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Aims: Impaction bone grafting creates new bone stock after hip joint replacement. Utilizing a synthetic bone substitute instead of bone might increase primary stability and is not associated with graft shortage and pathogen transmission. This study compares the initial stability of a graft layer of porous titanium particles (TiP), cancellous bone particles, and a 1:2 bone-titanium mix in synthetic cemented acetabular reconstructions. Displacement was measured by radiostereometric analysis after cyclic loading (1 Hz, maximum stress 2.5 MPa). Shear stress resistance was quantified by a lever out test of the cup. Cement penetration was quantified from cross-sections., Findings: Titanium reconstructions showed less residual displacement (0.13 ± 0.13 mm) than pure bone particle reconstructions (0.57 ± 0.18 mm) (p < 0.01). Titanium reconstructions were also more resistant to shear stress (p < 0.001). The bone-titanium mix showed intermediate results. Cement penetrated deeper into the bone particle graft layers (4.8 ± 0.7) than into the titanium graft layers (3.8 ± 0.5 mm) (p < 0.02)., Conclusions: Cemented acetabular revision reconstructions with porous TiP show better initial stability despite less cement penetration than bone particle reconstructions. Realistic preclinical in vivo testing should explore the hypothesis that porous TiP offer a safe alternative to the current gold standard of bone grafts., (Copyright © 2013 Wiley Periodicals, Inc., a Wiley Company.)

Aims: Impaction grafting restores bone defects in hip arthroplasty. Defects are reconstructed with bone particles (BoP) as substitute materials with adequate mechanical and biological properties are not yet available. Ceramic particles (CeP) have mechanical drawbacks as opposed to porous titanium particles (TiP). In this in vivo study, bone ingrowth and bone volume in coated and noncoated TiP were compared to porous biphasic calcium-phospate CeP and allograft BoP. Coatings consisted of silicated calcium-phosphate and carbonated apatite. Materials were implanted in goats and impacted in cylindrical defects (diameter 8 mm) in the cancellous bone of the femur. On the basis of fluorochrome labeling and histology, bone ingrowth distance was measured at 4, 8, and 12 weeks. Cross-sectional bone area was measured at 12 weeks., Findings: TiP created a coherent matrix of entangled particles. CeP pulverized and were noncoherent. Bone ingrowth in TiP improved significantly by the coatings to levels comparable to BoP and CeP. Cross-sectional bone area was smaller in CeP and TiP compared to BoP., Conclusions: The osteoconductive properties of impacted TiP with a calcium-phosphate coating are comparable to impacted allograft bone and impacted biphasic ceramics. A more realistic loaded in vivo study should prove that coated TiP is an attractive alternative to allograft bone., (Copyright © 2012 Wiley Periodicals, Inc.)

The bone ingrowth potential of three-dimensional E-beam-produced implant surfaces was examined by histology and compared to a porous plasma-sprayed control. The effects of acid etching and a hydroxyapatite (HA) coating were also evaluated by histology. Specimens were implanted in the distal femur of 10 goats. Histological analysis of bone ingrowth was performed 6 weeks after implantation. The E-beam-produced surfaces showed significantly better bone ingrowth compared to the plasma-sprayed control. Additional treatment of the E-beam surface structures with a HA coating, further improved bone ingrowth potential of these structures significantly. Acid etching of the E-beam structures did not influence bone ingrowth significantly. In conclusion, the HA-coated, E-beam-produced structures are promising potential implant surfaces.

Background and Purpose: Porous titanium (Ti) particles can be impacted like cancellous allograft bone particles, and may therefore be used as bone substitute in impaction grafting. We evaluated the effect of impaction and of a thin silicated biphasic calcium phosphate coating on osteoconduction by Ti particles., Methods: The bone conduction chamber of Aspenberg was used in goats and filled with various groups of coated or uncoated small Ti particles (diameter 1.0-1.4 mm). Impacted allograft bone particles and empty chambers were used in control groups. Fluorochromes were administered at 4, 8, and 12 weeks. Maximum bone ingrowth distance was evaluated by histomorphometric analysis., Results: Histology of Ti particle graft cylinders showed a dense matrix with narrow inter-particle and intra-particle pores (< 100 μm), occluding the lumen of the bone chamber. Bone ingrowth distances gradually increased with time in all groups. Maximum bone ingrowth distance was higher in originally empty chambers than those with allograft bone particles (p = 0.01) and Ti particles (p < 0.001). Maximum bone ingrowth in allograft bone particles was higher than in all Ti groups (p ≤ 0.001). Impaction reduced osteoconduction and the coating partially compensated for the negative effect of impaction, but these differences were not statistically significant. No osteolytic reactions were found., Interpretation: Osteoconduction in the bone conduction chamber was reduced more by the insertion of small Ti particles than by insertion of small allograft bone particles. The osteoconductive potential of porous Ti particles should be studied further with larger-sized particles, which may allow bone ingrowth after impaction through larger inter-particle pores.

Background: Electron beam melting (E-beam) is a new technology to produce 3-dimensional surface topographies for cementless orthopedic implants., Methods: The friction coefficients of two newly developed E-beam produced surface topographies were in vitro compared with sandblasted E-beam and titanium plasma sprayed controls. Bone ingrowth (direct bone-implant contact) was determined by implanting the samples in the femoral condyles of 6 goats for a period of 6 weeks., Results: Friction coefficients of the new structures were comparable to the titanium plasma sprayed control. The direct bone-implant contact was 23.9 and 24.5% for the new surface structures. Bone-implant contact of the sandblasted and titanium plasma sprayed control was 18.2 and 25.5%, respectively., Conclusions: The frictional and bone ingrowth properties of the E-beam produced surface structures are similar to the plasma-sprayed control. However, since the maximal bone ingrowth had not been reached for the E-beam structures during the relatively short-term period, longer-term follow-up studies are needed to assess whether the E-beam structures lead to a better long-term performance than surfaces currently in use, such as titanium plasma spray coating.

Aims: Impaction grafting with bone particles is a successful technique to restore bone stock loss during hip revision surgery. Allograft shortage is expected within the near future. This study investigates the feasibility of porous titanium particles (TiP) to replace bone particles (BoP) and to compare mechanical properties of TiP and a commercially available porous ceramic bone graft extender (CeP). Impactability and time-dependent mechanical properties (stability and stiffness during physiologic loading (0.1-2.5 MPa)) were assessed by standardized impaction and a confined compression test. Loaded samples were used for particle release analysis., Findings: TiP were more impactable than BoP and created a stable, highly entangled macroporous construct. CeP were crushed during impaction, resulting in non-cohesive specimens of small ceramic particles. TiP showed very little deformation at the end of physiological loading. Impacted TiP were stiffer than BoP but more elastic than CeP. TiP generated a low volume of microparticles (0.2% of original TiP weight) with a bimodal size distribution (diameter range, 7-2000 microm)., Conclusion: TiP are impactable and create a stable, elastic and highly entangled, macroporous layer. Further in-vitro testing and biological studies are warranted to verify whether the promising results are maintained with THA reconstructions.

The disadvantages of allografts to restore femoral bone defects during revision hip surgery have led to the search for alternative materials. We investigated the feasibility of using porous titanium particles and posed the following questions: (1) Is it possible to create a high-quality femoral graft of porous titanium particles in terms of graft thickness, cement thickness, and cement penetration? (2) Does this titanium particle graft layer provide initial stability when a femoral cemented stem is implanted in it? (3) What sizes of particles are released from the porous titanium particles during impaction and subsequent cyclic loading of the reconstruction? We simulated cemented revision reconstructions with titanium particles in seven composite femurs loaded for 300,000 cycles and measured stem subsidence. Particle release from the titanium particle grafts was analyzed during impaction and loading. Impacted titanium particles formed a highly interlocked graft layer. We observed limited cement penetration into the titanium particle graft. A total mean subsidence of 1.04 mm was observed after 300,000 cycles. Most particles released during impaction were in the phagocytable range (< 10 microm). There was no detectable particle release during loading. Based on the data, we believe titanium particles are a promising alternative for allografts. However, animal testing is warranted to investigate the biologic effect of small-particle release.

Reconstruction of bone defects with impacted morsellized cancellous bone grafts (MCB) is a popular method. Because of a shortage of human bone, mixing with biomaterials may be attractive. Ceramics may be used as bone graft extenders. In this study, various volume mixtures of biphasic tri-calciumphosphate/hydroxyl-apatite (TCP-HA) granules (1.5-2 mm) with MCB were examined in a non-loaded defect model in rabbits. Direct post-operatively, many 10-150 microm TCP-HA particles were present due to impaction. Irrespective to the group, after 8 weeks, virtually all MCB was resorbed and most TCP-HA granules were osseous-integrated with newly formed bone. The cross-sectional areas of TCP-HA after 8 weeks was generally smaller compared with direct post-operatively and the number of small 10-150 microm TCP-HA particles seemed reduced. Macrophages and giant cells were sparse after 8 weeks. In conclusion, the osteoconductivity of various mixtures of MCB and TCP-HA granules is not dependent on the ratio of TCP-HA over MCB. The reduced number of the 10-150microm TCP-HA particles after 8 weeks, may suggest that a cellular mediated resorption process of TCP-HA granules took place. Based on these favorable biological findings subsequent in-vivo experiments are warranted in load-bearing conditions to investigate whether these findings hold for joint reconstruction purposes.

Calcium phosphates such as TCP-HA granules are considered promising bone graft substitutes. In the future, they may completely replace allograft bone for impaction grafting procedures. Mechanically, acetabular reconstructions with TCP-HA granules show high stability, however this is partly caused by excessive cement penetration, which is unfavourable from a biological perspective. It has been hypothesised that mixtures of morselised cancellous bone grafts (MCB) and/or TCP-HA granules with a nano-crystalline hydroxyapatite paste (Ostim) may reduce cement penetration while maintaining adequate implant stability and biocompatibility of the graft mixture. To investigate this hypothesis, destructive lever-out tests and in vivo animal test were performed with various combinations of materials. Mechanically, the addition of 10% Ostim to mixtures of MCB and/or TCP-HA granules reduced cement penetration and resulted in a mechanical stability comparable to pure allograft (the current gold standard). Biologically, the application of Ostim with MCB or TCP-HA granules did not hamper the biocompatibility of the materials. Ostim was mostly osseous-integrated with MCB or TCP-HA granules after 8 weeks. Also, non-osseous-integrated Ostim remnants were observed. In tartrate resistant acid phosphatase stained sections, these few non-osseous integrated Ostim remnants were actively being resorbed by osteoclasts. In conclusion, Ostim HA-paste could be a valuable addition when TCP-HA ceramic granules are being used for acetabular bone impaction grafting procedures.

In the bone conduction chamber (BCC) various materials and factors have been tested for their effect on bone graft incorporation and bone healing. However, biomaterials often have to be crushed to fit in this small chamber. Since cellular responses to biomaterials are influenced by the size and shape of particles, research concerning the evaluation of biomaterials is limited by the dimensions of this bone chamber. We enlarged and modified the BCC in order to be able to investigate the in vivo influences of biomaterials, growth factors and bone graft processing on tissue and bone ingrowth. Seven goats received four bone chambers each, three modified models and a BCC. The first model (BCC+) had two ingrowth openings, similar to that of the BCC. The second model had two round ingrowth openings (ROU). The third model had a open bottom for bone ingrowth (BOT). After 12 weeks, bone ingrowth distances were measured on histological sections and using muCT. Bone ingrowth was significantly higher (p=0.009 and 0.008) in the ROU compared to the BCC+ and the BOT, respectively. Similar results were found using muCT. The ROU model performed most similar to the BCC (gold standard) and is considered to be a promising new tool in biomaterials research.

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.

Reconstructing large loaded bone defects with ceramic bone graft extenders is tempting considering the expected future donor bone shortage. However, whether there are negative effects is unknown. Standardized large defects in the acetabulum of goats were created and subsequently reconstructed with metal mesh and impacted morselized cancellous bone grafts or a 50/50% volume mixture of tricalcium phosphate-hydroxyapatite granules and morselized cancellous bone grafts using the bone impaction grafting technique. Subsequently, a cemented total hip prosthesis was inserted. Clinically, no differences were observed between groups. Most of the morselized cancellous bone graft had been resorbed and incorporated into new bone after 15 weeks. The large tricalcium phosphate-hydroxyapatite granules were integrated, the smaller crushed tricalcium phosphate-hydroxyapatite granules were surrounded by osteoclasts or engulfed by macrophages and giant cells. The cement penetration into the reconstructive layer and the quality of the bone based on a semiquantitative score were similar in both groups. We found no suggestion of tricalcium-hydroxyapatite granule-induced third-body wear in this short-term followup study. No negative effects were observed in this study, and therefore, it seems reasonable to use tricalcium-hydroxyapatite granules in a 50/50% volume mix with morselized cancellous bone graft as a bone graft extender in acetabular revision surgery with the bone impaction grafting technique.

Bone defects after failed total hip arthroplasty can be reconstructed with impacted morselized bone grafts and a cemented cup. In the near future the amount of bone grafts available for surgical purposes will be insufficient. Ceramic calcium phosphates [tricalcium phosphate (TCP) and hydroxyapatite (HA)] have been widely considered as potential bone graft substitutes or bone graft extenders. In the past, mechanical experiments have been performed to determine implant stability of bone grafts and ceramic TCP-HA granules mixes under a compressive load. However, in-vivo migration studies suggest that shear loading may be equally important. This in-vitro study investigated the initial stability of cups reconstructed with various mixes of bone grafts and ceramic TCP-HA granules in a lever-out situation, where shearing is the predominant loading mode. It was found that the cups reconstructed with mixes of bone graft and TCP-HA granules exhibited greater mechanical stability than the cups reconstructed with bone grafts only. It is concluded that from a mechanical standpoint, when considering shear force resistance, 50-50 per cent volume mix and 25-75 per cent volume mix of morselized cancellous bone graft and TCP-HA granules both provide adequate initial cup stability and can be used for acetabular reconstructions with the bone impaction grafting technique.

Tricalciumphosphate (TCP) and hydroxyapatite (HA) have been suggested as bone graft substitutes in a wide range of applications. In this study, the initial stability of cemented acetabular cups was determined after reconstructing a combined cavitary and segmental defect in a realistic acetabular revision surgery model. The defects were reconstructed with mixes of TCP/HA particles and human bone grafts using the bone impaction grafting technique. In comparison with defect reconstruction with human bone grafts only, cup translation and tilt decreased by 27% when mixes of bone grafts and porous TCP/HA particles were used and by 55% when mixing the bone grafts with solid TCP/HA particles. Increasing the TCP/HA ratio within the mix significantly decreased cup translation. From a biomechanical perspective, mixes of TCP/HA particles and bone grafts are an attractive alternative for morsellized bone grafts when using the bone impaction grafting technique in the reconstruction of large defects of the acetabulum.

In revision surgery of the acetabulum bone defects can be filled with impacted human morsellized bone grafts. Because of a worldwide limited availability of human bone, alternatives are being considered. In this study we compared the initial stability of acetabular cups after reconstructing a cavitary defect with various compositions of impacted tricalciumphosphate-hydroxyapatite (TCP/HA) particles and mixes of TCP/HA particles and human grafts in a realistic acetabulum model. Primary cemented cups and reconstructions with impacted human cancellous grafts were used as reference. A dynamic load displaced the acetabular cups superomedially. The primary cemented cups showed the highest stability. The cups with impacted human grafts produced the most displacement. All reconstructions with the TCP/HA particles showed a high stability of the cups. However, especially when using large TCP/HA particles this was probably due to a large amount of cement penetration. Mixing TCP/HA particles with human grafts seemed to decrease cement penetration. although still a high stability was obtained. In this perspective, we concluded that TCP/HA particles might be useful as a bone graft extender in the reconstruction of acetabular bone defects.

The aim of this study was to develop a new animal model in which we could assess the in vivo effects of mechanical stimuli in the incorporation process of impacted morsellized bone grafts. The subcutaneous pressure implant SPI was developed for use in the goat. This device can generate controlled loading conditions onto a fixed amount of bone graft in the distal femur. Twenty goats were divided into three groups: non-loaded, 2 or 4 MPa loads (1 Hz, 1 h/day). The goats were sacrificed after 3, 6 or 12 weeks. The results were documented by clinical observations, quantitative bone density from QCT-scanning and histomorphometry. Nine post-mortem knee specimens were prepared in a similar manner to the experimental knees to determine the reproducibility and mechanical stability of the grafting method. Three goats were lost due to complications, the others functioned clinically well. Histology showed invasion of the bone graft by a front of vascular fibrous tissue after which osteoclasts resorbed the dead bone graft, followed by woven bone apposition on the graft remnants. At 12 weeks the loaded grafts had transformed into a vital trabecular structure. QCT bone density measurements revealed persistently high densities in the 12-weeks 4 MPa specimens, but reduced densities in the 2 MPa and non-loaded specimens. Morphometrically, the mineralising surface was larger in the 4 MPa group (P = 0.02) and the incorporation and remodelling processes had advanced more rapidly in the 2 MPa specimens (P = 0.04). Although the numbers investigated in this study in each group were low, statistical differences were found in the amount of graft left after incorporation and in the apposition rate of the new bone. In the future this model will be used to study the incorporation potential of different types of bone graft and bone graft substitutes.

To reconstruct femoral intramedullary bone-stock loss in revision surgery of failed total hip arthro-plasties, morsellized trabecular bone grafts can be used. In 14 goats a noncemented hydroxyapatite-coated titanium stem was fixed within a circumferential construction of bone allografts. After 6 or 12 wk, four goats were used for mechanical tests and three for histology. The stability of the stems relative to the bone was determined in a loading experiment with Roentgenstereo-Photogrammatic Analysis (RSA). Owing to two loosenings and two fractures, only one 6-wk specimen and three 12-wk specimens were available for mechanical testing. The prostheses were very stable at 12 wk. The most important movements were axial rotation (maximal 0.17 degrees at 800 N) and subsidence (maximal 0.036 mm at 800 N). After unloading, there was 40-60% elastic recovery. Histological examination showed revascularization and remodelling of the graft in all the specimens investigated. At the graft site, bone apposition and bone resorption had resulted in a mixture of graft and new bone. Bone incorporation was mainly seen in the proximal areas. Graft lysis was evident in the midshaft region and at distal levels around the prostheses.

Intra‐articular defects can be filled with an autologous bone graft taken from the iliac crest. This can be indicated after trauma or following correcting osteotomy. Patients may encounter donor site morbidity after this procedure. In this in vivo study, we studied if coralline hydroxyapatite (CHA) is a suitable material to replace autologous bone graft to fill a defect in the femoral trochlea of goats. CHA did not evoke any negative reaction in the synovium, and the articular cartilage was comparable to controls. In the bone graft group, we found scattered areas of (enchondral formed) bone. Most bone graft had been resorbed or remodeled, and the scarce remnants were incorporated into new bone. Resorption of CHA was limited or absent and most CHA was surrounded by new bone. In areas with fragmented CHA, close to the joint surface, numerous giant cells were found. The study shows that in this animal model, CHA inserted in a defect that directly communicates with the joint space incorporates into bone. This study did not show any negative effects of CHA in a joint environment. © 2008 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2009 [ABSTRACT FROM AUTHOR]