A method for preparing and staining histological sections containing titanium implants for light microscopy

A bone preservation protocol that enables evaluation of osseointegration of implants with micro- and nanotextured surfaces

Development of surface treatments has enabled secure attachment of dental implants in less than 1 month. Consequently, it is necessary to characterize accurately the osseointegration of the implant surface in the region of the bone-implant contact (BIC). We developed a method for sample preparation that preserves both bone and BIC to permit analysis of the contact interface. We prepared eight nanotextured implants and implanted them in rabbit tibias. After healing for 30 days, outcomes were analyzed using both our bone preservation protocol and routine decalcification followed by preparation of histological sections stained by hematoxylin and eosin (H & E). Pull-out tests for implant osseointegration were performed after healing. Non-implanted samples of rabbit mandible were used as a control for assessing organic and mineralized bone characteristics and bone structure. Our bone preservation protocol enabled evaluation of many of the same bone characteristics as histological sections stained with H & E. Our protocol enables analysis of implant samples, implant surfaces and osseointegration without risk of BIC damage.

Healing in peri-implant gap with BMP-2 and systemic bisphosphonate is dependent on BMP-2 dose-A canine study

The bone-implant interface of cementless orthopedic implants can be described as a series of uneven sized gaps with discontinuous areas of direct bone-implant contact. Bridging these voids and crevices by addition of an anabolic stimulus to increase new bone formation can potentially improve osseointegration of implants. Bone morphogenetic protein 2 (BMP-2) stimulates osteoblast formation to increase new bone formation but also indirectly stimulates osteoclast activity. In this experiment, we investigate the hypothesis that osseointegration, defined as mechanical push-out and histomorphometry, depends on the dose of BMP-2 when delivered as an anabolic agent with systemic administration of the anti-resorptive agent zoledronate to curb an increase in osteoclast activity. Four porous coated titanium implants (one with each of three doses of surface-applied BMP-2 (15 µg; 60 µg; 240 µg) and untreated) surrounded by a 0.75 mm empty gap, were inserted into the distal femurs of each of twelve canines. Zoledronate IV (0.1 mg/kg) was administered 10 days into the observation period of 4 weeks. Bone-implant specimens were evaluated by mechanical push-out test and histomorphometry. The 15 µg implants had the best fixation on all mechanical parameters and largest surface area covered with new bone compared to the untreated, 60 and 240 µg implants, as well as the highest volume of new bone in the implant gap compared to 60 and 240 µg implants. The results in a canine implant model demonstrated that a narrow range of BMP-2 doses have opposite effects in bridging an empty peri-implant gap with bone, when combined with systemic zoledronate. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1406-1414, 2018.

Topical bisphosphonate augments fixation of bone-grafted hydroxyapatite coated implants, BMP-2 causes resorption-based decrease in bone

Bone allograft is used in total joint arthroplasties in order to enhance implant fixation. BMPs are known to stimulate new bone formation within allograft, but also known to accelerate graft resorption. Bisphosphonates are strong inhibitor of bone resorption. The aim of this study was to investigate whether the bisphosphonate zoledronate was able to counteract the accelerated graft resorption without interfering with the BMP induced bone formation. In the present study the two drugs alone and in combination were studied in our canine model of impaction bone grafting. We included 10 dogs in this study. Cancellous allograft bone grafts were soaked in either saline or zoledronate solution (0.005mg/mL) and then vehicle or BMP2 (0.15mg rhBMP2) was added. This produced four treatment groups: A) control, B) BMP2, C) zoledronate and D) BMP2+zoledronate. The allograft treated with A, B, C or D was impacted into a circumferential defect of 2.5mm around HA-coated porous Ti implants. Each dog received all four treatment groups with two implants in the distal part of each femur. The group with allograft soaked in zoledronate (C) showed better biomechanical fixation than all other groups (p<0.05). It had less allograft resorption compared to all other groups (p<0.005) without any statistically significant change in new bone formation. The addition of BMP2 to the allograft did not increase new bone formation significantly, but did accelerate allograft resorption. This was also the case where the allograft was treated with BMP2 and zoledronate in combination (D). This caused a decrease in mechanical implant fixation in both these groups compared to the control group, however only statistically significant for the BMP2 group compared to control. The study shows that topical zoledronate can be a valuable tool for augmenting bone grafts when administered optimally. The use of BMP2 in bone grafting procedures seems associated with a high risk of bone resorption and mechanical weakening.

Do Bone Graft and Cracking of the Sclerotic Cavity Improve Fixation of Titanium and Hydroxyapatite-coated Revision Implants in an Animal Model?

BACKGROUND

We previously introduced a manual surgical technique that makes small perforations (cracks) through the sclerotic bone shell that typically forms during the process of aseptic loosening ("crack" revision technique). Perforating just the shell (without violating the proximal cortex) can maintain overall bone continuity while allowing marrow and vascular elements to access the implant surface. Because many revisions require bone graft to fill defects, we wanted to determine if bone graft could further increase implant fixation beyond what we have experimentally shown with the crack technique alone. Also, because both titanium (Ti6Al4V) and hydroxyapatite (HA) implant surfaces are used in revisions, we also wanted to determine their relative effectiveness in this model.

QUESTIONS/PURPOSES

We hypothesized that both (1) allografted plasma-sprayed Ti6Al4V; and (2) allografted plasma-sprayed HA-coated implants inserted with a crack revision technique have better fixation compared with a noncrack revision technique in each case.

METHODS

Under approval from our Institutional Animal Care and Use Committee, a female canine animal model was used to evaluate the uncemented revision technique (crack, noncrack) using paired contralateral implants while implant surface (Ti6Al4V, HA) was qualitatively compared between the two (unpaired) series. All groups received bone allograft tightly packed around the implant. This revision model includes a cylindrical implant pistoning 500 μm in a 0.75-mm gap, with polyethylene particles, for 8 weeks. This engenders a bone and tissue response representative of the metaphyseal cancellous region of an aseptically loosened component. At 8 weeks, the original implants were revised and followed for an additional 4 weeks. Mechanical fixation was assessed by load, stiffness, and energy to failure when loaded in axial pushout. Histomorphometry was used to determine the amount and location of bone and fibrous tissue in the grafted gap.

RESULTS

The grafted crack revision improved mechanical shear strength, stiffness, and energy to failure (for Ti6Al4V 27- to 69-fold increase and HA twofold increases). The histomorphometric analysis demonstrated primarily fibrous membrane ongrowth and in the gap for the allografted Ti6Al4V noncrack revisions. For allografted HA noncrack revisions, bone ongrowth at the implant surface was observed, but fibrous tissue also was present in the inner gap. Although both Ti6Al4V and HA surfaces showed improved fixation with grafted crack revision, and Ti6Al4V achieved the highest percent gain, HA demonstrated the strongest overall fixation.

CONCLUSIONS

The results of this study suggest that novel osteoconductive or osteoinductive coatings and bone graft substitutes or tissue-engineered constructs may further improve bone-implant fixation with the crack revision technique but require evaluation in a rigorous model such as presented here.

CLINICAL RELEVANCE

This experimental study provides data on which to base clinical trials aimed to improve fixation of revision implants. Given the multifactorial nature of complex human revisions, such a protocoled clinical study is required to determine the clinical applicability of this approach.

Does tobramycin impregnation of allograft bone affect implant fixation? - an experimental study in 12 dogs

Clinical trials have used antibiotic impregnated impacted bone allograft in revisions of infected arthroplasties. By this method high local antibiotic concentration and good control of infection was achieved. Toxicity studies, however, suggest that high local antibiotic concentration can impair osteoblast replication. We therefore asked whether impregnating morselized allograft bone with different quantities of tobramycin before impaction would impair implant fixation. We implanted three cylindrical (10 mm × 6 mm) porous-coated titanium implants into the distal femurs of 12 dogs. The implants were surrounded by a circumferential gap of 2.5 mm into which a standardized volume of morselized allograft bone, with or without tobramycin, was impacted. In each animal, the bone graft was impregnated with either 0 mg (control), 50 mg (low dose), or 200 mg (high dose) of tobramycin per 1 mL of bone graft. At the end of the 4 weeks experimental period, the implants with surrounding bone were evaluated by histomorphometric analysis and mechanical push-out test. We found no difference between the treatment groups regarding new bone formation, bone graft resorption, or implant fixation. There was, however, a tendency toward a decrease in implant fixation with higher tobramycin dose. The present study is unable to provide evidence on whether the use of topical tobramycin with allograft is safe or whether it indeed can impair implant fixation. The tendency toward an impaired implant fixation warrants further preclinical studies. Its current clinical use should be weighed against its possible positive effects on preventing infection in complicated revisions.

Rinsing of allograft bone does not improve implant fixation: a study in 12 dogs

BACKGROUND AND PURPOSE

Impacted morselized allograft bone is a well-established method for reconstructing bone defects at revision surgery. However, the incorporation of bone graft is not always complete, and a substantial volume of fibrous tissue has been found around grafted implants. We hypothesized that rinsing the bone graft may improve graft incorporation by removing the majority of immunogenic factors present in blood, marrow, and fat.

METHODS

We implanted a cylindrical (10- × 6-mm) porous-coated Ti implant into each proximal tibia of 12 dogs. The implants were surrounded by a 2.5-mm gap into which morselized fresh frozen allograft bone was impacted. The bone graft was either (1) untreated or (2) rinsed in 37°C saline for 3 × 1 min. After 4 weeks, the animals were killed and implant fixation was evaluated by mechanical push-out and histomorphometry.

RESULTS

The groups (rinsed vs. control) were similar regarding mechanical implant fixation (mean (SD)): shear strength (MPa) 2.7 (1.0) vs. 2.9 (1.2), stiffness (MPa/mm) 15 (6.7) vs. 15 (5.6), and energy absorption (kJ/m(2)) 0.5 (0.2) vs. 0.6 (0.4), The same was evident for the new bone formation on the implant surface and around the implant: ongrowth (%) 6 vs. 7 and ingrowth (%) 9 vs. 9. Although not statistically significant, a 61% reduction in fibrous tissue ongrowth and 50% reduction in ingrowth were found in the rinsed group.

INTERPRETATION

Within the limits of this experimental model, we did not detect any benefits of rinsing morselized allograft bone prior to impaction grafting.

Periosteal augmentation of allograft bone and its effect on implant fixation - an experimental study on 12 dogs()

PURPOSE

Periosteum provides essential cellular and biological components necessary for fracture healing and bone repair. We hypothesized that augmenting allograft bone by adding fragmented autologous periosteum would improve fixation of grafted implants.

METHODS

In each of twelve dogs, we implanted two unloaded cylindrical (10 mm x 6 mm) titanium implants into the distal femur. The implants were surrounded by a 2.5-mm gap into which morselized allograft bone with or without addition of fragmented autologous periosteum was impacted. After four weeks, the animals were euthanized and the implants were evaluated by histomorphometric analysis and mechanical push-out test.

RESULTS

Although less new bone was found on the implant surface and increased volume of fibrous tissue was present in the gap around the implant, no difference was found between treatment groups regarding the mechanical parameters. Increased new bone formation was observed in the immediate vicinity of the periosteum fragments within the bone graft.

CONCLUSION

The method for periosteal augmentation used in this study did not alter the mechanical fixation although osseointegration was impaired. The observed activity of new bone formation at the boundary of the periosteum fragments may indicate maintained bone stimulating properties of the transplanted cambium layer. Augmenting the bone graft by smaller fragments of periosteum, isolated cambium layer tissue or cultured periosteal cells could be studied in the future.

Acid etching and plasma sterilization fail to improve osseointegration of grit blasted titanium implants

Interaction between implant surface and surrounding bone influences implant fixation. We attempted to improve the bone-implant interaction by 1) adding surface micro scale topography by acid etching, and 2) removing surface-adherent pro-inflammatory agents by plasma cleaning. Implant fixation was evaluated by implant osseointegration and biomechanical fixation.

The study consisted of two paired animal sub-studies where 10 skeletally mature Labrador dogs were used. Grit blasted titanium alloy implants were inserted press fit in each proximal tibia. In the first study grit blasted implants were compared with acid etched grit blasted implants. In the second study grit blasted implants were compared with acid etched grit blasted implants that were further treated with plasma sterilization. Implant performance was evaluated by histomorphometrical investigation (tissue-to-implant contact, peri-implant tissue density) and mechanical push-out testing after four weeks observation time.

Neither acid etching nor plasma sterilization of the grit blasted implants enhanced osseointegration or mechanical fixation in this press-fit canine implant model in a statistically significant manner.

Systemic intermittent parathyroid hormone treatment improves osseointegration of press-fit inserted implants in cancellous bone

BACKGROUND AND PURPOSE

Intermittent administration of parathyroid hormone (PTH) has an anabolic effect on bone, as confirmed in human osteoporosis studies, distraction osteogenesis, and fracture healing. PTH in rat models leads to improved fixation of implants in low-density bone or screw insertion transcortically.

MATERIAL AND METHODS

We examined the effect of human PTH (1-34) on the cancellous osseointegration of unloaded implants inserted press-fit in intact bone of higher animal species. 20 dogs were randomized to treatment with human PTH (1-34), 5 μg/kg/day subcutaneously, or placebo for 4 weeks starting on the day after insertion of a cylindrical porous coated plasma-sprayed titanium alloy implant in the proximal metaphyseal cancellous bone of tibia. Osseointegration was evaluated by histomorphometry and fixation by push-out test to failure.

RESULTS

Surface fraction of woven bone at the implant interface was statistically significantly higher in the PTH group by 1.4 fold with (median (interquartile range) 15% (13-18)) in the PTH group and 11% (7-13) in control. The fraction of lamellar bone was unaltered. No significant difference in bone or fibrous tissue was observed in the circumferential regions of 0-500, 500-1,000, and 1,000-2,000 μm around the implant. Mechanically, the implants treated with PTH showed no significant differences in total energy absorption, maximum shear stiffness, or maximum shear strength.

INTERPRETATION

Intermittent treatment with PTH (1-34) improved histological osseointegration of a prosthesis inserted press-fit at surgery in cancellous bone, with no additional improvement of the initial mechanical fixation at this time point.

Assessment of modified gold surfaced titanium implants on skeletal fixation

Noncemented implants are the primary choice for younger patients undergoing total hip replacements. However, the major concern in this group of patients regarding revision is the concern from wear particles, periimplant inflammation, and subsequently aseptic implant loosening. Macrophages have been shown to liberate gold ions through the process termed dissolucytosis. Furthermore, gold ions are known to act in an anti-inflammatory manner by inhibiting cellular NF-κB-DNA binding. The present study investigated whether partial coating of titanium implants could augment early osseointegration and increase mechanical fixation. Cylindrical porous coated Ti-6Al-4V implants partially coated with metallic gold were inserted in the proximal region of the humerus in ten canines and control implants without gold were inserted in contralateral humerus. Observation time was 4 weeks. Biomechanical push out tests and stereological histomorphometrical analyses showed no statistically significant differences in the two groups. The unchanged parameters are considered an improvement of the coating properties, as a previous complete gold-coated implant showed inferior mechanical fixation and reduced osseointegration compared to control titanium implants in a similar model. Since sufficient early mechanical fixation is achieved with this new coating, it is reasonable to investigate the implant further in long-term studies.

Coralline hydroxyapatite granules inferior to morselized allograft around uncemented porous Ti implants: unchanged fixation by addition of concentrated autologous bone marrow aspirate

We compared early fixation of titanium implants grafted with impacted allograft bone or coralline hydroxyapatite (HA) granules (Pro Osteon 200) with and without the addition of concentrated bone marrow cells (BMC). Autologous bone marrow aspirate was centrifuged to increase the BMC concentration. Four nonloaded cylindrical, porous coated titanium implants with a circumferential gap of 2.3 mm were inserted in the proximal humeri of eight dogs. Coralline HA granules +/- BMC were impacted around the two implants on one side, and allograft +/- BMC was impacted around the contra lateral implants. Observation time was 4 weeks. The implants surrounded by allograft bone had a three-fold better fixation than the HA-grafted implants. The concentration of BMC after centrifugation was increased with a factor 2.1. The addition of BMC to either of the bone graft materials had no statistically significant effects on implant fixation. The allografted implants were well osseointegrated, whereas the HA-grafted implants were largely encapsulated in fibrous tissue. The addition of concentrated autologous BMCs to the graft material had no effect on implant fixation. The HA-grafted implants were poorly anchored compared with allografted implants, suggesting that coralline HA granules should be considered a bone graft extender rather than a bone graft substitute.

Parathyroid hormone treatment increases fixation of orthopedic implants with gap healing: a biomechanical and histomorphometric canine study of porous coated titanium alloy implants in cancellous bone

Parathyroid hormone (PTH) administered intermittently is a bone-building peptide. In joint replacements, implants are unavoidably surrounded by gaps despite meticulous surgical technique and osseointegration is challenging. We examined the effect of human PTH(1-34) on implant fixation in an experimental gap model. We inserted cylindrical (10 × 6 mm) porous coated titanium alloy implants in a concentric 1-mm gap in normal cancellous bone of proximal tibia in 20 canines. Animals were randomized to treatment with PTH(1-34) 5 μg/kg daily. After 4 weeks, fixation was evaluated by histomorphometry and push-out test. Bone volume was increased significantly in the gap. In the outer gap (500 μm), the bone volume fraction median (interquartile range) was 27% (20-37%) for PTH and 10% (6-14%) for control. In the inner gap, the bone volume fraction was 33% (26-36%) for PTH and 13% (11-18%) for control. At the implant interface, the bone fraction improved with 16% (11-20%) for PTH and 10% (7-12%) (P = 0.07) for control. Mechanical implant fixation was improved for implants exposed to PTH. For PTH, median (interquartile range) shear stiffness was significantly higher (PTH 17.4 [12.7-39.7] MPa/mm and control 8.8 [3.3-12.4] MPa/mm) (P < 0.05). Energy absorption was significantly enhanced for PTH (PTH 781 [595-1,198.5] J/m(2) and control 470 [189-596] J/m(2)). Increased shear strength was observed but was not significant (PTH 3.0 [2.6-4.9] and control 2.0 [0.9-3.0] MPa) (P = 0.08). Results show that PTH has a positive effect on implant fixation in regions where gaps exist in the surrounding bone. With further studies, PTH may potentially be used clinically to enhance tissue integration in these challenging environments.

The combined effect of parathyroid hormone and bone graft on implant fixation

Impaction allograft is an established method of securing initial stability of an implant in arthroplasty. Subsequent bone integration can be prolonged, and the volume of allograft may not be maintained. Intermittent administration of parathyroid hormone has an anabolic effect on bone and may therefore improve integration of an implant. Using a canine implant model we tested the hypothesis that administration of parathyroid hormone may improve osseointegration of implants surrounded by bone graft. In 20 dogs a cylindrical porous-coated titanium alloy implant was inserted into normal cancellous bone in the proximal humerus and surrounded by a circumferential gap of 2.5 mm. Morsellised allograft was impacted around the implant. Half of the animals were given daily injections of human parathyroid hormone (1-34) 5 μg/kg for four weeks and half received control injections. The two groups were compared by mechanical testing and histomorphometry. We observed a significant increase in new bone formation within the bone graft in the parathyroid hormone group. There were no significant differences in the volume of allograft, bone-implant contact or in the mechanical parameters. These findings suggest that parathyroid hormone improves new bone formation in impacted morsellised allograft around an implant and retains the graft volume without significant resorption. Fixation of the implant was neither improved nor compromised at the final follow-up of four weeks.

Acid etching does not improve CoCrMo implant osseointegration in a canine implant model

Induction of bone ingrowth by topographical changes to implant surfaces is an attractive concept. Topographical modifications achieved by acid etching are potentially applicable to complex 3D surfaces. Using clinically relevant implant models, we explored the effect of wet etching porous bead-coated CoCrMo. The study was designed as two paired animal experiments with 10 dogs. Each dog received four implants; one in each medial femoral condyle (loaded 0.75-mm-gap model) and one in each proximal tibia (press-fit). The implants were observed for 6 weeks and were evaluated by biomechanical pushout tests and histomorphometry. We found that wet etching porous bead-coated CoCrMo implants failed to improve implant performance. Moreover, a tendency towards increased fibrous tissue formation, decreased new bone formation, and decreased mechanical fixation was observed. Surface topography on implants is able to stimulate bone-forming cells, but the clinical performance of an implant surface perhaps relies more on 3D geometrical structure and biocompatibility. Caution should be exercised regarding the results of wet etching of porous bead-coated CoCrMo and there is a need for more preclinical trials.

The effect on bone growth enhancement of implant coatings with hydroxyapatite and collagen deposited electrochemically and by plasma spray

Skeletal bone consists of hydroxyapatite (HA) [Ca(10)(PO(4))(6)(OH)(2)] and collagen type I, both of which are osseoconductive. The goal of osseointegration of orthopedic and dental implants is the rapid achievement of a mechanically stable long-lasting fixation between bone and an implant surface. In this study, we evaluated the mechanical fixation and tissue distribution surrounding implants coated with three surfaces: plasma-sprayed HA coating, thinner coating of electrochemical-assisted deposition of HA, and an identical thin coating with a top layer of mineralized collagen. Uncoated plasma-sprayed titanium (Ti-6Al-4V) served as negative control. The electrochemical-assisted deposition was performed near physiological conditions. We used a canine experimental joint replacement model with four cylindrical implants (one of each treatment group) inserted in the humeri cancellous metaphyseal bone in a 1 mm gap. Observation time was 4 weeks. The mechanical fixation was quantified by push-out test to failure, and the peri-implant tissue formation by histomorphometric evaluation. HA coatings deposited by plasma spray technique or electrochemically, increased the mechanical fixation and bone ongrowth, but there was no statistical difference between the individual HA applications. Addition of collagen to the mineralized phase of the coating to create a more bone natural surface did not improve the osseoconductive effect of HA.

No effect of autologous growth factors (AGF) around ungrafted loaded implants in dogs

Autologous growth factors (AGF) is a growth-factor-rich concentrate of platelets, white blood cells and fibrinogen. Application of AGF was presumed to improve implant fixation and gap healing of non-grafted, loaded implants. We inserted one loaded titanium implant intra-articularly in each medial femoral condyle of eight dogs. Each implant was surrounded by a 0.75 mm gap. One implant in each dog was coated with AGF prior to implantation whereas the contralateral implant served as a control. AGF was prepared by isolating the buffy-coat from blood and further concentrated using an Interpore Cross UltraConcentrator. Platelet counts were increased from a median baseline of 168x10(3)/microl to 1003x10(3)/microl in AGF. However, AGF had no significant effect on implant fixation or bone formation. Even though AGF increased ultimate shear strength and energy absorption by approximately 50%, these differences had a p-value less than 0.05. The sample size in this study was small and any negative conclusions should be taken with caution due to low statistical power. We have previously demonstrated that AGF significantly improves fixation and incorporation of grafted implants. AGF might require mixing with an osteoconductive grafting material in order to provide a scaffold on which to foster bone growth and to keep the growth factors on location for a prolonged period.

Fixation of hydroxyapatite-coated revision implants is improved by the surgical technique of cracking the sclerotic bone rim

Revision joint replacement has poorer outcomes that have been associated with poorer mechanical fixation. We investigate a new bone-sparing surgical technique that locally cracks the sclerotic bone rim formed during aseptic loosening. We inserted 16 hydroxyapatite-coated implants bilaterally in the distal femur of eight dogs, using a controlled weight-bearing experimental model that replicates important features of a typical revision setting. At 8 weeks, a control revision procedure and a crack revision procedure were performed on contralateral implants. The crack procedure used a splined tool to perform a systematic local perforation of the sclerotic bone rim of the revision cavity. After 4 weeks, the hydroxyapatite-coated implants were evaluated for mechanical fixation by a push-out test and for tissue distribution by histomorphometry. The cracking revision procedure resulted in significantly improved mechanical fixation, significantly more bone ongrowth and bone volume in the gap, and reduced fibrous tissue compared to the control revision procedure. The study demonstrates that the sclerotic bone rim prevents bone ingrowth and promotes fixation by fibrous tissue. The effect of the cracking technique may be due to improved access to the vascular compartment of the bone. The cracking technique is a simple surgical method that potentially can improve the fixation of revision implants in sclerotic regions important for obtaining the fixation critical for overall implant stability.

Compacted cancellous bone has a spring-back effect

A new surgical technique, compaction, has been shown to improve implant fixation. It has been speculated that the enhanced implant fixation with compaction could be due to a spring-back effect of compacted bone. However, such an effect has yet to be shown. Therefore we investigated in a canine model whether implant cavities prepared with compaction had spring back. Before killing the animals, we used one of two surgical techniques to make implant cavities of identical dimensions in both lateral femoral condyles of 7 dogs. One side had the implant cavity prepared with compaction, the other side with drilling. The cavities were left empty in vivo for 10 minutes before the dogs were killed. Postoperative micro-CT scanning showed that the diameters of the compacted cavities were significantly smaller than those of the drilled cavities, although they had had identical dimensions initially. Thus we found a spring-back effect of compacted bone, which may be important for increasing implant fixation by reducing initial gaps between the implant and bone.

Local bisphosphonate treatment increases fixation of hydroxyapatite-coated implants inserted with bone compaction

It has been shown that fixation of primary cementless joint replacement can independently be enhanced by either: (1) use of hydroxyapatite (HA) coated implants, (2) compaction of the peri-implant bone, or (3) local application of bisphosphonate. We investigated whether the combined effect of HA coating and bone compaction can be further enhanced with the use of local bisphosphonate treatment. HA-coated implants were bilaterally inserted into the proximal tibiae of 10 dogs. On one side local bisphosphonate was applied prior to bone compaction. Saline was used as control on the contralateral side. Implants were evaluated with histomorphometry and biomechanical push-out test. We found that bisphosphonate increased the peri-implant bone volume fraction (1.3-fold), maximum shear strength (2.1-fold), and maximum shear stiffness (2.7-fold). No significant difference was found in bone-to-implant contact or total energy absorption. This study indicates that local alendronate treatment can further improve the fixation of porous-coated implants that have also undergone HA-surface coating and peri-implant bone compaction.

Ceramic bone graft substitute with equine bone protein extract is comparable to allograft in terms of implant fixation: a study in dogs

BACKGROUND AND PURPOSE

We studied whether osseointegration and fixation of plasma-sprayed titanium implants grafted with beta-TCP granules (Ossaplast) can be improved by adding an osteogenic signal (Colloss E). The results were compared to implants grafted with fresh frozen morselized allograft with and without the Colloss E device.

METHODS

4 porous-coated Ti implants were placed in the proximal humeri in each of 10 dogs. All implants were surrounded by a 2.5-mm defect, which was grafted with: (A) beta-TCP, (B) beta-TCP+20 mg Colloss E, (C) allograft, or (D) allograft+20 mg Colloss E. The observation time was 4 weeks.

RESULTS

Mechanical testing showed that the beta-TCP group with Colloss E was twice as well fixed as the control group grafted with beta-TCP granules alone, and comparable to both allograft groups. We found that every control implant in the beta-TCP grafted group was covered by a dense fibrous membrane. No fibrous tissue was seen in the beta-TCP group augmented with Colloss. These implants were well osseointegrated, with new bone covering 10-25% of the implant surface. Both treated groups had increased graft resorption compared to their respective control groups. Colloss E had no effect on new bone formation or fibrous tissue reduction around the allografted implants.

INTERPRETATION

The Colloss E device improved early osseointegration of implants grafted with beta-TCP granules and increased their mechanical implant fixation to the level of allografted implants. The experiment indicates that ceramic bone substitutes may be a viable alternative to allograft when combined with an osteogenic signal such as Colloss E.

Soaking morselized allograft in bisphosphonate can impair implant fixation

The use of impacted, morselized allograft is a well-established way to provide initial stability of revision joint replacements. We investigated whether rinsing morselized allograft in bisphosphonate and subsequently impacting it around experimental titanium-coated implants would further facilitate biomechanical implant fixation and graft incorporation. In 10 dogs, a pair of titanium implants surrounded by a 2.5-mm gap was inserted into the proximal part of each humerus during two separate surgeries to allow two observation periods. The gap was filled with impacted, morselized allograft soaked in either bisphosphonate (alendronate, 2 mg/mL) or saline (control). Unbound alendronate was not rinsed away. During the first surgery, one pair of implants (alendronate and control) was inserted into one humerus. Eight weeks later, a second pair of implants was inserted into the contralateral humerus. The first pair of implants was observed for 12 weeks and the second pair for 4 weeks. Implants were evaluated by histomorphometry and biomechanical pushout test. We found substantially decreased biomechanical implant fixation for all implants surrounded by impacted, morselized allograft that had been soaked in alendronate. Furthermore, the alendronate treatment blocked formation of new bone and inhibited resorption of the graft material. Although limited by the specific dose of alendronate used and the omission of rinsing away excess bisphosphonate, this study warrants caution and calls for further experimental research before impacting alendronate-soaked morselized allograft around clinical joint replacements.

Osteogenic protein-1 increases the fixation of implants grafted with morcellised bone allograft and ProOsteon bone substitute: an experimental study in dogs

Impacted bone allograft is often used in revision joint replacement. Hydroxyapatite granules have been suggested as a substitute or to enhance morcellised bone allograft. We hypothesised that adding osteogenic protein-1 to a composite of bone allograft and non-resorbable hydroxyapatite granules (ProOsteon) would improve the incorporation of bone and implant fixation. We also compared the response to using ProOsteon alone against bone allograft used in isolation. We implanted two non-weight-bearing hydroxyapatite-coated implants into each proximal humerus of six dogs, with each implant surrounded by a concentric 3 mm gap. These gaps were randomly allocated to four different procedures in each dog: 1) bone allograft used on its own; 2) ProOsteon used on its own; 3) allograft and ProOsteon used together; or 4) allograft and ProOsteon with the addition of osteogenic protein-1. After three weeks osteogenic protein-1 increased bone formation and the energy absorption of implants grafted with allograft and ProOsteon. A composite of allograft, ProOsteon and osteogenic protein-1 was comparable, but not superior to, allograft used on its own. ProOsteon alone cannot be recommended as a substitute for allograft around non-cemented implants, but should be used to extend the volume of the graft, preferably with the addition of a growth factor.

Systemic alendronate treatment improves fixation of press-fit implants: a canine study using nonloaded implants

Bone resorption associated with local trauma occurring during insertion of joint prostheses is recognized as an early event. Being an osteoclastic inhibitor, alendronate is a potential candidate means to decrease early periprosthetic bone resorption and thereby improve implant fixation. We investigated the influence of oral alendronate treatment on early implant fixation in two implant interface settings representing sites of an implant that are in contact with surrounding bone, and other sites without intimate bone contact. One plasma-sprayed cylindrical titanium implant (6 mm diameter) was inserted into each proximal tibia of 16 dogs. On one side the implant was inserted press-fit whereas on the contralateral side, the implants were surrounded by a 2 mm concentric gap. Oral alendronate (0.5 mg/kg/day) was given 2 weeks following surgery to eight dogs. The dogs were euthanized after 10 weeks of alendronate treatment. Bone ongrowth (bone in contact with implant surface) was estimated using the linear intercept technique and shear strength was calculated as the slope on a load-displacement curve. For the press fit implants, alendronate treatment significantly increased bone ongrowth from 24% to 29% and significantly increased ultimate shear strength from 1.26 to 3.72 MPa. Also, the fraction of periprosthetic bone significantly increased from 10% to 18%. For implants surrounded by a gap, alendronate neither stimulated nor impaired implant fixation, bone ingrowth, or new bone formation in the gaps. Because early implant stability is an important predictor of longevity, systemic alendronate treatment could be an important clinical tool to positively influence the early stages of implant incorporation.

Local alendronate increases fixation of implants inserted with bone compaction: 12-week canine study

Bone compaction has been shown to increase initial implant fixation. Furthermore, bone compaction creates a peri-implant zone of autograft that exerts osteoconductive properties. We have previously shown that locally applied bisphosphonate (alendronate) at 4-week observation can preserve the autograft generated by bone compaction. We now investigate whether the increased amount of autograft, seen at 4 weeks, can increase implant osseointegration and biomechanical fixation. Porous-coated titanium implants were bilaterally inserted with bone compaction into the proximal part of tibia of 10 dogs. On the right side, local bisphosphonate was injected into the bone cavity prior to bone compaction immediately prior to implant insertion. On the left side, saline was used as control. Observation period was 12 weeks. Locally applied bisphosphonate significantly increased biomechanical implant fixation (approximately twofold), bone-to-implant contact (1.2-fold), and peri-implant bone volume fraction (2.3-fold). This study indicates that local alendronate treatment can increase early implant osseointegration and biomechanical fixation of implants inserted by use of bone compaction. Long term effects remain unknown.

Locally delivered TGF-beta1 and IGF-1 enhance the fixation of titanium implants: a study in dogs

BACKGROUND

Osteogenic growth factors have been suggested to enhance the fixation of implants used in joint replacement. We examined the effect of locally delivered transforming growth factor-beta1 and insulin-like growth factor-1 in a biodegradable poly (D, L-lactide) coating.

MATERIAL AND METHODS

In a paired study using 9 dogs, unloaded titanium implants surrounded by a 1-mm gap were inserted into the proximal humerus. The growth factors were incorporated in a poly (D, L-lactide) coating at a 1% (w/w) ratio of TGF-beta1 and a 5% (w/w) ratio of IGF-1. Control implants were uncoated. After 4 weeks, the implants were evaluated by mechanical push-out test and by histomorphometry.

RESULTS

A twofold increase was seen in mechanical fixation (strength, stiffness, energy absorption) for the growth factor-treated implants (p = 0.04). Similar results were seen in histomorphometry, as bone ongrowth was 2.5 times higher (p = 0.02), and gap healing was 30-110% higher (p = 0.04) for the growth factor-treated implants than for the control implants. Ongrowth of fibrous tissue was eliminated by the treatment.

INTERPRETATION

TGF-beta-1 and IGF-1, locally delivered in a biodegradable poly(D,L-lactide) coating, enhance the mechanical fixation and osseointegration of titanium implants in cancellous bone, and no fibrous tissue is produced in the growth factor treated implants.

The bovine bone protein lyophilisate Colloss improves fixation of allografted implants--an experimental study in dogs

BACKGROUND

Impacted morselized bone allograft is a well-established way of giving joint arthroplasties additional support in situations where there is insufficient bone stock. For long-term survival of the implant, early implant fixation is important. We hypothesized that Col-loss, a bone protein lyophilisate, might improve early implant fixation of allografted implants.

METHOD

We inserted 4 porous-coated Ti implants in the distal femurs of 16 dogs. All implants were surrounded by a 2.5-mm gap, which was impacted with morselized allograft with or without Colloss. In each dog, the implants were treated with no Collos or low-, middle- or high-dose (0, 10, 20 and 40 mg) Colloss per cm3 allograft. The observation time was 4 weeks.

RESULTS

Mechanical implant fixation was improved for all 3 groups with Colloss-treated implants (p < 0.05). The best anchorage was seen in the middle-dose group, where fixation was improved by 100%. We saw a dramatic reduction in fibrous tissue on the surface of the Colloss-treated implants (p < 0.001). The Colloss groups showed increased ongrowth of new bone (p < 0.01) and accelerated gap remodeling (p < 0.05).

INTERPRETATION

Colloss can improve early osseointegration and fixation of allografted implants.

Effect of topical alendronate treatment on fixation of implants inserted with bone compaction

Bone compaction has been shown to enhance the critical initial implant stability that is important for secure long-term fixation. We investigated whether topical bisphosphonate treatment improves fixation of implants inserted with bone compaction. Porous-coated titanium implants were inserted with bone compaction into the knees of eight dogs. In the right knee, topical bisphosphonate treatment was applied before bone compaction. Saline was used as a control in the left knee. The knees were observed for 4 weeks. We found an increase in total bone-to-implant contact and total bone density around the implants in the bisphosphonate-treated group. These were results of increased nonvital bone-to-implant contact and increased nonvital periimplant bone density. No change in biomechanical fixation was found. Studies with a longer followup are needed to investigate whether the preservative effect of alendronate on nonvital bone might enhance implant fixation by osteoconduction.

Bone compaction enhances fixation of weight-bearing hydroxyapatite-coated implants

The effect of bone compaction vs conventional drilling on the fixation of hydroxyapatite-coated implants was examined in a weight-bearing canine model. In each dog, one knee joint had the implant cavity prepared with drilling, the other with compaction. Eight dogs were euthanized after 2 weeks and 8 dogs after 4 weeks. Femoral condyles from additional 7 dogs represented time 0. Compacted specimens had significantly higher bone implant contact and energy absorption at time 0. Compaction significantly increased ultimate shear strength at 0 and 2 weeks. There was no significant difference in implant fixation after 4 weeks. The results of this study suggest that compaction may be beneficial in optimizing the crucial initial implant stability, even when hydroxyapatite-coated implants with osteoconductive properties are inserted in vivo.

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.

Particle migration and gap healing around trabecular metal implants

Bone on-growth and peri-implant migration of polyethylene particles were studied in an experimental setting using trabecular metal and solid metal implants. Cylindrical implants of trabecular tantalum metal and solid titanium alloy implants with a glass bead blasted surface were inserted either in an exact surgical fit or with a peri-implant gap into a canine knee joint. We used a randomised paired design. Polyethylene particles were injected into the knee joint. In both types of surgical fit we found that the trabecular metal implants had superior bone ongrowth in comparison with solid metal implants (exact fit: 23% vs. 7% [p=0.02], peri-implant gap: 13% vs. 0% [p=0.02]. The number of peri-implant polyethylene particles was significantly reduced around the trabecular metal implants with a peri-implant gap compared with solid implants.

The influence of surface porosity on gap-healing around intra-articular implants in the presence of migrating particles

The aim of the present study was to compare the effect of two different porous coatings on bone ongrowth and on the peri-implant migration of polyethylene (PE) particles. Porous-coated cylindrical implants with an either plasma-sprayed closed-pore coating (Pl) or titanium fiber metal open-pore coating (Fi) were inserted intra-articular in exact fit or with a 0.75 mm peri-implant gap. A weight-loaded implant device in the distal femur was used. We used a randomized paired design in eight dogs. PE particles were injected repeatedly intra-articular in the knee until the dogs were killed after 8 weeks. Fi implants had significantly more bone ongrowth 8 (0-21)% compared with Pl implants 0 (0-0)% in gap situations and reduced the number of peri-implant PE particles significantly. Among exact-fitted implants we found that peri-implant tissue around Pl implants consisted of significantly more fibrous tissue than around Fi implants. A sealing effect against the migration of PE particles was found for both Fi and Pl implants in exact fit.

Bone compaction enhances implant fixation in a canine gap model

A new bone preparation technique, compaction, has increased fixation of implants inserted with exact-fit or press-fit to bone. Furthermore, a demonstrated spring-back effect of compacted bone might be of potential value in reducing the initial gaps that often exist between clinical inserted implants and bone. However, it is unknown whether the compression and breakage of trabeculae during the compaction procedure results in impaired gap-healing of compacted bone. Therefore, we compared compaction with conventional drilling in a canine gap model. Grit-blasted titanium implants (diameter 6 mm) were bilaterally inserted into cavities initially expanded to 8 mm diameters in the proximal humeri. Each dog served as its own control; thus, one humerus had the implant cavity prepared with compaction, the other with drilling. Eight dogs were euthanized after 2 weeks, and 7 dogs after 4 weeks. Humeri from additional 7 dogs represented time 0. At time 0 a spring-back effect of compacted bone was demonstrated as cavities, initially expanded to 8 mm by compaction, were reduced to a median cavity diameter of 6.6 mm. In contrast, cavities initially expanded to 8 mm by drilling, had a median cavity diameter of 8.0 mm at time 0. Compaction significantly increased all push-out parameters at 2 weeks. Compaction significantly increased peri-implant bone density at 0 and 2 weeks, and bone implant contact at 2 and 4 weeks. The faster mechanical and histological fixation with compaction indicates that the beneficial effect of reduced gap size, as compacted bone springs back, is not eliminated by an impaired gap-healing of compacted bone.

In vivo study of the effect of RGD treatment on bone ongrowth on press-fit titanium alloy implants

Early bone ongrowth is known to increase primary implant fixation and reduce the risk of early implant failure. Arg-Gly-Asp (RGD) peptide has been identified as playing a key role in osteoblast adhesion and proliferation on various surfaces. The aim for this study is to evaluate the effect of RGD peptide coating on the bony fixation of orthopaedic implants, to justify its further evaluation in clinical applications. Sixteen unloaded cylindrical plasma sprayed Ti6Al4V implants coated with cyclic RGD peptide were inserted as press-fit in the proximal tibia of 8 mongrel dogs for 4 weeks. Uncoated control implants were inserted in the contralateral tibia. Results were evaluated by histomorphometry and mechanical push-out test. A significant two-fold increase was observed in bone ongrowth for RGD-coated implants. Also, fibrous tissue ongrowth was significantly reduced for RGD-coated implants. Bone volume was significantly increased in a 0-100 microm zone around the implant. The increased bony anchorage resulted in moderate increases in mechanical fixation as apparent shear stiffness was significantly higher for RGD-coated implants. Increases in median ultimate shear strength and energy to failure were also observed. This study demonstrates that cyclic RGD coating increases early bony fixation of unloaded press-fit titanium implants.

Light microscopic identification and semiquantification of polyethylene particles in methylmethacrylate and paraffin-embedded experimental bone implant specimens

The aim of this study was to evaluate the identification of polyethylene (PE) particles in relatively thick methylmethacrylate (MMA) sections widely used in bone implant research. The sensitivity and specificity were compared between decalcified paraffin-embedded oil red O (ORO) stained and MMA-embedded sections using polarized light. Furthermore, we introduced a grading system to semiquantify the level of PE particles in peri-implant tissue. Paraffin-embedded and MMA-embedded sections were compared concerning intra-observer agreement of the grading system. Moreover, the semiquantitative assessment of particle level was compared between the two section types. We found a sensitivity and specificity of polarized light of 100% for both paraffin ORO-stained and MMA sections. The intra-observer agreement on both types was comparable and acceptable. The ratings of differently processed blocks (MMA- and paraffin-embedded) originating from the same bone implant specimen showed good correlation. Our study showed that relatively thick MMA sections were just as suitable as ORO-stained paraffin sections concerning peri-implant PE particle migration analysis. MMA sections do not allow analysis at cellular level, but unbiased estimation of bone ingrowth into the implant surface based on stereological principles is possible.

Bone compaction enhances fixation of weightbearing titanium implants

Implant stability is crucial for implant survival. A new surgical technique, compaction, has increased in vitro implant stability and in vivo fixation of nonweightbearing implants. However, the in vivo effects of compaction on weightbearing implants are unknown. As implants inserted clinically are weightbearing, the effects of compaction on weightbearing implants were examined. The hypothesis was that compaction would increase implant fixation compared with conventional drilling. Porous-coated titanium implants were inserted bilaterally into the weightbearing portion of the femoral condyles of dogs. In each dog, one knee had the implant cavity prepared with drilling, and the other knee was prepared with compaction. Eight dogs were euthanized after 2 weeks, and eight dogs were euthanized after 4 weeks. Femoral condyles from an additional eight dogs represented Time 0. Compacted specimens had higher bone-implant contact and periimplant bone density at 0 and 2 weeks, but not at 4 weeks. A biphasic response of compaction was found with a pushout test, as compaction increased ultimate shear strength and energy absorption at 0 and 4 weeks, but not at 2 weeks. This biphasic response indicates that compaction enhances implant fixation by mechanical and biological mechanisms. Therefore, compaction might have potential value in total joint replacement in the future.

No effect of platelet-rich plasma with frozen or processed bone allograft around noncemented implants

We compared processed morselized bone allograft with fresh-frozen bone graft around noncemented titanium implants. Also, the influence of platelet-rich plasma (PRP) in combination with bone allograft was evaluated. Analysis was based on implant fixation and histomorphometry. PRP was prepared by isolating the buffy coat from autologous blood samples. Bone allograft was used fresh-frozen or processed by defatting, freeze drying, and irradiation. Cylindrical hydroxyapatite-coated titanium implants were inserted bilaterally in the femoral condyles of eight dogs. Each implant was surrounded by a 2.5-mm concentric gap, which was filled randomly according to the four treatment groups--group 1: fresh-frozen bone allograft; group 2: processed bone allograft; group 3: fresh-frozen bone allograft + PRP; group 4: processed bone allograft + PRP. Histological and mechanical evaluation demonstrated no influence of bone allograft processing. Even though the level of platelet in PRP was 7.7 times that found in whole blood, we found no improvement of bone formation or implant fixation by adding PRP.

Bone compaction enhances fixation of hydroxyapatite-coated implants in a canine gap model

Primary cementless joint replacement depends partly on the ability of bone to heal into those areas of an inserted implant where a gap to surrounding bone initially exists. A new bone preparation technique, compaction, has enhanced gap-healing around grit-blasted implants without osteo-conductive properties. However, hydroxyapatite (HA) porous-coated implants with osteo-conductive properties are often inserted clinically to enhance gap healing and implant fixation. It is unknown whether the osteo-conductive properties of HA porous-coated implants might overwhelm the beneficial effects of compaction on gap healing. Therefore, we compared the compaction technique with the conventional bone-removing technique, drilling, using HA porous-coated implants in a canine gap model. HA porous-coated titanium implants were bilaterally inserted into oversized cavities of the proximal humeri of seven dogs. Each dog served as its own control. Thus, one humerus had the implant cavity prepared with compaction, the other with drilling. Two weeks after surgery push-out test and histomorphometry was performed. Compaction significantly increased ultimate shear strength, energy absorption, apparent shear stiffness, bone implant contact, and peri-implant bone density. The results of this study suggest that compaction may enhance gap healing when osteo-conductive HA porous coated implants are inserted in joint replacements.

In vivo effects of RGD-coated titanium implants inserted in two bone-gap models

RGD (Arg-Gly-Asp) coating has been suggested to enhance implant fixation by facilitating the adhesion of osteogenic cells to implant surfaces. Orthopedic implants are unavoidably surrounded partly by gaps, and these regions represent a challenging environment for osseointegration. We examined the effects of cyclic RGD-coated implants on tissue integration and implant fixation in two cancellous bone-gap models. In canines, we inserted loaded RGD-coated implants with 0.75-mm gap (n = 8) and unloaded RGD-coated implants with 1.5-mm gap (n = 8) into the distal femur and proximal tibia, respectively. Control gap implants without RGD were inserted contralaterally. The titanium alloy (Ti-6Al-4V) implants were plasma sprayed and cylindrical. The observation period was 4 weeks and the fixation was evaluated by push-out test and histomorphometry. Mechanical implant fixation was improved for RGD-coated implants. Unloaded RGD-coated implants showed a significant increase in bone whereas both loaded and unloaded implants showed a significant reduction in fibrous tissue anchorage. The results are encouraging, because RGD had an overall positive effect on the fixation of titanium implants in regions where gaps exist with the surrounding bone. RGD peptide coatings can potentially be used to enhance tissue integration in these challenging environments.

No effect of hydroxyapatite particles in phagocytosable sizes on implant fixation: An experimental study in dogs

The influence of wear debris on bone healing around orthopedic implants is debated. Hydroxyapatite (HA) particles and polyethylene (PE) particles have been shown to have a negative effect on osteoblast cultures in vitro. The present study investigated the in vivo effects of HA and PE particles on the mechanical fixation and gap healing around experimental HA implants. Nonloaded implants (n = 30) were inserted bilaterally into the proximal tibia of 15 dogs with a 2-mm gap to the bone. The peri-implant gap was either (1) empty (n = 6) or filled with (2) hyaluronic acid (n = 8), (3) hyaluronic acid and HA particles (n = 8), or (4) hyaluronic acid and PE particles (n = 8). After 4 weeks, the animals were killed. The implant interface was evaluated by pushout testing until failure and by histomorphometry. Both HA and PE particles were found to be phagocytosed by macrophage-like cells in the interfacial tissue. HA particles were also integrated in newly formed bone. We found no negative effect of the particulate material on mechanical fixation of the implants or on bone formation around the implants.

Platelet rich plasma and fresh frozen bone allograft as enhancement of implant fixation. An experimental study in dogs

Platelet rich plasma (PRP) is an autologous source of growth factors. By application of PRP around cementless implants alone or in combination with bone allograft chips, early implant fixation and gap healing could be improved. We inserted two porous HA coated titanium implants extraarticularly in each proximal humerus of eight dogs. Each implant was surrounded by a 2.5 mm gap. Four treatments were block randomized to the four gaps in each dog: Treatment 1: empty gap, treatment 2: PRP, treatment 3: fresh frozen bone allograft, treatment 4: fresh frozen bone allograft+PRP. PRP was prepared from each dog prior to operation by isolating the buffycoat from centrifuged blood samples. Platelet count in PRP was increased 670% compared to baseline level. Calcium/thrombin was added to degranulate platelets and form a gel. Three weeks after surgery, push-out test and histomorphometri was performed. After three weeks, the non-allografted implants had poor mechanical properties. Bone grafting significantly increased implant fixation, bone formation in the gap and bone growth on the implant surface. We found no significant effect of PRP alone or mixed with bone allograft on implant fixation or bone formation. In conclusion, we showed the importance of bone allografting on early implant fixation and bone incorporation but we found no effect of PRP. More studies are needed to investigate the effect and possible clinical applications of platelet concentrates which are now being commercialised.

Soft tissue findings above submerged titanium implants--a histological and spectroscopic study

The aim of this study was to check the titanium level within the muco-periosteal flaps covering submerged titanium implants. The investigated material included 38 biopsies taken after 2.4-18 months (mean: 5.9) after implant insertion. Due to the evident time delay between implantation and taking the biopsy any influence of the implantation trauma itself was excluded. The implants came from the following producers: HaTi (Matthys, Switzerland), ITI (Straumann, Switzerland) and Branemark (Nobelbiocare. Sweden). The surface areas of these implants differ in size and structure. A comparison between the titanium impregnation of the investigated biopsies did not demonstrate any remarkable influence of the surface differences. This can be explained by the fact that only the top diameter and not the implant surface as a whole was the contact area with the excised tissue. Titanium in the biopsies was analysed in terms of its effect histologically and regarding the titanium quantity by spectrophotometry. Even the highest titanium contamination was without a negative effect on the muco-periosteal cover flaps. A correlation between time delay between implantation and biopsy or of the titanium amount and tissue reactions was not demonstrable. In summary, the results again highlighted the biological acceptance of titanium.

Osteogenic protein 1 device increases bone formation and bone graft resorption around cementless implants

In each femoral condyle of 8 Labrador dogs, a non weight-bearing hydroxyapatite-coated implant was inserted surrounded by a 3 mm gap. Each gap was filled with bone allograft or ProOsteon with or without OP-1 delivered in a bovine collagen type I carrier (OP-1 device). 300 microg OP-1 was used in the 0.75 cc gap surrounding the implant. After 3 weeks, the OP-1 device enhanced implant fixation by 800% (p <0.05) in the ProOsteon group, but OP-1 bad no significant effect on implant fixation in the allograft group. By adding the OP-1 device, the volume fraction of woven bone close to the implant increased from 12% to 20% (p < 0.05) in the bone allograft group and from 6% to 25% (p < 0.05) in the ProOsteon group. The volume fraction of bone allograft decreased from 29% to 9% (p < 0.05) in the OP-1 treated group versus 33% to 30% in the allograft group not treated with OP-1. No resorption of ProOsteen was found. In conclusion, OP-1 accelerates resorption of bone allograft and enhances new bone formation around cementless implants grafted with bone allograft or semisynthetic hydroxyapatite bone substitute. Our findings do not support the use of ProOsteon alone around cementless implants.

Loading improves anchorage of hydroxyapatite implants more than titanium implants

Roentgen Stereophotogrammetric Analysis (RSA) studies have shown that the quality of the early fixation of implants has a dominant effect on their long-term function. To evaluate methods to improve their fixation, we examined the influence of mechanical loading and surface coating on the quality of the bone-implant interface. We compared the fixation of a cylindrical, stable 6.0 mm implant initially surrounded by a 0.75 mm concentric gap, after 4 weeks of loaded or unloaded conditions. Two types of surfaces were analyzed: plasma sprayed hydroxyapatite (HA) and plasma sprayed titanium (Ti). The histomorphometric evaluation showed that HA implants had greater bone coverage than Ti implants, and this coverage was further increased under loaded conditions only for HA. Furthermore, loading reduced the fibrous tissue coverage for the HA implants, while it increased fibrous tissue coverage for Ti implants. These findings were in agreement with pushout results showing that HA implants had greater shear strength, stiffness, and energy than Ti implants, and (except for energy) these parameters were further increased under loaded conditions only for HA. In addition, because the two implant surfaces exhibited a different relative response to load, it is important to evaluate new surfaces under the more clinically relevant loaded condition.

Resorption of hydroxyapatite and fluorapatite ceramic coatings on weight-bearing implants: a quantitative and morphological study in dogs

Resorption (defined as loss of ceramic coating because of cellular activity or dissolution) of ceramic coatings is a matter of concern for the long-term performance of ceramic-coated implants. A new fluorine-containing coating, fluorapatite (FA), has been shown to be more stable than hydroxyapatite (HA) in unloaded models. In a weight-bearing model in trabecular bone, we evaluated loss (defined as reduction of coating irrespective of type of mechanism) of HA and FA coatings during 25 weeks of implantation. Eight mature dogs had HA- or FA-coated implants inserted bilaterally into the weight-bearing region of the medial femoral condyle. Quantified loss of ceramic coating was estimated at the light microscopic level using stereological methods. The experiment showed significant loss of both types of coatings. However, no statistical difference in loss of ceramic coating was found regarding surface area implant coverage, volume, and thickness (p = 0.77, p = 0.13, p = 0.56, p = 0.23, respectively). Completely resorbed HA coating was replaced by 36 +/- 6.0% (range: 26-42) bone in direct contact with the implant surface compared with 29 +/- 16.0% (range: 12-59) for FA (p = 0.40), suggesting that the implant was firmly fixed despite loss of the ceramic coating. Transmission electron microscopy in combination with electron energy spectroscopy and electron spectroscopic imaging showed that osteclast-like cells, osteocytes, macrophage-like cells, and fibroblasts had phagocytosed calcium-containing fragments, indicating cell-mediated resorption of the ceramic coating.

Improved fixation of porous-coated versus grit-blasted surface texture of hydroxyapatite-coated implants in dogs

We inserted, in 8 dogs, implants with either porous-coated or grit-blasted titanium surface and coated with hydroxyapatite (HA) into trabecular bone in the proximal humerus, using a 1 mm gap model. After 25 weeks, push-out tests showed that energy absorption for porous-coated implants was twice that of grit-blasted implants, whereas shear stiffness was reduced by one fifth, indicating a stronger fixation of porous-coated implants. Macroscopically, all grit-blasted implants had delamination of the HA coating, whereas porous implants failed mostly at the HA-tissue interface. Porous-coated implants had 47% bone ingrowth and grit-blasted implants 70% (p = 0.02), however, no difference in absolute surface area was found. Part of the HA coating was resorbed during the implantation period as regards volume and thickness. HA coverage was more reduced on porous-coated than on grit-blasted implants (p = 0.01). No foreign-body reaction or osteolysis was seen. An important finding was that one fifth of the surface with complete resorption of HA coating was replaced by newly formed bone.