Bone graft substitutes currently available in orthopaedic practice: the evidence for their use

In vitro and in vivo study of additive manufactured porous Ti6Al4V scaffolds for repairing bone defects

Metallic implants with a low effective modulus can provide early load-bearing and reduce stress shielding, which is favorable for increasing in vivo life-span. In this research, porous Ti6Al4V scaffolds with three pore sizes (300~400, 400~500, and 500~700 μm) were manufactured by Electron Beam Melting, with an elastic modulus range of 3.7 to 1.7 GPa. Cytocompatibility in vitro and osseointegration ability in vivo of scaffolds were assessed. hBMSCs numbers increased on all porous scaffolds over time. The group with intended pore sizes of 300 to 400 μm was significantly higher than that of the other two porous scaffolds at days 5 and 7. This group also had higher ALP activity at day 7 in osteogenic differentiation experiment. The scaffold with pore size of 300 to 400 μm was implanted into a 30-mm segmental defect of goat metatarsus. In vivo evaluations indicated that the depth of bone ingrowth increased over time and no implant dislocation occurred during the experiment. Based on its better cytocompatibility and favorable bone ingrowth, the present data showed the capability of the additive manufactured porous Ti6Al4V scaffold with an intended pore size of 300 to 400 μm for large segmental bone defects.

Three-dimensional printing akermanite porous scaffolds for load-bearing bone defect repair: An investigation of osteogenic capability and mechanical evolution

Some Ca-Mg-silicate ceramics have been widely investigated to be highly bioactive and biodegradable, whereas their osteogenic potential and especially biomechanical response in the early stage in vivo are scarcely demonstrated. Herein, the osteogenesis capacity and mechanical evolution of the akermanite (Ca₂MgSi₂O₇) porous materials manufactured by ceramic ink writing three-dimensional printing technique were investigated systematically in a critical size femur defect model, in comparison with the clinically available β-tricalcium phosphate porous bioceramic. Such three-dimensional printed akermanite scaffolds possess fully interconnected pores of ∼280 × 280 µm in size and over 50% porosity with appreciable compressive strength (∼71 MPa), that is 7-fold higher than that of the β-tricalcium phosphate porous bioceramics (∼10 MPa). After 6 weeks and 12 weeks of implantation, the percentage of newly formed bone and more new bone was observed in the akermanite group as compared with the β-tricalcium phosphate group (p < 0.01). Moreover, significant higher mRNA expressions of osteogenic genes were detected in the akermanite group by PCR analysis (p < 0.01). The in vivo mechanical strength decreased during the process of implantation, but maintained a relative high level (∼14 MPa) which was still higher than that of the host cancellous bone (5-10 MPa) at 12 weeks post-implantation. On the contrary, the β-tricalcium phosphate scaffold always exhibited a very low mechanical strength (∼8 MPa). These results suggest that the three-dimensional printed akermanite scaffolds are promising for the bone tissue regeneration and repair of load-bearing bone defects.

Innovating in the medical device industry - challenges & opportunities ESB 2015 translational research symposium

The European Society for Biomaterials 2015 Translational Research Symposium focused on 'Innovating in the Medical Device Industry - Challenges & Opportunities' from different perspectives, i.e., from a non-profit research organisation to a syndicate of small and medium-sized companies and large companies. Lecturers from regulatory consultants, industry and research institutions described the innovation process and regulatory processes (e.g., 510K, PMA, combination product) towards market approval. The aim of the present article is to summarise and explain the main statements made during the symposium, in terms of challenges and opportunities for medical device industries, in a constantly changing customer and regulatory environment.

Multilayer scaffolds in orthopaedic tissue engineering

PURPOSE

The purpose of this study was to summarize the recent developments in the field of tissue engineering as they relate to multilayer scaffold designs in musculoskeletal regeneration.

METHODS

Clinical and basic research studies that highlight the current knowledge and potential future applications of the multilayer scaffolds in orthopaedic tissue engineering were evaluated and the best evidence collected. Studies were divided into three main categories based on tissue types and interfaces for which multilayer scaffolds were used to regenerate: bone, osteochondral junction and tendon-to-bone interfaces.

RESULTS

In vitro and in vivo studies indicate that the use of stratified scaffolds composed of multiple layers with distinct compositions for regeneration of distinct tissue types within the same scaffold and anatomic location is feasible. This emerging tissue engineering approach has potential applications in regeneration of bone defects, osteochondral lesions and tendon-to-bone interfaces with successful basic research findings that encourage clinical applications.

CONCLUSIONS

Present data supporting the advantages of the use of multilayer scaffolds as an emerging strategy in musculoskeletal tissue engineering are promising, however, still limited. Positive impacts of the use of next generation scaffolds in orthopaedic tissue engineering can be expected in terms of decreasing the invasiveness of current grafting techniques used for reconstruction of bone and osteochondral defects, and tendon-to-bone interfaces in near future.

Calcaneal Ossoscopy

Both unicameral bone cysts and intraosseous lipoma of the calcaneus are rare entities that are mostly diagnosed because of unspecific heel pain, pathologic fracture, or as incidental finding. Minimally invasive ossoscopy with endoscopic resection of the tumor followed by grafting can potentially minimize risks of open surgery and speed up convalescence. We present our modifications to previously described techniques of endoscopic curettage with a particular focus on intraosseous lipoma and allogenic grafting. The key point for grafting is the use of a funnel-shaped ear speculum facilitating the plombage with allogenic cancellous bone chips. Compared with its alternatives, grafting with allogenic cancellous bone might prove favorable in this localization for several reasons: osteointegration, handling, availability, and costs. The objective of this technical note is to present a simple, safe, and cost-effective surgical technique for endoscopic surgical treatment of benign osteolytic lesions of the calcaneus.

Enhancement of the Regenerative Potential of Anorganic Bovine Bone Graft Utilizing a Polyglutamate-Modified BMP2 Peptide with Improved Binding to Calcium-Containing Materials

Autogenous bone is the gold standard material for bone grafting in craniofacial and orthopedic regenerative medicine. However, due to complications associated with harvesting donor bone, clinicians often use commercial graft materials that may lose their osteoinductivity due to processing. This study was aimed to functionalize one of these materials, anorganic bovine bone (ABB), with osteoinductive peptides to enhance regenerative capacity. Two peptides known to induce osteoblastic differentiation of mesenchymal stem cells were evaluated: (1) DGEA, an amino acid motif within collagen I and (2) a biomimetic peptide derived from bone morphogenic protein 2 (BMP2pep). To achieve directed coupling of the peptides to the graft surface, the peptides were engineered with a heptaglutamate domain (E7), which confers specific binding to calcium moieties within bone mineral. Peptides with the E7 domain exhibited greater anchoring to ABB than unmodified peptides, and E7 peptides were retained on ABB for at least 8 weeks in vivo. To assess the osteoinductive potential of the peptide-conjugated ABB, ectopic bone formation was evaluated utilizing a rat subcutaneous pouch model. ABB conjugated with full-length recombinant BMP2 (rBMP2) was also implanted as a model for current clinical treatments utilizing rBMP2 passively adsorbed to carriers. These studies showed that E7BMP2pep/ABB samples induced more new bone formation than all other peptides, and an equivalent amount of new bone as compared with rBMP2/ABB. A mandibular defect model was also used to examine intrabony healing of peptide-conjugated ABB. Bone healing was monitored at varying time points by positron emission tomography imaging with (18)F-NaF, and it was found that the E7BMP2pep/ABB group had greater bone metabolic activity than all other groups, including rBMP2/ABB. Importantly, animals implanted with rBMP2/ABB exhibited complications, including inflammation and formation of cataract-like lesions in the eye, whereas no side effects were observed with E7BMP2pep/ABB. Furthermore, histological analysis of the tissues revealed that grafts with rBMP2, but not E7BMP2pep, induced formation of adipose tissue in the defect area. Collectively, these results suggest that E7-modified BMP2-mimetic peptides may enhance the regenerative potential of commercial graft materials without the deleterious effects or high costs associated with rBMP2 treatments.

Bone grafts and their substitutes

The continual cycle of bone formation and resorption is carried out by osteoblasts, osteocytes, and osteoclasts under the direction of the bone-signaling pathway. In certain situations the host cycle of bone repair is insufficient and requires the assistance of bone grafts and their substitutes. The fundamental properties of a bone graft are osteoconduction, osteoinduction, osteogenesis, and structural support. Options for bone grafting include autogenous and allograft bone and the various isolated or combined substitutes of calcium sulphate, calcium phosphate, tricalcium phosphate, and coralline hydroxyapatite. Not all bone grafts will have the same properties. As a result, understanding the requirements of the clinical situation and specific properties of the various types of bone grafts is necessary to identify the ideal graft. We present a review of the bone repair process and properties of bone grafts and their substitutes to help guide the clinician in the decision making process.

Endoscopic resection and allografting for benign osteolytic lesions of the calcaneus

BACKGROUND

Both unicameral bone cysts and intra-osseous lipoma of the calcaneus are rare entities which are mostly diagnosed due to unspecific heel pain, pathologic fracture or as an incidental finding. Minimally-invasive ossoscopy with endoscopic resection of the tumor followed by grafting can potentially minimize risks of open surgery and speed up convalescence. The objective of this study is to present a simple, safe and cost-effective surgical technique for endoscopic surgical treatment of benign osteolytic lesions of the calcaneus.

DESCRIPTION OF TECHNIQUE

We present our modifications to previously described techniques of endoscopic curettage with a particular focus on intraosseous lipoma. The key point for grafting is the use of a funnel-shaped ear speculum facilitating the plombage with allogenic cancellous bone chips.

PATIENTS AND METHODS

Between June 2013 and January 2015 ten consecutive patients underwent ossoscopy of the calcaneus. There were 4 cases of intraosseous lipoma and 6 cases of unicameral bone cyst. In a retrospective study, radiological results were analyzed using the Glutting-Classification, functional outcome was recorded with the AOFAS Hindfoot score.

RESULTS

Radiographic follow-up and functional outcome showed good to excellent results. All lesions radiologically classified as "healed". AOFAS score (max. 100 pts) ranged from 74 to 100 (ø94.4 ± 9.3).

CONCLUSIONS

This technique is a simple and safe procedure for benign osteolytic bone lesions of the calcaneus. Compared to its alternatives, grafting with allogenic cancellous bone might prove favourable in this localization for several reasons: Osteointegration, handling, availability and costs. Our preliminary investigations show promising results although further clinical and radiographic results are needed.

Low-Temperature Additive Manufacturing of Biomimic Three-Dimensional Hydroxyapatite/Collagen Scaffolds for Bone Regeneration

Low-temperature additive manufacturing (AM) holds promise for fabrication of three-dimensional (3D) scaffolds containing bioactive molecules and/or drugs. Due to the strict technical limitations of current approaches, few materials are suitable for printing at low temperature. Here, a low-temperature robocasting method was employed to print biomimic 3D scaffolds for bone regeneration using a routine collagen-hydroxyapatite (CHA) composite material, which is too viscous to be printed via normal 3D printing methods at low temperature. The CHA scaffolds had excellent 3D structure and maintained most raw material properties after printing. Compared to nonprinted scaffolds, printed scaffolds promoted bone marrow stromal cell proliferation and improved osteogenic outcome in vitro. In a rabbit femoral condyle defect model, the interconnecting pores within the printed scaffolds facilitated cell penetration and mineralization before the scaffolds degraded and enhanced repair, compared to nonprinted CHA scaffolds. Additionally, the optimal printing parameters for 3D CHA scaffolds were investigated; 600-μm-diameter rods were optimal in terms of moderate mechanical strength and better repair outcome in vivo. This low-temperature robocasting method could enable a variety of bioactive molecules to be incorporated into printed CHA materials and provides a method of bioprinting biomaterials without compromising their natural properties.

Biomechanical evaluation of the rabbit tibia after implantation of porous hydroxyapatite/collagen in a rabbit model

PURPOSE

Porous hydroxyapatite/collagen composite (HAp/Col) is an artificial bone substitute with excellent osteoconduction and sponge-like elasticity. However, the porosity of porous HAp/Col is as high as 95% and its mechanical strength is very poor. The aim of this study was to biomechanically analyze sites implanted with porous HAp/Col.

METHODS

Rectangular cortical bone defects (3 × 8 mm) were made in the tibia of rabbits and filled with porous HAp/Col or porous β-tricalcium phosphate or left vacant. The tibia was harvested at 4 or 12 weeks after surgery. The harvested specimens were analyzed using a micro-CT system, and the mechanical strength of the specimens was examined by torsion testing.

RESULTS

Quantitative micro-CT analysis of the regenerated bone revealed that both bone substitutes equally facilitated bone regeneration. Biomechanical testing demonstrated that the torsional strength of HAp/Col-implanted sites was higher than that of the control (vs control: p = 0.030 and vs β-TCP: p = 0.056).

CONCLUSIONS

The results indicate that porous HAp/Col implantation is an effective strategy for recovery of the mechanical strength of bone defects.

The outstanding mechanical response and bone regeneration capacity of robocast dilute magnesium-doped wollastonite scaffolds in critical size bone defects

Mechanically strong, highly osteogenic dilute magnesium-doped wollastonite robocast scaffolds.

Fabrication, Properties and Applications of Dense Hydroxyapatite: A Review

In the last five decades, there have been vast advances in the field of biomaterials, including ceramics, glasses, glass-ceramics and metal alloys. Dense and porous ceramics have been widely used for various biomedical applications. Current applications of bioceramics include bone grafts, spinal fusion, bone repairs, bone fillers, maxillofacial reconstruction, etc. Amongst the various calcium phosphate compositions, hydroxyapatite, which has a composition similar to human bone, has attracted wide interest. Much emphasis is given to tissue engineering, both in porous and dense ceramic forms. The current review focusses on the various applications of dense hydroxyapatite and other dense biomaterials on the aspects of transparency and the mechanical and electrical behavior. Prospective future applications, established along the aforesaid applications of hydroxyapatite, appear to be promising regarding bone bonding, advanced medical treatment methods, improvement of the mechanical strength of artificial bone grafts and better in vitro/in vivo methodologies to afford more particular outcomes.

Biomaterials approaches to treating implant-associated osteomyelitis

Orthopaedic devices are the most common surgical devices associated with implant-related infections and Staphylococcus aureus (S. aureus) is the most common causative pathogen in chronic bone infections (osteomyelitis). Treatment of these chronic bone infections often involves combinations of antibiotics given systemically and locally to the affected site via a biomaterial spacer. The gold standard biomaterial for local antibiotic delivery against osteomyelitis, poly(methyl methacrylate) (PMMA) bone cement, bears many limitations. Such shortcomings include limited antibiotic release, incompatibility with many antimicrobial agents, and the need for follow-up surgeries to remove the non-biodegradable cement before surgical reconstruction of the lost bone. Therefore, extensive research pursuits are targeting alternative, biodegradable materials to replace PMMA in osteomyelitis applications. Herein, we provide an overview of the primary clinical treatment strategies and emerging biodegradable materials that may be employed for management of implant-related osteomyelitis. We performed a systematic review of experimental biomaterials systems that have been evaluated for treating established S. aureus osteomyelitis in an animal model. Many experimental biomaterials were not decisively more efficacious for infection management than PMMA when delivering the same antibiotic. However, alternative biomaterials have reduced the number of follow-up surgeries, enhanced the antimicrobial efficacy by delivering agents that are incompatible with PMMA, and regenerated bone in an infected defect. Understanding the advantages, limitations, and potential for clinical translation of each biomaterial, along with the conditions under which it was evaluated (e.g. animal model), is critical for surgeons and researchers to navigate the plethora of options for local antibiotic delivery.

Hope versus hype: what can additive manufacturing realistically offer trauma and orthopedic surgery?

Additive manufacturing (AM) is a broad term encompassing 3D printing and several other varieties of material processing, which involve computer-directed layer-by-layer synthesis of materials. As the popularity of AM increases, so to do expectations of the medical therapies this process may offer. Clinical requirements and limitations of current treatment strategies in bone grafting, spinal arthrodesis, osteochondral injury and treatment of periprosthetic joint infection are discussed. The various approaches to AM are described, and the current state of clinical translation of AM across these orthopedic clinical scenarios is assessed. Finally, we attempt to distinguish between what AM may offer orthopedic surgery from the hype of what has been promised by AM.

RhBMP-7 for the treatment of nonunion of fractures of long bones

We report the outcome of 84 nonunions involving long bones which were treated with rhBMP-7, in 84 patients (60 men: 24 women) with a mean age 46 years (18 to 81) between 2003 and 2011. The patients had undergone a mean of three previous operations (one to 11) for nonunion which had been present for a mean of 17 months (4 months to 20 years). The nonunions involved the lower limb in 71 patients and the remainder involved the upper limb. A total of 30 nonunions were septic. Treatment was considered successful when the nonunion healed without additional procedures. The relationship between successful union and the time to union was investigated and various factors including age and gender, the nature of the nonunion (location, size, type, chronicity, previous procedures, infection, the condition of the soft tissues) and type of index procedure (revision of fixation, type of graft, amount of rhBMP-7) were analysed. The improvement of the patients' quality of life was estimated using the Short Form (SF) 12 score. A total of 68 nonunions (80.9%) healed with no need for further procedures at a mean of 5.4 months (3 to 10) post-operatively. Multivariate logistic regression analysis of the factors affecting union suggested that only infection significantly affected the rate of union (p = 0.004).Time to union was only affected by the number of previous failed procedures (p = 0.006). An improvement of 79% and 32.2% in SF-12 physical and mental score, respectively, was noted within the first post-operative year. Rh-BMP-7 combined with bone grafts, enabled healing of the nonunion and improved quality of life in about 80% of patients. Aseptic nonunions were much more likely to unite than septic ones. The number of previous failed operations significantly delayed the time to union.

Progressing innovation in biomaterials. From the bench to the bed of patients

A Translational Research Symposium was organized at the 2014 annual meeting of the European society for biomaterials. This brought together leading Tier one companies in clinical biomaterials and medical device markets, small and medium enterprises and entrepreneurial academics who shared their experiences on taking biomaterials technologies to commercial endpoints, in the clinics. The symposium focused on "Progressing Innovation in Biomaterials. From the Bench to the Bed of Patients". The aim of the present document is to illustrate the content of the symposium and to highlight the key lessons from selected lectures.

Porous titanium granules are better than autograft bone as a bone void filler in lateral tibial plateau fractures: A randomised trial

A total of 20 patients with a depressed fracture of the lateral tibial plateau (Schatzker II or III) who would undergo open reduction and internal fixation were randomised to have the metaphyseal void in the bone filled with either porous titanium granules or autograft bone. Radiographs were undertaken within one week, after six weeks, three months, six months, and after 12 months. The primary outcome measure was recurrent depression of the joint surface: a secondary outcome was the duration of surgery. The risk of recurrent depression of the joint surface was lower (p < 0.001) and the operating time less (p < 0.002) when titanium granules were used. The indication is that it is therefore beneficial to use porous titanium granules than autograft bone to fill the void created by reducing a depressed fracture of the lateral tibial plateau. There is no donor site morbidity, the operating time is shorter and the risk of recurrent depression of the articular surface is less.

Bone augmentation using a new injectable bone graft substitute by combining calcium phosphate and bisphosphonate as composite--an animal model

Objective

The aim of this study was to create a new injectable bone graft substitute by combining the features of calcium phosphate and bisphosphonate as a composite bone graft to support bone healing and to evaluate the effect of alendronate to the bone healing process in an animal model.

Material and method

In this study, 24 New Zealand white rabbits were randomly divided into two groups: a calcium phosphate alendronate group and a calcium phosphate control group. A defect was created at the proximal medial tibia and filled with the new created injectable bone graft substitute calcium phosphate alendronate or with calcium phosphate. Healing process was documented by fluoroscopy. To evaluate the potential of the bone graft substitute, the proximal tibia was harvested 2, 4, and 12 weeks after operation. Histomorphological analysis was focused on the evaluation of the dynamic bone parameters using the Osteomeasure system.

Results

Radiologically, the bone graft materials were equally absorbed. No fracture was documented. The bones healed normally. After 2 weeks, the histological analysis showed an increased new bone formation for both materials. The osteoid volume per bone volume (OV/BV) was significantly higher for the calcium phosphate group. After 4 weeks, the results were almost equal. The trabecular thickness (Tb.Th) increased in comparison to week 2 in both groups with a slight advantage for the calcium phosphate group. The total mass of the bone graft (KEM.Ar) and the bone graft substitute surface density (KEM.Pm) were consistently decreasing. After 12 weeks, the new bone volume per tissue volume (BV/TV) was still constantly growing. Both bone grafts show a good integration. New bone was formed on the surface of both bone grafts. The calcium phosphate as well as the calcium phosphate alendronate paste had been enclosed by the bone. The trabecular thickness was higher in both groups compared to the first time point.

Conclusion

Calcium phosphate proved its good potential as a bone graft substitute. Initially, the diagrams seem to show a tendency that alendronate improves the known properties of calcium phosphate as a bone graft substitute. The composite graft induced a good and constant new bone formation. Not only the graft was incorporated into the bone but also a new bone was formed on its surface. But we could not prove a significant difference between the grafts. Both implants proved their function as a bone graft substitute, but the bisphosphonate alendronate does not support the bone healing process sufficiently that the known properties of calcium phosphate as a bone graft substitute were improved in the sense of a composite graft. In this study, alendronate used as a bone graft in a healthy bony environment did not influence the bone healing process in a positive or negative way.

3D Printing of Personalized Artificial Bone Scaffolds

Additive manufacturing technologies, including three-dimensional printing (3DP), have unlocked new possibilities for bone tissue engineering. Long-term regeneration of normal anatomic structure, shape, and function is clinically important subsequent to bone trauma, tumor, infection, nonunion after fracture, or congenital abnormality. Due to the great complexity in structure and properties of bone across the population, along with variation in the type of injury or defect, currently available treatments for larger bone defects that support load often fail in replicating the anatomic shape and structure of the lost bone tissue. 3DP could provide the ability to print bone substitute materials with a controlled chemistry, shape, porosity, and topography, thus allowing printing of personalized bone grafts customized to the patient and the specific clinical condition. 3DP and related fabrication approaches of bone grafts may one day revolutionize the way clinicians currently treat bone defects. This article gives a brief overview of the current advances in 3DP and existing materials with an emphasis on ceramics used for 3DP of bone scaffolds. Furthermore, it addresses some of the current limitations of this technique and discusses potential future directions and strategies for improving fabrication of personalized artificial bone constructs.

Precise and feasible measurements of lateral calcaneal lengthening osteotomies by radiostereometric analysis in cadaver feet

Objectives

Lengthening osteotomies of the calcaneus in children are in general grafted with bone from the iliac crest. Artificial bone grafts have been introduced, however, their structural and clinical durability has not been documented. Radiostereometric analysis (RSA) is a very accurate and precise method for measurements of rigid body movements including the evaluation of joint implant and fracture stability, however, RSA has not previously been used in clinical studies of calcaneal osteotomies. We assessed the precision of RSA as a measurement tool in a lateral calcaneal lengthening osteotomy (LCLO).

Methods

LCLO was performed in six fixed adult cadaver feet. Tantalum markers were inserted on each side of the osteotomy and in the cuboideum. Lengthening was done with a plexiglas wedge. A total of 24 radiological double examinations were obtained. Two feet were excluded due to loose and poorly dispersed markers. Precision was assessed as systematic bias and 95% repeatability limits.

Results

Systematic bias was generally below 0.10 mm for translations. Precision of migration measurements was below 0.2 mm for translations in the osteotomy.

Conclusion

RSA is a precise tool for the evaluation of stability in LCLO.

Cite this article: Bone Joint Res 2015;4:78–83.

Bone regeneration and gene expression in bone defects under healthy and osteoporotic bone conditions using two commercially available bone graft substitutes

Biosilicate(®) and Bio-Oss(®) are two commercially available bone substitutes, however, little is known regarding their efficacy in osteoporotic conditions. The purpose of this study was to evaluate the osteogenic properties of both materials, at tissue and molecular level. Thirty-six Wistar rats were submitted to ovariectomy (OVX) for inducing osteoporotic conditions and sham surgery (SHAM) as a control. Bone defects were created in both femurs, which were filled with Biosilicate(®) or Bio-Oss(®), and empty defects were used as control. For the healthy condition both Biosilicate(®) and Bio-Oss(®) did not improve bone formation after 4 weeks. Histomorphometric evaluation of osteoporotic bone defects with bone substitutes showed more bone formation, significant for Bio-Oss(®). Molecular biological evaluation was performed by gene-expression analysis (Runx-2, ALP, OC, OPG, RANKL). The relative gene expression was increased with Biosilicate(®) for all genes in OVX rats and for Runx-2, ALP, OC and RANKL in SHAM rats. In contrast, with Bio-Oss(®), the relative gene expression of OVX rats was similar for all three groups. For SHAM rats it was increased for Runx-2, ALP, OC and RANKL. Since both materials improved bone regeneration in osteoporotic conditions, our results suggest that bone defects in osteoporotic conditions can be efficiently treated with these two bone substitutes.

Bone substitutes and implantation depths for subchondral bone repair in osteochondral defects of porcine knee joints

PURPOSE

The purpose of this study was to identify the optimal material and implantation method for subchondral bone repair.

METHODS

Four osteochondral defects in a femoral groove were created in both knees of 12 pigs, and the total number of defects was 96. Eight defects were left empty (empty group). Beta-tricalcium phosphate (β-TCP) bone substitutes with 75 and 67 % porosity were implanted in 30 and 29 defects, respectively (β-TCP75 and β-TCP67 groups). Hydroxyapatite (HA) bone substitutes with 75 % porosity were filled in 29 defects (HA group). Bone substitutes were implanted at 0, 2, or 4 mm below the subchondral bone plate (SBP). The reparative tissue was assessed using microfocus computed tomography and histology 3 months after implantation.

RESULTS

Regardless of the kind of bone substitutes, the defects were filled almost completely after implanting them at the level of the SBP, while the defects remained after implanting them at 2 or 4 mm below the SBP. Reparative tissue of the β-TCP75 group was similar to the normal cancellous bone, while that of the β-TCP67 or HA group was not.

CONCLUSIONS

Subchondral bone defects were filled almost completely only when bone substitutes were implanted at the level of the SBP. The reparative tissue after implanting the β-TCP bone substitutes with 75 % porosity was the most similar to the normal cancellous bone. Therefore, implanting the β-TCP bone substitutes with 75 % porosity at the level of the SBP could be recommended as a treatment method for subchondral bone repair in osteochondral defects.

LEVEL OF EVIDENCE

I.

Advances in treating exposed fractures

The management of exposed fractures has been discussed since ancient times and remains of great interest to present-day orthopedics and traumatology. These injuries are still a challenge. Infection and nonunion are feared complications. Aspects of the diagnosis, classification and initial management are discussed here. Early administration of antibiotics, surgical cleaning and meticulous debridement are essential. The systemic conditions of patients with multiple trauma and the local conditions of the limb affected need to be taken into consideration. Early skeletal stabilization is necessary. Definitive fixation should be considered when possible and provisional fixation methods should be used when necessary. Early closure should be the aim, and flaps can be used for this purpose.

Bone substitute first or screws first? A biomechanical comparison of two operative techniques for tibial-head depression fractures

BACKGROUND

The aim of this study was to investigate a drillable and injectable bone substitute (calcium phosphate cement) and the operative technique enabled by the drillable option in a new biomechanical fracture model for tibial depression fractures in synthetic bones.

MATERIALS AND METHODS

Lateral depression fractures of the tibial plateau (AO 41-B2, Schatzker III) were created in a biomechanical fracture model in three different synthetic bones (Sawbone 3401, Synbone 1110/1116). Reproducible fractures were generated employing Synbone 1110, which exhibited a comparable strength to human osteoporotic bones and was used for the further experiments. After reduction of the fractures, the stabilization was performed with two different operative techniques. In group 1, first an osteosynthesis with four screws was performed and then the metaphyseal defect was filled up with calcium phosphate cement (Norian drillable). In group 2, initially the filling up with Norian drillable was done enabling a complete filling of the defect, followed by placing of the screws. Displacement under cyclic loading with 250 N for 3,000 cycles, stiffness, and maximum load in load-to-failure tests were determined.

RESULTS

A comparison of the two operative techniques of stabilization showed a distinctly lower displacement and higher stiffness for group 2 when the defect was filled up first. For the maximum load, no significant differences could be demonstrated.

CONCLUSIONS

A complete filling of the defect by first applying the calcium phosphate cement significantly reduces the secondary loss of reduction of the depression fracture fragment under cyclic loading with a clinically relevant partial weight bearing. The beneficial effects of drillable calcium phosphate cement may also be transferable to defects other than tibial-head depression fractures.

Hydroxyapatite-Based Biomaterials Versus Autologous Bone Graft in Spinal Fusion: An In Vivo Animal Study

STUDY DESIGN

An in vivo study was designed to compare the efficacy of biomimetic magnesium-hydroxyapatite (MgHA) and of human demineralized bone matrix (HDBM), both dispersed in a mixture of biomimetic MgHA nanoparticles, with that of an autologous bone graft.

OBJECTIVE

The objective of this study was to evaluate 2 new bone substitutes as alternatives to a bone autograft for spinal fusion, determining their osteoinductive and osteoconductive properties, and their capacity of remodeling, using a large animal model.

SUMMARY OF BACKGROUND DATA

Spinal fusion is a common surgical procedure and it is performed for different conditions. A successful fusion requires potentially osteogenic, osteoinductive, and osteoconductive biomaterials.

METHODS

A posterolateral spinal fusion model involved 18 sheep, bilaterally implanting test materials between the vertebral transverse processes. The animals were divided into 2 groups: 1 fusion level was treated with MgHA (group 1) or with HDBM-MgHA (group 2). The other fusion level received bone autografts in both groups.

RESULTS

Radiographical, histological, and microtomographic results indicated good osteointegration between the spinous process and the vertebral foramen for both materials. Histomorphometry revealed no significant differences between MgHA and autologous bone for all the parameters examined, whereas significantly lower values of bone volume were observed between HDBM-MgHA and autologous bone. Moreover, the normalization of the histomorphometric data with autologous bone revealed that MgHA showed a significantly higher value of bone volume and a lower value of trabecular number, more similar to autologous bone than HDBM-MgHA.

CONCLUSION

The study showed that the use of MgHA in an ovine model of spinal fusion led to the deposition of new bone tissue without qualitative and quantitative differences with respect to new bone formed with autologous bone, whereas the HDBM-MgHA led to a reduced deposition of newly formed bone tissue.

LEVEL OF EVIDENCE

N/A.

Bone formation in a rat tibial defect model using carboxymethyl cellulose/BioC/bone morphogenic protein-2 hybrid materials

The objective of this study was to assess whether carboxymethyl cellulose- (CMC-) based hydrogel containing BioC (biphasic calcium phosphate (BCP); tricalcium phosphate (TCP) : hydroxyapatite (Hap) = 70 : 30) and bone morphogenic protein-2 (BMP-2) led to greater bone formation than CMC-based hydrogel containing BioC without BMP-2. In order to demonstrate bone formation at 4 and 8 weeks, plain radiographs, microcomputed tomography (micro-CT) evaluation, and histological studies were performed after implantation of all hybrid materials on an 8 mm defect of the right tibia in rats. The plain radiographs and micro-CT analyses revealed that CMC/BioC/BMP-2 (0.5 mg) led to much greater mineralization at 4 and 8 weeks than did CMC/BioC or CMC/Bio/BMP-2 (0.1 mg). Likewise, bone formation and bone remodeling studies revealed that CMC/BioC/BMP-2 (0.5 mg) led to a significantly greater amount of bone formation and bone remodeling at 4 and 8 weeks than did CMC/BioC or CMC/BioC/BMP-2 (0.1 mg). Histological studies revealed that mineralized bone tissue was present around the whole circumference of the defect site with CMC/BioC/BMP-2 (0.5 mg) but not with CMC/BioC or CMC/BioC/BMP-2 (0.1 mg) at 4 and 8 weeks. These results suggest that CMC/BioC/BMP-2 hybrid materials induced greater bone formation than CMC/BioC hybrid materials. Thus, CMC/BioC/BMP-2 hybrid materials may be used as an injectable substrate to regenerate bone defects.

3D printing of composite calcium phosphate and collagen scaffolds for bone regeneration

Low temperature 3D printing of calcium phosphate scaffolds holds great promise for fabricating synthetic bone graft substitutes with enhanced performance over traditional techniques. Many design parameters, such as the binder solution properties, have yet to be optimized to ensure maximal biocompatibility and osteoconductivity with sufficient mechanical properties. This study tailored the phosphoric acid-based binder solution concentration to 8.75 wt% to maximize cytocompatibility and mechanical strength, with a supplementation of Tween 80 to improve printing. To further enhance the formulation, collagen was dissolved into the binder solution to fabricate collagen-calcium phosphate composites. Reducing the viscosity and surface tension through a physiologic heat treatment and Tween 80, respectively, enabled reliable thermal inkjet printing of the collagen solutions. Supplementing the binder solution with 1-2 wt% collagen significantly improved maximum flexural strength and cell viability. To assess the bone healing performance, we implanted 3D printed scaffolds into a critically sized murine femoral defect for 9 weeks. The implants were confirmed to be osteoconductive, with new bone growth incorporating the degrading scaffold materials. In conclusion, this study demonstrates optimization of material parameters for 3D printed calcium phosphate scaffolds and enhancement of material properties by volumetric collagen incorporation via inkjet printing.