Introduction; In contrast to hydroxyapatite (HA), carbonate substituted hydroxyapatite (CHA) is resorbed by osteoclasts, and is more osteoconductive in vivo. On bone, osteoclastic resorption results not only in topographical changes, but also changes in the proteinaceous matrix within the resorption pit to which osteoblasts respond [1]. This study sought to investigate a possible link between the different bioresorptive properties of these biomaterials and subsequent bone formation on their surfaces, analogous to the coupling seen in normal bone remodelling.

Methods; Phase-pure HA and 2.7wt% CHA were prepared by aqueous precipitation methods [2] and processed into dense sintered discs for cell culture. Human osteoclasts derived from CD14+ precursors were cultured for 21 days on discs of HA and CHA; subsequently, cells and the proteinaceous layer were removed from some discs leaving a topographically altered surface (assessed by SEM and profilometry), whilst in others the proteinaceous layer was left intact. Control (unresorbed) discs were also prepared. The discs were then seeded with human osteoblasts (HOBs) which were cultured for up to 28 days, in some cases in the presence of hydrocortisone and â-glycerophosphate. Proliferation (MTS assay), collagen synthesis (3-H Proline incorporation), and the formation of mineralised nodules (tetra-cycline labelling [3] and SEM) were assessed.

Results; Osteoclasts altered the ceramic surfaces. Large pits were seen on CHA in contrast to limited erosion of the HA surface, accompanied by a greater increase surface roughness (Ra) (p< 0.05). After 6 days of culture, proliferation of HOBs was increased on resorbed discs provided the proteinaceous layer resulting from osteoclastic activity was left intact. At 28 days, cells had formed confluent sheets and there were no significant differences in their number. At 6 days, collagen synthesis by HOBs on CHA was increased on resorbed surfaces, and further increased if the proteinaceous layer was left intact. A similar response was seen on HA, but not until 28 days. Mineralised nodules formed after 28 days of culture in the presence of hydrocortisone and â-glycerophosphate on tissue culture plastic, but not in their absence. By contrast on the ceramics there was no evidence of mineralised nodule formation on any of the discs, although globular accretions were present in small amounts throughout the collagenous matrix regardless of the presence or absence of supplements.

Conclusion; Prior osteoclastic activity on HA and CHA affects subsequent proliferation and collagen production by HOBs. The effects of topographical alteration and matrix conditioning appear synergistic, and are apparent at an earlier time-point on a more resorbable ceramic. Osteoclastic activity may be important in the osteoconductive properties of biomaterials.

Introduction

Achieving durable implant–host bone fixation is the major challenge in uncemented revision hip arthroplasty when significant bone stock deficiencies are encountered. The purpose of this study was to develop an experimental model which would simulate the clinical revision hip scenario and to determine the effects of alendronate coating on porous tantalum on gap filling and bone ingrowth in the experimental model.

Introduction: Achieving durable implant–host bone fixation is the major challenge in uncemented revision hip arthroplasty when significant bone stock deficiencies are encountered. The purpose of this study was

to develop an experimental model which would simulate the clinical revision hip scenario and

Methods: Thirty-six porous tantalum plugs were implanted into the distal femur, bilaterally of 18 rabbits for four weeks. There were 3 groups of plugs inserted; control groups of porous tantalum plugs (Ta) with no coating, a 2nd control group of porous tantalum plugs with micro-porous calcium phosphate coating, (Ta-CaP) and porous tantalum plugs coated with alendronate (Ta-CaP-ALN). Subcutaneous fluorochrome labelling was used to track new bone formation. Bone formation was analysed by backscattered electron microscopy and fluorescence microscopy on undecalcified histological sections.

Results: The relative increase in mean volume of gap filling, bone ingrowth and total bone formation was 124 %, 232 % and 170 % respectively in Ta-CaP-ALN compared with the uncoated porous tantalum (Ta) controls, which was statistically significant. The contact length of new bone formation on porous tantalum implants in Ta-CaP-ALN was increased by 700% (8-fold) on average compared with the uncoated porous tantalum (Ta) controls.

Discussion: Alendronate coated porous tantalum significantly modulated implant bioactivity compared with controls. This study has demonstrated the significant enhancement of bone-implant gap filling and bone ingrowth, which can be achieved by coating porous tantalum with alendronate. It is proposed that, when faced with the clinical problem of revision joint replacement in the face of bone loss, the addition of alendronate as a surface coating would enhance biological fixation of the implant and promote the healing of bone defects.

Introduction: Achieving durable implant–host bone fixation is the major challenge in uncemented revision hip arthroplasty when significant bone stock deficiencies are encountered. The purpose of this study was 1) to develop an experimental model which would simulate the clinical revision hip scenario and 2) determine the effects of alendronate coating on porous tantalum on gap filling and bone ingrowth in the experimental model.

Methods: Thirty-six porous tantalum plugs were implanted into the distal femur, bilaterally of 18 rabbits for four weeks. There were 3 groups of plugs inserted; control groups of porous tantalum plugs (Ta) with no coating, a 2^nd control group of porous tantalum plugs with micro-porous calcium phosphate coating, (Ta-CaP) and porous tantalum plugs coated with alendronate (Ta-CaP-ALN). Subcutaneous fluorochrome labelling was used to track new bone formation. Bone formation was analysed by backscattered electron microscopy and fluorescence microscopy on undecalcified histological sections.

Results: The relative increase in mean volume of gap filling, bone ingrowth and total bone formation was 124 %, 232 % and 170 % respectively in Ta-CaP-ALN compared with the uncoated porous tantalum (Ta) controls, which was statistically significant. The contact length of new bone formation on porous tantalum implants in Ta-CaP-ALN was increased by 700% (8-fold) on average compared with the uncoated porous tantalum (Ta) controls.

Discussion: Alendronate coated porous tantalum significantly modulated implant bioactivity compared with controls. This study has demonstrated the significant enhancement of bone-implant gap filling and bone ingrowth, which can be achieved by coating porous tantalum with alendronate. It is proposed that, when faced with the clinical problem of revision joint replacement in the face of bone loss, the addition of alendronate as a surface coating would enhance biological fixation of the implant and promote the healing of bone defects.

Purpose: Porous tantalum has been shown to be very effective in achieving bone ingrowth. However, in some circumstances, bone quality or quantity is insufficient to allow adequate bone ingrowth. We hypothesized that the addition of alendronate to porous tantalum would enhance the ability of porous tantalum to achieve bone ingrowth in these challenging situations, such as when a gap exists between the implant and bone. We evaluated the effect of alendronate coated porous tantalum on new bone formation in an animal model incorporating a gap between implant and bone.

Method: Thirty-six cylindrical porous tantalum implants were bilaterally implanted into the distal femur of 18 rabbits for 4 weeks. There were 3 groups of implants inserted; a control group of porous tantalum with no coatings, porous tantalum with micro-porous calcium phosphate coating, and porous tantalum coated with micro-porous calcium phosphate and alendronate. Subcutaneous fluorescent labeling was used to track new bone formation. Bone formation was analyzed by backscattered electron microscopy and fluorescent microscopy on undecalcified samples.

Results: The relative increase in mean volume of gap filling, bone ingrowth and total bone formation was 143% (p< 0.001), 259% (p< 0.001) and 193% (p< 0.001) respectively in the alendronate coated porous tantalum compared with the uncoated porous tantalum controls. The relative increase in the percentage of new bone-implant contact length was increased by 804% on average in the alendronate coated porous tantalum compared with the uncoated tantalum controls.

Conclusion: This study demonstrated the significant enhancement of bone-implant gap filling and bone ingrowth which can be achieved by coating porous tantalum with alendronate. It is proposed that, when faced with the clinical problem of revision joint replacement in the face of bone loss (at the hip, knee or elsewhere), the addition of an alendronate-delivery surface coating would enhance biological fixation of the implant and promote the healing of bone defects.

Titanium-alloy is a metal with excellent biocompatibility, but its osteoconduction is not as efficient as hydroxyapatite materials. Calcium-ion (Ca-ion) implantation is a surface modification technique that can improve osteoconduction of titanium without an additional layer of coating. We studied the effects of Ca-ion-implantation on osseointegration of a titanium-alloy stem in a bilateral canine THA model. The stem surface was grit-blasted and Ca-ion-implanted by the ion mixing technique. Fifteen mongrel dogs had bilateral single-stage THAs, with a Ca-ion-implanted stem used in one side and a non-Ca-ion-implanted stem in the contralateral side. They were sacrificed at 1, 6, and 12 months postoperatively, and microradiographs were taken. Undecalcified cross-sections were evaluated histologically. For quantitative evaluation, the length of new bone apposition to the implant surface was obtained using computer image analysis. Most implants were well integrated, and there was no apparent qualitative difference between the two types of stems radiographically and histologically. However, Ca-ion-implanted stems had significantly greater new bone apposition than non-Ca-ion-implanted stems at 1 month, although the overall effect of Ca-ion-implantation was not significant. The results showed enhanced osteoconduction with Ca-ion-implantation only in the early postoperative period. This could be related to the previous data of immersion tests that the dissolution rate of Ca-ion from Ca-ion-implanted titanium decreases with time. Clinically, early osteoconduction is desirable and could accelerate rehabilitation and outcome. Although further improvement of the Ca-ion-implantation technique for a sustained osteoconductive effect is necessary, Ca-ion-implantation will be beneficial for early fixation of titanium-alloy implants

Long-term survival of massive prostheses used to treat bone cancers is associated with extra-cortical bone growth and osteointegration into a grooved hydroxyapatite coated collar positioned adjacent to the transection site on the implant shaft [1]. The survivorship at 10 years reduces from 98% to 75% where osteointegration of the shaft does not occur. Although current finite element (FE) methods successfully model bone adaption, optimisation of adventitious new bone growth and osteointegration is difficult to predict. There is thus a need to improve existing FE models by including biological processes of osteoconduction and osteoinduction. The principal bone adaptation criteria is based on the standard strain-energy remodeling algorithm, where the rate of remodeling is controlled by the difference in the stimulus against the reference value [3]. The additional concept of bone connectivity was introduced, to limit bone growth to neighbouring elements (cells) adjoining existing bone elements. The algorithm was developed on a cylindrical model before it was used on an ovine model. The geometry and material properties from two ovine tibiae were obtained from computed tomography (CT) scans and used to develop FE models of the tibiae implanted with a grooved collar. The bones were assigned inhomogeneous material properties based on the CT grey values and typical ovine walking load conditions were applied. The FE results show a region of bone tissue growth below the implanted collar and a small amount of osteointegration with the implant, which is in good agreement to clinical results. Some histological results suggest that further bone growth is possible and potential improvements to the model will be discussed. In summary, by including an algorithm that describes osteoconduction, adventitious bone growth can be predicted

Kokubo and one of the present authors (T.N) have developed a new technique of bioactive coating using alkaline and heat treatment, which induces the formation of a thin HA layer on the surface of titanium after implantation in the body. This new coating technique is not associated with degradation or separation of the HA coating, because a bone-like apatite layer of 1 μm in width begins to form in the body tissue after implantation. Chemically and thermally treated titanium possesses bone-bonding ability, which has been confirmed by detachment tests. Bone ingrowth into bioactive titanium continues to increase throughout the 26 weeks of implantation, whereas bone ingrowth into non-treated or HA plasma coating implants tends to decrease between 6 and 12 weeks. These findings suggest the long-term stability and osteoconduction of the bioactive layer of chemically and thermally treated titanium. We carried out a series of 70 cementless primary total hip arthroplasties using this coating technique on a porous titanium surface, and followed up the patients for a mean period of 4.8 years. There were no instances of loosening or revision, or formation of a reactive line on the porous coating. Although radiography just after surgery showed a gap between the host bone and the socket in 70% of cases, all the gaps disappeared within a year, indicating the good osteoconduction provided by the coating. Alkaline-heat treatment of titanium to provide a HA coating has several advantages over plasma-spraying, including no degeneration or absorption of the HA coating, simplicity of the manufacturing process, and cost effectiveness. In addition, this method allows homogeneous deposition of bone-like apatite within a porous implant. Although this was a relatively short-term study, treatment that creates a bioactive surface on titanium and titanium alloy implants has considerable promise for clinical application

We report our 4 years’ experience using of demineralized human bone matrix (DBM) in the treatment of complex pathology characterised by bone loss or less regenerating ability, such as congenital or secondary bone mal-union, osteomyelitis, aseptic prosthetic failure, complex bone loss fractures, etc. Considering the known limitations of autologous transplants (limited quantity, infections and fractures of donor sites, operative and bleeding time increase, abdominal herniations, etc.), we have searched in the literature for alternative materials that would be as similar to the osteoconduction and osteoinduction ability of autologous transplant as possible, respecting bio- and immunocompatiblity. Since May 2000 we have used DBM in 50 cases: the first 15 patients with mixed technique (DBM and autologous transplant) and then the other 35 only with DBM. We have controlled each patient clinically and by X-ray: average follow up 34 months. With the same type of pathology and operative technique we have observed a similar recovery with both techniques (DBM with or without autologous transplant); in addition, in patients treated with rigid osteo-synthesis or in patients with osteoporosis we have noted early bone regeneration and no complications with respect to rejection or to osteolysis at the surgical site. In our opinion, this confirms the good osteoconduction and osteoinduction ability of DBM

The current gold standard bone substitute is still autologous bone, despite the fact that its harvest demands for a second operation site, causes additional pain, discomfort, potential destruction of the grafting site, and is limited in supply. Since newly developed clinical approaches like transplantation of cells are invasive and costly, and osteoinduction by bone morphogenetic proteins is expensive and is associated with mild to severe side effects, the optimization of osteoconduction appears as promising option to realize bone substitute-based bone tissue engineering. In the 90ties of the last century, the holy grail of pore size for scaffolds in bone tissue engineering was set between 0.3 and 0.5 mm. More recent, papers from others and us indicated that the optimal microarchitecture for bone tissue engineering scaffolds in terms of pore size, constrictions, rod thickness, or rod distance is still unknown. Additive manufacturing appears as an ideal tool to study those diverse microarchitecture options since it can generate scaffolds where size and location of pores and connections between pores can be tested. For the production of our test scaffolds, we applied laser sintering of titanium and lithography-based additive manufacturing of ceramics. Histomorphometry of calvarial defects in rabbits revealed that bone formation was significantly increased by scaffolds with pore diameters in the range of 0.7–1.2 mm. Scaffolds with pores of 1.5 and 1.7 mm perform significantly worse. Therefore, pore diameters in osteoconductive bone substitutes should be 1.0–1.2 mm and thus much bigger than previously suggested. In essence, osteoconductive microarchitectures of degradable bone substitutes can be realized by lithography based additive manufacturing and this methodology appears as a promising tool for the production of personalized bone tissue engineering scaffolds to be used in cranio-maxillofacial surgery, dentistry, and orthopedics

Bioabsorbable screws for anterior cruciate ligament reconstruction (ACLR) have been shown to be associated with femoral tunnel widening and cyst formation. To compare a poly-L-lactide–hydroxyapatite screw (PLLA-HA) with a titanium screw with respect to clinical and radiological outcomes over a 5 year period. 40 patients were equally randomized into 2 groups (PLLA-HA vs titanium) and ACLR performed with a 4 strand hamstring graft with femoral tunnel drilling via the anteromedial portal. Evaluation at 2 and 5 years was performed using the International Knee Documentation Committee assessment (IKDC), Lysholm knee score, KT 1000 arthrometer, single-legged hop test. Magnetic resonance imaging was used to evaluate tunnel and screw volume, ossification around the screws, graft integration and cyst formation. There was no difference in any clinical outcome measure at 2 or 5 years between the 2 groups. At 2 years, the PLLA-HA femoral tunnel was significantly smaller than the titanium screw tunnel (p=0.015) and at 5 years, there was no difference. At 2 years the femoral PLLA-HA screw was a mean 76% of its original volume and by 5 years, 36%. At 2 years the tibial PLLA-HA screw mean volume was 68% of its original volume and by 5 years, 46%. At 5 years, 88% of femoral tunnels and 56% of tibial tunnels demonstrated a significant ossification response. There was no increase in cyst formation in the PLLA-HA group and no screw breakages. The PLLA-HA screw provides adequate aperture fixation in ACLR with excellent functional outcomes. It was not associated with femoral tunnel widening or increased cyst formation when compared with the titanium screw. The resorbtion characteristics appear favourable and the hydroxyapatite component of the screw may stimulate osteoconduction, contributing to these results. The PLLA-HA screw is a good alternative to a titanium screw in ACLR, which may aid revision procedures and allow for imaging without artifact

Summary. A specialised 3D- printed scaffold, combined with fillers and bioactive molecules, can be designed and characterised to demonstrate the efficacy of synthetic, off-the-shelf and custom fabricated scaffolds for the repair of long bone defects. Introduction. Using specialised three-dimensional (3-D) printing technology, combined with fillers and bioactive molecules, 3-D scaffolds for bone repair of sizable defects can be manufactured with a level of design customization that other methods lack. Hydroxyapatite (HA)/Beta-Tri-Calcium Phosphate (β -TCP) scaffold components may be created that provide mechanical strength, guide osseo- conduction and integration, and remodel over time. Additionally, research suggests that bone morphogenic protein (BMP) stimulates growth and differentiation of new bone. Therefore, we hypothesise that with the addition of BMP, HA- β -TCP scaffolds will show improved regeneration of bone over critical sized bone defects in an in vivo model. Patients & Methods. Scaffolds were implanted in six New Zealand White rabbits with a 10mm radial defect for 2 and 8 weeks. The scaffolds, made from 15% HA: 85% β-TCP, were designed using ROBOCAD design software and fabricated using a 3-D printing Robocast machine. Scaffolds were sintered at 1100°C for 4 hours with a final composition of 5% HA: ∼95% β-TCP. Micro-CT, histological analysis, and nanoindentation were conducted to determine the degree of new bone formation and remodeling. Results. Reconstructed microCT images show increased bone formation, remodeling, and integration in HA/ β -TCP-BMP scaffolds compared to virgin HA/ β -TCP scaffolds. Histological analysis showed increased bone formation but decreased osteoconduction in HA/ β -TCP-BMP scaffolds. Nanoindentation showed no effect of BMP on hardness nor elastic modulus of bone formed on the scaffolds. Discussion/Conclusions. HA/ β -TCP scaffolds with/without BMP are highly biocompatible and can successfully augment and accelerate the regeneration and remodeling of bone in critically sized long bone defects in a rabbit model. However, the data in this study show both improvement and detriment with the addition of BMP. Therefore, further studies must be performed. Ideally, eventual translation of this research to humans would eliminate the need for allograft and/or autograft in large bony defects and allow for a customizable 3D scaffold material relative to patient needs

Background. The management of non-unions of subtrochanteric femoral fractures with associated implant failure is challenging. This study assessed the outcome of a cohort of patients treated according to the diamond concept. Methods. Between 2005–2010 all patients with subtrochanteric aseptic non-unions presented post implant failure (Gamma Nail breakage) were eligible in the absence of severe systemic pathologies and comorbidities. Demographics, initial fracture pattern, method of stabilisation, mode of failure of metal work, time to revision of fixation, complications, time to union, and functional outcome were recorded over a minimum period of follow-up of 12 months. The revision strategy was based on the “diamond concept;” optimising the mechanical and biological environment (revision of fixation, osteoinduction/BMP-7, osteoconduction/RIA harvested graft, and osteogenicity/concentrate of bone marrow aspirate). Results. Out of 280 nailing procedures 12 (4.3%) cases met the inclusion criteria. A consistent mode of metalwork failure was recorded with initial breakage of the proximal distal locking screw followed by nail breakage at the lag screw level. Biomechanical SEM analysis of the nails revealed no structural damage besides the standard fatigue striation. Varus mal-reduction was present in all cases, with an average of 7.3 degrees (5–11). The average time to screw failure was 4.3 months (2–6) and nail failure was 5.9 months (4–10). All but one of the cases were revised to a 95 degrees blade plate and one to an Affixus nail. Time to union was 6.5 months (5–10). All but one of the cases by 12 months have returned to their preinjury level of mobilisation. Conclusion. Varus mal-reduction must be avoided in the initial stabilisation of subtrochanteric fractures. Proximal distal screw failure is predictive of future fracture non-union and subsequent nail breakage. The diamond concept for optimising mechanics and bone biology is a successful method for managing complex sub-trochanteric non-unions with failed metalwork

Purpose of the study: Biphasic macroporous phosphocalcium ceramics are used in routine surgery to fill bone defects. This type of material presents the characteristics of an ideal substitute: free of the adverse effects of grafts, biocompatibility, bioactivity, osteoconduction, osteointegration, reproducibility, availability in sufficient quantity. The purpose of our work was to evaluate the role of osteointegration on the resistance of two macroporous biphasic phosphocalcium ceramics routinely proposed on the French market. These two macroprous materials have a similar chemical composition but vary by the presence or not of interpores. Material and methods: The experimental model involved the implantation of ceramic cylinders in a femoral cortical site in sheep, via the intermediary of conduction chambers with specific cortical entrances. The resistance to compression of the implanted samples an non implanted controls was measured using the same ISO norms. Results: After two months implantation in a cortical site in the sheep, Eurocer200plus. ®. exhibited a significant 38% increase in resistance to compression while in the same conditions, Triosite. ®. exhibited a 41% decline in resistance. For ceramics with open porosity, the interpores acted like tunnels enabling rapid colonization for osteoforming cells and early formation of new bone reaching the centre of the substitute, and leading to increased material resistance. Cell colonization of a ceramic with closed porosity is, on the contrary, slowed by the partitions, while its dissolution by biological fluids within the micropores occurs in all materials; there results an imbalance between absorption and synthesis, leading to loss of mechanical resistance as a first phase of osteointegration. Discussion: Open macroposity enables an improvement in the mechanical properties of a biphasic ceramic substitute due to more rapid osteointegration. In the future, material associated with osteoinduction cells or proteins should play an important role, together with changes in the architecture of the ceramic skeleton which should play a determining role in terms of physical and biological properties

Introduction. This study investigated the binding agent Calcium/Sodium Alginate fibre gel and the addition of autogenic bone marrow aspirate (BMA) on bone growth into a porous HA scaffold implanted in an ovine femoral condyle critical-sized defect. Our hypothesis was that Alginate fibre gel would have no negative effect on bone formation and osteoconduction within the scaffold and that BMA would augment the incorporation of the graft with the surrounding bone at 6 and 12 weeks post implantation. Methods. 24, 8mm x 15mm defects were filled with either porous HA granules, porous HA granules + Alginate fibre gel (HA putty) or porous HA granules + Alginate fibre gel + BMA (HA putty +BMA) and remained in vivo for 6 and 12 weeks (n=4). 1ml of bone marrow aspirate per cm3 of graft was used. Image analysis quantified bone apposition rates, bone ingrowth, bone-implant contact and quantity of graft. Mann Whitney U tests were used for statistical analysis where p<0.05 was considered significant. Results. Highest bone formation were measured in the 12 week HA putty+BMA group (1.57±0.24(micromillimetres/day). HA granules at 12 weeks encouraged the greatest increase in bone formation (33.56±3.53%). Smaller amounts of bone was measured in the 6 week HA putty+BMA group (8.57±2.86%). Bone formation in the HA group at 12 weeks was significantly higher when compared with the HA putty (p= 0.043) and the HA putty+BMA group (p= 0.043). At both the 6 and 12 week time point, highest bone-implant contact was seen in the HA granules group (59.34±10.89% and 72.65±3.38% respectively) when compared with both the HA putty (p=0.018) and HA putty+BMA (p=0.047). Results showed no significant difference in the amount of implant remaining when each group was compared. Conclusions. Results from this study showed that the inclusion of BMA did not augment bone growth to the scaffold or increase its osteoconductive capacity when combined with Calcium/Sodium Alginate fibre gel. Further research is necessary to optimise Calcium/Sodium Alginate fibre gel when used to bind HA granules and to investigate the effect of BMA with this type of HA alone

The use of autologous grafts for vertebral arthrodesis is associated with a number of complications that should be properly considered: pain at the harvesting site, increased blood loss, prolonged surgical time, and additional scar. Moreover, in many cases, the amount of autologous bone is insufficient. Novel materials, either natural or synthetic, are therefore needed to be used as bone substitutes in vertebral surgery. For this purpose, a number of synthetic materials have been developed, their characteristics varying considerably in terms of ostoinduction, osteoconduction, biomecanics, and cost. In particular, clinical and experimental studies have highlighted the potential of demineralized bone matrix (DBM), alone or in combination with autologous grafts, and of collagenic mineralized matrix (Healos). Aim of this study was the evaluation of the clinical value of these materials in vertebral surgery. We have analyzed a series of 60 patients who underwent vertebral arthrodesis by the addition of either DBM (30 cases) or Healos (30 cases). Bone substitutes were used both in posterior-lateral arthrodeses (on one side, the other being treated with autologous graft as a control) and in intersomatic arthrodeses in association with titanium or carbon fiber scaffolds. Patients were followed-up for a minimum 1-year interval, and evaluated with regard to clinical (Oswestry score, SF-36) and radiographic (static and dynamic X-rays, spiral CT, MRI) parameters. The area of arthrodesis was independently analyzed by three independent observers. Clinical results showed the reliability of both materials as a tool for a stable arthrodesis, since they were found to be able to achieve results comparable to those obtained with autologous grafts in the control arm of the study

Introduction Recent publications have confirmed that as many as one in four retrieved femoral heads can be significantly contaminated with potential pathogens. Reports from the Centre for Disease Control in Atlanta, Georgia have described fatal outcomes from the unwanted transmission of bacterial disease with inadequately processed allograft materials. Surgeons requesting non terminally sterilised bone refer to theoretical biological and biomechanical deleterious effects of gamma irradiation. This study examines the accuracy of those claims. Methods We have investigated the effects of varying levels of gamma irradiation (0kG, 15kG and 25kG) on the biological competence of morsellised allograft bone and its associated biomechanical impaction qualities. The biological study has used an in vivo model (nude rat) to quantify the effects of gamma irradiation on osteoinduction and osteoconduction. An in vitro impaction routine has been used to measure compaction, impaction and stiffness in the allograft product. Results There were no statistical differences in the biomechanical or biological properties of the 0kG and 15kG specimens (P< 0.05). Gamma irradiation at the 25kG level resulted in an allograft product of higher biomechanical stiffness, unchanged osteoinductivity and slightly lower osteoconductivity (P< 0.05). Conclusion Terminal gamma irradiation of 15kG reduces the risk of bacterial transmission with allograft products. It does not alter the efficacy of the allograft at biological and biomechanical levels. Gamma irradiation represents the mainstay of sterilisation of musculoskeletal allograft materials. Australian practices appear to be leading an international trend. In relation to the conduct of this study, one or more the authors have received, or are likely to receive direct material benefits

When investigating orthopaedic biomaterials and tissue engineered devices, biological investigations by means of in vitro and in vivo tests are mandatory to obtain a overall picture of biocompatibility and therapeutic efficacy. However, various aspects requiring careful consideration should be kept in mind and can explain the complex situations encountered by researchers when the skeletal tissue is involved. This presentation aimed to summarize some useful information in improving in vivo methodology to test present and future therapies for orthopaedic surgery. Some in vivo biological tests to study innovative reconstructive surgical techniques are summarized on the basis of the experience of the Experimental Surgery Department –IOR. After in vitro and in vivo biocompatibility tests, for the study of bone defect healing and of biomaterial osteo-inductive properties the subcutaneous and intramuscular implants are usually performed in laboratory animals while osteoconduction and bone healing evaluation require the development of “nonunions” (sites that never achieve functional bone continuity) and “critical size defects” (the smallest defect that will heal with less than 10% bony growth) models. Biomaterial osteointegration properties are investigated by means of metaphyseal, diaphyseal and intramedullary implantation. The use of pathological animals is also recommended to take into account the clinical situation where biomaterials are often implanted in aged and osteoporotic patients. As far as articular cartilage pathology is concerned, chondral and osteochondral “critical size defects” may be performed and the development of osteoarthritic animals could be also useful. At different experimental times post-explantation evaluations by means of radiology, histology, histomorphometry and biomechanics provide a complete characterization of biomaterials and biotechnologies showing their potential therapeutic efficacy for skeletal reconstruction. In vivo studies provide important pre-clinical information on new biomaterials and biotechnologies for the skeletal reconstruction Among the factors that are increasingly improving the reliability of in vivo testing are the continuous improvement in knowledge on bone biology and comparative science between humans and animals, the awareness that animal suffering should be reduced as much as possible, and, finally, the amount and the accuracy of in vivo post-explantation findings

Purpose: Unless exposed to stress, bone undergoes lysis. Osteoconduction is not observed in hydroxyapatite in contact with dead bone. We wanted to know whether bone blocks positioned on metal back cups in patients with total hip arthroplasty for acetabular dysplasia are destroyed lysis or “adhere” to the hydroxyapatite. Material and methods: The series included 22 bone blocks in 21 patients with low weight-bearing displacement (n=10), high weight-bearing displacement (n=6), high non-weight-bearing displacement (n=6). Mean follow-up was six years (17 patients > 5 years). Technique: all blocks were fashioned with autologous bone. The size of the cup, and thus the volume of the bone block, was determined by the largest anteroposterior diameter compatible with the desired position. The block was fashioned with a trial cup in place. The definitive cup was inserted separately then lag screwed to the bone block. Implants: twenty-two titanium cups (3 mm) with hydroxyapatite surfacing, bone block width: approximately 28° from the centre of the prosthetic head. Cup position: native acetabulum (n=11), neoacetabulum (n=11). Results: Complications were : sciatic paresia (n=0), displacement (n=0), shift in cup position (n=1 at day 21). Partial lysis of the bone block was observed but there was no case of total lysis. Titanium-hydroxyapatite-block adhesion: no lucent line was visible in 17 cases at more than five years. There were no cases of bony nonunion. Discussion: Are grafts necessary with a metal back cup? The cup is slightly exposed in some primary degenerative hips but all goes well for ten years without a bone block. At what point would cup “exposure” require a bony support? As autograft material is available, it would appear inappropriate to not use it, especially since the lack of lysis suggests grafts are useful. All bony structures behave in an intelligent manner: an oversized bone block undergoes lysis but the part under stress above the cup becomes more dense. Conclusion: Autologous bone blocks placed on metal back cups are not destroyed by lysis. The bone-hydroxyapatite couple adheres normally. Autologous bone blocks above metal back cups behave intelligently, like blocks inserted above cemented polyethylene cups

Bone impaction grafting (BIG) is a surgical technique for the restoration of bone stock loss with impaction of autograft or allograft bone particles (BoP). The goal of a series in-vitro and in-vivo experiments was to assess the suitability of deformable pure Ti (titanium) particles (TiP, FONDEL MEDICAL BV, Rotterdam, The Netherlands) for application as a full bone graft substitute in cemented revision total hip arthroplasty. TiP are highly porous (interconnective porosity before impaction 85 to 90%). In-vitro acetabular reconstructions were made in Sawbones (SAWBONES EUROPE, Malmö, Sweden) to evaluate migration by roentgen stereo photogrammetric analysis and shear force resistance by a lever out experiment. In-vitro femoral TiP reconstructions (SAWBONES, Malmö, Sweden) were used to evaluate micro-particle release and subsidence. Mature Dutch milk goats were used for two in-vivo experiments. A non-loaded femoral defect model was used to compare osteoconduction of bioceramic coated TiP with BoP and ceramic particles (CeP). Acetabular defects (AAOS type 3) were reconstructed in 10 goats using a metal mesh with impacted TiP acting as a full bone graft substitute in combination with a cemented polyethylene cup and a downsized cemented Exeter femoral stem (STRYKER BENOIST, Girard, France). Blood samples were taken for toxicological analysis. In-vitro: TiP were as deformable as BoP and created an entangled graft layer (porosity after impaction 70 to 75%). Acetabular TiP reconstructions were more stable and resistant to subsidence and shear force than BoP reconstructions (lever-out moment 56 ± 12 Nm respectively 12 ± 4 Nm, p < 0.001). After initial setting, femoral subsidence rates were smaller than seen in femoral bone impaction grafting (0.45 ± 0.04 mm after 300 000 loading cycles). Impaction generated 1.3 mg particles/g TiP (particle Ø 0.7–2 000 μm, tri-modal size distribution). In-vivo: Bioceramic coated (10 −40 μm) TiP showed bone ingrowth rates comparable to BoP and CeP. Reconstructed acetabular defects showed rapid bone ingrowth into the layer of TiP. Serum titanium concentrations slowly increased from 0.60 ± 0.28 parts per billion (ppb) preoperatively to 1.06 ± 0.70 ppb at fifteen weeks postoperatively (p = 0.04). Mechanical studies showed very good initial mechanical properties of TiP reconstructed defects. The in-vitro study showed micro-particle generation, but in the short-term goat studies, histology showed very few particles and no negative biological effects were found. The in-vivo acetabular study showed very favorable bone ingrowth characteristics into the TiP layer and a much thinner interface with the cement layer compared to similar defects reconstructed with BoP or mixtures of BoP with CeP. Further analysis in a human pilot study should proof that TiP is an attractive and safe alternative for allograft bone in impaction grafting revision arthroplasty