Critically sized osteo-periosteal femoral defects: a dog model

Bio-integrated scaffold facilitates large bone regeneration dominated by endochondral ossification

Repair of large bone defects caused by severe trauma, non-union fractures, or tumor resection remains challenging because of limited regenerative ability. Typically, these defects heal through mixed routines, including intramembranous ossification (IMO) and endochondral ossification (ECO), with ECO considered more efficient. Current strategies to promote large bone healing via ECO are unstable and require high-dose growth factors or complex cell therapy that cause side effects and raise expense while providing only limited benefit. Herein, we report a bio-integrated scaffold capable of initiating an early hypoxia microenvironment with controllable release of low-dose recombinant bone morphogenetic protein-2 (rhBMP-2), aiming to induce ECO-dominated repair. Specifically, we apply a mesoporous structure to accelerate iron chelation, this promoting early chondrogenesis via deferoxamine (DFO)-induced hypoxia-inducible factor-1α (HIF-1α). Through the delicate segmentation of click-crosslinked PEGylated Poly (glycerol sebacate) (PEGS) layers, we achieve programmed release of low-dose rhBMP-2, which can facilitate cartilage-to-bone transformation while reducing side effect risks. We demonstrate this system can strengthen the ECO healing and convert mixed or mixed or IMO-guided routes to ECO-dominated approach in large-size models with clinical relevance. Collectively, these findings demonstrate a biomaterial-based strategy for driving ECO-dominated healing, paving a promising pave towards its clinical use in addressing large bone defects.

Short term outcomes and complications of distal ulnar ostectomy in 23 juvenile dogs with carpal valgus secondary to discordant radial-ulnar physeal growth

Objective

The goal of this study was to report short term clinical and radiographic outcomes after distal ulnar ostectomy in dogs with carpal valgus due to discordant radial-ulnar growth.

Study design

Retrospective case study.

Sample group

Client owned dogs under 1 year of age with carpal valgus and open distal radial physes pre-operatively.

Methods

Medical records from four veterinary referral centers were searched from January 1, 2015 to January 1, 2022 for juvenile dogs that had been treated with distal ulnar ostectomy for carpal valgus due to premature closure of the distal ulnar physis. Patients were excluded if they were skeletally mature at the time of ostectomy; medical records were incomplete; radial physis was closed at surgery; or definitive corrective osteotomy was performed. Radiographs were evaluated pre-operatively and for short term follow up at ~8 weeks. Complications and short term clinical outcomes were evaluated also.

Results

31 limbs from 23 dogs were evaluated. Patients ranged from 4 to 10.8 months of age. All dogs presented for visible carpal valgus and varying degrees of thoracic limb lameness. Sixty-four percent of patients showed resolution of lameness while an additional 13% showed an improvement in clinical lameness without complete resolution. Complications were seen in 32% of patients with 70% percent of those being minor, bandage related complications. Radiographically, 38% of limbs showed bridging callus formation of the ostectomy at an average of 7.5 weeks post operatively and 75% percent of patients with elbow incongruity improved radiographically. There was no significant difference in radial joint angles pre-operatively and at the time of follow up.

Conclusion

Distal ulnar ostectomy ameliorates lameness in juvenile dogs with premature distal ulnar physeal closure and shows lack of progression of distal carpal valgus deformity, but does not improve joint angulation.

Clinical significance

Distal ulnar ostectomy is associated with mild bandage-related complications and halting of progressive limb deformity within the time frame evaluated, and should therefore be considered a treatment for premature closure of the distal ulnar physis. It does not lead to deformity correction at 8 weeks following surgery but is associated with improved elbow congruity.

An overview of de novo bone generation in animal models

Some of the earliest success in de novo tissue generation was in bone tissue, and advances, facilitated by the use of endogenous and exogenous progenitor cells, continue unabated. The concept of one health promotes shared discoveries among medical disciplines to overcome health challenges that afflict numerous species. Carefully selected animal models are vital to development and translation of targeted therapies that improve the health and well-being of humans and animals alike. While inherent differences among species limit direct translation of scientific knowledge between them, rapid progress in ex vivo and in vivo de novo tissue generation is propelling revolutionary innovation to reality among all musculoskeletal specialties. This review contains a comparison of bone deposition among species and descriptions of animal models of bone restoration designed to replicate a multitude of bone injuries and pathology, including impaired osteogenic capacity.

Human placenta-derived matrix with cancellous autograft and demineralized bone matrix for large segmental long-bone defects in two dogs with septic nonunion

OBJECTIVE

To report the successful treatment of septic nonunion in two dogs with large segmental defects secondary to long-bone fractures by using a novel human placenta-derived matrix (hPM) as adjunct to fixation.

ANIMALS

One 3-kg 9-year-old neutered male Yorkshire terrier with a distal antebrachial fracture and one 6-kg 4-year-old spayed female miniature pinscher with a distal humeral fracture.

STUDY DESIGN

Short case series.

METHODS

Both dogs presented for septic nonunion after internal fixation of Gustilo type II open diaphyseal fractures from dog bite injuries. During revision, debridement of nonviable bone resulted in segmental defects of 32% and 20% of the bone length for the antebrachial and humeral fractures, respectively. The antebrachial fracture was stabilized with a circular external fixator, and the humeral fracture was stabilized with biaxial bone plating. The fracture sites were not collapsed, and full length was maintained with the fixation. Autogenous cancellous bone graft and canine demineralized bone allograft were packed into the defects, and hPM was injected into the graft sites after closure.

RESULTS

Radiographic union was documented at 8 weeks and 6 weeks for the antebrachial and humeral fractures, respectively. Both dogs became fully weight bearing on the affected limbs and returned to full activity.

CONCLUSION

Augmenting fixation with grafts and hPM led to a relatively rapid union in both dogs reported here.

Low-velocity Gunshot Injuries to the Femur: What Is the Utility of Stabilizing Incomplete Fractures?

INTRODUCTION

Extremity involvement is common among nonfatal gunshot injuries. Most of these injuries are low energy in nature and may be associated with fractures. Although displaced fractures of lower extremity long bones are often treated surgically, the purpose of this study was to review our experience in managing incomplete femur fractures caused by gunshot penetration and to develop treatment recommendations.

METHODS

We retrospectively reviewed clinical and radiographic data for 46 consecutive patients with incomplete femur fractures secondary to low-energy gunshot wounds. Fracture patterns included OTA/AO 31 (n = 7), 32 (n = 20), and 33 (n = 19). All fractures were nondisplaced and extra-articular. Type of treatment, clinical and radiographic healing, and related complications were recorded.

RESULTS

Thirty-two patients (70%) were managed nonsurgically with progressive weight bearing from toe touch to full weight bearing by 6 weeks of follow-up, whereas 14 patients (30%) underwent prophylactic fixation of the femur. No differences in treatment were seen based on age, body mass index, fracture pattern, or the presence of other fractures or systemic injuries. Two of the 32 patients (6.2%) treated nonsurgically for femoral shaft fractures fell subacutely after the original injury and displaced their fractures. Both underwent reduction and fixation. All other fractures maintained alignment until union. No infections or nonunions were seen. Among patients who underwent prophylactic fixation, two underwent removal of prominent implants after union.

DISCUSSION

Only 6% of incomplete femur fractures treated at our hospital required later surgery for fracture displacement. Although incomplete fractures occur infrequently, nonsurgical management with limited weight bearing seems to be successful and cost-effective for most patients. We propose initial nonsurgical management of nondisplaced femoral fractures secondary to cortical penetration from low-energy gunshot wounds.

Adipose Tissue-Derived Stromal Vascular Fraction Increases Osteogenesis in an Experimental Design Zygomatic Bone Defect Model

INTRODUCTION

Facial bone defects are frequently encountered problems in clinical practice. Bone grafts, flaps, and alloplastic materials are often used in their treatment. This leads to donor site morbidity and prolongation of the operation. The authors have planned this study to examine whether adipose tissue derived stromal vascular fraction (SVF) has an osteogenic effect in the critical sized membranous bone defect of the zygomatic bone.

MATERIALS AND METHODS

Twenty male Wistar Albino rats were used. Bilateral zygomatic arches were opened with lateral incisions. A standard 3-mm bone defect was created bilaterally on the zygomatic arches of the rats. In the experiment side, the stem cell-rich SVF that was obtained by applying centrifugal process to the adipose tissue derived from the inguinal fat pad was injected into the site of the right zygomatic arch bone defect. In the control side, left zygomatic arch was left for secondary bone healing without any treatment after a 3-mm critical bone defect was created. In the postoperative 10th (n:5) and 20th weeks (n:13), the healing areas of bone defects were assessed by a 3-dimensional tomography, and then, the rats were sacrificed and bone healing was examined histologically.

RESULTS

There were no statistically significant differences on the 10th week results. At the 20th week new bone formation amount calculated from the 3-dimensional computed tomography results was significantly higher in the experiment side (P = 0.033). In the histological examination at the 20th week, there was significantly more callus formation in the experiment side (P = 0.0112).

DISCUSSION

Stem cells can increase the rate of bone healing by differentiating into certain tissues. It is predicted that adipose tissue-derived SVF rich with mesenchymal stem cells can increase bone healing in facial bone defects and this application could replace the use of bone grafts and flaps in clinical practice. As a result, it is concluded that adipose tissue-derived stem cells can potentiate osteogenesis and reduce the possibility of developing necrosis on the bone ends.

Inhibition of GDF8 (Myostatin) accelerates bone regeneration in diabetes mellitus type 2

Metabolic diseases like diabetes mellitus cause bone healing deficiencies. We found significant impairment of bone regeneration, osteogenic differentiation and proliferation in diabetic bone. Moreover recent studies suggest a highly underestimated importance of GDF8 (Myostatin) in bone metabolism. Our goal was to analyze the role of GDF8 as a regulator of osteogenic differentiation, proliferation and bone regeneration. We used a murine tibial defect model in diabetic (Lepr^db-/-) mice. Myostatin-Inhibitor Follistatin was administered in tibial bony defects of diabetic mice. By means of histology, immunohistochemistry and QRT-PC osteogenesis, differentiation and proliferation were analyzed. Application of Myostatin-inhibitor showed a significant improvement in diabetic bone regeneration compared to the control group (6.5 fold, p < 0.001). Immunohistochemistry revealed a significantly higher proliferation (7.7 fold, p = 0.009), osteogenic differentiation (Runx-2: 3.7 fold, p = 0.011, ALP: 9.3 fold, p < 0.001) and calcification (4.9 fold, p = 0.024) in Follistatin treated diabetic animals. Therapeutical application of Follistatin, known for the importance in muscle diseases, plays an important role in bone metabolism. Diabetic bone revealed an overexpression of the catabolic protein Myostatin. Antagonization of Myostatin in diabetic animals leads to a restoration of the impaired bone regeneration and represents a promising therapeutic option.

Angle stable nails provide improved healing for a complex fracture model in the femur

BACKGROUND

Conventional nails are being used for an expanding range of fractures from simple to more complex. Angle stable designs are a relatively new innovation; however, it is unknown if they will improve healing for complex fractures.

QUESTIONS/PURPOSES

When comparing traditional and angle stable nails to treat complex open canine femur fractures, the current study addressed the following questions: do the two constructs differ in (1) radiographic evidence of bone union across the cortices; (2) stability as determined by toggle (torsional motion with little accompanying torque) and angular deformation; (3) biomechanical properties, including stiffness in bending, axial compression, and torsional loading, and construct failure properties in torsion; and (4) degree of bone tissue mineralization?

METHODS

Ten hounds with a 1-cm femoral defect and periosteal stripping were treated with a reamed titanium angle stable or nonangle stable nail after the creation of a long soft tissue wound. Before the study, the animals were randomly assigned to receive one of the nails and to be evaluated with biomechanical testing or histology. After euthanasia at 16 weeks, all operative femora were assessed radiographically. Histological or biomechanical evaluation was conducted of the operative bones with nails left in situ compared with the nonoperative contralateral femora.

RESULTS

Radiographic and gross inspection demonstrated hypertrophic nonunion in all 10 animals treated with the nonangle stable nail, whereas six of 10 animals treated with the angle stable nail bridged at least one cortex (p = 0.023). The angle stable nail construct demonstrated no toggle in nine of 10 animals, whereas all control femora exhibited toggle. The angle stable nail demonstrated less angular deformation and toggle (p ≤ 0.005) and increased compressive stiffness (p = 0.001) compared with the conventional nonangle stable nail. Histology demonstrated more nonmineralized tissue in the limbs treated with the conventional nail (p = 0.005).

CONCLUSIONS

Angle stable nails that eliminate toggle lead to enhanced yet incomplete fracture healing in a complex canine fracture model.

CLINICAL RELEVANCE

Care should be taken in tailoring the nail design features to the characteristics of the fracture and the patient.

Influence of gender and fixation stability on bone defect healing in middle-aged rats: a pilot study

BACKGROUND

Gender and stability of fixation independently influence bone regeneration but their combined effects are unclear.

QUESTIONS/PURPOSES

In a pilot study we determined the combined influence of gender and fixation stability on the callus of middle-aged rats regarding (1) biomechanical properties; (2) bridging over time; (3) callus formation; and (4) callus size, geometry, mineralization, and microstructure.

METHODS

We osteotomized the left femur of 32 Sprague-Dawley rats (12 months old). Femurs were externally fixed with a gap of 1.5 mm in four groups of eight animals each: female semirigid, male semirigid, female rigid, and male rigid. Qualitative and quantitative in vivo radiographic analyses were performed twice weekly. Six weeks postoperatively, harvested femora were evaluated using micro-CT and biomechanical testing.

RESULTS

Torsional stiffness and maximum torque at failure were higher in male and in semirigidly fixed fractures. Radiographic analysis revealed earlier bridging and callus formation in both male groups. Micro-CT analysis showed a larger callus size, altered geometry, and microstructure in males and semirigidly fixed animals, whereas mineralization was similar in all animals.

CONCLUSION

Our data suggest female gender represents an independent risk factor for bone healing in middle-aged rats. Although healing in females was delayed compared with males, they exhibited a similar response (superior callus properties) to a more semirigid fixation.

CLINICAL RELEVANCE

While female gender appears to reflect a risk for impaired bone healing in middle-aged female rats, clinical studies would be required to confirm the finding in humans.

Radiographic Assessment of Implant Failures of Titanium 3.5 LCP vs. 4.5 LCP Used for Flexible Bridging Osteosynthesis of Large Segmental Femoral Diaphyseal Defects in a Miniature Pig Model

The study describes types, absolute and relative numbers of implant failures in flexible bridging osteosynthesis using a six-hole 3.5 mm titanium Locking Compression Plate (n = 9) or a five-hole LCP 4.5 mm titanium (n = 40) selected for the fixation of segmental ostectomy of femoral diaphysis in the miniature pig used as an in vivo model in a study on the healing of a critically sized bone defect using transplantation of mesenchymal stem cells combined with biocompatible scaffolds within a broader research project. Occasional implant failure was evaluated based on radiographic examination of femurs of animals 2, 4, 8, 12 and 16 weeks after surgery. When bone defect was stabilized using 3.5 mm LCP, in 6 cases (66.7%) the screw was broken/lost in the proximal fragment of the femur 2 weeks after implantation (n = 4) and 4 weeks after implantation (n = 2). In 4 cases of these, the implant failure was accompanied also by loosening of the screw in position 3 in the proximal fragment of the femur. During ostectomy stabilization with 4.5 mm LCP, in 3 cases (7.5%) LCP was broken at the place of the empty central plate hole (without inserted screw) at the level of the segmental bone defect. Compared to the six-hole 3.5 mm LCP, the five-hole titanium 4.5 mm LCP is more suitable implant for flexible bridging osteosynthesis of a critically sized segmental defect of femoral diaphysis in the miniature pig. The results of this study will allow reducing implant failures in time- and cost-demanding transplantation experiments focused on bone healing.

Osteogenic proliferation and differentiation of canine bone marrow and adipose tissue derived mesenchymal stromal cells and the influence of hypoxia

The aim of this study was to compare the osteogenic and proliferative potential of canine mesenchymal stromal cells (cMSCs) derived from bone marrow (BM-cMSCs) and adipose tissue (AT-cMSCs). Proliferation potential was determined under varying oxygen tensions (1%, 5%, and 21% O(2)). Effects of reduced oxygen levels on the osteogenic differentiation of AT-cMSCs were also investigated. AT-cMSCs proliferated at a significantly faster rate than BM-cMSCs, although both cell types showed robust osteogenic differentiation. Culture in 5% and 1% O(2) impaired proliferation in cMSC from both sources and osteogenic differentiation in AT-cMSCs. Our data suggests that AT-cMSCs might be more suitable for use in a clinical situation, where large cell numbers are required for bone repair, due to their rapid proliferation combined with robust osteogenic potential. Our data also suggests that the inhibitory effects of hypoxia on both cell proliferation and differentiation should be considered when using MSCs in a potentially hypoxic environment such as a fracture site.

Repair of a segmental long bone defect in human by implantation of a novel multiple disc graft

Large segmental defects of the weight bearing long bones are very difficult to reconstruct. Current treatment options are afflicted with several limitations and disadvantages. We describe a novel approach to regenerate a segmental long bone defect in a patient using a multiple disc graft. Decellularized bovine trabecular bone discs were seeded with autologous bone marrow cells and cultured in a perfusion chamber for three weeks. Multiple cell-seeded discs were implanted to close a 72 mm defect of the distal tibia in a 58-year-old woman, and fixed by an intramedullary nail. Bone formation was assessed non-invasively by plain radiographs and 18F-labeled sodium fluoride-based co-registration of positron emission- and computed tomography (PET/CT). Bone was actively formed around the grafted defect as early as six weeks after surgery. Because the tibia was sufficiently stabilized, the patient was able to freely walk with full weight bearing 6 weeks after surgery. The uneventful two-year follow-up and the satisfaction of the patient demonstrated the success of the procedure. Therefore the use of multiple cell-seeded disc grafts can be considered as a treatment alternative for patients with segmental long bone defects.

Influence of age and mechanical stability on bone defect healing: age reverses mechanical effects

Non-unions and delayed healing are still prevalent complications in fracture and bone defect healing. Both mechanical stability and age are known to influence this process. However, it remains unclear which factor dominates and how they interact. Within this study, we sought a link between both factors. In 36 female Sprague-Dawley rats, the left femur was osteotomized, distracted to an osteotomy gap of 1.5 mm and externally fixated. Variation of age (12 vs. 52 weeks - biologically challenging) and fixator stiffness (mechanically challenging) resulted in 4 groups (each 9 animals): YS: young semi-rigid, OS: old semi-rigid, YR: young rigid and OR: old rigid. Qualitative and quantitative radiographical analyses were performed at weeks 2, 4 and 6 after surgery. Six weeks post-op, rats were sacrificed and femora were harvested for biomechanical testing (torsional stiffness (TS) and maximum torque at failure (MTF)). Six weeks after surgery, TS showed a significant interaction between age and fixation stiffness (p<0.0001). TS in YR was significantly higher than that in the other groups (YS: p<0.001; OR: p<0.001; OS: p<0.001). Additionally, YS showed a significantly higher TS compared to the OS (p=0.006) and OR (p=0.046). Testing of MTF showed a significant interaction of both variables (p=0.0002) and led to significant differences between OR and YS (p<0.001), OS (p=0.046) and YR (p<0.001). The YR showed a higher MTF compared to YS (p=0.012) and OS (p=0.001), whereas OR's MTF was inferior compared to OS. At 2-week follow-up, YR (p=0.006), and at 6-week follow-up, YS and YR (p=0.032) showed significantly higher radiographic scores. At 2-week follow-up, YS's callus was larger than that of the old groups (OS: p=0.025; OR: p=0.003). In YR a significantly smaller callus was observed compared to YS at time points 4 and 6 weeks (p=0.002 for both) and compared to OS at 6-week follow-up (p=0.03). The effect of age seems to invert the effect of mechanical properties of the callus, which was not correlated to callus size. Optimization of mechanics alone seems to be not sufficient. The underlying mechanisms and causes of the age-related influences and their clinical counterparts need to be further investigated.

BMP-silk composite matrices heal critically sized femoral defects

Clinical drawbacks of bone grafting prompt the search for alternative bone augmentation technologies such as use of growth and differentiation factors, gene therapy, and cell therapy. Osteopromotive matrices are frequently employed for the local delivery and controlled release of these augmentation agents. Some matrices also provide an osteoconductive scaffold to support new bone growth. In this study, silkworm-derived silk fibroin was evaluated as an osteoconductive matrix for healing critical sized mid-femoral segmental defects in nude rats. Four treatment groups were assessed over eight weeks: silk scaffolds (SS) with recombinant human BMP-2 (rhBMP-2) and human mesenchymal stem cells (HMSC) that had been pre-differentiated along an osteoblastic lineage ex vivo (Group I; pdHMSC/rhBMP-2/SS); SS with rhBMP-2 and undifferentiated HMSCs (Group II; udHMSC/rhBMP-2/SS); SS and rhBMP-2 alone (Group III; rhBMP-2/SS); and empty defects (Group IV). Bi-weekly radiographs revealed a progressive and similar increase in Group I-III mean defect mineralization through post-operative week (POW) 8. Radiographs, dual energy x-ray absorptiometry, and micro-computed tomography confirmed that Groups I-III exhibited similar substantial and significantly (p<0.05) greater defect mineralization at POW 8 than the unfilled Group IV defects which remained void of bone. No significant differences in Groups I-III defect healing at POW 8 were apparent using these same assays or mechanical testing. Histology at POW 8 revealed moderately good bridging of the parent diaphyseal cortices with woven and lamellar bone bridging islands of silk matrix in Groups I and III. Group II defects possessed comparatively less new bone which was most abundant adjacent to the parent bone margins. Elsewhere the silk matrix was more often enveloped by poorly differentiated loose fibrous connective tissue. Group IV defects showed minimal new bone formation. None of the treatment groups attained the mean mineralization or the mean biomechanical strength of identical defects implanted with SS and pdHMSCs alone in a previous study. However, addition of rhBMP-2 to SS prompted more bone than was previously generated using udHMSC/SS or SS alone. These data imply the clinical potential of silk scaffolds and rhBMP-2 as composite osteopromotive implants when used alone or with select stem cell populations. Additional studies in larger species are now warranted.

Nonlinear stiffness profiles of external fixators constructed with composite rods

OBJECTIVE

To determine if composite connecting rods confer nonlinear stiffness characteristics on unilateral and bilateral external skeletal fixators (ESF) in cranial-caudal bending and axial loading.

STUDY DESIGN

Mechanical testing performed on models.

SAMPLE POPULATION

Six models of 6-pin ESF constructs composed of birch dowels, a commercial ESF system, and composite connecting rods.

METHODS

Unilateral and bilateral ESF configurations were assembled using either specially designed composite titanium and silicone (composite group) or solid titanium (solid group) connecting rods. Mechanical testing was performed in axial loading and 4-point cranial-caudal bending. Stiffness was determined at a low and high-load range, and was considered increasing and nonlinear if the stiffness at high loads was greater than at low loads.

RESULTS

The stiffness of the solid group was linear in all testing modes and configurations. Bilateral composite fixators had a nonlinear increasing stiffness in axial loading and cranial-caudal bending. Unilateral composite fixators had a nonlinear increasing stiffness in axial loading, but not cranial-caudal bending. Solid connecting rods conferred a higher stiffness in all testing modes and configurations.

CONCLUSIONS

Composite connecting rods resulted in nonlinear increasing axial and bending stiffness in bilateral fixators, and in axial load in unilateral fixators.

CLINICAL RELEVANCE

Conventional ESF can be constructed so that the stiffness increases as load increases. This provides the surgeon with additional options to control the local mechanical environment of a healing fracture, which may be used to enhance fracture healing.

Mesenchymal stem cells and bone regeneration

OBJECTIVE

To review the role of mesenchymal stem cells (MSC) in bone formation and regeneration, and outline the development of strategies that use MSC in bone healing and regeneration.

STUDY DESIGN

Literature review.

METHODS

Medline review, synopses of authors' published research.

RESULTS

The MSC is the basic cellular unit of embryologic bone formation. Secondary bone healing mimics bone formation with proliferation of MSC then their differentiation into components of fracture callus. Bone regeneration, where large amounts of bone must form, mimics bone healing and can be achieved with MSC combined with strategies of osteogenesis, osteoinduction, osteoconduction, and osteopromotion. MSC based strategies first employed isolated and culture expanded stem cells in an osteoconductive carrier to successfully regenerate a critical segmental defect in the femur of dogs, which was as effective as autogenous cancellous bone. Because MSC appeared to be immunologically privileged, a study using mismatched allogeneic stem cells demonstrated that these cells would regenerate bone without inciting an immunologic response, documenting the possibility of banked allogeneic MSC for bone regeneration. A technique was developed for selectively retaining MSC from large bone marrow aspirates at surgery for bone regeneration. These techniques utilized osteoconductive and osteoinductive carriers and resulted in bone regeneration that was similar to autogenous cancellous bone.

CONCLUSION

MSC can be manipulated and combined with carriers that will result in bone regeneration of critically sized bone defects.

CLINICAL RELEVANCE

These techniques can be employed clinically to regenerate bone and serve as an alternative to autogenous cancellous bone.

Bone grafts prepared with selective cell retention technology heal canine segmental defects as effectively as autograft

Using a canine critical-size segmental defect model, a two-phased study was undertaken to evaluate the healing efficacy of demineralized bone and cancellous chips (DBM-CC) enriched with osteoprogenitor cells using a Selective Cell Retention (SCR) technology. The goals of this study were: 1) to determine the bone-healing efficacy of SCR-enriched grafts versus autograft, and 2) to assess the value of clotting SCR-enriched grafts with platelet-rich plasma (PRP). Thirty dogs were included in Phase I: 18 dogs were treated with an SCR-enriched DBM-CC graft clotted with autologous bone marrow, and were compared to 12 autograft controls. In Phase II, 24 animals were divided into 4 groups of 6 animals, each treated with a different bone graft material: 1) iliac crest autograft, 2) DBM-CC alone, 3) DBM-CC saturated with marrow, and 4) SCR-enriched DBM-CC clotted with PRP. All grafts were placed unilaterally in a 21-mm long osteoperiosteal femoral, instrumented, critical-size defect. Radiographs were obtained for all animals postoperatively and every 4-16 weeks; animals were then sacrificed. All femurs were prepared for histology. Femurs in the Phase II study were also analyzed by micro-CT. At 16 weeks, healing--defined by bridging bone across the defects--was observed in 50% of the DBM-CC alone group and 67% of the DBM-CC saturated with marrow group; 100% of the autograft and SCR-enriched DBM-CC groups were healed. Histologically, grafts clotted with PRP showed more mature bone than those implanted with autologous bone, which in turn were similar to those implanted with bone marrow clotted SCR-enriched grafts. These results demonstrated that: 1) SCR-enriched DBM-CC was equivalent to autograft to repair critical-size defects, and 2) while not statistically significant, PRP may have accelerated bone maturation when used to clot osteoprogenitor-enriched DBM-CC grafts--as compared to cell-enriched, DBM-CC grafts without PRP--in large animal models.

Vascular endothelial growth factor (VEGF-A) expression in human mesenchymal stem cells: autocrine and paracrine role on osteoblastic and endothelial differentiation

Angiogenesis is essential in bone fracture healing for restoring blood flow to the fracture site. Vascular endothelial growth factor (VEGF) and its receptor have been implicated in this process. Despite the importance of angiogenesis for the healing processes of damaged bones, the role of VEGF signaling in modulation of osteogenic differentiation in human mesenchymal stem cells has not been investigated in great detail. We examined the expression of VEGF-A and VEGFR-1 in human adult mesenchymal stem cells derived from trabecular bone (hTBCs). VEGF-A was found to be secreted in a differentiation dependent manner during osteogenesis. Transcripts for VEGF-A were also seen to be elevated during osteogenesis. In addition, transcripts for VEGF-A and the corresponding receptor VEGFR-1 were upregulated under hypoxic conditions in undifferentiated hTBCs. To investigate the signaling of VEGF-A on osteogenesis recombinant hTBCs were generated. High expression of VEGF-A stimulated mineralization, whereas high expression of sFLT-1, an antagonist to VEGF-A, reduced mineralization suggesting that VEGF-A acts as autocrine factor for osteoblast differentiation. In addition, VEGF-A secreted by hTBCs promotes sprouting of endothelial cells (HUVE) demonstrating a paracrine role in blood vessel formation. In summary, an in vitro analysis of transgene effects on cellular behavior can be used to predict an effective ex vivo gene therapy.

Properties of Human Trabecular Bone Cells from Elderly Women: Implications for Cell-Based Bone Engraftment

Tissue-engineered bone regeneration offers new therapeutic options in the treatment of patients with fractures. Due to the changes in the hormone levels, elderly women are most affected by bone fractures and thus constitute one of the future target groups of cell-based bone therapy. For designing cell-based therapy approaches, a better understanding of individual-dependent variations in bone-derived cells of the host is required. In this study, a simple, high-yield procedure is described for the collection of cells from bone tissue of a high number of elderly women. The cultured cells display stem cell characteristics indicated by the presence of a CD13+, CD44+, CD90+, CD147+, CD14-, CD34-, CD45- and CD144- cell populations and by a stable undifferentiated phenotype as well as by the ability to proliferate extensively while retaining the potential to differentiate along the osteoblastic lineage even after 27 cell doublings. A high variability in the number of cell-forming units (CFUs) within a donor population of 34 samples, in the morphology within 50 donors, in the expression of alkaline phosphatase within 15 samples and in the responsiveness to BMP-2 was evident, but no age-related correlation could be found. In conclusion, the data indicate that individual variations in cell number, cell morphology and in the osteogenic potential of progenitor cells of the patient may be relevant for a successful treatment of bone fractures in the elderly by cell-based therapy approaches.