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Oro-facial bone loss is a major problem in oral and maxillofacial rehabilitation. They have various and varied causes: cancer, cysts, cleft palates, infections or trauma. The management of such bone defects requires the use of bone grafts. Autogenous bone or autograft is the standard gold but has disadvantages: i) the need for a second surgical site, ii) morbidity, iii) increased operating time, iv) limited amount of bone to be removed. To overcome these pitfalls, alternative therapeutics to bone autograft are used, in particular bone substitutes derived from human (allografts), animal (xenografts) or synthetic (alloplastic) bone tissue. Allografts are a credible alternative to autografts and are nowaday widely used in reconstructive and regenerative surgery. These allografts are either mineralized (FDBA: Freeze-Dried Bone Allograft) or demineralized (DFDBA: Demineralized Freeze-Dried Bone Allograft) and come in powder or gel form depending on the support used in the case of DBM (Demineralized Bone Matrix). This PhD project aims to show the osteoformative potential of a new bone allograft formulation, partially demineralized as an injectable paste, in two different models for rat calvaria; it is a PDBM (Partially Demineralized Bone Matrix). The first model is the rat calvarial defect model. Critical size defects (8 mm diameter) and sub-critical size defects (6 mm and 4 mm diameter) are performed on rat calvaria and then left empty or filled with the PDBM. Micro sacnner (µCT) and histological results showed the positive effect of PDBM in the bone repair of 6 and 8 mm diameter defects. Similarly, molecular biology (RT-PCR) showed the positive effect of PDBM in the early expression of genes involved in osteoformation. The 2nd model is a vertical bone augmentation model. A bone chamber (custom-made cylinder of Polyetheretherketone) of 6 mm high and 5 mm in diameter is attached to the rat calvarias after perforating it with 3 small holes 1 mm in diameter. The bone chambers are filled with either PDBM or Bio-Oss®. The µCT and histological results revealed an osteoformative potential for PDBM in the bone chambers. These results support the idea that allografts are a viable option for the treatment of periodontal and maxillofacial defects.; Les pertes osseuses de la sphère oro-faciale constituent un problème majeur dans la réhabilitation orale et maxillo-faciale. Elles ont des causes diverses et variées : cancers, kystes, fentes palatines, infections ou traumatismes. La prise en charge de tels défauts osseux nécessite l’utilisation de greffes osseuses. L’os autogène ou autogreffe constitue le gold standard mais présente des inconvénients: i) la nécessité de recourir à un second site opératoire, ii) morbidité subséquente, iii) une augmentation du temps opératoire, iv) une quantité limitée d’os à prélever. Pour pallier à ces écueils, des alternatives thérapeutiques à l’autogreffe osseuse sont utilisés notamment des substituts osseux dérivés des tissus osseux humains (allogreffes), animaux (xénogreffes) ou synthétiques (alloplastiques). Les allogreffes constituent une bonne alternative aux autogreffes et sont, aujourd’hui, largement utilisées en chirurgie reconstructive et régénérative. Ces allogreffes sont soit minéralisées (FDBA : Freeze-Dried Bone Allograft) ou déminéralisées (DFDBA : Demineralized Freeze-Dried Bone Allograft) et se présentent sous forme de poudre ou de gel selon le support utilisé dans le cas des DBM (Demineralized Bone Matrix). Ce projet de Doctorat avait pour but de montrer le potentiel ostéoformateur d’une nouvelle formulation d’allogreffe osseuse, partiellement déminéralisée sous forme de pâte injectable, dans deux modèles différents au niveau de la calvaria de rat : il s’agit d’une Matrice Osseuse Partiellement Déminéralisée (MOPD). Le 1er modèle est celui de défauts de calvaria de rat. Des défauts de taille critique (8 mm de diamètre) et sub-critique (6 mm et 4 mm de diamètre) sont réalisés sur la calvaria des rats puis laissés vides ou comblés avec la MOPD. Les résultats du micro scanner (µCT) et ceux histologiques ont montré l’effet positif de la MOPD dans la réparation osseuse des défauts de 6 et 8 mm de diamètre. De même, la biologie moléculaire (RT-PCR) a montré l’effet positif de la MOPD dans l’expression précoce des gènes impliqués dans l’ostéoformation. Le 2e modèle est celui d’augmentation osseuse verticale. Une chambre à os en Polyétherétherkétone (PEEK) de 6 mm de haut et 5 mm de diamètre est fixée sur la calvaria des rats après avoir perforé cette dernière de 3 petits trous de 1 mm de diamètre. Les chambres à os sont remplies soit de MOPD soit d’os bovin déprotéinisé (Bio-Oss®). Les résultats du µCT et ceux histologiques ont révélé un potentiel ostéoformateur de la MOPD dans les chambres à os. Ces résultats confortent l’idée que les allogreffes sont une option viable pour le traitement des défauts parodontaux et maxillo-faciaux.

В статье рассмотрены погребения средневекового некрополя у церкви Благовещения в южной части Тверского кремля. На основании анализа относительной стратиграфии и датировки находок установлена хронология некрополя XIV первая половина XV вв., выделено три этапа его функционирования. Определены границы юго-восточной части некрополя в указанный период. Проанализирован погребальный обряд., The article represents burials in medieval necropolis near the Church of Annunciation in the south side of Tver kremlin. The authors defi ne chronology of necropolis by the XIV the fi rst part of the XV centuries and outline three stages of its existence in reliance on relative stratigraphy analysis and dating of fi ndings. The authors also defi ne borders of southeast side of necropolis in that period and analyze funeral rite.

Despite a myriad of studies confirming the interaction between biology and mechanics, the exact nature of the main mechanical stimuli and their influence on the bone regeneration processes are still unclear. The hypothesis of this study was that the outcome of peri-implant healing under different implant loading regimens can be explained by the influence of fluid flow on the combination of angiogenesis and osteogenesis through its influence on cell proliferation and differentiation. To investigate this hypothesis a mathematical model of bone regeneration was applied to simulate the peri-implant healing in an in vivo repeated sampling bone chamber for different axial micromechanical implant loading regimes. When mechanical loading was modeled to influence both osteogenic and angiogenic processes, a good agreement was observed between simulations and experiments concerning the amount of bone in the bone chamber, its radial and longitudinal distribution, and the bone-implant contact for different implant displacement magnitudes.

Contains fulltext : 71116.pdf (Publisher’s version ) (Open Access) BACKGROUND AND PURPOSE: There is increasing awareness that non-steroidal anti-inflammatory drugs (NSAIDs), and especially the cyclooxygenase-2 (COX-2) selective ones, may retard bone healing. We have used NSAIDs (indomethacin for at least 7 days) to prevent heterotopic ossification after acetabular reconstructions using impacted bone grafts. The long-term clinical results have been satisfying, making it difficult to believe that there is an important negative effect of NSAIDs on graft incorporation. We studied the effect of two different NSAIDs on bone and tissue ingrowth in a bone chamber model in goats, using autograft, rinsed allograft, and allograft that had been rinsed and subsequently irradiated. METHODS: 9 goats received no NSAIDs, 9 received ketoprofen, and 9 received meloxicam--all for 6 weeks. In each goat 6 bone chambers were implanted: 2 filled with autograft, 2 with rinsed allograft, and 2 with allograft that had been rinsed and irradiated. The amount of bone ingrowth and total tissue ingrowth was compared between the groups. RESULTS: There were no statistically significant differences in bone ingrowth between the different groups. Also, no differences in bone ingrowth were found with respect to the type of graft used. Furthermore, there was no statistically significant difference in the total amount of ingrowth of fibrous tissue between the treatment groups. INTERPRETATION: No differences in bone ingrowth in titanium bone chambers could be detected with both ketoprofen and meloxicam compared to untreated control animals. This confirms our hypothesis that the effect of NSAIDs on the incorporation and ingrowth of bone graft is limited.

Both implant surface characteristics and mechanical loading are known to affect implant osseointegration. Their interaction and the underlying mechanisms by which they affect peri-implant healing processes are still unknown. The aim of this study is therefore to investigate the influence of a turned versus a rough (Plus®, Dentsply Friadent) implant surface on peri-implant bone formation in case of unloaded or loaded implant healing. Material and Methods: Bone formation was evaluated around screw-shaped implants under four experimental conditions using a repeated sampling bone chamber methodology: (1) unloaded turned implant (CU), (2) unloaded implant with a rough surface (TU), (3) loaded turned implant (CL), and (4) loaded implant with a rough surface (TL). Peri-implant tissue samples were paraffin embedded after implant removal and examined histologically and histomorphometrically. A mixed model was used for statistical analysis. Results: The surface of bone tissue relative to the total tissue area (bone area fraction) was not affected by the experimental conditions. The areas of bone trabeculae relative to the bone area (bone fraction) were significantly higher for TL compared with CU and TU. The bone fraction in the vicinity (100 μm zone) of the implant (BFZ) was significantly the highest around the loaded roughened implants (TL). Conclusion: Implant loading did not affect bone formation in the absence of surface roughness, and implant surface roughness had no effect in the absence of loading. However, a bone-stimulating effect in the implant's vicinity was assigned to the rough surface when the implant was loaded.

Impacted, morselized bone allografts are used with good clinical results in revision of hip prostheses with loosening and osteolysis. The impacted bone graft appears radiographically to remodel, but histological analyses have shown a heterogeneous picture with a mixture of living and dead bone. Thus, complete remodeling of the graft may be neither a prerequisite nor a cause of the good clinical results. The present study concerns the mechanical effect of the mere armoring of the bone graft by ingrowing fibrous tissue. We compared the compression strength of freshly-impacted grafts to grafts that had been inserted into a bone chamber and thus were penetrated by fibrous tissue growing in between the graft trabeculae. The compressive strength was doubled after 4 weeks of fibrous ingrowth. We conclude that the mechanical properties of an impacted graft are enhanced by armoring with ingrowing fibrous tissue. Strengthening of the parts of the impacted grafts which have not yet remodeled, would be clinically relevant for the outcome of the operation, since these parts are at high stress during the whole remodeling period. Complete osseous remodeling may not be necessary to obtain a good clinical result with a morselized impacted graft.

This study compares the effects of parathyroid hormone (PTH) treatment on new bone formation and normal baseline remodelling in rats. To study new bone formation we used a titanium bone chamber, and to study normal remodelling we used the femur and vertebrae from the same animals. One titanium bone chamber was inserted in the proximal tibia of each of 37 rats. The rats were randomly assigned to daily injections of human PTH (1-34) 60 microg/kg) or vehicle control and killed after 2, 4 or 6 weeks. The total distance of bone growth into the chamber was slightly increased by PTH. Body weight was not affected, and there was only a minor increase in trabecular density of the vertebral and femoral cancellous bone after 6 weeks. The only dramatic effect of PTH was seen in the chambers. In the controls, a marrow cavity formed in the chamber so that the cancellous density decreased from 44% to 24%, and 11% over 2, 4 and 6 weeks. In the PTH-treated animals, a dense network of bone trabeculae was found in the entire bone chamber at all times. The cancellous density increased from 48% to 60%, and 73% at 2, 4 and 6 weeks, respectively. The results suggest that PTH treatment can reduce the development of a resorption cavity. Thus, PTH in this model had a net antiresorptive effect, probably solely because it stimulated osteoblastic activity. Even though osteoclastic activity was present throughout the PTH specimens, it was not sufficient to resorb all newly formed bone. Since PTH seemed to have a greater effect on new bone formation in the chamber than on normal bone remodeling, it might become useful for improving the incorporation of orthopedic implants and stimulating fracture repair.

Histomorphometry is a useful tool for assessing the dynamics of bone in orthopaedic research. We compared a new fluorescence imaging method with a commonly used computer-interactive manual method using hematoxylin and eosin staining to quantify the total bone area in 6-μm thick frozen undecalcified sections processed from a bone chamber. Eighteen sections were analyzed by both methods, and the correlation coefficient was 0.92. The advantages of the fluorescence imaging are that it is simple, objective, and correlates strongly with traditional more tedious methods for histomorphometric analysis of bone. (The J Histotechnol 31:15, 2008)Submitted July 24, 2007; accepted with revisions January 9, 2008

The effects of recombinant human fibroblast growth factor-2 in the presence of eroding 50:50 poly(DL-lactide-co-glycolide) on angiogenesis during acute bone defect healing were studied in the optical bone chamber. Bone chambers were loaded with disks of poly(DL-lactide-co-glycolide) surrounded by one of four doses of recombinant human fibroblast growth factor-2. Fifty-two female rabbit right tibias were implanted. Commencing with the third postimplantation week, healing into the bone chamber compartment was observed weekly, with use of intravital microscopy, until week 8. The treatment groups were as follows: unloaded, loaded with polymer only, and loaded with polymer plus-0.5, -1.0, and -10 microg recombinant human fibroblast growth factor-2. Videotaped and photographed bone images were measured and analyzed with a frame-grabber digitizing system. Comparison with controls or polymer alone revealed that angiogenesis rates were significantly above normal in rabbits loaded with polymer plus either of the two highest recombinant human fibroblast growth factor-2 doses. The effects of these doses were not, however, significantly different from each other, indicating a plateauing rather than monotonically increasing response. It was concluded that recombinant human fibroblast growth factor-2 in the dose- range studied can effectively overcome the retarding effects of eroding polymer on angiogenesis in bone, which has been reported previously by this laboratory. In contrast to these results, no statistically significant differences in angiogenesis rate as a function of time could be detected. It is suggested that this apparent lack of variation is linked to observed alterations in vessel patterns from week-to-week. The clinical relevance of these results is that inhibitory carrier effects can be compensated for by increasing the dose of loaded agent where the effect being inhibited is the one being treated, or by adding an agent specific for the inhibited effect. In either case, geometry of the carrier must be considered when programming for delivery rate.

Eroding poly(DL-lactide-co-glycolide) (PDLLG) washers and poly(L-lactide-co-glycolide) (PLLG) threads were observed chronically in vivo following loading in a bone chamber tibial implant (BCI). Images were recorded using intravital microscopy of the implanted rabbit. Erosion and bone healing, as represented by angiogenesis and osteogenesis, was determined from changes in projected area of observed polymer, vessels and bone, respectively. Erosion rates of the two polymers were significantly different. Healing adjacent to both polymers differed significantly from controls. Healing response to each polymer was also different, with the faster eroding PDLLG causing more deviation from normal osteogenesis and angiogenesis than did PLLG. It was speculated that the faster eroding polymer released macrophage-stimulating fragments earlier in the healing process, thus altering the normal macrophage-endothelial cell interaction which in turn affected angiogenesis-linked components of osteogenesis.

We found increased penetration of new bone into a frozen bone allograft which had been pretreated with basic fibroblast growth factor (bFGF). Pairs of grafts were placed in newly designed titanium bone chambers implanted bilaterally in rat tibiae. The ingrowing bone can enter the cylindrical interior of the chamber only at one end. It then penetrates the graft inside the chamber but, due to the length of the cylinder, it never reaches the other end. The distance which the ingrown bone has reached into the graft can then be measured on histological slides. With bFGF there was a 51 percent increase in the bone penetration distance at 6 weeks in this model. It also appeared that further penetration had almost ceased in the controls, whereas in the bFGF-treated specimens, membranous ossification was still going on.

It is well established that the mechanical environment modulates tissue differentiation, and a number of mechanoregulatory theories for describing the process have been proposed. In this study, simulations of an in vivo bone chamber experiment were performed that allowed direct comparison with experimental data. A mechanoregulation theory for mesenchymal stem cell differentiation based on a combination of fluid flow and shear strain (computed using finite element analysis) was implemented to predict tissue differentiation inside mechanically controlled bone chambers inserted into rat tibae. To simulate cell activity, a lattice approach with stochastic cell migration, proliferation, and selected differentiation was adopted; because of its stochastic nature, each run of the simulation gave a somewhat different result. Simulations predicted the load-dependency of the tissue differentiation inside the chamber and a qualitative agreement with histological data; however, the full variability found between specimens in the experiment could not be predicted by the mechanoregulation algorithm. This result raises the question whether tissue differentiation predictions can be linked to genetic variability in animal populations.

Tissue differentiation can be regulated by mechanical loading. A bone chamber experiment has been conducted in order to investigate the effect of loading on tissue differentiation in vivo. In this study a computational model of the experiment was developed in which a mechano-regulation algorithm for stem cell differentiation in response to mechanical stimulus was combined with algorithms for cell migration, proliferation and apoptosis. The results show that the simulation is feasible to forecast the tissue differentiation process inside a bone chamber.

Thermal preconditioning induces a cytoprotective effect and promotes tissue recovering. Laser is an appropriated method to generate a controlled and reproducible heating. Bone healing, a crucial challenge in medicine, is affected by X- ray radiation which induces a chronic antiangiogenic effect. So, this study aims to investigate the role of laser preconditioning on the vascularisation of bone after X-ray radiation. An optical bone chamber allowed the study of the vascularization process. The vascular density (VD) was determined using image processing. A longitudinal study was performed on 20 rabbits divided in four groups: #1: control group (n=5); #2: laser irradiation alone (diode laser 810 nm, fluence= 48 J/cm2) (n=5). #3: X-ray radiation (18.75 Gy) alone (n=5), #4: laser preconditioning 24 hours before a X-ray radiation (n=5). VD remained stable during 12-week follow up for groups #1 and #2. X-ray radiation lead to an important decrease of the superficial bone vascularization in group #3. The decrease of the vascularization was limited in group #4 highlighting a different evolution between group #3 and #4. Those results were confirmed by histological analysis. Our preliminary findings show that laser preconditioning preserves vascularization in X-ray radiated bone site, outlining a novel approach for the bone healing in which the vascular supply has been injured.

Objectives: The local mechanical environment influences early peri-implant tissue formation. It is still unclear whether immediate loading limits or promotes peri-implant osteogenesis and which mechanical parameters are important herein. The present study evaluated the influence of well-controlled mechanical stimuli on the tissue response around immediately loaded cylindrical turned titanium implants at two different observation periods. Material and methods: A repeated sampling bone chamber, consisting of dual-structure perforated hollow cylinders with a cylindrical implant, was installed in the tibia of 14 rabbits and used to conduct three displacement-controlled immediate loading experiments: (i) 30 μm – 400 cycles/day – 1 Hz frequency – 2 ×/week – 6 weeks; (ii) 30 μm – 400 cycles/day – 1 Hz – 2 ×/week – 6 weeks, followed by another 6 weeks with a 50 μm – 800 cycles/day – 1 Hz – 2 ×/week loading protocol; and (iii) 0 μm implant displacement for 12 weeks. A linear mixed model and logistic mixed model with α=5% were conducted on the data set. Results: The tissue area fraction was significantly the highest after 12 weeks of loading. The bone area fraction was significantly different between all three loading conditions, with the highest values for the 12-week loading experiment. Twelve-week stimulation resulted in a significantly higher mineralized bone fraction than 6 weeks. Loading did have a significantly positive effect on the mineralized bone fraction. The incidence of osteoid-to-implant and bone-to-implant contact increased significantly when loading the implant for 12 weeks. Conclusion: Immediate loading had a positive effect on the tissue differentiation and bone formation around cylindrical turned titanium implants. Controlled implant micro-motion up to 50 μm had a positive effect on the bone formation at its interface.

Aim: Tissue formation at the implant interface is known to be sensitive to mechanical stimuli. The aim of the study was to compare the bone formation around immediately loaded versus unloaded implants in two different implant macro-designs. Material and Methods: A repeated sampling bone chamber with a central implant was installed in the tibia of 10 rabbits. Highly controlled loading experiments were designed for a cylindrical (CL) and screw-shaped (SL) implant, while the unloaded screw-shaped (SU) implant served as a control. An F-statistic model with α= 5% determined statistical significance. Results: A significantly higher bone area fraction was observed for SL compared with SU (p< 0.0001). The mineralized bone fraction was the highest for SL and significantly different from SU ( p

Contains fulltext : 52973.pdf (Publisher’s version ) (Open Access) BACKGROUND: Bone morphogenetic proteins (BMPs) have the potential to improve clinical outcome after hip revision surgery by improving graft incorporation and implant fixation. However, impaction of cancellous bone grafts and TCP/HA bone substitute mixed with OP-1 device in a bone chamber in goats in a previous study led to reduced fibrous tissue ingrowth after 4 weeks. New bone formation was not promoted by OP-1. In the current study we examined whether this reduction represented a final loss of ingrowth or was just a delay, and whether the reduction can be overcome and ultimately results in a better late ingrowth. METHODS: Bone chambers with impacted allografts and impacted TCP/HA granules mixed with 2 doses of OP-1 device were implanted in proximal medial goat tibias. Impacted allografts and TCP/HA not treated with OP-1 served as controls. After 8 weeks, the incorporation was evaluated using histology and histomorphometry. RESULTS: Histology revealed evidence of bone graft incorporation, which proceeded in a similar way in both allografts and TCP/HA, with and without the addition of OP-1. After 8 weeks, no difference in bone ingrowth was found between the OP-1 groups and their controls. It was only in the allografts that the addition of OP-1 resulted in more fibrous tissue ingrowth. INTERPRETATION: We conclude that the previously observed delay in fibrous tissue ingrowth can be only partially overcome.

Contains fulltext : 51711.pdf (Publisher’s version ) (Open Access) BACKGROUND: Gamma irradiation has been widely used for sterilization of bone allografts. However, gamma irradiation alters proteins. This is favorable when it reduces immunogenicity, but is undesirable when osteoinductive proteins are damaged. Although the effect of gamma irradiation on BMPs has been studied, the effect of irradiation on the process of incorporation of morselized bone chips remains unclear. We studied the effects of sterilization by gamma irradiation on the incorporation of impacted morselized allografts. METHODS: Bone chambers with impacted allografts, rinsed impacted allografts, allografts that were rinsed and subsequently irradiated, and an empty control were implanted in proximal medial tibiae of goats. Incorporation was evaluated using histology and histomorphometry. RESULTS: Histology revealed evidence of bone graft incorporation, which proceeded in a similar way in unprocessed, rinsed, and both rinsed and irradiated bone grafts. After 12 weeks, no difference in bone and tissue ingrowth was found between the unprocessed, the rinsed, and the rinsed and subsequently irradiated allografts. The amount of unresorbed graft remnant was highest in the unprocessed bone grafts. INTERPRETATION: We conclude that sterilization with gamma irradiation does not influence the incorporation of impacted rinsed bone allografts.

Treatment of large bone defects is currently performed using mainly autograft or allograft bone. There are important drawbacks to bone grafting, such as limited availability, donor site morbidity in the case of autograft and inferior performance of allografts. Therefore, there is a great need for a suitable bone graft substitute. In order to evaluate efficiently newly developed biomaterials and factors intended for orthopaedic surgery, the bone chamber is a very suitable model. To allow longitudinal investigation of bone growth with mu CT, a new bone chamber made of radiolucent polyether ether ketone (PEEK) was developed and studied for its feasibility. Therefore, PEEK bone chambers were placed on rat tibiae, and filled with vehicle (Matrigel without growth factors, negative controls), with bone morphogenetic protein 2 (BMP-2, positive controls), or a mix of growth factors combining BMP-2, vascular endothelial growth factor and the chemokine stromal cell-derived factor 1 alpha, all laden on gelatin microspheres for controlled release (combined growth factors). Growth factor presence led to a significant increase in bone formation after 8 weeks, which subsided after 12 weeks, underlining the importance of longitudinal analysis. We conclude that the PEEK-bone chamber is a suitable translational animal model to assess orthotopic bone formation in a longitudinal manner.

Contains fulltext : 50000.pdf (Publisher’s version ) (Closed access) 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.

In impaction allografting, the host bone interface may consist of morsellized allograft alone or as a composite with bone cement. The objective of this study was to investigate the temporal changes in the interface for these two materials in a rat bone chamber model. To simulate the impaired endosteal circulation after impaction allografting, bone chambers were tightened bilaterally to the endosteal surfaces of proximal tibiae of mature rats and filled with pure allograft or cement/allograft composite. The cement/allograft composite-host bone interface strength was significantly higher at 3 weeks and was higher than the allograft construct failure strength. Limited allograft, but extensive periosteal remodeling, was observed at 3 weeks which resulted in a significantly increased cortical porosity and cortical thickness. The allograft porosity decreased significantly at 6 weeks indicating extensive remodeling of the allograft bone. Little or no remodeling of the allograft particles in the cement was found. At 6 weeks a new medullary canal was formed, and the endosteal cortex was partially absorbed. Endosteal absorption resulting in medullary canal widening in revision THR may be responsible for clinically unstable stems after impaction allografting.

Subchondral bone necrosis is important in osteonecrosis, Mb Kienboeck, intraarticular fractures or osteochondral grafting. As revascularization follows, bone resorption may lead to collapse in load bearing areas during the remodeling. Bisphosphonates are potent osteoclast inhibitors. Our hypothesis was that local bisphosphonate treatment of an osteochondral graft, in a high load environment, would protect the subchondral bone from collapse and maintain the joint architecture during remodeling. To investigate this, we used a rat bone chamber model to subject a necrotic osteochondral graft to a large mechanical load during remodeling.Cylindrical osteochondral grafts were taken from the patellar groove of rats, one end of the cylinder being the joint surface. The grafts were frozen, thawed and treated with alendronate. The length of the cylinder was measured and the grafts were placed in the chambers, which were inserted into the proximal tibia of rats. The chambers were left to heal in for two weeks to allow establishment of a vascular supply, and then the transplanted osteochondral plugs were mechanically loaded for 4 weeks, once a day with 10 cycles of 2 MPa pressure at 0.16 Hz.At harvest, the graft length had decreased during remodeling in 5 of the 6 untreated controls, but only in 2 out of 8 alendronate-treated rats (p = 0.05). Histologically, the bone graft in the non-treated controls was resorbed in the remodeled part of the graft, whereas in the alendronate-treated rats a dense trabecular bone was found consisting of both new bone and graft.Local treatment of the graft with bisphosphonate diminishes the risk of collapse during revascularization and bone remodeling in a mechanically loaded osteochondral graft. This could be useful in a variety of situations when bone remodeling occurs after a necrosis close to a joint, either spontaneously after osteonecrosis or a fracture, or after surgical procedures such as mosaic-plasty or other osteochondral grafting.

A repeated sampling bone chamber methodology was developed for the study of the influence of the mechanical environment on skeletal tissue differentiation and bone adaptation around titanium implants. Via perforations, bone grows into the implanted outer bone chamber, containing an inner bone chamber with a central test implant. An actuator—easily mounted on the outer bone chamber—allows a controlled mechanical stimulation of the test implant. After each experiment, the inner bone chamber—with its content—can be harvested and analysed. A new inner bone chamber with a central implant can be inserted consecutively in the outer bone chamber and a new experiment can start. Pilot studies led to a reliable surgical protocol and showed the applicability of the methodology, offering the possibility to study skeletal tissue differentiation and adaptation around implants under well-controlled mechanical conditions, and this protected from external loading. Repeated sampling of the bone chamber allows conducting several experiments within the same animal at the same site, thereby excluding subject- and site-dependent variability and reducing the amount of experimental animals.

Nowadays, there is a growing consensus on the impact of mechanical loading on bone biology. A bone chamber provides a mechanically isolated in vivo environment in which the influence of different parameters on the tissue response around loaded implants can be investigated. This also provides data to assess the feasibility of different mechanobiological models that mathematically describe the mechanoregulation of tissue differentiation. Before comparing numerical results to animal experimental results, it is necessary to investigate the influence of the different model parameters on the outcome of the simulations. A 2D finite element model of the tissue inside the bone chamber was created. The differentiation models developed by Prendergast, et al. ["Biophysical stimuli on cells during tissue differentiation at implant interfaces", Journal of Biomechanics, 30(6), (1997), 539-548], Huiskes et al. ["A biomechanical regulatory model for periprosthetic fibrous-tissue differentiation", Journal of Material Science: Materials in Medicine, 8 (1997) 785-788] and by Claes and Heigele ["Magnitudes of local stress and strain along bony surfaces predict the course and type of fracture healing", Journal of Biomechanics, 32(3), (1999) 255-266] were implemented and integrated in the finite element code. The fluid component in the first model has an important effect on the predicted differentiation patterns. It has a direct effect on the predicted degree of maturation of bone and a substantial indirect effect on the simulated deformations and hence the predicted phenotypes of the tissue in the chamber. Finally, the presence of fluid also causes time-dependent behavior. Both models lead to qualitative and quantitative differences in predicted differentiation patterns. Because of the different nature of the tissue phenotypes used to describe the differentiation processes, it is however hard to compare both models in terms of their validity.

Intermittent treatment with parathyroid hormone (PTH) has an anabolic effect on both intact cancellous and cortical bone. Very little is known about the effect of the administration of PTH on the healing of fractures or the incorporation of orthopaedic implants. We have investigated the spontaneous ingrowth of callus and the formation of bone in a titanium chamber implanted at the medioproximal aspect of the tibial metaphysis of the rat. Four groups of ten male rats weighing approximately 350 g were injected with human PTH (1-34) in a dosage of 0, 15, 60 or 240 μg/kg/day, respectively, for 42 days from the day of implantation of the chamber. During the observation period the chamber became only partly filled with callus and bone and no difference in ingrowth distance into the chamber was found between the groups. The cancellous density was increased by 90%, 132% and 173% in the groups given PTH in a dosage of 15, 60 or 240 μg/kg/day, respectively. There was a linear correlation between bone density and the log PTH doses (r2= 0.6). Our findings suggest that treatment with PTH may have a potential for enhancement of the incorporation of orthopaedic implants as well as a beneficial effect on the healing of fractures when it is given in low dosages.

We came across a bone growing situation in which BMP-2 inhibits bone formation. Collagen sponges with BMP-2 were inserted in titanium bone chambers in rabbits. In this model, bone formation occurs spontaneously. With 2.4 and 0.12 micrograms BMP-2 per mm3 of the chamber volume, bone ingrowth was reduced to 16% and 42% of collagen controls, respectively. Sponges with 2.4 micrograms BMP-2 per mm3 that were placed in a similar titanium chamber in an intramuscular subfascial site induced bone formation in 4 cases of 5. The BMP-2 concentrations used are considered optimal for extraskeletal bone induction, and intramuscular sponges in rats all induced bone. The inhibitory effect is most likely model-related, but indicates unknown effects of BMP-2.

Autografts, because they are histocompatible, are the standard by which other bone grafts are judged. There is, however, increased morbidity for the patient from which large autografts, of limited supply in any case, must be obtained. In contrast, allografts are readily obtainable in large quantities and are used routinely in procedures for major limb salvage, trauma involving bone loss, and joint reconstruction. They have achieved sufficient success to warrant continued use, although a high incidence of nonunions, fatigue fractures, and occasional premature graft resorption suggest they are often poorly incorporated [3]. Of the two allograft materials, cancellous and cortical bone, the former shows a faster and more complete incorporation when donor and recipient are immuno- and histocompatible, as shown by Goldberg et al. [5]. Yet, they also display a higher incidence of histoincompatibility and cannot provide the immediate structural support required in some long bone procedures. Accordingly, cortical allografts with improved incorporability are viable alternatives to both autografts and cancellous allografts. The achievement of such improvement is enhanced with an understanding of cortical allograft incorporation in general and creeping substitution in particular. Because of the central role of neovascularization in all forms of healing, including that characteristic of graft incorporation, a study of neovascularization in cortical allografts was undertaken using the rabbit tibia implanted with an allograft-bearing bone chamber as its model. The goal of the subproject reported here was to test the hypothesis that the model yields data consistent with that of other cortical allograft models. An additional goal was to obtain the data in the form of quantitative measurements.

Titanium implants containing a chamber that allowed ingrowth of bone were modified from a previous design to allow the use of oxygen microelectrodes. The modification consisted of the placement of ports in the superior surface of the implant for the insertion of oxygen electrodes into the tissue within the bone growth chamber. Forty titanium bone growth chambers were inserted into the proximal tibial metaphyses of 20 rabbits. From 2 to 20 days, oxygen tension was measured inside the chambers of 2 rabbits immediately prior to death. The oxygen tensions increased, declined, and increased again. Our results indicate that oxygen tensions fluctuate during the initial period of healing reflecting cellular changes in the callus.