Enhanced bone ingrowth and fixation strength with hydroxyapatite-coated porous implants

The effect of a hydroxyapatite (HA) coating on the interface attachment strength, rate of development of attachment strength, and degree of bone ingrowth of porous implants was investigated. Implants with ideal surgical fits and those having interface gap spaces were evaluated using femoral transcortical and intramedullary models. The application of a thin HA coating to porous implants significantly enhanced both interface attachment strength and bone ingrowth. The rate of development of interface strength and bone ingrowth was also more rapid with the HA-coated system. There was no evidence of any disruption, loss, or resorption of the HA coating.     

Skeletal fixation of implants by bone ingrowth into surface pores

Summary An alternative skeletal fixation by bone ingrowth into porous coatings has been studied.Stainless steel fiber coatings using different fiber diameters (50–100 m) and different pore sizes have been tested.Plugs, intramedullary rods and various types of knee prostheses have been implanted in dogs in non functional and also in functional loading conditions.Histological and mechanical evaluation of the bone implant interface has been performed.Consistent bone ingrowth was observed for implants in non functional conditions if the pore size exceeded 70 m. Ingrowth in functional loading conditions requires rigid initial stability of the implant and intimate contact of implantcoating and surrounding bone tissue.Supported by Grant No. 3.0071.76: Fonds voor Geneeskundig Wetenschappelijk Onderzoek     

Restoration of bone defect and enhancement of bone ingrowth using partially demineralized bone matrix and marrow stromal cells

PURPOSE: This study aimed to investigate the capability of combining marrow stromal cells (MSC) and partially demineralized bone matrix (PDBM) to fill bone defect and enhance bone ingrowth using a canine non-weight-bearing gap model. METHODS: Custom-made implants with 3mm gap between the porous surface and the host bone were used. The implants were inserted into the distal femurs of 25 mongrel dogs and the gaps were randomly assigned to be filled with culture-expanded autologous MSC-loaded PDBM, autograft, fresh-frozen allograft, PDBM alone, or nothing as controls. Histomorphometry using backscattered scanning electron microscopic examination, and mechanical push-out test were performed at 6 months after surgery. RESULTS: Histomorphometry showed that amounts of bone regeneration in the gap and bone ingrowth into the porous-coated surface in the MSC-loaded PDBM-treated group were comparable to those of autograft-treated group and were significantly greater than those of allograft-treated, PDBM-treated, or non-grafted groups. Mechanical test showed the same differences. CONCLUSION: The results of this study showed that combining PDBM and autologous culture-expanded MSC restored bone stock and enhanced bone ingrowth into the porous-coated area in a canine non-weight-bearing gap model. This combination may provide an option for reconstructing bone defect when we perform a cementless revision arthroplasty.     

Powder metal-made orthopedic implants with porous surface for fixation by tissue ingrowth

Powder metal-made orthopedic implants with a porous coating provide an effective means for implant fixation by tissue ingrowth. Additionally, the use of metal alloy powders for forming porous surfaces offers the advantage of uniform coatings on complex part shapes. With proper processing, implants with strong, porous surface layers and good substrate mechanical properties can be formed. The in vivo tests have demonstrated the need for initial implant stability to achieve bony ingrowth. Animal studies indicate an optimum pore size range of 50-400 mu, and human hip prostheses with pores in this range appear to function well. A porous surface integrated with a compatible implant design avoids undesirable bone remodeling with these types of implants.     

Bioactive glass enhances bone ingrowth into the porous titanium coating on orthopaedic implants

Purpose

The aim of the study was to verify the ability of nanoparticulate bioactive glass (BAG) to infiltrate into the porous titanium (Ti) layer on Ti-based implants to promote osseointegration.

Methods

The porous titanium layer on Ti-based implants was impregnated with nanoparticulate BAG. The implants without or with BAG were implanted bilaterally in tibial holes of ten New Zealand white rabbits. The rabbits were sacrificed after ten weeks for examinations. Beside histological examination, EDXS analysis of polished cross-sections of explanted implants was also performed with the aim to quantitatively evaluate the bone-to-pore contact and bone-in-pore ratio.

Results

After ten weeks, EDXS analyses of cross-sections of the explanted implants confirmed that bioactive glass was fully resorbed and that the pores throughout the thickness of the porous titanium layer were to a large extent filled with a new bone. In the absence of bioactive glass, only the outer part of the porous layer was filled with bone. The implants without BAG in the porous Ti-layer exhibited similar bone-to-pore contact, while significant improvement of bone ingrowth into the pores was observed for the implants with BAG (38%), as opposed to those without it (22%).

Conclusion

This study confirmed that the nanoparticulate bioactive glass within the porous titanium surface layer on implants promotes osseointegration and stimulates the formation of bone within the pores.     

Biologic fixation and bone ingrowth

Total hip arthroplasty has provided thousands of patients with pain relief and has improved their quality of life. Advances in orthopaedic surgical techniques and implant biomaterials now allow predictable surgical results in most patients. Despite the overwhelming success of this surgical procedure, the debate continues surrounding the optimal choice of implants. Femoral and acetabular implants with varying geometries and fixation methods are currently available. Acrylic bone cement has been used extensively in the past for acetabular and femoral fixation. This mode of component fixation currently remains the technique used most frequently throughout Europe and has shown excellent long-term results. Problems inherent with acrylic bone cement, however, have encouraged other surgeons to use alternative surfaces to allow biologic fixation.     

Observations on the effect of movement on bone ingrowth into porous-surfaced implants

Although porous-surfaced orthopedic implants have been designed for fixation by bone ingrowth, there is clinical evidence that this does not always occur. Initial implant movement relative to host bone can result in attachment by a nonmineralized fibrous connective tissue layer. The ranges of movement that result in either bone or fibrous connective tissue fixation are observed in dogs in two independent studies. Experimentally, bone ingrowth can occur in the presence of some movement, albeit very small (up to 28 mu), while excess movement (150 mu or more) can result in attachment by mature connective tissue ingrowth.     

Aging effect on inductive capacity of human demineralized bone matrix

Demineralized bone powder (DBP) prepared from human cortical bone was implanted into subcutaneous pouches of athymic Nu/Nu mice for 28 days. The osteoinductive capacity was evaluated by histomorphometry of the induced cartilage and bone, and by alkaline phosphatase activity in the implant. Very small amounts of new bone and cartilage were found at histological analysis, confirming that human DBP is much less osteoinductive than that from other species. Whereas the morphometric data of the implants from the young and aged donors were not significantly different, the alkaline phosphatase activity was significantly lower in the implants from the old donors than from the younger ones. This difference between the morphometric and biochemical results could reflect the fact that the enzymatic activity is already present in the osteoprogenitor cells. At 28 days, the osteoblastic activity in contact with DBP from the aged group is characterized by a decrease in the enzymatic amount which is not yet visible at the tissue level. This tendency to a decrease in the osteoinductive capacity of bone matrix is an additional aspect of the age-related alterations which occur in bone tissue and could be attributed to modifications of different proteins of the bone matrix, including bone morphogenetic protein.     

Implant fixation by bone ingrowth

The term osseointegration referred originally to an intimate contact of bone tissue with the surface of a titanium implant; the term bone ingrowth refers to bone formation within an irregular (beads, wire mesh, casting voids, cut grooves) surface of an implant. The section dealing with the historical background describes the development of macroporous, microporous, and textured surfaces with an emphasis on the evolution of porous and textured metal surfaces. The principal requirements for osseointegration and bone ingrowth are systematically reviewed as follows: i) the physiology of osseointegration and bone ingrowth, including biomaterial biocompatibility with respect to cellular and matrix response at the interface; ii) the implant surface geometry characteristics; iii) implant micromotion and fixation modes; and iv) the implant-bone interface distances. Based on current methods of bone ingrowth assessment, this article comparatively reviews and discusses the results of experimental studies with the objective of determining local and systemic factors that enhance bone ingrowth fixation.     

The effect of impaction and a bioceramic coating on bone ingrowth in porous titanium particles

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.     

The effect of impaction and a bioceramic coating on bone ingrowth in porous titanium particles

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.Allograft bone impaction grafting restores the original bone stock (Halliday et al. 2003). Morselized cancellous allograft bone chips remain the gold standard material, but they have their limitations such as limited availability, risk of pathogen transmission, and religious considerations (Conrad et al. 1995, Galea et al. 1998). Calcium phosphate particles have been used successfully with good long-term clinical results (Oonishi et al. 2008). However, bioceramics show inferior handling characteristics (Bolder et al. 2002, van Haaren et al. 2005), and accelerated resorption could compromise construct stability (Ninomiya et al. 2001).Porous commercially pure titanium (Ti) particles are not resorbed by osteoclasts; thus, the stability of the graft layer is not reduced by remodeling. Long-term stability is probably dependent on ingrowth of fibrous tissue and bone. A canine model and a human retrieval model have shown that non-impacted, non-coated small Ti particles are osteoconductive when they are used in the femur in combination with an uncemented, vibration-based technique to insert the stem into the bed of Ti particles (Alffram et al. 2007, Turner et al. 2007). We intend to use larger and highly porous Ti particles with a different surgical technique: cemented impaction grafting of the acetabulum and femur. Impaction of large Ti particles creates a graft layer with good entanglement and primary stability (Aquarius et al. 2009, Walschot et al. 2010). However, we do not know whether impacted Ti particles allow tissue ingrowth like non-impacted Ti particles: impaction poses a threat to the osteoconduction of a non-degradable material like Ti particles by obliteration of ingrowth spaces, which is even observed with a resorbable material like allograft bone (Tägil and Aspenberg 1998, Jeppsson et al. 2003). Thus, we evaluated the effect of impaction on osteoconduction by small Ti particles in a bone conduction chamber (Aspenberg et al. 1996) in goats. We expected that the addition of a thin sol-gel-formed silicated calcium phosphate coating would favor osteoconduction of this porous titanium graft material (Nguyen et al. 2004).     

The effect of bone compaction on early fixation of porous-coated implants

The effect of a bone compaction technique versus conventional drilling on the early fixation of porous-coated implants was examined in a canine model. Compaction dilation resulted in a significant increase in implant fixation stiffness (P < .01) and ultimate fixation strength (P < .01) at 0 and 3 weeks. Fixation stiffness remained significantly increased at 6 weeks (P < .01); however, the ultimate fixation strength was not statistically significant between the 2 techniques (P > .05). There was no significant difference in either fixation value at 9 weeks (P > .05). Histological examination of the bone-implant interface demonstrated an increase in the density of cancellous bone immediately adjacent to the implants placed in the compaction dilated holes. The results of this study suggest that the compaction method of host bone preparation may optimize the initial stability of the implant interface of porous-coated prostheses.     

The effects of pulsed fluid irrigation on bony ingrowth in porous polyethylene implants

Twelve adult dogs were used to evaluate the effect of pulsed isotonic saline irrigation on bony ingrowth. The distal supracondylar ridge of the knee was transected. Six dogs had the area irrigated with a pulsed lavage system for 15 sec and six dogs did not. A porous piece of polyethylene was then stapled to the cancellous surface. Three of each were evaluated histologically at 3 weeks and 6 weeks. The pulsed irrigation significantly decreased the depth of bone penetration into the sections of polyethylene.     

富血小板血浆促纤维多孔钛颈椎椎间融合器中骨长入作用

目的观察富血小板血浆(PRP)促进纤维多孔钛椎体间融合器(fiber porous titanium Cage,FPT Cage)的骨长入作用。方法健康成年比格犬6只,体质量12.5~15.0 kg,雌雄各3只。取比格犬前肢外周静脉血20.0 m L,采用二次离心法制备PRP,同时对外周静脉血及PRP行血小板计数。行颈椎前路C4/C5/C6椎间盘切除FPT Cage椎间融合术,C4/C5节段单纯使用FPT Cage,C5/C6节段采用激活的PRP浸泡的FPT Cage。术后4个月处死比格犬后行硬组织切片检查,观察C4/C5/C6节段FPT Cage中骨长入的情况。结果 C4/C5节段椎间隙FPT Cage-骨界面附近可见少量软骨细胞和成骨细胞;FPT Cage中央孔隙内发现少量成骨细胞,类骨质较少,大部分孔隙内仍然为纤维组织。C5/C6节段椎间隙FPT Cage-骨界面可见成熟骨组织形成;FPT Cage边缘孔隙内可见骨组织长入;FPT Cage中央孔隙内发现大量成骨细胞;大部分中央孔隙内为类骨组织,少部分中央孔隙内仍然为纤维组织。结论在比格犬体内实验研究中,复合PRP可以促进FPT Cage内的骨长入。     

Osteoinduction by implants of demineralized allogeneic bone matrix is diminished in vitamin D-deficient rats

Summary Experimental heterotopic bone formation was produced by subcutaneous implants of demineralized allogeneic bone matrix (DABM) in vitamin D-deficient (−D) animals that were either not treated or given vitamin D₃ (+D) or 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃) to determine the role of vitamin D and its most active metabolite in osteoinduction and implant remodeling. Histologically, implants in both +D and −D groups caused a similar acute inflammatory response, formation of a fibrous capsule, and chondrogenesis by 1 to 2 weeks after implantation. However, by 3 weeks after implantation implants in the −D animals had formed less bone matrix, had developed a defect in matrix mineralization, had reduced bone forming and bone resorbing surfaces, and had altered bone architecture resulting from defective bone remodeling. The altered histology in −D animals was not corrected by 10 weeks after implantation. Treatment of vitamin D-deficient rats with 1,25(OH)₂D₃, 65 pmol/day for 3 weeks, corrected both the defect in mineralization and the abnormal histology. The results indicate that (1) vitamin D deficiency does not alter either the timing or the sequence of histologic events associated with osteoinduction but dramatically reduces the magnitude of the response, (2) vitamin D deficiency not only impairs mineralization but also reduces bone formation and resorption, and (3) 1,25(OH)₂D₃ mimics all of the actions of vitamin D with regard to correcting the abnormal osteoinductive response and bone histomorphometry.     

Recombinant and nonrecombinant factor XIII and its effect on bone ingrowth and strength of fixation

Thirty cylindrical, commercially pure, titanium fiber, porous-coated Ti₆Al₄V implants were inserted pressfit into the proximal humeral portion of 30 sheep humeri to determine the systemic effect of recombinant factor XIII and placenta-derived factor XIII concentrate on bone ingrowth and strength of fixation. For both the recombinant factor XIII and the factor XIII concentrate group, the volume of bone ingrowth and the strength of fixation were higher than for the control specimens. However, the difference was only significant for the factor XIII concentrate group.     

Calcificationin vitro of demineralized bone matrix

Collagen was prepared from compact sheep bone by decalcification with EDTA and from rat tail tendons by acetic acid extraction and reconstitution with NaCl. The deposition of apatite in sheep bone collagen in a metastable calcification solution was studied chemically and by electron microscopy. The bone collagen was shown to be a good nucleation catalyst for mineral deposition, while rat tail collagen was a poor catalyst. Mineral deposition in bone collagen occured in two separate kinetic phases, a rapid phase of nucleation and crystal growth, giving rise to small calcified islands, and a second slow phase, ascribed to growth in regions not involving the catalytic sites. This second phase of mineral deposition is considered to be the result of impaired ion diffusion through the closely-aligned collagen fibrils, thus leaving large areas of the collagen free of mineral even though the buffer remains highly supersaturated. Electron micrographs suggested that the catalytic sites might be in some relationship to the 640 Å periodicity of collagen, but a role for non-collagenous material bound to the collagen has not been excluded.The poor catalytic activity of reconstituted collagen was not due to the presence of loosely-bound inhibitors, although inhibitors could be strongly bound to this type of collagen and be absent from bone collagen. The differences in catalytic activity may have a bearing on physiological calcification. A more general hypothesis for nucleation of a mineral phase in biological systems is required.This work was supported in part by the European Atomic Energy Community (EURA-TOM), Brussels, Belgium.     

Progression of human bone ingrowth into porous-coated implants: Rate of bone ingrowth in humans

We report the measured progression of human cancellous bone ingrowth into load-bearing porous-coated titanium implants over 5 time periods (0,3,6, 9, and 12 months). There was a statistically significant progression of bone ingrowth into the implants over a 9-month period, but the 9- and 12-month data were not different. Investigators are advised to analyze time “0” implants in order to distinguish mechanical impaction of bone from the biological process of bone ingrowth.     

Influence of disodium (1-hydroxythylidene) diphosphonate on bone ingrowth into porous,titanium fiber-mesh implants

The influence of disodium (1-hydroxythylidene) diphosphonate on the bonding between bone and porous, titanium fiber-mesh implants was studied. Rectangular, porous, titanium fiber-mesh implants (15 × 10 × 2.4 mm) were implanted into the tibial bone of mature male rabbits. The rabbits were divided into six groups. Disodium diphosphonate was administered daily by subcutaneous injection to groups 1–5. Groups 1–4 received doses of 5.0, 2.5, 1.0, and 0.1 mg per kilogram of body weight per day for 8 weeks, respectively. Group 5 received a dose of 5 mg per kilogram of body weight per day for 4 weeks. Group 6 (control group) was given saline injections. At 8 weeks after implantation, the rabbits were killed. The tibiae containing the implants were dissected out and subjected to detachment tests. The failure load, when an implant became detached from the bone or when the bone itself broke, was measured. The interface of the bone and implant was investigated by Giemsa surface staining and contact microradiography. Giemsa surface staining and contact microradiography showed that porous implant bonding to bone tissue was inhibited by a high dose of disodium diphosphonate in groups 1, 2, and 5. Soft tissue was observed at the interface. In groups 3, 4, and 6, bone tissue ingrowth was observed at the interface between the porous implant and bone tissue. Growth of bone into the porous fiber-mesh implant of a cementless prosthesis is possible if a low dose of diphosphonate below 1.0 mg per kilogram of body weight is given subcutaneously     

The effect of various sterilization procedures on the osteoinductive properties of demineralized bone matrix]

To minimize potential infection following the transplantation of allogeneic bone, extremely rigorous selection of donors and careful processing and storage of samples are required. Other major problems related to allogeneic transplants, such as reduced osteogenic properties and immunological reactions, led to the development of demineralized bone matrix (DBM). This osteoinductive bone extract is largely free of antigens and is easy to produce. However, to eliminate the potential risk of infection, DBM should be sterilized prior to implantation. The purpose of this study was to investigate the influence of different sterilization techniques on the osteoinductive properties of DBM. A series of 76 cortical defects (drill holes) 0.6 cm in diameter in the tibiae of 11 Merino sheep were filled with DBM in addition to autogeneic and allogeneic cancellous bone. Prior to implantation DBM was sterilized by autoclaving, gamma irradiation, or application of ethylene oxide or ethyl alcohol. A further 12 drill holes were left empty as controls. The formation of new bone was examined 3 and 6 weeks postoperatively, using histological, fluorescent-optical and microradiographical techniques. The amount of newly formed bone was also quantified. Apart from autoclaved DBM all matrix grafts showed excellent new bone formation following sterilization, by far exceeding the formation with allogeneic cancellous bone.