Bonding behavior of a glass-ceramic containing apatite and wollastonite in segmental replacement of the rabbit tibia under load-bearing conditions

Glass-ceramic implants containing apatite and wollastonite were studied under load-bearing conditions in a segmental replacement model in the tibia of the rabbit. Alumina-ceramic implants were used as a control. A sixteen-millimeter segment of the middle of the shaft of the tibia was resected at a point distal to the junction of the tibia and the fibula. The defect was replaced by a fifteen-millimeter-long hollow, cylindrical implant that was fixed by intramedullary nailing using a Kirschner wire. Two groups of eight rabbits each (one group with a glass-ceramic implant and the other with an alumina implant) were killed twelve weeks after implantation. Two similar groups were killed twenty-five weeks after implantation. The segment of the tibia that contained the implant was excised and tension-tested. The load to failure of glass-ceramic implants containing apatite and wollastonite increased with time. The loads to failure of the glass-ceramic and alumina implants at twelve weeks after implantation were 19.8 +/- 7.06 and zero newtons, respectively. The loads to failure of glass-ceramic and alumina implants at twenty-five weeks after implantation were 126.4 +/- 32.54 and 19.6 +/- 13.92 newtons, respectively. No glass-ceramic implants broke. A calcium-phosphorus layer at the interface of the glass-ceramic and the bone was observed by scanning electron microscopy and electron-probe microanalysis. There was no interposition of soft tissue between the glass-ceramic and the bone, as observed by Giemsa surface staining.     

Comparison of alloplastic implants for facial bones by scintigraphy and histology: an experimental study

Reconstruction of bone defects and contour irregularities in the craniofacial region is difficult and often requires complex solutions. This study investigated the tissue response, vascularization and bone ingrowth, in hydroxyapatite, porous polyethylene and silicone elastomer when used as bone graft substitutes. 24 albino rabbits (8 rabbits for each implant) were used in this investigation. Hydroxyapatite 500 particles, silicone rubber and porous high-density polyethylene were placed in the cavities formed with a drill in the rabbit frontal bones. As a part of a prospective study the vascularization rates of all implant materials were analyzed 10 days and 2 months after surgery using ^99mTechnetium-MDP (Methylene diphosphonate) scintigraphy of the skull. The scintigraphic studies were performed 2 hours after intravenous injection of 4 mCi (148 MBq) ^99mTc-MDP. The frontal bone was excised on the 10th and 60th days. All tissue specimens were placed first in 10% formalin and then in 10% nitric acid solution for decalcification. The vascularization, connective tissue ingrowth, foreign body reaction and bone regeneration around the implant were evaluated. Results of this study suggested that hydroxyapatite and porous polyethylene were stabilized in bone while as expected silicone was mobile, also hydroxyapatite implants are vascularized better and are more biocompatible than porous polyethylene. Received: 19 July 1998 / Accepted: 27 November 1998     

Influence of disodium (1-hydroxythylidene) diphosphonate on bonding between glass-ceramics containing apatite and wollastonite and mature male rabbit bone

Summary It has been reported that bioactive glass-ceramics containing crystalline oxy- and fluoroapatite [Ca₁₀(PO₄)₆(O,F₂) and wollastonite (CaSiO₃), chemical composition: MgO 4.6, CaO 44.9, SiO₂ 34.2, P₂O₅ 16.3, CaF₂ 0.5 in weight ratio] bond to bone tissue through the formation of an apatite (a calcium and phosphorus-rich layer) on the ceramic surface. In this study, the influence of disodium (1-hydroxythylidene) diphosphonate (DHTD) on the bonding between bone and glass-ceramics containing apatite and wollastonite was investigated. Rectangular ceramic plates (15 mm x 10 mm x 2 mm, abraded with #2000 alumina powder) were implanted into the tibial bone of mature male rabbits. DHTD was administered daily by subcutaneous injection to groups 1–5: group 1–4 at doses of 20, 5.0, 1.0, and 0.1 mg/kg body wt/day for 8 weeks; and group 5 at a dose of 5 mg/kg body wt/day for 4 weeks. Group 6 was given injections of saline as a control. At 8 weeks after implantation, the rabbits were killed. The tibiae containing the ceramics were dissected out and used for a detachment test. The failure load, when an implant became detached from the bone, or when the bone itself broke, was measured. The failure loads for groups 1–6 were 0 kg, 0 kg, 8.08±2.43 kg, 7.28±2.07 kg, 5.56±1.63 kg, and 6.38±1.30 kg, respectively. Ceramic bonding to bone tissue was inhibited by a higher dose of DHTD (groups 1 and 2). In groups 3–6, SEM-EPMA showed a calcium-phosphorus-rich layer (Ca-P-rich layer) at the interface between the ceramic and bone tissue. However, at higher doses (5 and 20 mg), the Ca-P-rich layer was not observed on the surface of the glass-ceramic. DHTD suppressed both the formation of the Ca-P-rich layer on the surface of galss-ceramics and also apatite formation by bone. Thus, bonding between the Ca-P-rich layer of glass-ceramics and the apatite of bone tissue did not occur. This study verified that the apatite crystals in bone tissue bonded chemically to the Ca-P-rich layer on the surface glass-ceramics. The organic matrix (osteoid) did not participate in the bonding between bone and glass-ceramics.     

Enhancement of bone bonding to bioactive ceramics by demineralized bone powder.

In an attempt to enhance the bonding of bone to bioactive ceramics, allogeneic demineralized bone powder (DBP) was used in combination with bioactive ceramic implants in rabbit tibiae. Rectangular plates (10 x 15 x 2 mm) made of apatite-wollastonite-containing glass ceramics were implanted in the proximal metaphyses of the bilateral tibiae of 20 rabbits, with DBP packed into the medullary cavity. In the control group, only the plates of A-W GC were implanted in the bilateral tibiae of 20 rabbits. Four rabbits from each group were killed at two, four, eight, 12, and 25 weeks after implantation for the tensile test. Results of the tensile test and histologic examination of the undecalcified specimens by Giemsa surface stain and contact microradiography confirmed that DBP significantly accelerated the process of bone bonding to the implant and increased the strength of bone-implant bonding.     

骨髓基质干细胞联合血管束植入构筑血管化组织工程骨修复兔大段骨缺损

目的 研究兔骨髓基质干细胞(BMSCs)联合动静脉血管束植入异种脱蛋白松质骨(XDCB)构筑血管化组织工程骨修复兔桡骨中远段完全骨膜骨缺损的能力. 方法 从兔髂嵴捕骨髓培养制备兔BMSCs,将第5代BMSCs种植于多孔XDCB,并进行成骨诱导2周制备组织工程骨,手术中分离兔桡动、静脉血管束.动物模型为制备24只兔舣侧桡骨中远段完全骨膜骨缺损1.5 cm共48侧,分4组修复(n=12),A组为空白未治疗组,B组为单纯材料+血管束植入组(XDCB+VB),C组为组织工程骨组(XDCB+BMSCs),D组为组织工程骨+血管束植入组(XDCB+BMSCs+VB),符组交叉配对.分别于术后4、8、12周行X线片、大体解剖、组织切片、生物力学等检查,观察各组骨缺损修复效能及移植物血管化情况.结果 D组骨缺损修复效能(术后12周新骨面积比2.02%±0.16%)及血管化情况(术后12周血管面积比6.89%±0.32%)优于C组(1.50%±0.28%和3.17%±0.19%),而C组又优于B组(1.59%±0.19%和6.52%±0.23%),A组骨缺损未修复,各组结果差异有统计学意义(P<0.05).结论 BMSCs联合动静脉血管束植入构筑的血管化组织工程骨能促进成骨过程和新生骨的血管化,显著提高组织工程骨修复大段骨缺损的能力.     

Interface mechanics and bone growth into porous Co-Cr-Mo alloy implants

The interface mechanics and bone growth into porous Co-Cr-Mo alloy implants were evaluated. Three mean pore sizes (155, 235, and 350 microns) were studied for implants fabricated with one, two, and three layers of spherical powder particles and totally porous implants. All implants had a pore volume of 38%-40%. Ten implants were inserted transcortically in the femora of six adult mongrel dogs and were allowed to remain in situ for a period of 12 weeks. Postretrieval mechanical testing and histologic and microradiographic analyses were used to evaluate the implant systems. A statistically significant increase in interface shear strength (p less than .05) was determined as the number of powder particle layers was increased from one and two layers to three layers. However, a decrease in interface strength was determined for totally porous implants (seven to 12 particle layers) below the value for the single-porous-layer implants. Pore size, in the range investigated, was not found to influence the interface attachment strength. Neither pore size nor porous layer thickness was found to affect interface stiffness. Histologic and microradiographic sections revealed extensive mineralized bone growth deep into the pores of all implant types and often extending to the core of the one-, two- and three-layered porous-coated implants. Both mature haversian bone and less mature woven bone were found within the porous structure. Extensive but incomplete bone infiltration was found in the totally porous implants, with the remainder of the porosity filled with macrophage-laden connective tissue. No difference in the histologic response was observed as a function of pore size in any of the implant systems. Active bone labels were present at the 12-week time period, indicating continued bone remodeling.     

Autologous osteoblasts enhance osseointegration of porous titanium implants.

The goal of this study was to assess the osseointegration of porous titanium implants by means of coating with autologous osteoblasts. Titanium implants (8 x 5 x 4 mm) having drill channels with diameters of 400, 500, and 600 microm were coated with autologous osteoblasts obtained from spongiosa chips. The implants were inserted into the distal femora of 17 adult Chinchilla Bastard rabbits (group I). Uncoated implants were inserted as controls in the contralateral femur (group II). The animals were sacrificed after 5, 11, and 42 days. Intravital fluorochrome labeling and microradiography were used for the assessment of bone ingrowth into the titanium channels. In both groups, no bone tissue was formed in the channels up to day 5. On day 11, group I exhibited significantly more (p<0.05) bone tissue (19.8+/-14.0% vs. 5.8+/-9.1%) with greater bone-implant contact (13.3+/-15.1% vs. 5.7+/-5.3%, p<0.05) at the channel mouths than group II. Bone tissue was formed mainly between day 15 and 30 in group I, in group II between day 25 and 40. Six weeks after implantation, bone tissue filled on an average 68.8+/-15.1% of the mouths of the drill channels in implants in group I, the filling for group II was 49.8+/-18.1% (p<0.05). The average bone-implant contact at the channel mouths after six weeks was 56.5+/-13.5% in group I, 40.2+/-21.9% in group II (p<0.05). 600-microm channels showed at this time point the best osseous integration (p<0.05). Coating with autologous osteoblasts accelerates and enhances the osseointegration of titanium implants and could be a successful biotechnology for future clinical applications.     

Electron microscopic analysis of the bone-titanium interface

Ten cylindrical implants, made of polycarbonate and covered with a 120-250-nm-thick layer of pure titanium, were implanted into each tibial metaphysis of five rabbits. Observation time was 12 weeks. The implants were surrounded by mature, living bone. No soft tissue intervened between bone and implant at any point. With TEM microscopy the titanium was shown to be bordered by a 20-nm-thick layer of proteoglycans, showing the characteristics of ground substance, and separating the collagen from the implant surface. Cells at the interface were likewise separated from the titanium by such a layer. Hydroxyapatite crystals were observed within the ground substance layer, occasionally seemingly in direct contact with the titanium. Normal mineralization was present 100-500 nm from the implant surface. While this study aims at defining interface anatomy, it also shows that macroscopically smooth-surfaced titanium can readily heal into bone without a soft tissue envelope. This could be of help for materials' choice and design of permanently fixed implants.     

Bone ingrowth to implant surfaces in an inflammatory arthritis model

Many studies have shown enhanced bone apposition to implants coated with hydroxyapatite, but the optimum implant texture, especially in abnormal trabecular bone, is unclean The purpose of this project was to evaluate the histological and mechanical properties of cylindrical implants with three different surface textures that were placed in the cancellous bone of the distal femur of the rabbit after the production of an inflammatory knee arthritis. The three implant surfaces included a beaded surface (Group A), a beaded surface coated with hydroxyapatite (Group B), and a smooth surface coated with hydroxyapatite (Group C). The right knees of 36 rabbits were injected with carrageenan twice a week for 2 weeks. Then bilateral implantations were performed, with 12 rabbits in each group receiving identical implants in the right and left knees. The rabbits were killed 6 weeks after surgery. Mechanical (push-out test) and histomorphometric analyses were performed to determine the quality and quantity of bone ingrowth. In Group A, there was virtually no direct contact (a 20–60-μm clearance) between the bone and the beaded surfaces. Direct contact between the bone and the implant surfaces was seen in Groups B and C. The thickness and number of trabeculae were smaller on the arthritic side than on the control side for all groups but were not different between groups for either the control or the arthritic side. Mechanical testing showed that the shear strength of the interface was weaker on the arthritic side in all groups. The results suggest that inflammatory arthritis induced by carrageenan may influence the quality of local bone (osteopenic changes) and hence compromise the bone apposition and mechanical stability of the interface between the implant and bone.     

Analysis of performance of root-form endosseous implants placed in the maxillary sinus

To evaluate the long-term effect on metal-bone interface of the perforation of the maxillary antral floor by root-form titanium implants, a study was undertaken in five mature Macaca fascicularis monkeys. One root-form titanium implant was placed bilaterally in the maxillary sinus perforating the sinus 5 mm and a second implant was placed completely in bone tissue. The protruding implant in the right antrum was grafted with autogenous cancellous bone and porous bone mineral (Bio-Oss) and the contralateral antral implant protruding in the antrum was left without grafting. The bilateral implants were used to support "free-standing" fixed prostheses, which were in full function for 14 months, during which time there was excellent clinical function and no mobility of the implants. Histomorphometric analysis of specimens revealed that there was no difference in the trabecular pattern or the amount of calcified matrix vs. marrow vascular spaces along the titanium implant interface. New reparative bone partially restored the osseous surface along the implant on the ungrafted side. Implants in the grafted antrum demonstrated bone regeneration over the implant surface ranging from 2 cm to complete regeneration. Histomorphometric analysis revealed the peri-implant bone to contain some particles of the Bio-Oss, although most of the implant bone interface exhibited only vital bone and marrow vascular spaces. The study indicates that the protrusion of implants maximally into the sinus floor does not necessarily require a bone graft to produce functional abutments for fixed prostheses and that implants can function well with 5 mm of protrusion into the antrum with excellent bone-metal interface.     

Controlled‐release of bone morphogenetic protein‐2 from a microsphere coating applied to acid‐etched Ti6AL4V implants increases biological bone growth in vivo

A central clinical challenge regarding the surgical treatment of bone and joint conditions is the eventual loosening of an orthopedic implant as a result of insufficient bone ingrowth at the bone–implant interface. We investigated the in vivo effectiveness of a coating containing recombinant human bone morphogenetic protein‐2 (rhBMP‐2)‐loaded microspheres applied to acid‐etched Ti6Al4V cylinders for implantation. Three groups of rabbits (24 per group) were used for implantation: (1) acid‐etched Ti6Al4V implants coated with a mixture of rhBMP‐2‐loaded microspheres (125 ng rhBMP‐2/mg microspheres) and α‐butyl cyanoacrylate; (2) acid‐etched, uncoated implants; and (3) bare, smooth uncoated implants. After implantation, 12 rabbits from each group were used for bone ingrowth determination at 4, 5, 6, 7, 8, and 12 weeks (2 rabbits per time point), while the remainder were used for histological analysis and push‐out testing at 12 weeks. Scanning electron microscopy showed significant improvement in bone growth of the rhBMP‐2 microspheres/α‐butyl cyanoacrylate group compared with the other groups (p < 0.01). Histological analysis and push‐out testing also demonstrated enhanced bone growth of the rhBMP‐2 group over that in the other two groups (p < 0.01). The rhBMP‐2 group showed the most significant bone growth, suggesting that coating acid‐etched implants with a mixture of rhBMP‐2‐loaded microspheres and α‐butyl cyanoacrylate may be an effective method to improve the osseointegration of orthopedic implants. © 2014 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 32:744–751, 2014.     

Electron Microscopic Analysis of the Bone-Titanium Interface

Ten cylindrical implants, made of polycarbonate and covered with a 120-250-nm-thick layer of pure titanium, were implanted into each tibial metaphysis of five rabbits. Observation time was 12 weeks. The implants were surrounded by mature, living bone. No soft tissue intervened between bone and implant at any point. With TEM microscopy the titanium was shown to be bordered by a 20-nm-thick layer of proteoglycans, showing the characteristics of ground substance, and separating the collagen from the implant surface. Cells at the interface were likewise separated from the titanium by such a layer. Hydroxyapatite crystals were observed within the ground substance layer, occasionally seemingly in direct contact with the titanium. Normal mineralization was present 100-500 nm from the implant surface.

While this study aims at defining interface anatomy, it also shows that macroscopi-cally smooth-surfaced titanium can readily heal into bone without a soft tissue envelope. This could be of help for materials' choice and design of permanently fixed implants.     

Bioactive porous titanium: an alternative to surgical implants

Abstract:  Porous titanium implants have been used to improve implant–bone attachment by the ingrowth of bone tissue within the porous structure. Despite the efficient bone adhesion of porous titanium implants, chemical bonds are required at bone–implant interface. These implants can become bioactive by a biomimetic precipitation process. The aim of this work was to enhance the bioactivity of pure porous titanium implants by biomimetic process. The samples immersed in a simulated body fluid promoted the nucleation and growth of calcium phosphate (Ca-P) crystals, such as hydroxyapatite (Hap), on the material surface. Scanning electron microscopy, energy dispersive spectroscopy, and Fourier transform infrared spectroscopy analyses revealed that a Ca-P deposition occurred without the need of pretreatments to improve the surface bioactivity. This present study indicates the potential for growing a bone-like Hap layer on porous titanium implants by biomimetic processes.     

No adverse effects of bone compaction on implant fixation after resorption of compacted bone in dogs

BACKGROUND: A new bone preparation technique, compaction, has been shown to enhance initial implant fixation. However, short-term compaction has resulted in more non-vital bone being in contact with the implant. Also, compaction may result in inferior long-term implant fixation as the compacted non-vital bone at the bone-implant interface is resorbed. METHODS: We tested the hypothesis that compaction would result in inferior implant fixation after 10 weeks of weight bearing. We compared compaction with the conventional bone removal technique (drilling) for (1) porous coated titanium (Ti) implants inserted exact-fit into medial femoral condyles, and for (2) hydroxy-apatite (HA) porous coated implants inserted press-fit into lateral femoral condyles. In each of 8 dogs, we prepared the implant cavities of one knee joint with drilling, and the other with compaction. Implants were tested mechanically to failure by push-out test, and histomorphometry was done. RESULTS: For all specimens, non-vital bone implant contact contributed very little to the total bone implant contact. Inferior mechanical or histological implant fixation with compaction was not found for either Ti implants or HA implants. INTERPRETATION: Compaction does not appear to result in inferior implant fixation as the compacted bone at the bone implant interface is resorbed.     

Effect of disodium etidronate (EHDP) on bone ingrowth in a porous material

This study evaluated the effect of disodium etidronate (EHDP) on biomechanical and histologic characteristics of bone ingrowth in a porous material. EHDP was administered parenterally to six adult mongrel dogs at a dose of 2 mg/kg/day for eight weeks. Six additional dogs served as controls and were injected with saline. Porous titanium fiber composites were inserted into the proximal humeri and the left olecranons of all animals after the first four weeks of treatment. Upon completing a total of eight weeks of treatment, all animals were sacrificed and the bone-porous implant interfacial shear strength was determined by a pull-out test to failure. Mean shear strength of fixation for the EHDP-treated group was reduced by 76% compared to the control group (p less than 0.001). Bone ingrowth was mineralized in all of the control specimens. Mineralization of tissue ingrowth was inhibited, however, in all specimens from EHDP-treated animals. These findings suggest that cementless skeletal fixation of porous-coated implants by bone ingrowth may be delayed or prevented by the administration of EHDP.     

A controlled experimental model of revision implants: Part II. Implementation with loaded titanium implants and bone graft

We used an experimental model producing an aggressive tissue response associated with implant loosening in humans: a 6 mm polymethylmethacrylate (PMMA) cylinder was pistoning 500 microm concentrically in a 7.5 mm hole, with polyethylene (PE) particles, for 8 weeks. At 8 weeks, the PMMA implant was revised with a titanium alloy (Ti) implant, and an identical primary Ti implant was inserted contralaterally for 4 weeks. With this protocol, we evaluated primary and revision plasma-sprayed Ti implants which were loaded under stable conditions with or without allograft, or under unstable conditions without allograft (bilateral primary and revision implants, n 8 per group, 48 implants in 24 dogs). Revision implants had lower interfacial shear strength, less bone in contact with and adjacent to the implant, and resulted in higher levels of IL-6beta and TNFalpha and lower levels of TGFbeta. In both the revision and primary settings, allograft increased shear strength, stiffness and energy, bone-implant contact, and bone area adjacent to the implant. Unstable implants could not generate a mechanically sound interface, and further exacerbated the difference between primary and revision. We conclude that factors important for improving the fixation of revision implants were bone graft and a stable interface.     

Short-term alendronate treatment does not maintain a residual effect on spinal fusion with interbody devices and bone graft after treatment withdrawal: an experimental study on spinal fusion in pigs

Purpose

Whether alendronate treatment has a residual effect on bone ingrowth into porous biomaterial in humans or experimental animals after treatment withdrawal is still unknown. The purpose of this study was to investigate bone ingrowth into porous tantalum and carbon fiber interbody implants after discontinuing alendronate treatment in experimental spinal fusion in pigs.

Methods

Twenty-four pigs were randomly divided into two groups of each 12 pigs. The pigs underwent anterior intervertebral lumbar arthrodeses at L2–3, L4–5 and L6–7. Each level was randomly allocated to one of the three implants: a porous tantalum ring with pedicle screw fixation, a porous tantalum ring or a carbon fiber cage with anterior staple fixation. The central hole of implants was packed with an autograft. Alendronate was given orally for the first 3 months to one of the two groups. The pigs were observed for 6 months postoperatively. Histology and micro-CT scans were done at the endpoint.

Results

The spinal fusion rates of each implant showed no differences between two treatment groups. Furthermore, no differences were found between two groups as for bone ingrowth into the central holes of implants and bone–implant interface in each implant, or as for the pores of tantalum implants. Trabecular bone microarchitecture in the central hole of the carbon fiber cage did not differ between two treatment groups.

Conclusion

The application of ALN, with a dose equivalent to that given to humans during the first 3 months after surgery, does not maintain a residual effect on spinal fusion with porous tantalum ring and autograft after treatment withdrawal in a porcine ALIF model.     

Effects of the systemic administration of alendronate on bone formation in a porous hydroxyapatite/collagen composite and resorption by osteoclasts in a bone defect model in rabbits

Several bisphosphonates are now available for the treatment of osteoporosis. Porous hydroxyapatite/collagen (HA/Col) composite is an osteoconductive bone substitute which is resorbed by osteoclasts. The effects of the bisphosphonate alendronate on the formation of bone in porous HA/Col and its resorption by osteoclasts were evaluated using a rabbit model. Porous HA/Col cylinders measuring 6 mm in diameter and 8 mm in length, with a pore size of 100 μm to 500 μm and 95% porosity, were inserted into a defect produced in the lateral femoral condyles of 72 rabbits. The rabbits were divided into four groups based on the protocol of alendronate administration: the control group did not receive any alendronate, the pre group had alendronate treatment for three weeks prior to the implantation of the HA/Col, the post group had alendronate treatment following implantation until euthanasia, and the pre+post group had continuous alendronate treatment from three weeks prior to surgery until euthanasia. All rabbits were injected intravenously with either saline or alendronate (7.5 μg/kg) once a week. Each group had 18 rabbits, six in each group being killed at three, six and 12 weeks post-operatively. Alendronate administration suppressed the resorption of the implants. Additionally, the mineral densities of newly formed bone in the alendronate-treated groups were lower than those in the control group at 12 weeks post-operatively. Interestingly, the number of osteoclasts attached to the implant correlated with the extent of bone formation at three weeks. In conclusion, the systemic administration of alendronate in our rabbit model at a dose-for-weight equivalent to the clinical dose used in the treatment of osteoporosis in Japan affected the mineral density and remodelling of bone tissue in implanted porous HA/Col composites.     

No adverse effects of bone compaction on implant fixation after resorption of compacted bone in dogs

Background?A new bone preparation technique, compaction, has been shown to enhance initial implant fixation. However, short-term compaction has resulted in more non-vital bone being in contact with the implant. Also, compaction may result in inferior long-term implant fixation as the compacted non-vital bone at the bone-implant interface is resorbed.

Methods?We tested the hypothesis that compaction would result in inferior implant fixation after 10 weeks of weight bearing. We compared compaction with the conventional bone removal technique (drilling) for (1) porous coated titanium (Ti) implants inserted exact-fit into medial femoral condyles, and for (2) hydroxy-apa-tite (HA) porous coated implants inserted press-fit into lateral femoral condyles. In each of 8 dogs, we prepared the implant cavities of one knee joint with drilling, and the other with compaction. Implants were tested mechanically to failure by push-out test, and histomor-phometry was done.

Results?For all specimens, non-vital bone implant contact contributed very little to the total bone implant contact. Inferior mechanical or histological implant fixation with compaction was not found for either Ti implants or HA implants.

Interpretation?Compaction does not appear to result in inferior implant fixation as the compacted bone at the bone implant interface is resorbed.

?     

Locally delivered rhBMP-2 enhances bone ingrowth and gap healing in a canine model.

The purpose of the present study was to determine if recombinant human bone morphogenetic protein-2 (rhBMP-2) enhances bone ingrowth into porous-coated implants and gap healing around the implants. In the presence of a 3-mm gap between the implant and host bone, porous-coated implants were placed bilaterally for four weeks in the proximal humeri of skeletally mature, adult male dogs. In three treatment groups, the test implant was treated with HA/TCP and rhBMP-2 in buffer at a dose of 100 microg/implant (n=5), 400 microg/implant (n=6), or 800 microg/implant (n=5) and placed in the left humerus. In these same animals, an internal control implant was treated only with HA/TCP and buffer and placed in the right humerus. These groups were compared with a previously reported external control group of seven animals in which no growth factor was delivered [J. Orthop. Res. 19 (2001) 85]. The BMP treated implants in the two lower dose groups had significantly more bone ingrowth than the external controls with the greatest effect in the 100 g/implant group (a 3.5-fold increase over the external control, p=0.008). All three dose groups had significantly more bone formation in the 3-mm gap surrounding the BMP treated implants than the external controls with the greatest effect in the 800 microg group (2.9-fold increase, p<0.001). Thus, application of rhBMP-2 to a porous-coated implant stimulated local bone ingrowth and gap healing. The enhancement of bone formation within the implant (bone ingrowth) was inversely related to dose.