4 (P < 0.02) weeks.

CONCLUSIONS

The PEG matrix serves as scaffold for cell-mediated BMP-2 gene delivery in guided bone regeneration facilitating cell survival and protein synthesis for at least 4 weeks. Local BMP-2 gene delivery by PEG matrix-embedded cells leads to increased bone formation during critical size defect regeneration.

Human adipose derived stem cells reduce callus volume upon BMP-2 administration in bone regeneration

INTRODUCTION

The demand for new therapeutic approaches to treat bone defects and fractures is increasing in trauma surgery and orthopaedics because the number of patients with degenerative diseases is continuously growing. "Tissue Engineering" offers promising new technologies that combine the three components - cells, growth factors and matrix. Efforts are targeted at improving and accelerating recovery, especially for long bone fractures, and reducing the risk of delayed bone healing or pseudoarthrosis. Adult human adipose-derived stem cells (ASC) can differentiate into osteoblasts in an osteogenic surrounding. Bone morphogenetic protein-2 (BMP-2) accelerates and initiates this differentiation. Fibrin, a matrix that promotes wound healing, is a promising carrier for ASCs and BMP-2.

MATERIALS AND METHODS

In this study, a 2mm transcortical drill hole in the femur of male rats served as a small non-critical size defect model for fracture simulation. In vivo bone healing was investigated upon administration of the growth factor BMP-2 embedded with ASCs in a locally applied fibrin matrix. Groups with the components alone were also investigated. After 2 and 4 weeks, μCT and histology were performed to determine the bone and callus volume.

RESULTS AND DISCUSSION

After only a short period of time (2 and 4 weeks), this animal model discloses comparative information about the osteogenetic potential and bone regeneration with little effort (no osteosynthesis necessary). The most significant result found in this model is that the combination of ASCs and BMP-2 in a fibrin matrix significantly reduces callus formation after 2 weeks compared to BMP-2 alone. BMP-2 alone significantly increased callus formation. ASCs embedded alone in the fibrin matrix did not lead to increased bone regeneration.

CONCLUSION

Transplantation of ASC modulated the callus induction by BMP-2 to a normal volume.

Apatite-coated collagen scaffold for bone morphogenetic protein-2 delivery

Bone morphogenetic proteins (BMPs) are the most potent osteoinductive growth factors. BMP-2 is clinically used for spine fusion and bone fracture healing. Commercially available BMP-2 uses a type I collagen scaffold as a carrier, but it only releases BMP-2 for a short period of time, which may release the bone formation efficacy. In the present study, we hypothesize that apatite coating of a collagen scaffold increases the release period as well as the osteogenic efficacy of BMP-2. Apatite coating was achieved by incubating collagen scaffolds in simulated body fluids (SBFs). Apatite coating on collagen scaffolds was confirmed by X-ray diffraction, electron spectroscopy for chemical analysis, attenuated total reflectance-Fourier transform infrared spectroscopy, and scanning electron microscopy. The rate and period of BMP-2 release from apatite-coated collagen scaffolds varied depending on the concentration of SBFs used. The 5× and 10× SBF apatite-coated collagen scaffolds released 91.8%±11.5% and 82.2%±13.1% of their loaded BMP-2 over 13 days in vitro, respectively, whereas noncoated collagen scaffold released 98.3%±2.2% over the initial one day. BMP-2 released from apatite-coated collagen scaffold significantly increased the alkaline phosphatase activity of cultured osteoblasts, compared with BMP-2 released from noncoated collagen scaffold. Computed tomography and histomorphometry showed that BMP-2 delivery using apatite-coated collagen scaffolds resulted in 2.5-fold higher bone formation volume and 4.0-fold higher bone formation area than BMP-2 delivery using noncoated collagen scaffolds. This study shows that simple apatite coating of a collagen scaffold results in a BMP-2 carrier that renders long-term release of BMP-2 and dramatically enhances osteogenic efficacy.

Bone morphogenic protein: an elixir for bone grafting--a review

Bone morphogenetic proteins (BMPs) are multifunctional growth factors that belong to the transforming growth factor beta superfamily. This literature review focuses on the molecular biology of BMPs, their mechanism of action, and subsequent applications. It also discusses uses of BMPs in the fields of dentistry and orthopedics, research on methods of delivering BMPs, and their role in tissue regeneration. BMP has positive effects on bone grafts, and their calculated and timely use with other growth factors can provide extraordinary results in fractured or nonhealing bones. Use of BMP introduces new applications in the field of implantology and bone grafting. This review touches on a few unknown facts about BMP and this ever-changing field of research to improve human life.

Reindeer bone extract can heal the critical-size rat femur defect

Bone extract from reindeer induces new ectopic bone formation (BF) in muscle pouches, but its feasibility in experimental bone lesions has not been evaluated. We investigated the effects of implants, containing 2, 5, 15, 20 or 50 mg of reindeer bone extract in a collagen carrier, on the healing of 8-mm femur defects in 78 rats. We used 30 µg of recombinant human bone morphogenetic protein-2 (rhBMP-2) in a collagen carrier, collagen and untreated defects as controls. Bone healing was evaluated with radiographs, peripheral quantitative computed tomography (pQCT), biomechanics and histology. In comparison with empty defects, the groups receiving bone extracts showed more BF at three weeks and had better bone union (BU), larger mean cross-sectional bone area at the defect site in groups receiving higher doses of extract, showed greater torsional stiffness of the bones and higher maximum breaking load of bones at six weeks. In comparison to all other groups, in the rhBMP-2 group, BF and BU were best at the three- and six-week follow-up, bone area was largest and mechanical test results were best. Although rhBMP-2 is superior for new bone regeneration, native reindeer bone extract is also effective in the six-week follow-up period.

Enhancement of difficult nonunion in children with osteogenic protein-1 (OP-1): early experience

Numerous studies have described the use of osteogenic protein-1 (OP-1) in adults, but there are few reports in children. The objectives of this short-term followup cohort study were (1) to examine clinical and radiographic healing of persistent nonunions after OP-1 application in children; and (2) to determine the safety of OP-1 use in this sample. Clinical healing was defined by absence of pain and tenderness at the nonunion site and the ability to fully weight bear on the affected limb. Radiographic healing was determined by bony bridging of the nonunion site in at least one view. Safety was defined as the absence of major adverse events, including allergic reactions, infections, local inflammatory reactions, and heterotopic ossification. OP-1 was used in 19 patients who had an operative procedure for the bridging of persistent nonunions between 1999 and 2007. The mean age was 11.6 years (range, 4.8-20.3 years). Thirteen patients had persistent nonunion after one or more previous surgeries, prior to the initial OP-1 application. A single dose of 3.5 mg of OP-1 mixed with 1 g of Type I bovine collagen was applied to 23 sites of 19 patients. Three patients received additional OP-1 applications. Healing occurred clinically and radiographically in 17 of the 23 sites. Complications included four superficial pin site infections, one deep infection, and two fractures. No major local adverse event related to OP-1 application was noted in our sample. Our findings suggest OP-1 stimulates healing of persistent nonunions without major adverse events in our patient population.

LEVEL OF EVIDENCE

Level IV, case series. See the guidelines online for a complete description of levels of evidence.

Bone morphogenetic proteins in open fractures: past, present, and future

The management of open fractures continues to be complicated by high rates of treatment failure and significant patient disability and dissatisfaction. The use of bone morphogenetic proteins (BMPs) in the treatment of open fractures has been assessed by a number of different clinical trials, both in the acute management of open fractures and in the delayed reconstruction of bone defects secondary to open fracture. This review describes the scientific basis for the use of BMPs in open fractures, reviews the current evidence for their use in open fractures, provides grades of recommendation for the different uses of BMPs in open fractures, and identifies important areas for additional research.

Polyethylenimine-PEG coated albumin nanoparticles for BMP-2 delivery

Bone Morphogenetic Protein-2 (BMP-2) plays an important role in stimulating new bone formation, and has been utilized in clinical bone repair by implantation. In this study, we report a nanoparticulate (NP) system for BMP-2 delivery based on bovine serum albumin (BSA) NPs stabilized with a poly(ethylene glycol) modified polyethylenimine (PEI-PEG) coating. PEI-PEG with different PEG substitutions were synthesized, and the cell viability assay showed PEG substitution greatly reduced the cytotoxicity of the native PEI. Furthermore, PEI-PEG coated BSA NPs demonstrated smaller size and decreased zeta potential compared to PEI-coated NPs. The bioactivity of the encapsulated BMP-2 and the toxicity of PEI-PEG coated NPs were examined by the alkaline phosphatase (ALP) induction assay and the MTT assay, respectively, using human C2C12 cells. The results indicated that BMP-2 remained bioactive in NPs and PEI-PEG coating was advantageous in reducing the NP toxicity as compared to PEI. A 7-day pharmacokinetics study showed the BMP-2 retention in PEI-PEG coated NPs was similar to the uncoated NPs, but lower than that of the PEI-coated NPs. The osteoinductivity of BMP-2 delivered in NPs was determined by subcutaneous implantation in rats, and the results revealed that PEI-PEG coated BSA NPs induced significant de novo bone formation after implantation, while PEI-coated NPs demonstrated much less bone formation. We conclude that BMP-2 delivered by PEGylated PEI-coated BSA NPs displays favorable biocompatibility and promotes new bone formation after implantation.

Delivery of recombinant bone morphogenetic proteins for bone regeneration and repair. Part A: Current challenges in BMP delivery

Recombinant human bone morphogenetic proteins (rhBMPs) have been extensively investigated for developing therapeutic strategies aimed at the restoration and treatment of orthopaedic as well as craniofacial conditions. In this first part of the review, we discuss the rationale for the necessary use of carrier systems to deliver rhBMP-2 and rhBMP-7 to sites of bone tissue regeneration and repair. General requirements for growth factor delivery systems emphasizing the distinction between localized and release-controlled delivery strategies are presented highlighting the current limitations in the development of an effective rhBMP delivery system applicable in clinical bone tissue engineering.

Metallic Scaffolds for Bone Regeneration

Bone tissue engineering is an emerging interdisciplinary field in Science, combining expertise in medicine, material science and biomechanics. Hard tissue engineering research is focused mainly in two areas, osteo and dental clinical applications. There is a lot of exciting research being performed worldwide in developing novel scaffolds for tissue engineering. Although, nowadays the majority of the research effort is in the development of scaffolds for non-load bearing applications, primarily using soft natural or synthetic polymers or natural scaffolds for soft tissue engineering; metallic scaffolds aimed for hard tissue engineering have been also the subject of in vitro and in vivo research and industrial development. In this article, descriptions of the different manufacturing technologies available to fabricate metallic scaffolds and a compilation of the reported biocompatibility of the currently developed metallic scaffolds have been performed. Finally, we highlight the positive aspects and the remaining problems that will drive future research in metallic constructs aimed for the reconstruction and repair of bone.

Low-magnitude high-frequency vibration accelerates callus formation, mineralization, and fracture healing in rats

Fracture healing is a biological regenerative process that follows a well-orchestrated sequence. Most healing is uneventful and enhancement of normal fracture healing is not commonly done, although it is clinically important in the recovery and regain of functions after fracture. This study investigated the osteogenic effect of low-magnitude high-frequency vibration (LMHFV, 35 Hz, 0.3 g) on the enhancement of fracture healing in rats with closed femoral shaft fracture by comparing with sham-treated control. Assessments with plain radiography, micro-CT as well as histomorphometry showed that the amount of callus was significantly larger (p = 0.001 for callus area, 2 weeks posttreatment); the remodeling of the callus into mature bone was significantly faster (p = 0.039, 4 weeks posttreatment) in the treatment group. The mechanical strength of the healed fracture in the treatment group at 4 weeks was significantly greater (p < 0.001). The results showed the acceleration of callus formation, mineralization, and fracture healing in the treatment group. It is concluded that LMHFV enhances healing in the closed femoral shaft fracture in rats. The potential clinical advantages shall be confirmed in the subsequent clinical trials.

Growth factors in bone repair

The role of growth factors (GF) in bone repair is widely recognised, particularly for bone morphogenetic proteins (BMPs), fibroblast growth factor (FGF), insulin-like growth factors (IGFs), platelet-derived growth factor (PDGF), transforming growth factor-beta (TGF-beta) and vascular endothelial growth factor (VEGF). GF are usually stored in the extracellular matrix (ECM), but after injury are actively released by ECM, cells and platelets. In this paper, the use of different recombinant GF for bone repair stimulation is summarised in experimental research and clinical applications. Drug delivery systems, including carriers, cell or gene therapy, are needed to ensure a sustained local release of the factors, but efficacy and potential side effects of such systems require additional research prior to clinical applications. Current sources for delivery of a GF mixture into the site of bone repair are platelet gel and demineralised bone matrix. Nevertheless, the levels of GF in such preparations are affected by variability among donors and differences in preparation. Autogenous GF, produced by the patient himself during the bone repair process, potentially interfere with prosthetic devices or even have a role in implant loosening due to the periprosthetic tissue reaction. In conclusion, GF are key components of functional bone regeneration: screening of basic research results and controlled clinical trials are accelerating the development of GF in orthopaedic surgery.

Regional and cellular localisation of BMPs and their inhibitors' expression in human fractures

The objective of this study was to determine whether BMP-2 and -14, noggin, and chordin could be detected in human fractures and to assess their regional and cellular distribution. The expression of these proteins was detected by immunohistochemistry in an archive of human fractures. BMP-2 and BMP-14 expression was strongest in areas of cartilage formation and, to a lesser extent, in areas of bone formation. Within areas of cartilage formation, both BMP-2 and BMP-14 were expressed more strongly by the non-hypertrophic chondrocytes. The BMP inhibitors noggin and chordin were also expressed most intensely in areas of cartilage formation and there was no difference in their expression between the non-hypertrophic and hypertrophic chondrocytes. Our study demonstrates the expression of BMP-14 and the BMP inhibitors in human fractures for the first time, and our findings will contribute to an improved understanding of the physiological processes in bone repair.

Chordin knockdown enhances the osteogenic differentiation of human mesenchymal stem cells

INTRODUCTION

Bone morphogenetic proteins (BMPs) are critical growth factors in the osteogenic differentiation of progenitor cells during development in embryos and fracture repair in adults. Although recombinant BMPs are in use clinically, their clinical efficiency needs to be improved. The biological activities of BMPs are naturally regulated by extracellular binding proteins. The specific hypotheses tested in this study were as follows: the BMP inhibitor chordin is produced endogenously during the osteogenic differentiation of human mesenchymal stem cells (MSCs); and blockade of the activity of the BMP inhibitor increases the rate of osteogenic differentiation of human MSCs in vitro.

METHODS

Human MSCs were derived from bone marrow from an iliac crest aspirate and from patients undergoing hip hemiarthroplasty. The MSCs were induced down the osteogenic pathway using standard osteogenic differentiation media, and expressions of BMP-2 and chordin were determined by gene expression analysis. During osteogenic differentiation, chordin knockdown was induced using RNA interference. Osteogenic differentiation was assessed by measuring the expression of alkaline phosphatase and calcium deposition. The differences in expression of osteogenic makers between groups were compared by analysis of variance, followed by Gabriel post hoc test.

RESULTS

We demonstrate the expression of BMP-2 and chordin in human MSCs during osteogenic differentiation. Knockdown of chordin by RNA interference in vitro resulted in a significant increase in the expression of the osteogenic marker alkaline phosphatase and the deposition of extracellular mineral, in response to osteogenic stimulation.

CONCLUSION

We conclude that endogenously produced chordin constrains the osteogenic differentiation of human MSCs. The targeting of BMP inhibitors, such as chordin, may provide a novel strategy for enhancing bone regeneration.

Treatment of chronic nonunion of a sternal fracture with bone morphogenetic protein

Chronic nonunion of sternal fractures, up until now, has been treated by osteosynthetic plating with or without autologous bone grafting. A new technique is described involving the use of bone morphogenic protein to stimulate bone growth at the fracture site, thereby eliminating the need for bone grafting.

Expression of genes for bone morphogenetic proteins BMP-2, BMP-4 and BMP-6 in various parts of the human skeleton

Background

Differences in duration of bone healing in various parts of the human skeleton are common experience for orthopaedic surgeons. The reason for these differences is not obvious and not clear.

Methods

In this paper we decided to measure by the use of real-time RT-PCR technique the level of expression of genes for some isoforms of bone morphogenetic proteins (BMPs), whose role is proven in bone formation, bone induction and bone turnover. Seven bone samples recovered from various parts of skeletons from six cadavers of young healthy men who died in traffic accidents were collected. Activity of genes for BMP-2, -4 and -6 was measured by the use of fluorescent SYBR Green I.

Results

It was found that expression of m-RNA for BMP-2 and BMP-4 is higher in trabecular bone in epiphyses of long bones, cranial flat bones and corpus mandibulae then in the compact bone of diaphyses of long bones. In all samples examined the expression of m-RNA for BMP-4 was higher than for BMP-2.

Conclusion

It was shown that m-RNA for BMP-6 is not expressed in the collected samples at all. It is postulated that differences in the level of activation of genes for BMPs is one of the important factors which determine the differences in duration of bone healing of various parts of the human skeleton.

Bone morphogenetic proteins in clinical applications

The role of bone morphogenetic proteins (BMPs) in bone healing has been shown in numerous animal models. To date, at least 20 BMPs have been identified, some of which have been shown in vitro to stimulate the process of stem cell differentiation into osteoblasts in human and animal models. Having realized the osteoinductive properties of BMPs and having identified their genetic sequences, recombinant gene technology has been used to produce BMPs for clinical application - most commonly, as alternatives or adjuncts in the treatment of cases in which fracture healing is compromised. BMP-2 and BMP-7 are approved for clinical use in open fractures of long bones, non-unions and spinal fusion. However, despite significant evidence of their potential benefit to bone repair and regeneration in animal and preclinical studies, there is, to date, a dearth of convincing clinical trials. The purpose of this paper is to give a brief overview of BMPs and to critically review the clinical data currently available on the use of BMP-2 and BMP-7 in fracture healing.

Fracture healing: the diamond concept

Fracture healing is a complex physiological process. With the latest advances made in molecular biology and genetics it is now known that it involves the spatial and temporal coordinated action of several different cell types, proteins and the expression of hundreds of genes working towards restoring its structural integrity without scar formation. The standard tissue engineering approach to provide solutions for impaired fracture healing, bone restoration and regeneration includes the utilisation of growth factors, scaffolds and mesenchymal stem cells (triangular concept). However, although the mechanical environment is discussed and is considered as an important element in bone regeneration, its importance is often underestimated and it is not always given the necessary attention. The available scientific evidence supports the view that all the 4 known factors contributing to bone restoration should be given an equal acknowledgment and recognition. The traditional discussed triangular concept therefore should be reconsidered and be accepted as the 'diamond concept'.

Osteoinduction in human fat-derived stem cells by recombinant human bone morphogenetic protein-2 produced in Escherichia coli

Bioactive recombinant human bone morphogenetic protein-2 (rhBMP-2) was obtained using Escherichia coli pET-25b expression system: 55 mg purified rhBMP-2 were achieved per g cell dry wt, with up to 95% purity. In murine C2C12 cell line, rhBMP-2 induced an increase in the transcription of Smads and of osteogenic markers Runx2/Cbfa1 and Osterix, measured by semi-quantitative RT-PCR. Bioassays performed in human fat-derived stem cells showed an increased activity of the early osteogenic marker, alkaline phosphatase, and the absence of cytotoxicity.

Autologous iliac crest bone graft: should it still be the gold standard for treating nonunions?

Nonunion is a common complication following long-bone fracture, with a prevalence that ranges from 2.5-46%, depending on the location and severity of the injury to the bone, soft tissue, and vascular structures. The treatment of nonunions involves addressing the biology of fracture repair and the mechanical stability of fracture fixation, which are interrelated. Nonunion treatment has traditionally included the addition of autograft from the iliac crest to enhance healing. However, there an associated morbidity with the harvesting of the graft, and alternatives such as bone marrow aspirate, platelet-rich plasma, allograft, and ceramics have also been studied. In addition, new advances in the understanding of the cellular and molecular mechanisms of fracture repair have led to the use of growth factors, such as bone morphogenetic proteins, to accelerate bone healing. This article reviews the benefits of iliac crest bone graft relative to those of other modalities in the treatment of nonunions.