Demineralized bone implants

There are three mechanisms of bone formation that underlie the use of the different types of implants. In osteogenesis, viable osteoblasts and preosteoblasts are transplanted from one part of the body to the site where new bone is needed; cancellous marrow grafts are an example of such osteogenic engraftment. In osteoconduction, the implant does not provide many viable cells but rather acts as a scaffolding for the ingrowth of new bone from the margins of the defect with the concurrent resorption of the implant; cortical bone grafts or banked bone segments are examples of this "creeping substitution." In osteoinduction, the implant stimulates the transformation of connective tissue to produce endochondral bone, even in extraskeletal sites; demineralized bone implants promote bone formation by osteoinduction. The physiology, cell biology, biochemistry, and endocrinologic regulation of induced osteogenesis are areas of active investigation. Fresh autogenous cancellous bone grafts are preferred for non-stress-bearing defects, but are often of limited availability for extensive procedures, especially in infants. Demineralized bone implants have been used successfully in certain types of craniomaxillofacial, orthopedic, periodontal, and hand reconstruction. Tissue transformation may become as important to reconstructive surgery as is tissue transplantation.     

Tissue response to porous-coated implants lacking initial bone apposition

Although initial bone apposition of a porous-surfaced implant is desirable, it is not always achieved surgically. A model to study the effect of a gap on the quantity and quality of bone growth in both the cancellous and cortical regions has been developed. Implants were surgically placed in the intramedullary canals of adult dogs producing uniform gap spaces 0.0-2.0 mm wide. Histologic and microradiographic evaluations were conducted after 3, 6, and 12 weeks in situ. The results demonstrate that the initial apposition of a porous implant to the surrounding bone surface is not necessary for fixation by bone ingrowth. New bone will grow up to and within the porous structure of an implant even when there is a gap as large as 2.0 mm. However, the rate and degree of maturity and mineralization is enhanced when the gap width is 0.5 mm or less. The amount of bone activity in the cortical region was greater than in the cancellous region at 3 and 6 weeks after operation. After 12 weeks in situ bone growth in gap spaces and into the porous coating was approximately equal.     

Mediators of bone resorption around implants.

An important cause of prosthetic loosening is bone resorption that results from the interaction of macrophages with implant surfaces and particulate debris. The mediators involved in this bone resorption were investigated in vitro. Medium conditioned by macrophages interacting with foreign materials was assayed for bone resorption stimulation and inhibition, and for prostaglandin E2 (PGE2). In some experiments, the medium was dialyzed, and in others indomethacin was added. Macrophages were found to release stimulators and inhibitors of bone resorption. The relative amount of these was variable. When macrophages interacted with foreign surfaces, their stimulatory effect was ten times their inhibitory effect. Further activation by phagocytosis caused a further 15-fold increase in stimulation, with no change in inhibition. It is probable that before macrophages encounter foreign materials their stimulatory and inhibitory effects are the same so that they do not cause net bone resorption. Important stimulatory and inhibitory mediators were not dialyzable and so were probably cytokines or possibly collagenase. Prostaglandins were neither important stimulators nor inhibitors. There was only enough PGE2 released to account for 2% of the bone resorption that was stimulated.     

Comparative study of human cancellous bone remodeling to titanium and hydroxyapatite-coated implants

The human cancellous bone response was compared in weight-bearing porous hydroxyapatite (HA) and titanium-coated implants placed in the distal medial femoral condyles of consenting staged bilateral knee patients. The Institutional Review Board approved study quantified the amount of bone ingrowth, the mineral apposition rate, and the bone mineral content. Results showed that the osteoconductive HA coating increased the amount of bone ingrowth by 8% (P=.018). The HA coating did not effect the mineral apposition rate of the bone but had an 8% lower bone mineral content at the implant interface (P=.042). The influence of HA coatings on human cancellous bone appears highly focal along the coating surface. Gaps of 50–500 μm filled with fibrous connective tissue were observed along the porous-coated surfaces of both implant types suggesting that HA coatings still require precision placement adjacent to human cancellous bone.     

Accumulation of LPS by polyethylene particles decreases bone attachment to implants.

Molecules absorbed on the surface of particulate wear debris may contribute to inflammatory reactions that lead to aseptic loosening of implants. Lipopolysaccharide (LPS), a bacterial endotoxin, can attach to many biomaterials and stimulate macrophages to secrete osteoclast-activating cytokines. We tested the adsorption of LPS by polyethylene particles in vitro and examined the biological effects of LPS absorption on bone remodeling around implants in vivo. Polyethylene particles were incubated in radiolabeled LPS solutions, and adsorption of LPS by the particles was quantified by radioassay. Because polyethylene particles are hydrophobic and less dense than water, they floated and clumped when incubated in a water solution of LPS, resulting in low adsorption of LPS. However, when particles were incubated in an ethanol solution of LPS, most of the LPS was adsorbed by the particles, and was resistant to washing with water. Triton X-100 (10%), however, effectively washed the LPS off the particles. In a rat model, the presence of polyethylene particles around the implant in the femoral canal decreased bone attachment to the implant at 6 weeks. Incubating the particles with LPS before implantation, or intermittent administration of LPS systemically, further decreased bone-implant attachment to similar extents, but had no effect on the bone density of the control side femurs. Our data indicate that polyethylene particles have high affinity for LPS, depending on many factors, especially the solvents of the LPS. Intermittent systemic administration of LPS affects bone remodeling but only occurs in the area containing polyethylene particles and titanium implants, supporting the hypothesis that the presence of polyethylene particles around implants can result in accumulation of LPS from exogenous sources. This may cause local levels of LPS that are high enough to affect bone remodeling around implants.     

Unalloyed titanium for implants in bone surgery

Commercially pure (c.p.) titanium has proven its suitability as an implant material in bone surgery over many years in the fields of osteosynthesis, oral implantology, and in certain applications in joint prosthetics. Excellent biocompatibility and corrosion resistance are outstanding features. Furthermore, c.p. titanium is known for not causing allergic reactions. The different grades of c.p. titanium and their minimum mechanical properties are specified in ISO and ASTM standards for implant materials. Typical mechanical properties are given for AO ASIF implant applications. The properties and clinical performance of c.p. titanium are discussed and compared to those of implant stainless steel and titanium alloys. In brief some specific features relating to c.p. titanium implant material are treated, including biocompatibility and soft tissue and bone response and taking into account the effects of implant surface configurations at the same time. In addition, issues are addressed which arise from frequent inquiries from clinics.     

The healing of biologic and synthetic bone implants

Summary The aim of the present study was to investigate the osteogenic properties of different types of cancellous bone grafts inserted in large osseous defects in dogs and to compare these with those of sintered hydroxyapatite implants. Fresh cancellous autografts were rapidly revascularized and invariably induced a complete healing of the defect. Frozen and fresh cancellous allografts were largely resorbed, the latter evoking a strong antigenic response in two of the five cases. Sintered hydroxyapatite granules were largely encapsulated in fibrous tissue, neither stimulating nor inhibiting osseous ingrowth. Degradation of the hydroxyapatite implant was not observed.     

Experimental induction of heterotopic bone in abdominal implants

Induction of bone tissue requires three elements: osteoprogenitor cells, osteoinductive factors, and a supporting extracellular matrix. In this study, we report on an experimental model in dogs of heterotopic bone tissue production, based on the integration of these osteo-inductive factors into abdominal implants. The implants consist of either a type I collagen sponge wrapped with periosteum and omentum or a type I collagen sponge embedded with demineralized bone powder, platelet-rich plasma, thrombin, and calcium chloride wrapped with omentum, with or without periosteum. Automated histomorphometric analysis showed an efficient production of trabecular bone, which corresponded to 50-70% of the total tissue composition 4 months after implant formation. High expression of the osteoinductive cytokines transforming growth factor-beta and bone morphogenetic proteins-2 and -4 was shown by immunohistochemistry in macrophages, endothelial cells from neoformed capillaries, osteoblasts, osteoclasts, and the mesenchymal tissue around the bone trabeculae. These approaches are novel and efficient surgical procedures to produce mature trabecular bone that could be used as a potential source of bone tissue for autotransplantation.     

Osteogenic protein 1 device stimulates bone healing to hydroxyapaptite-coated and titanium implants

This study evaluated the effects of osteogenic protein 1 (OP-1) placed in a gap around uncoated and hydroxyapatite (HA)-coated implants. Unloaded cylindrical titanium alloy implants were inserted in the femoral condyles of 16 skeletally mature dogs surrounded by a 3-mm gap. The gap around the implants was filled with 325 microg OP-1 in 130 mg bovine collagen type I as carrier (OP-1 device) or collagen carrier alone or left empty. All groups were tested with both HA-coated and uncoated implants, and the animals were sacrificed after 6 weeks. Implant fixation was determined by push-out test. Bone ongrowth and bone formation were evaluated by quantitative histomorphometry. OP-1 device enhanced mechanical fixation of uncoated and HA-coated implants, resulting in a higher shear strength than implants with collagen matrix and control implants. Bone ingrowth and bone formation in the gap were also stimulated 3-fold for OP-1 groups when compared with empty controls, but no difference was found between OP-1 groups and collagen matrix groups. This study suggests that the OP-1 device placed in a gap around uncoated and HA-coated implants is capable of enhancing mechanical fixation and periimplant bone formation. The collagen carrier alone also enhanced bone ongrowth and fixation significantly.     

Computer predictions of bone remodeling around porous-coated implants

Computer simulations of bone remodeling in response to mechanical stresses can be used to understand normal growth and development of the skeleton or to predict the remodeling of bone in response to prosthetic devices. Using a previously derived bone maintenance theory, a technique for computing bone density distributions was applied to the proximal femur and tibia using two-dimensional, multiple-loading finite element models. The models initially represented solid, homogeneous structures. Using an iterative bone remodeling technique that relates bone apparent density to loading history, the internal distributions of apparent density and elastic modulus for the normal bones were predicted. The finite element models were then modified to represent bones in which porous-coated femoral surface replacements and tibial tray components had been implanted. The same iterative remodeling method was then applied to predict the distribution of bone around these components. The predicted bone density distributions for the natural femur and tibia agree with previously documented normal bone morphology. The predicted bone density distributions around various implanted prostheses were characteristic of the component under investigation and were consistent with clinical and experimental findings of other investigators. In the femoral head, stress shielding occurred underneath the metal surface replacement cup, resulting in lower densities in the femoral head. The addition of a central femoral cup fixation peg caused bone hypertrophy around the peg. In the tibia, the stress concentrations around the pegs also resulted in denser bone, with a concomitant decrease in bone density at more peripheral locations underneath the prosthetic tray. This remodeling technique has the potential to be an important tool in predicting the possible remodeling consequences of new implant design features.     

Filling-in of bone margin defects with carbon implants

The article contains data of using carbon implants of syntactic foam to replace marginal defects of bone tissue of finger phalanges and metacarpal bones after excision of enchondromas. Sixteen clinical observations are reported.     

Cast metal spongioid bone implants in animal experiments

Spongyimplant cubes produced out of an alloying DIN 58800 are driven in an artificial produced split in the ileosacral articulation of sheeps. The animals were killed after a period of 70 til 181 days. All the implants are enclosed by bone and so bring about an ankylosis of the ileosacral articulation. In different degree the porous slices of the implant are grown through by bone. By producing spongyimplants with more porous slices the transfer of the animal experiment to human beings is justified, for example for special problems in osteosynthesis of in the arrange of the surface from artificial implants. The produced spongy implants out of metal are characterized specially by its primary stability.     

Early bone in-growth ability of alumina ceramic implants loaded with tissue-engineered bone.

To enhance early bonding of an alumina ceramic implant to bone, we evaluated a method of seeding the implant surface with bone marrow mesenchymal cells that differentiated to osteoblasts and bone matrix prior to implantation. The usefulness of the method was evaluated in Japanese white rabbits. In our study, an alumina ceramic test piece loaded with differentiated osteoblasts and bone matrix by a tissue engineering technique was implanted into rabbit bones. Three weeks after the procedure, evaluation of mechanical bonding and histological examination were performed. Histological examination of the noncell-loaded implant surfaces showed no bone infiltration into the implant gap. However, the cell-loaded implant surfaces exhibited new bone infiltration into the implant gap with mechanical bonding. In the mechanical test, the average failure load was 0.60 kgf for the noncell-loaded side and 1.49 kgf for the cell-loaded side. Preculturing mesenchymal cells on the surface of the alumina ceramic prior to implantation increased the debonding strength by two and half times. The present findings indicate early bonding between the implant and bone three weeks after the procedure.     

Biodegradable implants for potential use in bone infection

Summary Local antibiotic therapy by diffusion from plaster of Paris beads has proved promising in bone surgery. Sustained local delivery depends on thermostability, so we tested the antibacterial activity of 11 antibiotic solutions after storage at 37°C using a microbiological method. Cephalosporins and penicillins were unstable, but aminoglycosides remained fully stable with 100% activity after 2 weeks. About 60% of the initial bactericidal activity of quinolone, glycopeptides and sodium fusidate were still detectable after 2 weeks. Release of these antibiotics from plaster of Paris beads was evaluated in vitro. Even those in the same family differed in their release rate. Plaster beads with sodium fusidate were the most effective association. A therapeutic level of glycopeptides, aminoglycosides and amoxicillin was leached for about 3 weeks. Cephalosporins and sodium amoxicillin were released in 2 to 3 days, and quinolone beads were too brittle to be used. Plaster of Paris, which is cheap, biocompatible and biodegradable, is an excellent carrier for sodium fusidate, aminoglycosides and glycopeptides.

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Résumé L'antibiothérapie locale par diffusion d'antibiotique(s) à partir d'implants de plâtre de Paris constitue une approche prometteuse en chirurgie osseuse. Etant donné que l'administration locale et prolongée d'un antibiotique dépend de sa thermostabilité, l'activité antibactérienne de onze solutions d'antibiotiques a été mesurée par une méthode microbiologique après stockage à 37°C. Les céphalosporines et les pénicillines sont instables dans ces conditions (moins de 10% de leur activité initiale est maintenue après deux semaines). A l'opposé, les aminoglycosides sont tout-à-fait stables (100% de leur activité est mesurée après deux semaines). Environ 60% de l'activité antibactérienne initiale des quinolones, des glycopeptides et du fusidate sodique est encore détectable après deux semaines. La libération de ces antibiotiques à partir des billes de plâtre de Paris a été évaluée in vitro. Le fusidate sodique associé à ce vecteur présente une libération constante et soutenue du principe actif. Cette propriété le rend particulièrement adapté pour le traitement d'infections osseuses. Des concentrations thérapeutiques en glycopeptides, en aminoglycosides et en amoxicilline trihydrate sont obtenues pendant une à deux semaines. Par contre, les céphalosporines et l'amoxicilline sodique sont trop rapidement libérés (2 à 3 jours) et finalement les billes chargées de quinolones sont trop friables pour être utilisables. Grâce à son coût, sa facilité d'utilisation et de stérilisation ainsi que sa biocompatibilité, le plâtre de Paris constitue un excellent vecteur d'antibiotiques tels que le fusidate sodique, les aminoglycosides et les glycopeptides.

     

Structural interaction between bone and implants due to arthroplasty of the first metatarsophalangeal joint

Background

Currently, the metatarsophalangeal joint replacement through a restorative arthroplasty, where implants are used, is a viable invasive surgical medical procedure in the treatment of severe cases of osteoarthritis in this joint, better known as hallux rigidus. However, few things are known about the postoperative complications that implants can cause on the joint, like Swanson and Tornier implants.Research in this field can provide a valuable information that would help the specialist surgeon in the decision-making during the selection of the more suitable joint implant in each patient, as well as the redesign of the devices, to make them more efficient, durable and biocompatible with the human body.