Porous tricalcium phosphate and transforming growth factor used for anterior spine surgery

Peptide Enhanced Bone Graft Substitute Presents Improved Short-Term Increase in Bone Volume and Construct Stiffness Compared to Iliac Crest Autologous Bone in an Ovine Lumbar Interbody Fusion Model

STUDY DESIGN

Preclinical ovine model.

OBJECTIVE

To assess the in vivo efficacy and safety of the P-15 L bone graft substitute and compare its performance to autologous iliac crest bone graft (ICBG) for lumbar interbody fusion indications.

METHODS

Thirty skeletally mature sheep underwent lumbar interbody fusion surgery. Half of the sheep received autologous ICBG and the other half the peptide enhanced bone graft substitute (P-15 L). Following termination at 1, 3, and 6 months after surgery, the operated segments were analyzed using micro computed tomography (µCT), histology, and destructive mechanical testing. Additional systemic health monitoring was performed for the P-15 L group.

RESULTS

One month after surgery, there was only minor evidence of bone remodeling and residual graft material could be clearly observed within the cage. There was active bone remodeling between 1 and 3 months after surgery. At 3 months after surgery significantly denser and stiffer bone was found in the P-15 L group, whereas at 6 months, P-15 L and ICBG gave similar fusion results. The P-15 L bone graft substitute did not have any adverse effects on systemic health.

CONCLUSIONS

The drug device combination P-15 L was demonstrated to be effective and save for lumbar interbody fusion as evidenced by this ovine model. Compared to autologous ICBG, P-15 L seems to expedite bone formation and remodeling but in the longer-term fusion results were similar.

Local bone metabolism during the consolidation process of spinal interbody fusion

INTRODUCTION

Although computed tomography (CT) can identify the presence of eventual bony bridges following lumbar interbody fusion (LIF) surgery, it does not provide information on the ongoing formation process of new bony structures. ¹⁸F sodium fluoride (¹⁸F-NaF) positron emission tomography (PET) could be used as complementary modality to add information on the bone metabolism at the fusion site. However, it remains unknown how bone metabolism in the operated segment changes early after surgery in uncompromised situations. This study aimed to quantify the changes in local bone metabolism during consolidation of LIF.

MATERIALS AND METHODS

Six skeletally mature sheep underwent LIF surgery. ¹⁸F-NaF PET/CT scanning was performed 6 and 12 weeks postoperatively to quantify the bone volume and metabolism in the operated segment. Bone metabolism was expressed as a function of bone volume.

RESULTS

Early in the fusion process, bone metabolism was increased at the endplates of the operated vertebrae. In a next phase, bone metabolism increased in the center of the interbody region, peaked, and declined to an equilibrium state. During the entire postoperative time period of 12 weeks, bone metabolism in the interbody region was higher than that of a reference site in the spinal column.

CONCLUSION

Following LIF surgery, there is a rapid increase in bone metabolism at the vertebral endplates that develops towards the center of the interbody region. Knowing the local bone metabolism during uncompromised consolidation of spinal interbody fusion might enable identification of impaired bone formation early after LIF surgery using ¹⁸F-NaF PET/CT scanning.

Early bone ingrowth and segmental stability of a trussed titanium cage versus a polyether ether ketone cage in an ovine lumbar interbody fusion model

BACKGROUND CONTEXT

Lumbar interbody fusion is an effective treatment for unstable spinal segments. However, the time needed to establish a solid bony interbody fusion between the two vertebrae may be longer than twelve months after surgery. During this time window, the instrumented spinal segment is assumed to be at increased risk for instability related complications such as cage migration or subsidence. It is hypothesized that the design of new interbody cages that enable direct osseointegration of the cage at the vertebral endplates, without requiring full bony fusion between the two vertebral endplates, might shorten the time window that the instrumented spinal segment is susceptible to failure.

PURPOSE

To quantify the bone ingrowth and resulting segmental stability during consolidation of lumbar interbody fusion using two different cage types.

STUDY DESIGN

Preclinical ovine model.

METHODS

Seven skeletally mature sheep underwent bi-segmental lumbar interbody fusion surgery with one conventional polyether ether ketone (PEEK) cage, and one newly developed trussed titanium (TT) cage. After a postoperative time period of 13 weeks, non-destructive range of motion testing, and histologic analysis was performed. Additionally, sample specific finite element (FE) analysis was performed to predict the stability of the interbody fusion region alone.

RESULTS

Physiological movement of complete spinal motion segments did not reveal significant differences between the segments operated with PEEK and TT cages. The onset of creeping substitution within the cage seemed to be sooner for PEEK cages, which led to significantly higher bone volume over total volume (BV/TV) compared with the TT cages. TT cages showed significantly more direct bone to implant contact (BIC). Although the mean stability of the interbody fusion region alone was not statistically different between the PEEK and TT cages, the variation within the cage types illustrated an all-or-nothing response for the PEEK cages while a more gradual increase in stability was found for the TT cages.

CONCLUSIONS

Spinal segments operated with conventional PEEK cages were not different from those operated with newly developed TT cages in terms of segmental stability but did show a different mechanism of bone ingrowth and attachment. Based on the differences in development of bony fusion, we hypothesize that TT cages might facilitate increased early segmental stability by direct osseointegration of the cage at the vertebral endplates without requiring complete bony bridging through the cage.

CLINICAL SIGNIFICANCE

Interbody cage type affects the consolidation process of spinal interbody fusion. Whether different consolidation processes of spinal interbody fusion result in clinically significant differences requires further investigation.

β-tricalcium phosphate for bone substitution: Synthesis and properties

β-tricalcium phosphate (β-TCP) is one the most used and potent synthetic bone graft substitute. It is not only osteoconductive, but also osteoinductive. These properties, combined with its cell-mediated resorption, allow full bone defects regeneration. Its clinical outcome is sometimes considered to be "unpredictable", possibly due to a poor understanding of β-TCP physico-chemical properties: β-TCP crystallographic structure is not fully uncovered; recent results suggest that sintered β-TCP is coated with a Ca-rich alkaline phase; β-TCP apatite-forming ability and osteoinductivity may be enhanced by a hydrothermal treatment; β-TCP grain size and porosity are strongly modified by the presence of minute amounts of β-calcium pyrophosphate or hydroxyapatite impurities. The aim of the present article is to provide a critical, but still rather comprehensive review of the current state of knowledge on β-TCP, with a strong focus on its synthesis and physico-chemical properties, and their link to the in vivo response. STATEMENT OF SIGNIFICANCE: The present review documents the richness, breadth, and interest of the research devoted to β-tricalcium phosphate (β-TCP). β-TCP is synthetic, osteoconductive, osteoinductive, and its resorption is cell-mediated, thus making it one of the most potent bone graft substitutes. This comprehensive review reveals that there are a number of aspects, such as surface chemistry, crystallography, or stoichiometry deviations, that are still poorly understood. As such, β-TCP is still an exciting scientific playground despite a 50 year long history and > 200 yearly publications.

ß-TCP bone substitutes in tibial plateau depression fractures

BACKGROUND

The use of beta-tricalciumphospate (ß-TCP, Cerasorb®) ceramics as an alternative for autologous bone-grafting has been outlined previously, however with no study focusing on both clinical and histological outcomes of ß-TCP application in patients with multi-fragment tibial plateau fractures. The aim of this study was to analyze the long-term results of ß-TCP in patients with tibial plateau fractures.

METHODS

52 patients were included in this study. All patients underwent open surgery with ß-TCP block or granulate application. After a mean follow-up of 36months (14-64months), the patients were reviewed. Radiography and computed-tomography were performed, while the Rasmussen score was obtained for clinical outcome. Furthermore, seven patients underwent biopsy during hardware removal, which was subsequently analyzed by histology and backscattered electron microscopy (BSEM).

RESULTS

An excellent reduction with two millimeters or less of residual incongruity was achieved in 83% of the patients. At follow-up, no further changes occurred and no nonunions were observed. Functional outcome was good to excellent in 82%. Four patients underwent revision surgery due to reasons unrelated to the bone substitute material. Histologic analyses indicated that new bone was built around the ß-TCP-grafts, however a complete resorption of ß-TCP was not observed.

DISCUSSION

ß-TCP combined with internal fixation represents an effective and safe treatment of tibial plateau depression fractures with good functional recovery. While its osteoconductivity seems to be successful, the biological degradation and replacement of ß-TCP is less pronounced in humans than previous animal studies have indicated.

Biomaterials for Craniofacial Bone Regeneration

Functional reconstruction of craniofacial defects is a major clinical challenge in craniofacial sciences. The advent of biomaterials is a potential alternative to standard autologous/allogenic grafting procedures to achieve clinically successful bone regeneration. This article discusses various classes of biomaterials currently used in craniofacial reconstruction. Also reviewed are clinical applications of biomaterials as delivery agents for sustained release of stem cells, genes, and growth factors. Recent promising advancements in 3D printing and bioprinting techniques that seem to be promising for future clinical treatments for craniofacial reconstruction are covered. Relevant topics in the bone regeneration literature exemplifying the potential of biomaterials to repair bone defects are highlighted.

Radiographic and computed tomographic evaluation of bone union after medial opening wedge high tibial osteotomy with filling gap

BACKGROUND

We evaluated bone union and remodelling in patients undergoing opening-wedge high tibial osteotomy (OWHTO) with bone gaps filled with beta-tricalcium phosphate. We examined the effectiveness of radiography and computed tomography (CT) for the evaluation of bone union and remodelling, and investigated whether lateral hinge fractures affected bone union.

METHODS

Sixty-six cases underwent OWHTO with a combination of a TomoFix plate and a bone substitute. Bone union and remodelling were assessed using the rating system for OWHTO at three and six months, postoperatively.

RESULTS

Radiographic evaluation showed that bone union of the lateral hinge was 85% and 100% at three and six months, respectively. Based on CT evaluation, bone union of the lateral hinge and the flange was achieved in all cases at six months, and the bone union of the posterior cortex reached Zone 3 in 83% at six months. Based on radiographic evaluation, bone remodelling phases of bone substitute had progressed in each zone in six months compared with three months. Radiographic and CT analyses identified a Takeuchi type I hinge fracture in fourteen (21.2%) and five (7.6%) knees at two weeks postoperatively, respectively. There were no differences in bone union with and without the lateral hinge fracture.

CONCLUSIONS

The use of CT enabled us to evaluate the bone union of the flange and the extent of the bone union of the posterior cortex. Plain radiographs are useful to evaluate bone union of the lateral hinge similar to CT analysis. The presence of a Takeuchi type I hinge fracture did not affect bone union.

Nanohydroxyapatite promotes the healing process in open-wedge high tibial osteotomy: A CT study

BACKGROUND

The aim of this prospective and randomized study was to evaluate the effectiveness of adding nanohydroxyapatite (NHA) to heterologous bone graft in open wedge high tibial osteotomy (OWHTO) by measuring the bone density of the tibial osteotomy gap.

METHODS

Twenty-seven patients (26 knees) were operated by OWHTO and randomly divided into two groups: pure graft group, in which the osteotomy gap was filled with only heterologous bone graft; nanohydroxyapatite group, in which the osteotomy gap was filled with heterologous bone graft and NHA. All patients underwent computed tomography (CT) examination within one week after operation (Time 0), and after two months (Time 1) and 12months (Time 2). CT volume acquired Hounsfield Units (HU) were calculated and the mean value of bone density on three planes was measured.

RESULTS

At Time 0, the mineral density of the nanohydroxyapatite group appeared significantly higher compared with the pure graft group, due to the presence of NHA. At Time 1, the mineral density of the nanohydroxyapatite group had decreased relative to Time 0, while in the pure graft group it remained unchanged. At Time 2, the mineral density in the nanohydroxyapatite group had further decreased, reaching values close to the mineral density of normal bone. In contrast, in the pure graft group the mineral density had increased, probably due to the lack of reabsorption of the graft and the development of sclerosis in the osteotomy borders.

CONCLUSIONS

The results of the present study show better osseointegration of the heterologous graft when nanohydroxyapatite is added.

Design and characterization of calcium phosphate ceramic scaffolds for bone tissue engineering

OBJECTIVES

Our goal is to review design strategies for the fabrication of calcium phosphate ceramic scaffolds (CPS), in light of their transient role in bone tissue engineering and associated requirements for effective bone regeneration.

METHODS

We examine the various design options available to meet mechanical and biological requirements of CPS and later focus on the importance of proper characterization of CPS in terms of architecture, mechanical properties and time-sensitive properties such as biodegradability. Finally, relationships between in vitro versus in vivo testing are addressed, with an attempt to highlight reliable performance predictors.

RESULTS

A combinatory design strategy should be used with CPS, taking into consideration 3D architecture, adequate surface chemistry and topography, all of which are needed to promote bone formation. CPS represent the media of choice for delivery of osteogenic factors and anti-infectives. Non-osteoblast mediated mineral deposition can confound in vitro osteogenesis testing of CPS and therefore the expression of a variety of proteins or genes including collagen type I, bone sialoprotein and osteocalcin should be confirmed in addition to increased mineral content.

CONCLUSIONS

CPS are a superior scaffold material for bone regeneration because they actively promote osteogenesis. Biodegradability of CPS via calcium and phosphate release represents a unique asset. Structural control of CPS at the macro, micro and nanoscale and their combination with cells and polymeric materials is likely to lead to significant developments in bone tissue engineering.

Tri-calcium phosphate (ß-TCP) can be artificially synthesized by recycling dihydrate gypsum hardened

Calcium phosphate is known as a major component of biological hard tissues. This study aimed to produce calcium phosphate by recycling kneaded surplus gypsum. β-dihydrate gypsum was derived from commercial dental β-hemihydrate gypsum, which was mechanically powdered and mixed with the liquid component of a commercial zinc phosphate cement. This mixture was fired at 1,200°C and evaluated by XRD analysis, thermal analysis and scanning electron microscopy (SEM). An acceptable ratio of mixing was 4 g of β-dihydrate gypsum powder to 1.5 mL of phosphoric acid liquid. XRD peaks were monotonic below 800°C, but new ß-TCP was formed by firing at 900°C or more, although TG-DTA analysis of synthetic ß-TCP suggested that some residual dihydrate gypsum remained in the sample. SEM images indicated a fused-block bone-like structure covered with phosphorus and calcium. These results suggest that production of synthetic β-TCP is possible through ecological techniques using recycled materials.

Self-setting calcium orthophosphate formulations

In early 1980s, researchers discovered self-setting calcium orthophosphate cements, which are bioactive and biodegradable grafting bioceramics in the form of a powder and a liquid. After mixing, both phases form pastes, which set and harden forming either a non-stoichiometric calcium deficient hydroxyapatite or brushite. Since both of them are remarkably biocompartible, bioresorbable and osteoconductive, self-setting calcium orthophosphate formulations appear to be promising bioceramics for bone grafting. Furthermore, such formulations possess excellent molding capabilities, easy manipulation and nearly perfect adaptation to the complex shapes of bone defects, followed by gradual bioresorption and new bone formation. In addition, reinforced formulations have been introduced, which might be described as calcium orthophosphate concretes. The discovery of self-setting properties opened up a new era in the medical application of calcium orthophosphates and many commercial trademarks have been introduced as a result. Currently such formulations are widely used as synthetic bone grafts, with several advantages, such as pourability and injectability. Moreover, their low-temperature setting reactions and intrinsic porosity allow loading by drugs, biomolecules and even cells for tissue engineering purposes. In this review, an insight into the self-setting calcium orthophosphate formulations, as excellent bioceramics suitable for both dental and bone grafting applications, has been provided.

Long-term results of implants immediately placed into extraction sockets grafted with β-tricalcium phosphate: a retrospective study

PURPOSE

The aim of this 10 year retrospective study was to evaluate the crestal bone loss around immediate implant placed in tricalcium phosphate (TCP) grafted extraction sockets

MATERIALS AND METHODS

Data were collected from files of 58 patients (33 females, 25 males, average age 54.78 years) undergoing immediate implant placement into fresh extraction socket with or without the use of TCP (Cerasorb, Curasan AG, Kleinostheim, Germany) grafting. After implant placement, horizontal gaps larger than 1.5 mm between the implant surface and the bony plate were grafted with TCP without the use of a membrane, while smaller gaps were not grafted. Two hundred fifty-four implants were inserted: 79 were placed immediately with the use of β-TCP as grafting material (group A), 175 were placed in healed extraction sites, with 61 implants placed with the use of β-TCP graft material (group B), and 114 implants were placed without any grafting material (group C). Bone loss recordings were performed using periapical radiography. Measurements were performed from the neck of the implant to level of the surrounding bone in the vertical dimension.

RESULTS

No implant was lost during the follow-up period. Statistical analysis showed no correlation between implant placement timing (delayed or immediate), the use of bone graft, and extent of bone loss.

CONCLUSION

The use of TCP (Cerasorb) as a grafting material during immediate implant placement allowed no bone loss in 72.1% of the implants, which was very similar to the nongrafted cases for which implants were placed in favorable conditions.

Synthesis of spherical calcium phosphate particles for dental and orthopedic applications

Calcium phosphate materials have been used increasingly in the past 40 years as bone graft substitutes in the dental and orthopedic fields. Accordingly, numerous fabrication methods have been proposed and used. However, the controlled production of spherical calcium phosphate particles remains a challenge. Since such particles are essential for the synthesis of pastes and cements delivered into the host bone by minimally-invasive approaches, the aim of the present document is to review their synthesis and applications. For that purpose, production methods were classified according to the used reagents (solutions, slurries, pastes, powders), dispersion media (gas, liquid, solid), dispersion tools (nozzle, propeller, sieve, mold), particle diameters of the end product (from 10 nm to 10 mm), and calcium phosphate phases. Low-temperature calcium phosphates such as monetite, brushite or octacalcium phosphate, as well as high-temperature calcium phosphates, such as hydroxyapatite, β-tricalcium phosphate or tetracalcium phosphate, were considered. More than a dozen production methods and over hundred scientific publications were discussed.

Controlling the biological function of calcium phosphate bone substitutes with drugs

There is a growing interest in bone tissue engineering for bone repair after traumatic, surgical or pathological injury, such as osteolytic tumor or osteoporosis. In this regard, calcium phosphate (CaP) bone substitutes have been used extensively as bone-targeting drug-delivery systems. This localized approach improves the osteogenic potential of bone substitutes by delivering bone growth factors, thus extending their biofunctionality to any pathological context, including infection, irradiation, tumor and osteoporosis. This review briefly describes the physical and chemical processes implicated in the preparation of drug-delivering CaPs. It also describes the impact of these processes on the intrinsic properties of CaPs, especially in terms of the drug-release profile. In addition, this review focuses on the potential influence of drugs on the resorption rate of CaPs. Interestingly, by modulating the resorption parameters of CaP biomaterials, it should be possible to control the release of bone-stimulating ions, such as inorganic phosphate, in the vicinity of bone cells. Finally, recent in vitro and in vivo evaluations are extensively reported.

Biomaterial delivery of morphogens to mimic the natural healing cascade in bone

Complications in treatment of large bone defects using bone grafting still remain. Our understanding of the endogenous bone regeneration cascade has inspired the exploration of a wide variety of growth factors (GFs) in an effort to mimic the natural signaling that controls bone healing. Biomaterial-based delivery of single exogenous GFs has shown therapeutic efficacy, and this likely relates to its ability to recruit and promote replication of cells involved in tissue development and the healing process. However, as the natural bone healing cascade involves the action of multiple factors, each acting in a specific spatiotemporal pattern, strategies aiming to mimic the critical aspects of this process will likely benefit from the usage of multiple therapeutic agents. This article reviews the current status of approaches to deliver single GFs, as well as ongoing efforts to develop sophisticated delivery platforms to deliver multiple lineage-directing morphogens (multiple GFs) during bone healing.

Fabrication, mechanical and in vivo performance of polycaprolactone/tricalcium phosphate composite scaffolds

This paper explores the use of selective laser sintering (SLS) for the generation of bone tissue engineering scaffolds from polycaprolactone (PCL) and PCL/tricalcium phosphate (TCP). Different scaffold designs are generated, and assessed from the point of view of manufacturability, porosity and mechanical performance. Large scaffold specimens are produced, with a preferred design, and are assessed through an in vivo study of the critical size bone defect in sheep tibia with subsequent microscopic, histological and mechanical evaluation. Further explorations are performed to generate scaffolds with increasing TCP content. Scaffold fabrication from PCL and PCL/TCP mixtures with up to 50 mass% TCP is shown to be possible. With increasing macroporosity the stiffness of the scaffolds is seen to drop; however, the stiffness can be increased by minor geometrical changes, such as the addition of a cage around the scaffold. In the animal study the selected scaffold for implantation did not perform as well as the TCP control in terms of new bone formation and the resulting mechanical performance of the defect area. A possible cause for this is presented.

BMP-2 and TGF-β3 do not prevent spontaneous degeneration in rabbit disc explants but induce ossification of the annulus fibrosus

INTRODUCTION

Different approaches for disc regeneration are currently under investigation. Beside gene therapy and tissue engineering techniques, the application of growth and differentiation factors own promising potential. Studies using reduced intervertebral disc models, such as cell or tissue fragment cultures, have limited validity and show controversial results depending on the employed experimental model. Therefore, the goal of the current study was to investigate the effect of BMP-2 and TGF-β3 on intervertebral disc degeneration using an in vitro full-organ disc/endplate culture system.

MATERIALS AND METHODS

Intervertebral rabbit disc explants were cultured in the presence of 1 μg/ml BMP-2 or TGF-β3 for 21 days in DMEM/F12 media. Nucleus and annulus were analyzed for gene expression of collagen type I and II (Col I/II), aggrecan, collagenases (MMP-1/MMP-13) with RT-qPCR, histological changes with bone and proteoglycan-specific staining (von Kossa, toluidine blue) and differences in cellularity (DNA) and proteoglycan content (alcian blue binding assay).

RESULTS

The results demonstrate that disc proteoglycan concentration decreased with time in the TGF-β3 and BMP-2 groups. In the annulus fibrosus (AF), TGF-β3 and BMP-2 resulted in an up-regulation of Col I and type II, and of aggrecan gene expression. In contrast, MMP genes were inhibited. In the nucleus, the growth factors decreased gene expression of aggrecan and spontaneous Col I up-regulation was inhibited by TGF-β3, whereas expression of Col II was decreased with BMP-2. There was no effect on expression of MMP-1 and MMP-13 for most sampling points. However, TGF-β3 and BMP-2 induced ossification of the AF was demonstrated by histology.

CONCLUSION

It can be concluded that both growth factors, at the tested concentrations, may not be suitable to regenerate the whole intervertebral disc organ but they are interesting candidates for being injected alone or in combination into a painful intervertebral disc to induce osseous fusion (spondylodesis).

Macroporous bioceramics: A remarkable material for bone regeneration

This review summarises the major developments of macroporous bioceramics used mainly for repairing bone defects. Porous bioceramics have been receiving attention ever since their larger surface area was reported to be beneficial for the formation of more rigid bonds with host tissues. The study of porous bioceramics is important to overcome the less favourable bonds formed between dense bioceramics and host tissues, especially in healing bone defects. Macroporous bioceramics, which have been studied extensively, include hydroxyapatite, tricalcium phosphate, alumina, and zirconia. The pore size and interconnections both have significant effects on the growth rate of bone tissues. The optimum pore size of hydroxyapatite scaffolds for bone growth was found to be 300 µm. The existence of interconnections between pores is critical during the initial stage of tissue ingrowth on porous hydroxyapatite scaffolds. Furthermore, pore formation on β-tricalcium phosphate scaffolds also allowed the impregnation of growth factors and cells to improve bone tissues growth significantly. The formation of vascularised tissues was observed on macroporous alumina but did not take place in the case of dense alumina due to its bioinert nature. A macroporous alumina coating on scaffolds was able to improve the overall mechanical properties, and it enabled the impregnation of bioactive materials that could increase the bone growth rate. Despite the bioinertness of zirconia, porous zirconia was useful in designing scaffolds with superior mechanical properties after being coated with bioactive materials. The pores in zirconia were believed to improve the bone growth on the coated system. In summary, although the formation of pores in bioceramics may adversely affect mechanical properties, the advantages provided by the pores are crucial in repairing bone defects.

Effect of β-tricalcium phosphate coated with zoledronic acid on human osteoblasts and human osteoclasts in vitro

The combination of a bone graft material with bisphosphonates (BPs) might be advantageous for an optimal balance of material resorption and stimulation of bone formation. This study investigated the effect of β-tricalcium phosphate (β-TCP) bone grafts coated with zoledronic acid (ZOL) on osteoblast-like cells and osteoclast-like cells (OLC). As a drug carrier, the polymer poly(D,L-lactide) was used and three different concentrations of ZOL were tested. β-TCP coated with ZOL stimulated the production of osteocalcin (OC), osteoprotegerin, and sRANKL in osteoblast-like cells. The polymer coating alone caused a significant increase in collagen type 1 and OC production. OLC viability was inhibited and the tartrate-resistant acidic phosphatase isoform-5b was significantly decreased after cultivation on polymer-coated β-TCP for 12 days. The three different concentrations of ZOL decreased cell viability and no TRAPiso-5b was detectable, indicating a strong reduction of the TRAPiso-5b after 12 days in culture. After 21 days in culture, only the higher ZOL concentrations significantly reduced cell viability and TRAPiso-5b. The results of this study show that coating of β-TCP with ZOL has stimulating effects on osteoblast-like cells. Additionally, an inhibition of osteoclasts was seen. The combination of this bone grafting material with BPs might, therefore, be effective in the treatment of large bone defects.

Personalized implant for high tibial opening wedge: Combination of solid freeform fabrication with combustion synthesis process

In this work a new generation of bioceramic personalized implants were developed. This technique combines the processes of solid freeform fabrication (SFF) and combustion synthesis (CS) to create personalized bioceramic implants with tricalcium phosphate (TCP) and hydroxyapatite (HA). These porous bioceramics will be used to fill the tibial bone gap created by the opening wedge high tibial osteotomy (OWHTO). A freeform fabrication with three-dimensional printing (3DP) technique was used to fabricate a metallic mold with the same shape required to fill the gap in the opening wedge osteotomy. The mold was subsequently used in a CS process to fabricate the personalized ceramic implants with TCP and HA compositions. The mold geometry was designed on commercial 3D CAD software. The final personalized bioceramic implant was produced using a CS process. This technique was chosen because it exploits the exothermic reaction between P2O5 and CaO. Also, chemical composition and distribution of pores in the implant could be controlled. To determine the chemical composition, the microstructure, and the mechanical properties of the implant, cylindrical shapes were also fabricated using different fabrication parameters. Chemical composition was performed by X-ray diffraction. Pore size and pore interconnectivity was measured and analyzed using an electronic microscope system. Mechanical properties were determined by a mechanical testing system. The porous TCP and HA obtained have an open porous structure with an average 400 µm channel size. The mechanical behavior shows great stiffness and higher load to failure for both ceramics. Finally, this personalized ceramic implant facilitated the regeneration of new bone in the gap created by OWHTO and provides additional strength to allow accelerated rehabilitation.

Bone substitutes in the Netherlands - a systematic literature review

Autologous bone grafting is currently considered as the gold standard to restore bone defects. However, clinical benefit is not guaranteed and there is an associated 8-39% complication rate. This has resulted in the development of alternative (synthetic) bone substitutes. The aim of this systematic literature review was to provide a comprehensive overview of literature data of bone substitutes registered in the Netherlands for use in trauma and orthopedic surgery. Brand names of selected products were used as search terms in three available databases: Embase, PubMed and Cochrane. Manuscripts written in English, German or Dutch that reported on structural, biological or biomechanical properties of the pure product or on its use in trauma and orthopedic surgery were included. The primary search resulted in 475 manuscripts from PubMed, 653 from Embase and 10 from Cochrane. Of these, 218 met the final inclusion criteria. Of each product, structural, biological and biomechanical characteristics as well as their clinical indications in trauma and orthopedic surgery are provided. All included products possess osteoconductive properties but differ in resorption time and biomechanical properties. They have been used for a wide range of clinical applications; however, the overall level of clinical evidence is low. The requirements of an optimal bone substitute are related to the size and location of the defect. Calcium phosphate grafts have been used for most trauma and orthopedic surgery procedures. Calcium sulphates were mainly used to restore bone defects after tumour resection surgery but offer minimal structural support. Bioactive glass remains a potential alternative; however, its use has only been studied to a limited extent.

The progress of early phase bone healing using porous granules produced from calcium phosphate cement

Objective

Bone grafting is a vital component in many surgical procedures to facilitate the repair of bone defects or fusions. Autologous bone has been the gold standard to date in spite of associated donor-site morbidity and the limited amount of available donor bone. The aim of this study was to investigate the progress of bone regeneration and material degradation of calcium phosphate granules (CPG) produced from a calcium phosphate self-setting cement powder compared to the use of autologous bone grafting in the treatment of "critical size defects" on load-bearing long bones of minipigs.

Methods

A critical size defect in the tibial metaphysis of 16 mini-pigs was filled either with autologous cancellous graft or with micro- and macroporous carbonated, apatic calcium phosphate granules (CPG) produced from a calcium phosphate self-setting cement powder. After 6 weeks, the specimens were assessed by X-ray and histological evaluation. The amount of new bone formation was analysed histomorphometrically.

Results

The semi-quantitative analysis of the radiological results showed a complete osseous bridging of the defect in three cases for the autograft group. In the same group five animals showed a beginning, but still incomplete bridging of the defect, whereas in the CPG group just two animals developed this. All other animals of the CPG group showed only a still discontinuous new bone formation. Altogether, radiologically a better osseous bridging was observed in the autograft group compared to the CPG group.

Histomorphometrical analysis after six weeks of healing revealed that the area of new bone was significantly greater in the autograft group concerning the central area of the defect zone (p < 0.001) as well as the cortical defect zone (p < 0.002). All defects showed new bone formation, but only in the autograft group defects regenerated entirely

Conclusions

Within the limits of the present study it could be demonstrated that autologous cancellous grafts lead to a significantly better bone regeneration compared to the application of calcium phosphate granules (CPG) produced from a calcium phosphate self-setting cement powder after 6 weeks. In the early phase of bone-healing, the sole application of CPG appears to be inferior to the autologous cancellous grafts in an in vivo critical size defect on load-bearing long bones of mini-pigs.

Remodeling potentials of biphasic calcium phosphate granules in open wedge high tibial osteotomy

INTRODUCTION

Biphasic calcium phosphate (BCP) has proved to be an effective bone substitute, but it's effectiveness and remodeling potential in open wedge high tibial osteotomy (OWHTO) has not been analyzed yet. This study sought to evaluate the bone healing and remodeling potentials of BCP granules using a radiographic rating system in biplanar OWHTO.

MATERIALS AND METHODS

Fifteen patients (15 knees) underwent biplanar OWHTO. Bone gaps were filled with BCP granules. For radiographic evaluation, remodeling was divided into four phases. Phase 1 was accepted as rounded osteotomy sites, with clear distinction between BCP and bone, phase 2 was accepted as whitened osteotomy sites, with distinction between BCP and bone still visible, phase 3 was accepted as distinction between BCP and bone not visible and cloudy bone formation and phase 4 was accepted as full reformation of BCP granules (4A-BCP visible, 4B-disappearence of BCP) with no sign of osteotomy. Bone union was confirmed with clinical (full weight bearing without pain) and radiographic evaluation (cortical bridging callus on radiographs and phase 3 or greater remodeling). The time to full remodeling and the starting point of the consolidation on anteroposterior radiographs were noted. Complications were also noted at each clinical follow-up.

RESULTS

Mean follow-up was 27.2 months. The mean age was 55.8 years. At clinical follow-up, there were no wound healing problems, no loss of corrections, no infections, and no complications. All osteotomies successfully healed. According to the radiologic classification system, at the 6th week, 73.3% (11/15) of patients were in phase 1 and the remaining 26.7% (4/15) were in phase 2. At 12-month follow-up, 46.7 (7/15) of the patients were still in phase 3. After 2 years, all radiographs showed to be in phase 4A. Radiographic union was noted to progress from lateral to medial and finally central.

CONCLUSIONS

BCP can be successfully used as a bone substitute. The radiographic remodeling and consolidation process of BCP was found to be different from that of beta-tricalcium phosphate. In our patients with more than 2 years of follow-up, BCP granules did not completely remodel. As a result, this clinical study demonstrated that calcium phosphate granules containing hydroxyapatite had a long period of "creeping substitution" that lasts longer than 2 years.

Platelet-derived growth factor BB treated osteoprogenitors inhibit bone regeneration

The study evaluates the ability of osteoprogenitors treated with platelet-derived growth factor BB (PDGF-BB) delivered on vinyl styrene microbeads (VSM) to regenerate rat calvarial critical-size defects (CSDs). Fetal rat calvarial cells were cultured and tested for their ability to attach to VSM using scanning electron microscopy. Twenty-five rats were equally divided into 5 groups; a negative control (GPI), vinyl styrene microbeads (GPII), PDGF-BB (GPIII), VSM plus osteoblastic progenitors (GPIV), and VSM plus PDGF-BB treated osteoblastic progenitors (GPV). CSDs were created and reconstructed according to the mentioned study design. After 16 weeks, animals were sacrificed and defect areas evaluated for bone regeneration. Cells attached to the microbeads; however, their morphology and topography were affected by the PDGF-BB. Transplanting the VSM/cells constructs to CSDs revealed significant reduction of bone regeneration upon pretreatment of the cells with PDGF-BB. However, short-term application of PDGF-BB to CSD stimulated bone regeneration. The ability of osteoprogenitor cells to regenerate bone was significantly reduced upon pretreatment with PDGF-BB in vitro. However, adding PDGF-BB at the time of surgery had stimulated bone regeneration.

Calcium Orthophosphate Cements and Concretes

In early 1980s, researchers discovered self-setting calcium orthophosphate cements, which are a bioactive and biodegradable grafting material in the form of a powder and a liquid. Both phases form after mixing a viscous paste that after being implanted, sets and hardens within the body as either a non-stoichiometric calcium deficient hydroxyapatite (CDHA) or brushite, sometimes blended with unreacted particles and other phases. As both CDHA and brushite are remarkably biocompartible and bioresorbable (therefore, in vivo they can be replaced with newly forming bone), calcium orthophosphate cements represent a good correction technique for non-weight-bearing bone fractures or defects and appear to be very promising materials for bone grafting applications. Besides, these cements possess an excellent osteoconductivity, molding capabilities and easy manipulation. Furthermore, reinforced cement formulations are available, which in a certain sense might be described as calcium orthophosphate concretes. The concepts established by calcium orthophosphate cement pioneers in the early 1980s were used as a platform to initiate a new generation of bone substitute materials for commercialization. Since then, advances have been made in the composition, performance and manufacturing; several beneficial formulations have already been introduced as a result. Many other compositions are in experimental stages. In this review, an insight into calcium orthophosphate cements and concretes, as excellent biomaterials suitable for both dental and bone grafting application, has been provided.

Implantation of canine umbilical cord blood-derived mesenchymal stem cells mixed with beta-tricalcium phosphate enhances osteogenesis in bone defect model dogs

This study was performed to evaluate the osteogenic effect of allogenic canine umbilical cord blood-derived mesenchymal stem cells (UCB-MSCs) mixed with beta-tricalcium phosphate (beta-TCP) in orthotopic implantation. Seven hundred milligrams of beta-TCP mixed with 1 x 10(6) UCB-MSCs diluted with 0.5 ml of saline (group CM) and mixed with the same volume of saline as control (group C) were implanted into a 1.5 cm diaphyseal defect and wrapped with PLGC membrane in the radius of Beagle dogs. Radiographs of the antebrachium were made after surgery. The implants were harvested 12 weeks after implantation and specimens were stained with H&E, toluidine blue and Villanueva-Goldner stains for histological examination and histomorphometric analysis of new bone formation. Additionally, UCB-MSCs were applied to a dog with non-union fracture. Radiographically, continuity between implant and host bone was evident at only one of six interfaces in group C by 12 weeks, but in three of six interfaces in group CM. Radiolucency was found only near the bone end in group C at 12 weeks after implantation, but in the entire graft in group CM. Histologically, bone formation was observed around beta-TCP in longitudinal sections of implant in both groups. Histomorphometric analysis revealed significantly increased new bone formation in group CM at 12 weeks after implantation (p < 0.05). When applied to the non-union fracture, fracture healing was identified by 6 weeks after injection of UCB-MSCs. The present study indicates that a mixture of UCB-MSCs and beta-TCP is a promising osteogenic material for repairing bone defects.

Resorbability of rigid beta-tricalcium phosphate wedges in open-wedge high tibial osteotomy: a retrospective radiological study

The open-wedge high tibial osteotomy (OWHTO) is a well accepted treatment modality for patients with osteoarthritis of the medial compartment associated with genu varum. To fill in the osteotomy gap 30% macroporosity rigid beta-tricalcium phosphate (beta-TCP) is frequently used as a stable resorbable bone substitute. However, the resorbability of these beta-TCP wedges is not known. The aim of this study was to investigate this. Twenty-one OWHTO procedures in seventeen patients were performed with the use of 30% macroporosity rigid beta-TCP wedges. The osteotomies were fixed using an angle-stable locking plate. Conventional AP and lateral radiographs were examined in order to assess the resorbability of the 30% macroporosity rigid beta-TCP wedges as a function of time. A radiological classification system consisting of five phases was used to monitor the resorption of the 30% macroporosity rigid beta-TCP wedges. The mean duration of follow-up was 62 months (+/-23 range of 28-99). In all 21 cases, remnants of the 30% macroporosity rigid beta-TCP wedges were still present at maximum follow-up. Although the boundaries between 30% macroporosity rigid beta-TCP wedges and bone remained slightly visible, all osteotomies were completely consolidated and full osseointegration took place. In 16 out of 21 knees the fixation system was removed after a mean duration of 32 months (+/-19 range of 6-62). In six out of 21 knees a conversion to a knee arthroplasty was performed after a mean duration of 56 months (+/-18 range of 37-82). The OWHTO did not interfere with the placement of knee prostheses. Complete resorption of 30% macroporosity rigid beta-TCP wedges did not take place up to 8 years after operation.

Single-level instrumented posterolateral fusion of lumbar spine with beta-tricalcium phosphate versus autograft: a prospective, randomized study with 3-year follow-up

STUDY DESIGN

A prospective, randomized clinical study comparing beta-tricalcium phosphate (beta-TCP) with autograft bone graft with follow-up of 3 years.

OBJECTIVE

To determine the efficacy of beta-TCP as a bone graft substitute combined with local autograft obtained from decompression compared with the use of autologous iliac crest bone graft in single-level instrumented posterolateral lumbar fusion.

SUMMARY OF BACKGROUND DATA

A variety of bone graft substitutes have been used in posterolateral lumbar fusion with different efficacy reported, but no controlled study was conducted on the clinical performance of beta-TCP in instrumented posterolateral lumbar fusion.

METHODS

Sixty-two patients with symptomatic degenerative lumbar spinal stenosis were treated with single-level instrumented posterolateral lumbar fusion. They were randomly assigned to fusion with beta-TCP combined with local bone obtained from the decompression (group A, n = 32) or autogenous iliac crest bone graft plus decompression bone (group B, n = 30). The patients were observed up for 3 years after surgery. The results were assessed clinically and radiographically.

RESULTS

There were no significant differences in recovery rate of Japanese Orthopedic Association score and SF-36 score at all time intervals. Successful radiographic fusion was documented in all patients in both treatment groups. All patients in group B, however, complained bone graft donor site pain although significant improvement of pain was observed during the follow-up.

CONCLUSION

Instrumented posterolateral fusion with beta-TCP combined with local autograft results in the same radiographic fusion rates and similar improvement of clinical outcomes and life quality compared with autograft alone. The authors therefore recommend the use of beta-TCP as bone graft substitute for instrumented posterolateral fusion of lumbar spine to eliminate the need of bone grafting harvesting from the ilium.

Osteopromotion with a plasmatransglutaminase on a beta-TCP ceramic

We investigated the osteopromotive properties of plasmatransglutaminase (F XIII), bone marrow and venous blood on a resorbable beta-tricalcium phosphate (beta-TCP) scaffold. A baseline binding and release study of F XIII from the scaffold showed a continuous release of 18% of the total dose after 48 h. The main study consisted of 18 adult sheep with cylindrical defects in both tibiae. The defects were filled with a beta-TCP cylinder impregnated either with bone marrow, venous blood, F XIII or sheep were treated with 1250 IU F XIII intravenously over 14 days (n = 4 in each group). The defects were left open in two sheep. QCT and histology was performed after 6 and 12 weeks. The best bone ingrowth was seen after 6 weeks in the bone marrow group and after 12 weeks in the local F XIII group. The highest ingrowth on the inside of the cylinder proving the osteopromoting potential of F XIII was found in the local F XIII group. In our opinion F XIII is a good and readily available osteopromoting agent which can be used with beta-TCP in cases of bone deficit to promote bone regeneration.

Use of 3D beta-tricalcium phosphate (Vitoss) scaffolds in repairing bone defects

Vitoss is the most porous (90%) of a number of beta-tricalcium phosphate osteoconductive bone fillers. Its inherent limitations are those of the calcium phosphate class, being a purely osteoconductive product without inherent structural stability and with a moderate resorption rate. Currently, a number of additives, composites and related compounds are under study at various stages. In animal experiments, Vitoss performs well in comparison with other synthetic grafts, and with marrow added in various ways, it rivals autograft. Clinical efficacy is established for Vitoss as a spinal graft extender, as well as for periodontal, dental and orthopedic tumor defects. Apart from recombinant human platelet-derived growth factor, clinical data is lacking on the addition of bone marrow, stem cells and growth factors.

Opening wedge high tibial osteotomy using 3D biomodelling Bonelike macroporous structures: case report

Two synthetic calcium phosphates in porous wedge shape, Bonelike and a commercial HA/beta-TCP biphasic material, were used as an alternative to bone autografts and allografts in the treatment of medial compartment osteoarthritis of varus knees. The structure of Bonelike has a 3D architecture that is computer controlled, and a composition that mimics the mineral composition of natural bone. The HA/beta-TCP biphasic material used as a control material in this study was prepared using conventional foaming based methods. No signs of inflammatory reactions were observed post-operatively for both materials. After 4 months signs of fusion at the osteotomy site and good integration of the implanted wedges were observed, showing good mechanical resistance. Concerning the final correction attained, the left knee revealed a satisfactory valgus of 10 degrees , but the right one only had a final value of 6 degrees . The clinical evaluation using International Knee Score (IKS) showed good outcome in all parameters with complete range of motion in both knees and climbing stairs without crutches with only slight pain.

Osteoconductive effects of vinyl styrene microbeads in rat calvarial defects

PURPOSE

The aim of the present study was to evaluate the use of the nonresorbable vinyl styrene microbeads (VSM) alloplast as a delivery vehicle for platelet-derived growth factor (PDGF-BB) in rat calvarial critical size defects.

MATERIALS AND METHODS

Seventy-three Long-Evans male rats were divided into 4 groups; a negative control, vinyl styrene microbeads (VSM), PDGF-BB, and VSM plus PDGF-BB. Critical size calvarial defects were carried out and isolated with membranes sandwiching the defects with their fillers. Animals were sacrificed after 2, 4, and 16 weeks classifying each group into 3 subgroups. Calvarial specimens were radiographed for evaluation of regenerated bone volume and densitometry histogram analysis. Specimens were divided mid-sagittally and stained with hematoxylin and eosin (H&E) and trichrome stain for qualitative and histomorphometric analysis using an image analysis software.

RESULTS

The VSM groups showed statistically higher defect fills than the VSM-free groups at all sacrifice times except for the VSM/PDGF group that showed this difference after 2 weeks in relation to the PDGF group and the negative control after 4 and 16 weeks. For the radiographic analysis, the VSM/PDGF group showed the lowest bone volume compared with the other groups except when it was compared with the 4 weeks VSM group. In contrast, the PDGF showed the highest bone volumes at all sacrifice times that were only significant when compared with the 4 weeks VSM group and the 4 and 16 weeks VSM/PDGF group.

CONCLUSIONS

VSM enhances bone defect fill whereas the VSM/PDGF-BB is not able to improve bone regeneration capacity when compared with VSM alone.

In vivo behavior of calcium phosphate scaffolds with four different pore sizes

The goal of the present study was to assess the effect of macropore size on the in vivo behavior of ceramic scaffolds. For that purpose, beta-tricalcium phosphate (beta-TCP) cylinders with four different macropore sizes (150, 260, 510, and 1220 microm) were implanted into drill hole defects in cancellous bone of sheep and their resorption behavior was followed for 6, 12 and 24 weeks. The scaffolds were evaluated for biocompatibility, and new bone formation was observed macroscopically, histologically and histomorphometrically. Histomorphometrical measurements were performed for the whole defect area and for the area subdivided into three concentric rings (outer, medial, and inner ring). All implants were tolerated very well as evidenced by the low amount of inflammatory cells and the absence of macroscopic signs of inflammation. Resorption proceeded fast since less than 5% ceramic remained at 24-week implantation. Hardly any effect of macropore size was observed on the in vivo response. Samples with an intermediate macropore size (510 microm) were resorbed significantly faster than samples with smaller macropore sizes (150 and 260 microm). However, this fast resorption was associated with a lower bone content and a higher soft tissue content. At 12 and 24 weeks, the latter differences had disappeared. Bone was more abundant in the outer ring than in the rest of the blocks at 6 weeks, and in the outer and medial ring compared to the inner ring at 12 weeks.

A preliminary study of the efficacy of Beta Tricalcium Phosphate as a bone expander for instrumented posterolateral lumbar fusions

The associated morbidity of allograft(s) as bone graft expanders in spinal surgery has prompted the search for alternatives. The efficacy of Vitoss/Beta Tricalcium Phosphate (B-TCP: OrthoVita, Malvern PA, USA), an artificial bone substitute, combined with lamina autograft (50:50 mix) in 40 prospective posterolateral fusions utilizing pedicle/screw instrumentation was analyzed. Multilevel lumbar laminectomies (average 3.7 levels) were accompanied by 1 (27 patients) and 2 level (13 patients) fusions. Two neuroradiologists independently assessed fusion progression on dynamic x-rays and 2D-CT studies performed at 3, 6, and up to 12 months postoperatively. Outcomes were quantified utilizing Odom Criteria and Short-Form 36 (SF-36) questionnaires (preoperatively; and 3, 6, and 12 months postoperatively). By the sixth postoperative month, fusion was neuroradiologically confirmed on both dynamic x-rays and CT studies for 26 of 27 single level fusions (1 pseudarthrosis), and 11 of 13 two level fusions (L4-S1). Odom Criteria 3, 6, and 12 months postoperatively revealed continued improvement for all patients. SF-36 outcomes, however, revealed deterioration on 2 Health Scales (Role Physical, Role Emotional) 3 and 6 months post-operatively, and minimal to marked improvement on 6 Health Scales (PF, V, PF, V, SF, BP). Twelve months postoperatively improvement occurred on all 8 Health Scales, exceeding pre-operative baselines; minimal (RP, GH), mild (MH), moderate (PF, BP, V, SF), and marked improvement (RE). Although Vitoss/B-TCP and laminar autograft resulted in pseudarthrosis for 1 of 27 single level and 2 of 13 two level posterolateral instrumented lumbar fusions, only 1 of the latter patients required a secondary fusion.

Mechanical and radiological assessment of the influence of rhTGFbeta-3 on bone regeneration in a segmental defect in the ovine tibia: pilot study

Limitations in the use of autologous bone graft, which is the gold standard therapy in bone defect healing, drive the search for alternative treatments. In this study the influence of rhTGFbeta-3 on mechanical and radiological parameters of a healing bone defect in the sheep tibia was assessed. In the sheep, an 18-mm long osteoperiosteal defect in the tibia was treated by rhTGFbeta-3 seeded on a poly(L/DL-lactide) carrier (n = 4). In a second group (n = 4), the defect was treated by the carrier only, in a third group (n = 4) by autologous cancellous bone graft, and in a fourth group (n = 2) the defect remained blank. The healing process of the defect was assessed by weekly in vivo stiffness measurements and radiology as well as by quantitative computed tomographic assessment of bone mineral density (BMD) every 4 weeks. The duration of the experiment was 12 weeks under loading conditions. In the bone graft group, a marginally significant higher increase in stiffness was observed than in the PLA/rhTGFbeta-3 group (p = 0.06) and a significantly higher increase than in the PLA-only group (p = 0.03). The radiographic as well as the computed tomographic evaluation yielded significant differences between the groups (p = 0.03), indicating the bone graft treatment (bone/per area, 83%; BMD, 0.57 g/cm(3)) performing better than the PLA/rhTGFbeta-3 (38%; 0.23 g/cm(3)) and the PLA-only treatment (2.5%; 0.09 g/cm(3)), respectively. Regarding the mechanical and radiological parameters assessed in this study, we conclude that rhTGFbeta-3 has a promoting effect on bone regeneration. However, under the conditions of this study, this effect does not reach the potential of autologous cancellous bone graft transplantation.

Harvesting local cylinder autograft from adjacent vertebral body for anterior lumbar interbody fusion: surgical technique, operative feasibility and preliminary clinical results

Autogenous iliac crest has long served as the gold standard for anterior lumbar arthrodesis although added morbidity results from the bone graft harvest. Therefore, femoral ring allograft, or cages, have been used to decrease the morbidity of iliac crest bone harvesting. More recently, an experimental study in the animal showed that harvesting local bone from the anterior vertebral body and replacing the void by a radio-opaque beta-tricalcium phosphate plug was a valid concept. However, such a concept precludes theoretically the use of posterior pedicle screw fixation. At one institution a consecutive series of 21 patients underwent single- or multiple-level circumferential lumbar fusion with anterior cages and posterior pedicle screws. All cages were filled with cancellous bone harvested from the adjacent vertebral body, and the vertebral body defect was filled with a beta-tricalcium phosphate plug. The indications for surgery were failed conservative treatment of a lumbar degenerative disc disease or spondylolisthesis. The purpose of this study, therefore, was to report on the surgical technique, operative feasibility, safety, benefits, and drawbacks of this technique with our primary clinical experience. An independent researcher reviewed all data that had been collected prospectively from the onset of the study. The average age of the patients was 39.9 (26-57) years. Bone grafts were successfully harvested from 28 vertebral bodies in all but one patient whose anterior procedure was aborted due to difficulty in freeing the left common iliac vein. This case was converted to a transforaminal interbody fusion (TLIF). There was no major vascular injury. Blood loss of the anterior procedure averaged 250 ml (50-350 ml). One tricalcium phosphate bone plug was broken during its insertion, and one endplate was broken because of wrong surgical technique, which did not affect the final outcome. One patient had a right lumbar plexopathy that was not related to this special technique. There was no retrograde ejaculation, infection or pseudoarthrosis. One patient experienced a deep venous thrombosis. At the last follow up (mean 28 months) all patients had a solid lumbar spine fusion. At the 6-month follow up, the pain as assessed on the visual analog scale (VAS) decreased from 6.9 to 4.5 (33% decrease), and the Oswestry disability index (ODI) reduced from 48.0 to 31.7 with a 34% reduction. However, at 2 years follow up there was a trend for increase in the ODI (35) and VAS (5). The data in this study suggest that harvesting a cylinder of autograft from the adjacent vertebral body is safe and efficient. Filling of the void defect with a beta-tricalcium phosphate plug does not preclude the use of posterior pedicle screw stabilization.

Successful posterior interlaminar fusion at the thoracic spine by sole use of beta-tricalcium phosphate

We report on a 43-year-old male who sustained an isolated distraction injury of the thoracic spine Th7/Th8 (AO/ASIF B 2.3) with wedge compression Th8 and sagittal split Th10 without neurological injury. A bisegmental posterior stabilisation and a monosegmental interlaminar fusion was the treatment of choice. A synthetic bone substitute, beta-tricalcium phosphate (beta-TCP, Chronos) without additional autogenous bone was used to achieve the monosegmental posterior fusion. The clinical course was favourable and 10 months postoperatively the implant was removed. On implant removal the CT scan showed a fused segment and intraoperatively it was found that the fusion was solidly healed. A biopsy was taken from the fusion mass and histology showed vital bone that was rich with osteocytes. Noncalcified osteoid surrounding the bone marrow cavity could be identified. Several studies and the reported case might indicate that osteoconductive material alone can be sufficient for achieving a solid fusion.

Osteopromotion by a beta-tricalcium phosphate/bone marrow hybrid implant for use in spine surgery

STUDY DESIGN

Experimental animal study. OBJECTIVE.: Evaluate osteopromotive properties of a beta-tricalcium phosphate (TCP) implant with different osteogenic substances in an animal study.

SUMMARY OF BACKGROUND DATA

Current research in spine surgery is focusing on resorbable bone implants because of the high morbidity after iliac crest graft harvesting. Therefore, several osteoconductive scaffolds are combined with osteoinductive substances.

METHODS

In 14 sheep, a critical size defect was performed on both tibiae. The sheep were randomized into 3 groups (4 sheep each) and a control group (2 sheep). In the treatment groups, the defects were filled with the beta-TCP scaffold impregnated with either venous blood, bone marrow from sternal aspiration, or a concentrated mononuclear cell suspension derived from sternal bone marrow aspiration. The sheep in each group were euthanized 6 and 12 weeks after the operation; the investigation included quantitative computerized tomography and histology.

RESULTS

The best bone formation occurred in the bone marrow group after 6 and 12 weeks, whereas no difference was found between the cell and venous blood groups. Only the bone marrow group showed bone formation inside the scaffold after 6 weeks. We conclude that a beta-TCP scaffold filled with bone marrow aspiration creates a biologic resorbable bone substitute with high osteopromoting capacity. Surprisingly, no better bone formation occurred in the concentrated cells group, which may be a result of technical reasons and needs to be further evaluated.

CONCLUSIONS

The combination of beta-TCP and bone marrow has superior osteopromotive properties to venous blood or concentrated mononuclear cells and can be used effectively as a substitute to iliac crest graft.

Biocompatibility and osseointegration of beta-TCP: histomorphological and biomechanical studies in a weight-bearing sheep model

The aim of the study was to investigate the biocompatibility, degradation, and biomechanical properties of beta-TCP (Cerasorb) in a weight-bearing sheep model. beta-TCP implant prototypes were implanted in the tibial head of adult merino sheep. After 6 and 12 months material explants were harvested for biomechanical, histological, and histomorphometrical analysis. Corresponding bone specimens of the intact bone of the contralateral leg were used as controls in the biomechanical test. Compression tests showed higher values for maximum fracture load, yield strength, and compression modulus after 6 and 12 months compared to control. Microscopically, the implants showed good osteoconduction and were incorporated into the bone; however, relevant amounts of beta-TCP were still present after 12 months. Histomorphological results revealed that beta-TCP had partially degraded between implantation and 6 months, but its share remained constant between 6 and 12 months. The bone volume fraction in the area of the implant (46% +/- 6.5%) was initially higher than in the corresponding bone area of the contralateral leg (31% +/- 9.6%), but after 12 months declined to 29% +/- 9.4% (control: 33% +/- 8.3%), while the share of beta-TCP remained constant at 36% +/- 12.2%. These findings were supported by microradiographic data. In conclusion, in a weight bearing implantation model beta-TCP showed good biocompatibility, osseointegration and beginning degradation, even though it was not further degraded between 6 and 12 months.

Mechanism of bone incorporation of β-TCP bone substitute in open wedge tibial osteotomy in patients

A histological study was performed of bone biopsies from 16 patients (17 biopsies) treated with open wedge high tibial osteotomies for medial knee osteoarthritis. The open wedge osteotomies were filled with a wedge of osteoconductive beta tricalcium phosphate (beta-TCP) ceramic bone replacement. At the time of removal of the fixation material, core biopsies of the area where the beta-TCP was located were taken at different follow-up periods (6-25 months). beta-TCP resorption, bone ingrowth and bone remodelling were studied. We hypothesized that the incorporation and remodelling process occurs similarly as in animals. Histology showed a good resorption of the beta-TCP with complete incorporation and remodelling into new bone. The different phases as described in animal studies were found. A correlation was found between histological findings and radiological assessment. In conclusion, beta-TCP appeared to be a bone replacement material with optimal biocompatibility, resorption characteristics and bone conduction properties for the clinical use.

Technological issues for the development of more efficient calcium phosphate bone cements: a critical assessment

The first calcium phosphate cements (CPCs) were discovered in the 1980s. Two decades later, the interest for these materials is still rising. The goal of the present document is to review the most recent achievements in the field and to analyze future directions in research and development.

Localized delivery of growth factors for bone repair

Delivery of growth factors for tissue (e.g. bone, cartilage) or cell repair (e.g. nerves) is about to gain important potential as a future therapeutic tool. Depending on the targeted cell type and its state of differentiation, growth factors can activate or regulate a variety of cellular functions. Therefore, strictly localized delivery regimens at well-defined kinetics appear to be logical prerequisites to assure safe and efficacious therapeutic use of such factors and avoid unwanted side effects and toxicity, a major hurdle in the clinical development of growth factor therapies so far. This review summarizes various approaches for localized growth factor delivery as focused on bone repair. Similar considerations may apply to other growth factors and therapeutic indications. Considering the vast number of preclinical studies reported in the area of growth factor-assisted bone repair, it surprises though that only two medical products for bone repair have so far been commercialized, both consisting of a collagen matrix impregnated with a bone morphogenetic protein. The marked diversity of the reported growth factors, delivery concepts and not yet standardized animal models adds to the complexity to learn from past preclinical studies presented in the literature. Nonetheless, it is now firmly established from the available information that the type, dose and delivery kinetics of growth factors all play a decisive role for the therapeutic success of any such approach. Very likely, all of these parameters have to be adapted and optimized for each animal model or clinical case. In the future, systems for localized growth factor delivery thus need to be designed in such a way that their modular components are readily adaptable to the individual pathology. To make such customized systems feasible, close cooperative networks of biomedical and biomaterials engineers, pharmaceutical scientists, chemists, biologists and clinicians need to be established.

Development of multifunctional polymer-mineral composite materials for bone tissue engineering

The main goal of this article is the development of a novel approach to construct multifunctional composite scaffolds for bone tissue engineering. For this purpose, different kinds of mineral macroporous supports, water-soluble aldehyde-containing copolymers of N-vinylpyrrolidone, as well as different nonspecific and biospecific ligands governing cell adhesion and growth have been used. The composite materials were tested initially for cytotoxicity in cell culture experiments using a model cell line.