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

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.

A collagen membrane containing osteogenic protein-1 facilitates bone regeneration in a rat mandibular bone defect

OBJECTIVES

Osteogenic protein-1 (OP-1) has shown osteoinductive activities and is useful for clinical treatments, including bone regeneration. Regenerative procedures using a bioabsorbable collagen membrane (BCM) are well established in periodontal and implant dentistry. We evaluated the subsequent effects of the BCM in combination with OP-1 on bone regeneration in a rat mandibular circular critical-sized bone defect in vivo.

DESIGN

We used 8 rats that received surgery in both sides of the mandible, and created the total 16 defects which were divided into 4 groups: Group 1; no treatment, as a control, Group 2; BCM alone, Group 3; BCM containing low dose 0.5μg of OP-1 (L-OP-1), and Group 4; BCM containing high dose 2.0μg of OP-1 (H-OP-1). Newly formed bone was evaluated by micro computed tomography (micro-CT) and histological analyses at 8 weeks postoperatively. In quantitative and qualitative micro-CT analyses of the volume of new bone formation, bone density, and percentage of new bone area was evaluated.

RESULTS

BCM with rhOP-1 significantly increased and accelerated bone volume, bone mineral density, and percentage of new bone area compared to control and BCM alone at 8 weeks after surgery; these enhancements in bone regeneration in the OP-1-treated groups were dose-dependent.

CONCLUSIONS

OP-1 delivered with a BCM may have effective osteoinductive potency and be a good combination for bone regeneration. The use of such a combination device for osteogenesis may result in safer and more predictable bone regenerative outcomes in the future.

Sclerostin antibody treatment improves implant fixation in a model of severe osteoporosis

BACKGROUND

The mechanical fixation of orthopaedic and dental implants is compromised by diminished bone volume, such as with osteoporosis. Systemic administration of sclerostin antibody (Scl-Ab) has been shown to enhance implant fixation in normal animals. In the present study, we tested whether Scl-Ab can improve implant fixation in established osteoporosis in a rat model.

METHODS

We used an ovariectomized (ovx) rat model, in which we found a 78% decrease in trabecular bone volume at the time of implant surgery; sham-ovx, age-matched rats were used as controls. After placement of a titanium implant in the medullary cavity of the distal aspect of the femur, the rats were maintained for four, eight, or twelve weeks and treated biweekly with Scl-Ab or with the delivery vehicle alone. Outcomes were measured with use of microcomputed tomography, mechanical testing, and static and dynamic histomorphometry.

RESULTS

Scl-Ab treatment doubled implant fixation strength in both the sham-ovx and ovx groups, although the enhancement was delayed in the ovx group. Scl-Ab treatment also enhanced bone-implant contact; increased peri-implant trabecular thickness and volume; and increased cortical thickness. These structural changes were associated with an approximately five to sevenfold increase in the bone-formation rate and a >50% depression in the eroded surface following Scl-Ab treatment. Trabecular bone thickness and bone-implant contact accounted for two-thirds of the variance in fixation strength.

CONCLUSIONS

In this model of severe osteoporosis, Scl-Ab treatment enhanced implant fixation by stimulating bone formation and suppressing bone resorption, leading to enhanced bone-implant contact and improved trabecular bone volume and architecture.

CLINICAL RELEVANCE

Systemic administration of anti-sclerostin antibodies might be a useful strategy in total joint replacement when bone mass is deficient.

Systematic review of pre-clinical models assessing implant integration in locally compromised sites and/or systemically compromised animals

OBJECTIVE

The aim was to systematically search the dental literature for pre-clinical models assessing implant integration in locally compromised sites (part 1) and systemically compromised animals (part 2), and to evaluate the quality of reporting of included publications.

METHODS

A Medline search (1966-2011) was performed, complimented by additional hand searching. The quality of reporting of the included publications was evaluated using the 20 items of the ARRIVE (Animals in Research In Vivo Experiments) guidelines.

RESULTS

One-hundred and seventy-six (part 1; mean ARRIVE score = 15.6 ± 2.4) and 104 (part 2; 16.2 ± 1.9) studies met the inclusion criteria. The overall mean score for all included studies amounted to 15.8 ± 2.2. Housing (38.3%), allocation of animals (37.9%), numbers analysed (50%) and adverse events (51.4%) of the ARRIVE guidelines were the least reported. Statistically significant differences in mean ARRIVE scores were found depending on the publication date (p < 0.05), with the highest score of 16.7 ± 1.6 for studies published within the last 2 years.

CONCLUSIONS

A large number of studies met the inclusion criteria. The ARRIVE scores revealed heterogeneity and missing information for selected items in more than 50% of the publications. The quality of reporting shifted towards better-reported pre-clinical trials within recent years.

The effect of adding an equine bone matrix protein lyophilisate on fixation and osseointegration of HA-coated Ti implants

Joint replacements should be firmly anchored in vital bone to avoid early implant subsidence and late aseptic loosening. We investigated whether the fixation of orthopedic implants could be improved by adding an osteoinductive extract of lyophilized equine bone matrix proteins (Colloss E, Ossacur AG, Germany), between the implant and the surrounding bone. Eighteen uncemented HA-coated implants were inserted pairwise in the proximal tibia of nine dogs. All implants were surrounded by a 2 mm concentric defect. In each dog, the intervention implant was added 20 mg protein lyophilisate. The contralateral control implant was inserted untreated. After four weeks, the treated HA-coated implants had better mechanical fixation than the untreated control implants. The treated implants were better osseointegrated, there was more newly formed bone around these implants, and fibrous tissue was eliminated. The mechanical implant fixation had a strong positive correlation to new bone formation on and around the implant, and a strong negative correlation to fibrous tissue encapsulation. The results suggest that bone protein extracts such as the Colloss E device may augment early implant fixation of even HA-coated Ti implants and thereby reduce the risk of long-term failure. This may be particularly useful in revision arthroplasty with bone loss.

Osteogenic protein-1 delivered by hydroxyapatite-coated implants improves bone ingrowth in extracortical bone bridging

BACKGROUND

Extracortical bone bridging for treatment of massive bone loss can improve stability and longevity of massive endoprostheses. Osteogenic protein-1 (OP-1), when used with allograft bone, reportedly improves extracortical bone bridging and bone ingrowth.

QUESTIONS/PURPOSES

We asked whether OP-1 delivered by hydroxyapatite (HA) without bone grafting could improve bone ingrowth and bone formation in the context of extracortical bone bridging.

METHODS

We implanted unilateral segmental femoral diaphyseal replacement prostheses in 18 dogs (three groups of six dogs). The groups consisted of an HA-coated group augmented with OP-1, an HA-coated group, and a plain porous group. Bone grafting techniques were not used to augment bone formation. The implants were retrieved at 12 weeks for histologic assessment.

RESULTS

After removing one specimen owing to a complication, 17 femora were analyzed (six HA-coated augmented with OP-1, five HA-coated, and six plain). We observed better bone ingrowth in the HA-coated OP-1 group than in the plain porous and HA-coated groups, with no difference between the latter two groups. There also was better bone apposition and callus height in the HA-coated OP-1 group than in the plain group but no differences between the HA-coated OP-1 and HA-coated groups or between the HA-coated and plain groups.

CONCLUSIONS

OP-1 (2.9 mg) delivered by HA-coated segmental replacement prostheses in this canine extracortical bone bridging model revealed improved bone ingrowth over HA-coated implants without OP-1 or plain porous-coated prostheses.

Osseointegration by bone morphogenetic protein-2 and transforming growth factor beta2 coated titanium implants in femora of New Zealand white rabbits

BACKGROUND

Intramembranous bone formation is essential in uncemented joint replacement to provide a mechanical anchorage of the implant. Since the discovery of bone morphogenic proteins (BMPs) by Urist in 1965, many studies have been conducted to show the influence of growth factors on implant ingrowth. In this study, the influence of bone morphogenetic protein-2 (rhBMP-2) and transforming growth factor β2 (TGF-β2) on implant osseointegration was investigated.

MATERIALS AND METHODS

Thirty-two titanium cylinders were implanted into the femoral condyles of both hind legs of New Zealand White Rabbits. Four experimental groups were investigated: controls without coating, a macromolecular copolymer + covalently bound BMP-2, adsorbed BMP-2, and absorbed BMP-2+TGF-β2. All samples were analyzed by ex vivo high-resolution micro-computed-tomography after 28 days of healing. Bone volume per total volume (BV/TV) was recorded around each implant. Afterward, all samples were biomechanically tested in a pull-out setup.

RESULTS

The highest BV/TV ratio was seen in the BMP-2 group, followed by the BMP-2+TGF-β2 group in high-resolution micro-computed-tomography. These groups were significantly different compared to the control group (P < 0.05). Copolymer+BMP-2 showed no significant difference in comparison to controls. In the pull-out setup, all groups showed higher fixation strength compared to the control group; these differences were not significant.

CONCLUSIONS

No differences between BMP-2 alone and a combination of BMP-2+TGF-β2 could be seen in the present study. However, the results of this study confirm the results of other studies that a coating with growth factors is able to enhance bone implant ingrowth. This may be of importance in defect situations during revision surgery to support the implant ingrowth and implant anchorage.

BMP-7-induced ectopic bone formation and fracture healing is impaired by systemic NSAID application in C57BL/6-mice

Nonsteroidal antiinflammatory drugs (NSAIDs) are known to potentially impair the fracture healing process. The aim of the present study was to determine if the impairment of bone healing by systemic NSAID application is, at least in part, due to an interaction of NSAIDs with the bone anabolic BMP-7 pathway. Therefore, we first analyzed fracture healing in control and diclofenac-treated mice, where we not only found a significant impairment of fracture healing due to diclofenac treatment as assessed by biomechanical testing and microCT imaging, but also found high coexpression of bone morphogenetic protein-7 (BMP-7) and cyclooxygenase-2 (COX-2) within the fracture callus of both groups. To experimentally address the possible interaction between BMP-7 and COX-2, we then induced ectopic bone formation in control (n = 10) and diclofenac-treated mice (n = 10) by application of BMP-7 (recombinant human OP-1, rhOP-1) into the hamstring muscles. After 20 days of treatment, each ectopic bone nodule was analyzed by contact-radiography, microCT, histology, and histomorphometry. Diclofenac application decreased the trabecular number and bone mass in the ectopic bone nodules significantly due to reduced osteoblast number and activity. These data demonstrate that the bone anabolic effect of BMP-7 and fracture healing is impaired by diclofenac application, and suggest that the potential negative impact of NSAIDs on fracture healing is, at least in part, due to interference with BMP-7 signaling.

Reconstruction of peri-implant bone defects using impacted bone allograft and BMP-2 gene-modified bone marrow stromal cells

Impaction bone allografting represents an attractive procedure for bone defects reconstruction in joint replacement. And it was found that bone morphogenetic protein-2(BMP-2) gene therapy can enhance bone healing. The purpose of this study was to determine if combined adenovirus mediated human BMP-2(Adv-hBMP-2) gene-modified bone marrow stromal cells(BMSCs) with allograft enhanced the defects healing and improved the strength of implant fixation in 3-mm bone defect around a titanium alloy implant. Using the impaction grafting technique, the defects were reconstructed using freeze-dried allograft, freeze-dried allografts loaded with autogenous BMSCs, or freeze-dried allografts loaded with autogenous BMSCs modified with the human bone morphogenetic protein-2 (hBMP-2) gene. At 6 and 12 weeks, the Bone-implant Contact rate and strength of the interface in the group with BMP-2 gene medication were significantly higher than those of the non-cell or cell groups. BMP-2 gene medication also showed significant effects on allograft healing and replacement compared with those of two other groups, as evidenced by increased new bone formation and reduced graft remnants. The results suggest that BMP-2 gene medication can enhance allograft healing and osseointegration of the bone-implant interface.

The synergistic effects of lysophosphatidic acid receptor agonists and calcitriol on MG63 osteoblast maturation at titanium and hydroxyapatite surfaces

Successful osseointegration stems from the provision of a mechanically competent mineralised matrix at the implant site. Mature osteoblasts are the cells responsible for achieving this and a key factor for ensuring healthy bone tissue is associated with prosthetic materials will be 1 alpha,25 dihydroxy vitamin D3 (calcitriol). However it is known that calcitriol per se does not promote osteoblast maturation, rather the osteoblasts need to be in receipt of calcitriol in combination with selected growth factors in order to undergo a robust maturation response. Herein we report how agonists of the lysophosphatidic acid (LPA) receptor, LPA and (2S)-OMPT, synergistically co-operate with calcitriol to secure osteoblast maturation for cells grown upon two widely used bone biomaterials, titanium and hydroxyapatite. Efforts could now be focussed on functionalizing these materials with LPA receptor agonists to support in vivo calcitriol-induced osseointegration via heightened osteoblast maturation responses.

Bone morphogenetic proteins in total hip arthroplasty, osteonecrosis and trauma surgery

This review provides an overview of the use of bone morphogenetic proteins to enhance bone healing and bone graft incorporation in difficult defects created from failed total hip arthroplasties, osteonecrosis of the femoral head and trauma. Multiple publications have demonstrated that bone morphogenetic proteins are osteoinductive in preclinical trials (i.e., animal models); however, there is controversy and limited understanding of the use of this technology in orthopedic surgical practice. The question remains as to whether they are useful in difficult fractures, nonunions and large defects created from failed total hip arthroplasty or femoral head osteonecrosis. There might be a small risk for infection by the process of introducing foreign materials in a clinical situation, but this has not yet been realized to date. In addition, these materials offer an advantage in large defects where there is not enough transplantable material available from the host. We believe that the use of these materials will become more widespread with newer carriers, minimally invasive applications and diminished commercial costs.

Bone morphogenetic protein as an adjuvant in the treatment of Kienbock's disease by vascular pedicle implantation

This case report documents the first use of bone morphogenetic protein (BMP) as an adjuvant to revascularisation with a first dorsal metacarpal arterio-venous pedicle in the treatment of a patient with Stage III Kienbock's disease. The patient had complete relief of her symptoms of wrist pain by 8 months postoperatively, when X-rays showed no further evidence of lunate collapse and an MRI scan demonstrated islands of revascularisation. It is impossible to prove unequivocably that BMP contributed to the result seen in this one patient, but this adjuvant concept is based on experimental evidence demonstrating that optimal bioengineering of vascularised bone is dependent on four factors - a structural matrix, progenitor cells, BMP and a vascular supply, and BMP may play a future role in promoting new bone formation in Kienbock's disease.

Chemical interaction of polyphosphoric acid with titanium and its effect on human bone marrow derived mesenchymal stem cell behavior

The aim of this study was to evaluate the effect of treating titanium (Ti) with polyphosphoric acid on the attachment and proliferation of human bone marrow derived mesenchymal stem cells (hBMSCs). Cleaned Ti disks were immersed into three different concentrations of polyphosphoric acid solution (0.1, 1, and 10 wt %) and 10 wt % orthophosphoric acid solution for 24 h at 37 degrees C. Ti immersed in distilled water for 24 h at 37 degrees C served as control. The level of polyphosphoric acid that interacted with the Ti surface was determined by measuring the surface P/Ti ratio (atom%/atom%) using X-ray photoelectron spectroscopy. Degrees of cell attachment (1, 3, 5 h after cell seed) and proliferation (1, 3, 5, and 7 days after cell seed) on each treated Ti disk were evaluated by MTS assay. The mean surface P/Ti ratios increased in a polyphosphoric acid concentration dependent manner. A significantly higher cell attachment was found on Ti treated with polyphosphoric acid in contrast to untreated Ti (control) for all three culture periods. MTS assay also revealed that cell proliferation levels significantly increased following a polyphosphoric acid dose dependency. Ti surface treatment with orthophosphoric acid did not influence the cell attachment and proliferation. It was concluded that polyphosphoric acid treatment of Ti enhanced the attachment and proliferation of hBMSCs.

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.

Effects of local infusion of OP-1 on particle-induced and NSAID-induced inhibition of bone ingrowth in vivo

Excessive polyethylene wear particles from joint replacements may lead to periprosthetic osteolysis and loosening. Nonsteroidal anti-inflammatory drugs (NSAIDs) decrease fracture healing and bone ingrowth. We hypothesized that continuous local infusion of OP-1 (BMP-7) would increase local bone formation in the presence of two different adverse stimuli, polyethylene particles, and an oral NSAID. The Drug Test Chamber (DTC) was implanted in the proximal tibia of mature rabbits. The tissue growing into the chamber was exposed to OP-1 solution (110 ng/day), which was infused via an osmotic pump. Infusion of OP-1 alone for 6 weeks enhanced local bone formation in the chamber by 80% (p < 0.05) over infusion of carrier alone. In the presence of polyethylene particles, infusion of OP-1 increased local bone formation by 38% (p < 0.05) over treatment with particles and carrier. Oral administration of NSAID reduced local bone formation by 58% (p < 0.05); this suppressive effect caused by NSAIDS was completely reversed by the infusion of OP-1 (p < 0.05). These findings underline a potential role for local treatment with OP-1 to increase bone formation in the presence of potentially adverse stimuli such as polyethylene wear particles or NSAID use.

No effect of bone morphogenetic protein-7 (OP-1) on the incorporation of impacted bone grafts in a realistic acetabular model

Bone morphogenetic proteins (BMPs) accelerate bone repair in experimental and clinical conditions. Impacted Morsellized Cancellous Bone grafts (MCB) are successfully used to reconstruct bone defects after failed hip implants. The main question in this study was if BMP-7 (OP-1) mixed with MCB could accelerate the incorporation of MCB and prevents the formation of a soft tissue interface after remodeling of the MCB. A large loaded defect in the acetabulum of goats was reconstructed with a wire mesh and with MCB or MCB mixed with OP-1. After 6 weeks, no differences were found in the revascularization process, in the number of osteoclasts resorbing the MCB, and in the thickness and appearance of the fibrous interface between MCB with or without OP-1. After 6 weeks, enchondral bone had formed in the bone graft layer and on the periosteal anterior and superior rim in the OP-1 group only. More periosteal bone and more bone in the holes of the mesh had been formed in most OP-1 goats. Most MCB was replaced by new lamellar bone after 15 weeks in both groups. We speculate that during or directly after impaction most of the OP-1 is released from the carrier inducing an early effect outside the reconstructive layer at the periosteal side of the acetabulum. Probably most OP-1 has left the reconstruction by the time new vessels and progenitors reached the bone graft. These results do not support the use of OP-1 in impaction bone grafting in patients.

High doses of OP-1 inhibit fibrous tissue ingrowth in impaction grafting

A major concern in using growth factors in impaction grafting is the potential stimulation of the osteoclastic lineage. A solution would be using an osteoconductive material resistant to resorption and providing initial stability after reconstruction. Growth factors may promote bone formation in combination with such graft materials. We determined whether OP-1 would promote the incorporation of impacted morselized allografts and tricalcium phosphate/hydroxyapatite (TCP/HA) into host bone, whether bone formation would be preceded by an initial process of accelerated resorption, and whether the response to OP-1 remodeling/incorporation would be dose-related. We performed two bone chamber studies in goats to ascertain the early effects of OP-1 dose on resorption and incorporation of impacted morselized allografts and TCP/HA. After 4 weeks, the incorporation process of impacted morselized allografts and TCP/HA was not promoted by OP-1. We observed no signs of accelerated resorption preceding bone formation. An increase in OP-1 dose resulted in an inhibition of fibrous tissue formation but OP-1 did not promote bone formation. Early failures in impaction grafting, using mixes with OP-1, might be explained by the lack of fibrous tissue ingrowth and not by increased resorption and remodeling.

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.

Regenerative potential of platelet-rich plasma added to xenogenic bone grafts in peri-implant defects: a histomorphometric analysis in dogs

BACKGROUND

The purpose of this investigation was to evaluate the regenerative influence of platelet-rich plasma (PRP) added to xenogenic bone grafts on bone histomorphometric parameters in a dog model.

METHODS

Ninety endosseous dental implants were inserted in the mandibles of nine hound dogs. Mesial and distal 3-wall peri-implant defects were surgically created adjacent to the implants. Defects were randomly assigned to three groups: demineralized freeze dried bone with platelet-rich plasma (DFDB + PRP), DFDB alone, and no treatment (NT). Animals were sacrificed at 1, 2, and 3 months according to a previously established randomization schedule, and specimens were subjected to histomorphometric analysis. Percentages of bone area inside the implant threads (BiIT), bone-to-implant contact (BIC), and bone area outside implant threads (BoIT) were recorded. Treatment effects were evaluated using analysis of variance models.

RESULTS

The effect of the three treatments on the outcome measures did not differ significantly by healing time (P > 0.05 for the healing time by treatment interaction). However, the average (standard deviation) percentage of BIC and BoIT was significantly different between the treatment groups. In particular, the average percentage of BIC differed between peri-implant defects treated with DFDB + PRP (33.8% [11.0]) and those treated with DFDB alone (28.5% [10.8]; P = 0.042), as well as those in the NT group (27.9% [11.0]; P = 0.024). Furthermore, the average percentage of BoIT differed significantly between defects treated with DFDB + PRP compared to defects in the NT group (51.6% [12.2] versus 43.3% [10.3]; P = 0.005). There was borderline evidence to suggest that the average percentage of BiIT and BIC was significantly different depending on the length of the healing time (P = 0.054 and P = 0.085, respectively).

CONCLUSION

This study found that the addition of PRP to xenogenic bone grafts demonstrated a low regenerative potential in this animal model.

Healing of a scaphoid nonunion using human bone morphogenetic protein

A chronic nonunion of a proximal pole fracture of the scaphoid was treated by curettage of the nonunion, single K-wire fixation, and implantation of 50 mg of human bone morphogenetic protein followed by 12 weeks of cast immobilization without any conventional corticocancellous bone grafting or rigid screw fixation. Radiographs showed signs of bony healing by 12 weeks and a magnetic resonance imaging scan 6 years after surgery showed no signs of avascular necrosis. The potential future applications of human bone morphogenetic protein in hand surgery are discussed.

Osteogenic protein-1 enhances osseointegration of titanium implants coated with peri-apatite in rabbit femoral defect

This study evaluated the effect of osteogenic protein-1 (OP-1) carried by Peri-Apatite (PA) on bone healing in the gap surrounding implants in a rabbit model. Cylindrical titanium implants (3 x 9 mm) were uniformly coated with PA precipitated from a calcium and phosphate solution. OP-1 solution containing 60 microg OP-1 was directly loaded on the implants immediately before implantation for the experimental group, whereas buffer solution was loaded on the implants for the control. The implant was placed in the distal femur and surrounded by a 1-mm gap. The implants were retrieved and examined 6 weeks after implantation. Mechanical testing (push-out) data showed that OP-1 enhanced implant fixation by 80%. Histomorphometric measurements indicated that bone ingrowth in the initial gap expressed as a percentage of the whole gap was significantly higher in the specimens treated with OP-1 than the control group (25.4% vs. 8.9%, p < 0.05). The percentage of the surface of implants, which was covered by bone, was significantly higher in the OP-1-treated group compared to the control group (65% vs. 25%, p < 0.05). This study suggests that OP-1 can be loaded on orthopedic implants through PA to enhance the osseointegration of orthopedic implant.

No effect of a type I collagen gel coating in uncemented implant fixation

Uncemented joint replacement with a variety of substrate materials, structures, and coatings are commonplace in arthroplasty. Even with specialized surgical preparation of bone, intimate contact between the implant and host bone may not always be achieved. This study evaluated the in vivo effect of fibrillar atelopeptide and PEG crosslinked collagens coatings placed directly into porous sintered bead structures on bone ingrowth using a skeletally mature bicortical, bilateral ovine tibia model. Bone ingrowth into the implants increased with time, although differences were not significant. At 4 weeks woven bone was present within the pores that remodeled with time. Significantly lower levels of ingrowth were observed in the intramedullary region of the implants when compared with the cortical region. Implant metal type did not affect ingrowth in both regions analyzed. Both fibrillar and crosslinked forms of dermal type I collagen did not significantly alter bone ingrowth.

Ectopic bone formation using osteogenic protein-1 carried by a solution precipitated hydroxyapatite

Solution precipitation of calcium and phosphate is a technique to generate hydroxyapatite [Peri-Apatitetrade mark (PA), Stryker Orthopaedics, Mahwah, NJ] on metal substrate. This study was carried out to determine the capacity of PA to adsorb osteogenic protein-1 (OP-1) and the time course of release, and to determine the osteoinductive activity of OP-1. The adsorption and release studies were conducted with (125)I-labeled OP-1- and PA-coated titanium alloy disks. The results indicate that the adsorption of OP-1 on the PA-coated disks is linear with the concentration of OP-1 up to 5 mg/mL. There is an initial release of 75% to 80% of adsorbed OP-1 within the first hour, and 92% of OP-1 is released in 3 days. The osteoinductive activity of OP-1 was determined in the rat intramuscular ectopic bone formation assay. A total of 24 titanium alloy disks were evenly divided into 3 groups with different treatments for implantation, plain disks (group A), disks coated with PA (group B), and disks coated with PA plus 40 microg OP-1 (group C). Osteogenic protein-1, 40 microg in solution, was injected into the muscle pouch in animals of group D (n = 8). The rats were sacrificed 3 weeks postoperatively and the implants were retrieved. Ectopic bone formation was evaluated with radiography and histology. Results demonstrated that OP-1 induced ectopic bone in all the animals of group C and group D. The titanium alloy disks were surrounded by trabecular bone and marrow tissue. None of the animals of group A or group B showed any evidence of osteoinduction. Our findings indicate that PA can deliver OP-1 directly to titanium alloy implants and maintain the osteoinductive activity of OP-1.

Osteogenic protein-1 in knee arthritis and arthroplasty

The use of graft materials to restore bone stock and promote healing and implant stabilization is a crucial part of total knee arthroplasty, especially in revision surgery. Recent research has centered on the use of osteoinductive materials to promote bone formation. Osteogenic proteins are members of a superfamily of proteins called transforming growth factor-beta that, either alone or in combination with other regulatory molecules, induce new bone formation. The cloning and genetic expression of recombinant human osteogenic proteins has led to production of quantities sufficient for their clinical use. Recombinant human osteogenic protein-1 has been combined with bone-derived Type I collagen for delivery to an implant site. Preclinical studies have shown that the osteoinductive capacity of autograft and allograft bone and bone graft substitute materials can be notably improved with the addition of osteogenic protein-1. The use of this protein consistently improved the amount and rate of new bone formation compared with graft alone, resulting in earlier graft incorporation and consolidation. In addition, because osteogenic proteins are chondrogenic, they also may have a role in the treatment of cartilage injury and degeneration. Osteogenic protein-1 has been shown to induce hyalinelike cartilage repair of full thickness osteochondral defects in animal models with no degradation of the tissue with time. Although no detailed clinical studies in knee surgery have been reported with the use of osteogenic protein-1, in anecdotal cases its use alone and with bone graft materials indicate results consistent with those obtained in preclinical studies.

Differential effect of a bone morphogenetic protein-7 (OP-1) on primary and revision loaded, stable implants with allograft

Morselized impacted bone allograft is often used to reconstruct the bone bed in the revision of failed total joint arthroplasties. We hypothesized that addition of the bone morphogenetic protein OP-1 (BMP-7) to bone allograft would improve early implant fixation. We inserted one loaded 6-mm-diameter titanium implant (surrounded by 0.75-mm gap) in each medial condyle of 24 canines. On one side, the implant was inserted in a controlled experimental revision setting resembling the clinical revision situation. A primary implant was inserted on the contralateral side in a previously unoperated site. Three groups were studied: 1) allograft alone, 2) allograft + 0.4 mg OP-1, and 3) allograft + 0.8 mg OP-1. Implant fixation was evaluated at 4 weeks. Grafted implants inserted in the primary setting without OP-1 had better fixation than the grafted revision setting with or without OP-1 (significantly more bone coverage, more mineralized tissue in the gap, and better mechanical interface strength). However, grafted primary implants with OP-1 had impaired fixation compared with grafted primary implants without OP-1 (less bone coverage of the implant and less bone formation in the gap). In contrast, grafted revision implants with OP-1 significantly increased implant fixation compared with grafted revision implants without OP-1 (increased mechanical interface strength and fraction of mineralized tissue in the gap). We found no differences between the two doses in any of the settings. Addition of OP-1 to bone allografted implants may show benefit at sites with impaired bone healing capacities, such as the revision setting.

Electrochemically assisted co-precipitation of protein with calcium phosphate coatings on titanium alloy

A bovine serum albumin protein-containing calcium phosphate coating (BSA/brushite) was prepared by electrochemically assisted co-precipitation onto a hydroxyapatite (HA) coated Ti-6Al-4V surface. Electrochemically assisted co-precipitation of BSA/brushite coatings onto HA resulted in a 70-fold increase in BSA inclusion compared to simple adsorption, and was subsequently released by a slower mechanism (15% loss over 70 h). Thus, this electrochemically assisted co-precipitation technique provides an efficient method of protein incorporation at physiological temperature, with a potential for sustained release of therapeutic agents as may be required for metallic implant fixation.

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.

The efficacy of BMP-2 to induce bone ingrowth in a total hip replacement model

The purpose of this canine total hip arthroplasty (THA) study was fourfold: (1) to quantify the efficacy of rhBMP-2 in a carrier (alphaBSM) versus alphaBSM alone, and versus untreated controls to induce bone formation across a defect between a porous acetabular component and host bone; (2) to quantify whether rhBMP-2/alphaBSM improves bone growth into the porous surface beneath that defect; (3) to quantify the efficacy of rhBMP-2/alphaBSM in inducing bone ingrowth into the porous layer at points of intimate bone-implant contact; and (4) to determine whether rhBMP-2/alphaBSM placed in the lateral uncovered aspect of the porous acetabular component promotes de novo bone formation. Fifteen dogs were sacrificed 12 weeks after uncemented THA. Five dogs received rhBMP-2/alphaBSM, five dogs received alphaBSM, and five dogs were controls. In contrast to the controls in which no bone filled the defect, the rhBMP-2/alphaBSM induced defect filling and full bone formation in the underlying porous coating. The alphaBSM produced an intermediary response. However, no increase in new bone formation occurred at sites of intimate bone porous surface contact. Recombinant bone morphogenetic protein-2/alphaBSM promoted defect filling and bone ingrowth into the porous coating beneath the defect region, both of potential value in future total joint replacement surgery.

Osteoinductive agents in reconstructive hip surgery: a look forward

The use of autograft and allograft material to restore bone stock and promote healing and implant stabilization is a crucial part of total hip arthroplasty, especially in the revision situation. Recent research has centered on the use of osteoinductive materials such as osteogenic proteins or bone morphogenetic proteins to promote bone formation. These proteins are members of the transforming growth factor-beta superfamily of proteins that either alone or in combination with other regulatory molecules induce new bone formation. The cloning and genetic expression of recombinant human bone proteins has led to production of quantities sufficient for their clinical development. Preclinical studies have shown that the osteoinductive capacity of autograft and allograft bone can be improved with the addition of osteogenic proteins. Although these proteins are effective alone, their use with cancellous and cortical allograft and autograft consistently improved the amount and rate of new bone formation compared with graft alone resulting in earlier graft incorporation and consolidation. When placed in defects adjacent to porous acetabular components, the use of an osteogenic protein resulted in earlier defect healing and improved component fixation by the enhancement of bone ongrowth and ingrowth. Although no detailed clinical studies have been reported to date, an anecdotal report of their use with and without bone graft indicate results consistent with those obtained in preclinical studies.

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.

Titanium surface topography alters cell shape and modulates bone morphogenetic protein 2 expression in the J774A.1 macrophage cell line

Macrophage cytokine expression significantly affects wound healing. Macrophage secretion of transforming growth factor beta 1 (TGFbeta1) and bone morphogenetic proteins (BMP) may affect osteogenesis at endosseous implant surfaces. The aim of this investigation was to determine the effect of commercially pure titanium (cpTi) substrate topography on adherent macrophage osteogenic and osteoinductive cytokine expression. J774A.1 murine macrophage cell adhesion was examined by scanning electron microscopy, 0-72 h following plating onto polished, machined, and grit-blasted cpTi surfaces. TGFbeta1 and BMP-2 gene expression by adherent macrophages was determined by the reverse transcription polymerase chain reaction. Macrophage adhesion increased with time on all surfaces and spreading increased with increasing surface roughness (polished < machined < grit-blasted). BMP-2 expression was not evident for cells adherent to polished cpTi at 24 h. In contrast, BMP-2 expression occurred at 24 h in cells adherent to machined and grit-blasted cpTi. BMP-2 expression was evident on all surfaces at 72 h and was greatest in grit-blasted titanium adherent cells. Increasing concentrations of cytochalasin B (0-50 microM) inhibited macrophage spreading and reduced BMP-2 mRNA expression, suggesting a relationship between cell shape and BMP-2 expression. This was further characterized using anti-beta1 and anti-beta3 integrin antibodies. The anti-beta1 integrin antibodies inhibited adherent macrophage BMP-2 mRNA expression. Anti-beta3 integrin antibody treatment only modestly reduced BMP-2 mRNA expression. Endosseous implant surface topography induced changes in macrophage shape that were associated with changes in BMP-2 expression in J774A.1 mouse macrophage cell line. This first demonstration of BMP-2 expression by cpTi adherent macrophages suggests that the macrophage may contribute surface-specific osteoinductive signals during bone formation at implanted alloplastic surfaces.

Osteoconductive coatings for total joint arthroplasty

Osteoconductive calcium phosphate coatings for total joint arthroplasty have been in clinical use since the mid1980s. The basic principles involved and basic science evidence for the efficacy of osteoconductive coatings were examined. Hydroxyapatite coatings provide consistent and better filling with bone of the gaps and spaces around cementless joint components after surgery as compared with porous-coated implant surfaces, resulting in better implant stability. Of all the calcium phosphate coatings, hydroxyapatite coatings have had the most widespread application in hip arthroplasty. Their clinical advantages over more conventional implant surfaces are evident in primary and revision hip arthroplasties. A clinical survival rate in the author's series of 97% at a minimum of 11 years followup for the femoral component in a young active patient population (average age, 53 years) was obtained with no mechanical failures. The average polyethylene wear rate in this group was 0.129 mm/year. In a similar group of young patients with revision arthroplasty using hydroxyapatite-coated femoral components, an 11-year survival rate of 93% was obtained. Histologic analysis of specimens retrieved at autopsy confirmed the excellent bony fixation of components. Advantages of the more recent biomimetic hydroxyapatite coatings were examined.

Osteogenic protein-1 induced bone formation in an infected segmental defect in the rat femur

The goal of this study was to use a segmental defect model in the rat femur to determine if osteogenic protein-1 (OP-1) is capable of inducing bone formation in the presence of bacterial contamination. A 6 mm segmental defect was surgically created and stabilized with a polyacetyl plate and Kirschner wires in one femur in each of 126 Sprague-Dawley rats. The animals were divided into eight groups in which the defect was either left untreated, or subjected to various combinations of OP-1 (11 or 50 microg), lyophilized bovine type I collagen (carrier for the OP-1), and 10(5) colony-forming units of Staphylococcus aureus. The animals were euthanized at either 2, 4, or 9 weeks. Quantitative radiographic and histologic analyses were performed on the harvested tissue. The initial contamination progressed to infection in all animals receiving bacteria, as determined by qualitative bacteriology. There was very little, if any, bone formation in the untreated defects, and in the contaminated defects with or without collagen carrier. Bone formation was significantly greater in contaminated defects with either dose of OP-1, compared with contaminated defects without OP-1. The 50 microg dose of OP-1 induced significantly more bone formation than the 11 microg dose, both with and without bacteria. This investigation has demonstrated that OP-1 maintains its osteoinductive capability in a contaminated segmental defect. OP-1 may potentially be used in the clinical management of contaminated fractures.

Skeletal tissue engineering: opportunities and challenges

Tissue engineering is a field of biomedicine that is growing rapidly and is critically driven by scientific advances in the areas of developmental and cell biology and biomaterial sciences. Regeneration of skeletal tissues is among the most promising areas of biological tissue repair and is providing a broad spectrum of potential clinical applications, including joint resurfacing. The availability of novel tools such as pluripotent stem cells, morphogens, smart biomaterials and gene transfer technologies, makes us dream of many exciting novel therapeutic approaches. Despite these opportunities in regenerative medicine, good clinical practice requires the clinician to question the consistency, reproducibility, validation and appropriate regulation of these new biological treatments.

Effect of osteogenic protein 1/collagen composite combined with impacted allograft around hydroxyapatite-coated titanium alloy implants is moderate

This study evaluated the effects of osteogenic protein 1/collagen composite (OP-1/col) mixed with impacted allograft around hydroxyapatite (HA)-coated titanium alloy implants in a canine model. The aim of the study was to test different doses of OP-1 growth factor in a collagen composite for stimulatory effect on allograft incorporation around an implant. Unloaded implants were inserted in each proximal humerus of 16 skeletally mature dogs. The cylindrical implants (4 x 9 mm) coated with HA were initially surrounded by a 3-mm gap into which allograft mixed with OP-1/col was impacted. Two different doses of OP-1 were investigated. In eight animals 325 mg OP-1 protein and 130 mg bovine collagen type I as carrier were mixed with the allograft chips. This composite is identical to the clinically used OP-1 device called Novus. In another eight animals a lower dose of 65 mg OP-1 protein and 130 mg bovine collagen type I was used. Control implants placed in the contralateral humerus were surrounded by allograft mixed with collagen carrier only. The dogs were euthanized at 6 weeks. Implant fixation was determined by push-out testing. Bone ingrowth and bone formation were evaluated by quantitative histomorphometry on serial sections of the bone-implant interface. Impacted allograft together with low-dose OP-1 enhanced bone volume in a zone adjacent to HA-coated titanium alloy implants. The high dose had no effect on bone formation. Mechanical fixation, bone ingrowth, and bone volume in the gap near the original trabecular bone were unaffected by both low and high OP-1/col composite. In this model and observation period, the low dose of OP-1/col composite mixed with impacted allograft has a moderate effect on bone healing around HA-coated implants and no effect on implant fixation.

A role for surface topography in creating and maintaining bone at titanium endosseous implants

STATEMENT OF PROBLEM

A variety of claims are made regarding the effects of surface topography on implant osseointegration. Many in vivo and in vitro experimental observations have key limitations in their interpretations.

PURPOSE

This review considers the major claims made concerning the effects of commercially pure (cp) titanium implant surface topography on osseointegration. Important findings of consensus are highlighted, and existing controversies are revealed.

MATERIAL AND METHODS

This review considers many of the research publications listed in MEDLINE and presented in biomedical research publications and textbooks.

RESULTS

Implant surface topography is not well defined in the marketplace or consistently reported among experimental studies. Many in vitro evaluations are not predictive of or correlated with in vivo outcomes. In some culture models, increased surface topography positively affects pro-osteogenic cellular activities. Animal models reveal modest increases in bone-to-implant contact and increases in the biomechanical interlock of the implant with bone for implants of increased surface topography. Existing information fails to define increased surface topography as a risk factor for peri-implant inflammation.

CONCLUSION

Increased cp titanium implant surface topography improves the bone-to-implant contact and the mechanical properties of the enhanced interface. Growing clinical evidence for increased bone-to-implant contact at altered cp titanium implants confirms the temporally limited observations made in preclinical studies. In the absence of controlled comparative clinical trials, the aggregate experimental evidence supports the use of cp titanium implants with increased surface topography.