Stainless steel screws coated with bisphosphonates gave stronger fixation and more surrounding bone. Histomorphometry in rats

Peri-implant and systemic effects of high-/low-affinity bisphosphonate-hydroxyapatite composite coatings in a rabbit model with peri-implant high bone turnover

Background

Hydroxyapatite (HA) coatings composed with bisphosphonates (BPs) which have high mineral-binding affinities have been confirmed to successfully enhance implant stability. However, few previous studies focused on HA coatings composed with low-affinity BPs or on systemic effects of locally released BPs.

Methods

In this long-term study, we developed two kinds of BP-HA composite coatings using either high-affinity BP (alendronate, ALN) or low-affinity BP (risedronate, RIS). Thirty-six rabbits were divided into three groups according to different coating applications (group I: HA, group II: ALN-HA, and group III: RIS-HA). Implants were inserted into the proximal region of the medullary cavity of the left tibiay. At insertion, 2 × 10⁸ wear particles were injected around implants to induce a peri-implant high bone turnover environment. Both local (left tibias) and systemic (right tibias and lumbar vertebrae) inhibitory effect on bone resorption were compared, including bone-implant integration, bone architecture, bone mineral density (BMD), implant stability, and serum levels of bone turnover markers.

Results

The results indicated that ALN-HA composite coating, which could induce higher bone-implant contact (BIC) ratio, bone mass augmentation, BMD, and implant stability in the peri-implant region, was more potent on peri-implant bone, while RIS-HA composite coating, which had significant systemic effect, was more potent on non-peri-implant bone, especially lumbar vertebrae.

Conclusions

It is instructive and meaningful to further clinical studies that we could choose different BP-HA composite coatings according to the patient’s condition.

A bisphosphonate-coating improves the fixation of metal implants in human bone. A randomized trial of dental implants

Many surgical procedures use metal implants in bone. The clinical results depend on the strength of the bone holding these implants. Our objective was to show that a drug released from the implant surface can improve parameters reflecting the quality or amount of this bone. Sixteen patients received paired dental titanium implants in the maxilla, in a randomized, double-blinded fashion. One implant in each pair was coated with a thin fibrinogen layer containing 2 bisphosphonates. The other implant was untreated. Fixation was evaluated by measurement of resonance frequency (implant stability quotient; ISQ) serving as a proxy for stiffness of the implant-bone construct. Increase in ISQ at 6months of follow-up was the primary variable. None of the patients had any complications. The resonance frequency increased 6.9 ISQ units more for the coated implants (p=0.0001; Cohen's d=1.3). The average difference in increase in ISQ, and the effect size, suggested a clinically relevant improvement. X-ray showed less bone resorption at the margin of the implant both at 2months (p=0.012) and at 6months (p=0.012). In conclusion, a thin, bisphosphonate-eluting fibrinogen coating might improve the fixation of metal implants in human bone. This might lead to new possibilities for orthopedic surgery in osteoporotic bone and for dental implants.

Effect of local zoledronate on implant osseointegration in a rat model

Background

An implant coating with poly(D, L-lactide) (PDLLA) releasing incorporated Zoledronic acid (ZOL) has already proven to positively effect osteoblasts, to inhibit osteoclasts and to accelerate fracture healing. Aim of this study was to investigate the release kinetics of the chosen coating and the effect of different concentrations of ZOL locally released from this coating on the osseointegration of implants.

Methods

For release kinetics the release of C14-labled ZOL out of the coating was monitored over a period of six weeks in vitro. For testing the osseointegration, titanium Kirschner wires were implanted into the medullary canal of right femurs of 100 Sprague Dawley rats. The animals were divided into five groups receiving implants either uncoated or coated with PDLLA, PDLLA/ZOL low (1.2% w/w) or PDLLA/ZOL high (2% w/w). Additionally, a group with uncoated implants received ZOL intravenously (i.v.). After 56 days animals were sacrificed, femurs dissected and either strength of fixation or histological bone/implant contacts and newly formed bone around the implants were determined.

Results

Release kinetics revealed an initial peak in the release of C14-ZOL with a slight further progression over the following weeks. There was no significant enhancement of osseointegration for both groups who received ZOL-coated implants or ZOL i.v. compared to the controls in biomechanical or histological analyses, except for a significant raise in strength of fixation of ZOL i.v. versus PDLLA.

Conclusions

Even though the investigated local ZOL application did not enhance the osseointegration of the implant, the findings might support its application in fracture treatment, since fracture stabilization devices are often explanted after consolidation.

Local bisphosphonate release versus hydroxyapatite coating for stainless steel screw fixation in rat tibiae

Implant fixation in bone can be improved by a coating that delivers bisphosphonates locally, or by a hydroxyapatite (HA) coating. In this study, we compared these different types of coatings. For mechanical testing, 30 rats were assigned into three groups, and similar screws were implanted bilaterally in the proximal tibiae. The rats received screws that were either uncoated, coated with nano-crystalline hydroxyapatite or coated with a bisphosphonate releasing protein matrix. After 4 weeks, one screw was subjected to pull-out testing, and the contra-lateral one to torsion testing. For morphology, 30 rats were assigned to similar treatment groups, but received only one screw each. Bisphosphonates enhanced the pull-out force by 41% (P = 0.02) compared to controls, HA increased the pull-out force although not significantly. Conversely, HA increased the maximal torque by 64% (P = 0.02). Morphometry showed higher bone volume around bisphosphonate screws in comparison to HA-coated screws (P < 0.001) and controls (P < 0.001). The results suggest that bisphosphonates improve fixation by increasing the amount of surrounding bone, whereas HA mainly improves bone to implant attachment.

Nanostructured model implants for in vivo studies: influence of well-defined nanotopography on de novo bone formation on titanium implants

An implantable model system was developed to investigate the effects of nanoscale surface properties on the osseointegration of titanium implants in rat tibia. Topographical nanostructures with a well-defined shape (semispherical protrusions) and variable size (60 nm, 120 nm and 220 nm) were produced by colloidal lithography on the machined implants. Furthermore, the implants were sputter-coated with titanium to ensure a uniform surface chemical composition. The histological evaluation of bone around the implants at 7 days and 28 days after implantation was performed on the ground sections using optical and scanning electron microscopy. Differences between groups were found mainly in the new bone formation process in the endosteal and marrow bone compartments after 28 days of implantation. Implant surfaces with 60 nm features demonstrated significantly higher bone-implant contact (BIC, 76%) compared with the 120 nm (45%) and control (57%) surfaces. This effect was correlated to the higher density and curvature of the 60 nm protrusions. Within the developed model system, nanoscale protrusions could be applied and systematically varied in size in the presence of microscale background roughness on complex screw-shaped implants. Moreover, the model can be adapted for the systematic variation of surface nanofeature density and chemistry, which opens up new possibilities for in vivo studies of various nanoscale surface-bone interactions.

In vivo assessment of local effects after application of bone screws delivering bisphosphonates into a compromised cancellous bone site

BACKGROUND

The primary stability of cancellous screw is difficult to obtain in bone of compromised quality and failure of screw fixation is common. To overcome this problem, it is proposed to locally deliver bisphosphonate from the screw. An in vivo validation of the increase in fixation of the cancellous screw is then needed in compromised bone.

METHODS

In this study, we used an overdrilling procedure, which enables consistent modeling of reduced screw stability comparable to compromised cancellous bone. Forty eight adult NZW rabbits were used in this study and all animals underwent bilateral femur implantation. One leg was implanted with the screw containing the bisphosphonate (biocoated group) while the other was used as control (control group) with the screw only. Mechanical testing and micro-CT imaging were used to assess the effect of local drug delivery of Zoledronate on screws fixation at 5 time points.

FINDINGS

At the early time points (1, 5, and 10 days), no significant difference could be seen between the biocoated and control groups. At 6 weeks, the bone volume fraction was significantly higher in the trabecular region of the biocoated group. However, this increase did not have a significant effect on the pull-out force. At the last time point, 11 weeks, both the bone volume fraction and the pull-out force were significantly higher in the biocoated group.

INTERPRETATION

The results of this study suggest that, in compromised bone, local delivery of bisphosphonate enhances the stability of bone screws.

The effect of plasma chemical oxidation of titanium alloy on bone-implant contact in rats

Many different technologies have been used to enhance osseointegration in orthopaedic and dental implant surgery. Hydroxyapatite coatings, pure or in combination with growth factors or bisphosphonates, showed improved osseointegration of titanium alloy implants. We choose a different approach to enhance osseointegration: plasma chemical oxidation was used to modify the surface of titanium alloy implants. This technique converts the nm-thin natural occurring titanium oxide layer on an implant to a 4 μm thick ceramic coating (TiOB surface). Bioactive TiOB surfaces have a macroporous structure and were loaded with calcium and phosphorus, while bioinert TiOB surfaces are smooth. A rat tibial model with bilateral placement of titanium alloy implants was employed to analyze the bone response to TiOB surfaces in vivo. 64 rats were randomly assigned to four groups of implants: (1) titanium alloy (control), (2) titanium alloy, type III anodization, (3) bioinert TiOB surface and (4) bioactive TiOB surface. Mechanical fixation, peri-implant-bone area and bone contact were evaluated by pull-out tests and histology at three and eight weeks. Shear strength and bone contact at eight weeks were significantly increased in the bioactive TiOB group compared to all other groups. The results of plasma chemical oxidation in a rat model showed that the bioactive TiOB surface has a positive effect on implant anchorage by enhancing the bone-implant contact in normal bone.

Administration of sodium ibandronate in the treatment of complicated giant cell tumor of the spine

STUDY DESIGN

Case study.

OBJECTIVE

To present three complicated cases of giant cell tumor of the spine treated with sodium ibandronate.

SUMMARY OF BACKGROUND DATA

Spinal giant cell tumors are a rare clinical entity with a high recurrence rate after operation. Furthermore, complete resection of such lesions remains a challenging surgical problem. Up to this point, no effective adjuvant therapy has been reported for primary or recurrent spinal giant cell tumors.

METHODS

One patient with a recurrent giant cell tumor of the seventh thoracic vertebra, one patient with a fifth lumbar vertebral giant cell tumor, and one patient with recurrent giant cell tumor of the sacrum were treated with sodium ibandronate either postoperatively or upon recurrence of the tumor.

RESULTS

The first patient with recurrent thoracic giant cell tumor recovered both clinically and radiologically after treatment with sodium ibandronate without reoperation at 6-years follow-up. The second patient also recovered with no recurrence of the tumor at 4-years follow-up. In the third case, although not fully recovered, the recurrent sacral tumor was under control after treatment with sodium ibandronate at 2-years follow-up.

CONCLUSION

These case studies demonstrate the potential promise of using sodium ibandronate in the treatment of primary and recurrent giant cell tumors of the spine. Furthermore, clinical evaluation should be performed in future studies.

Freezing of rat tibiae at -20°c does not affect the mechanical properties of intramedullary bone/implant-interface: brief report

Background:

The effects of freezing-thawing cycles on intramedullary bone-implant interfaces have been studied in a rat model in mechanical pull-out tests.

Implants:

Twenty TiAl6V4 rods (Ø 0.8 mm, length 10 mm) implanted in rat tibiae

Methods:

10 rats underwent bilateral tibial implantation of titanium rods. At eight weeks, the animals were sacrificed and tibiae harvested for biomechanical testing. Eight tibiae were frozen and stored at -20°C for 14 days, the remaining eight were evaluated immediately post-harvest. Pull-out tests were used to determine maximum force and interfacial shear strength.

Results:

There were no significant differences between fresh and those of the frozen-thawed group in maximum force or in interfacial shear strength.

Conclusion:

Frozen Storage of rat tibiae containing implants at -20° C has no effects on the biomechanical properties of Bone/ Implant interface.

The effects of Dickkopf-1 antibody on metaphyseal bone and implant fixation under different loading conditions

The secreted protein Dickkopf-1 (Dkk1) is an antagonist of canonical Wnt signaling, expressed during fracture healing. It is unclear how it is involved in the mechanical control of bone maintenance. We investigated the response to administration of a Dkk1 neutralizing antibody (Dkk1-ab) in metaphyseal bone under different loading conditions, with or without trauma. In this three part experiment, 120 rats had a screw or bone chamber inserted either unilaterally or bilaterally in the proximal tibia. Mechanical (pull-out) testing, μCT and histology were used for evaluation. The animals were injected with either 10mg/kg Dkk1-ab or saline every 14days for 14, 28, or 42days. Antibody treatment increased bone formation around the screws and improved their fixation. After 28days, the pull-out force was increased by over 100%. In cancellous bone, the bone volume fraction was increased by 50%. In some animals, one hind limb was paralyzed with Botulinum toxin A (Botox) to create a mechanically unloaded environment. This did not increase the response to antibody treatment with regard to screw fixation, but in cancellous bone, the bone volume fraction increased by 233%. Thus, the response in unloaded, untraumatized bone was proportionally larger, suggesting that Dkk1 may be up-regulated in unloaded bone. There was also an increase in thickness of the metaphyseal cortex. In bone chambers, the antibody treatment increased the bone volume fraction. The results suggest that antibodies blocking Dkk1 might be used to stimulate bone formation especially during implant fixation, fracture repair, or bone disuse. It also seems that Dkk1 is up-regulated both after metaphyseal trauma and after unloading, and that Dkk1 is involved in mechano-transduction.

Sclerostin antibody treatment enhances metaphyseal bone healing in rats

Sclerostin is the product of the SOST gene. Loss-of-function mutations in the SOST gene result in a high-bone-mass phenotype, demonstrating that sclerostin is a negative regulator of bone mass. Primarily expressed by osteocytes in bone, sclerostin is reported to bind the LRP5/6 receptor, thereby antagonizing canonical Wnt signaling and negatively regulating bone formation. We therefore investigated whether systemic administration of a sclerostin-neutralizing antibody would increase the regeneration of traumatized metaphyseal bone in rats. Young male rats had a screw inserted in the proximal tibia and were divided into six groups given 25 mg/kg of sclerostin antibody or control twice a week subcutaneously for 2 or 4 weeks. In four groups, the screws were tested for pull-out strength. At the time of euthanasia, a similar screw also was inserted in the contralateral tibia and pull-out tested immediately. Sclerostin antibody significantly increased the pull-out force by almost 50% compared with controls after 2 and 4 weeks. Also, the screws inserted at the time of euthanasia showed increased pull-out force. Micro-computed tomography (µCT) of the remaining two groups showed that the antibody led to a 30% increase in bone volume fraction in a region surrounding the screw. There also was a general increase in trabecular thickness in cancellous bone. Thus, as measured by the amount of bone and its mechanical resistance, the sclerostin antibody increased bone formation during metaphyseal repair but also in untraumatized bone.

Surface immobilized zoledronate improves screw fixation in rat bone: a new method for the coating of metal implants

Previous studies show that surface immobilized bisphosphonates improve the fixation of stainless steel screws in rat tibia after 2-8 weeks of implantation. We report here about the immobilization of a potent bisphosphonate, zoledronate, to crosslinked fibrinogen by the use of another technique, i.e. ethyl-dimethyl-aminopropylcarbodiimide (EDC)/imidazole immobilization. Bone fixation of zoledronate-coated screws was compared to screws coated with crosslinked fibrinogen only and ditto with EDC/N-hydroxy-succinimide immobilized pamidronate. Fixation in rat tibia was evaluated by a pull-out test at either 2 or 6 weeks after implantation. Both bisphosphonate coatings increased the pull-out force at both time points, and zoledronate showed a significantly higher pull-out force than pamidronate. To further evaluate the new coating technique we also performed a morphometric study, focusing on the area surrounding the implant. The zoledronate coating resulted in an increased bone density around the screws compared to controls. No pronounced increase was seen around the pamidronate coated screws. Together, the results demonstrate the possibility of obtaining a significant local therapeutic effect with minute amounts of surface immobilized zoledronate.

Sol-gel derived titania coating with immobilized bisphosphonate enhances screw fixation in rat tibia

A variety of surface modifications have been tested for the enhancement of screw fixation in bone, and locally delivered anti-osteoporosis drugs such as bisphosphonates (BP) are then of interest. In this in vivo study, the impact of surface immobilized BP was compared with systemic BP delivery and screws with no BP. After due in vitro characterization, differently treated stainless steel (SS) screws were divided into four groups with 10 rats each. Three of the groups received screws coated with sol-gel derived TiO(2) and calcium phosphate (SS+TiO(2)+CaP). One of these had no further treatment, one had alendronate (BP) adsorbed to calcium phosphate mineral, and one received systemic BP treatment. The fourth group received uncoated SS screws and no BP (control). The screw pullout force was measured after 4 weeks of implantation in rat tibiae. The immobilized amount and release rate of alendronate could be controlled by different immersion times. The SS+TiO(2)+CaP coating did not increase the pullout force compared to SS alone. Surface delivered alendronate enhanced the pullout force by 93% [p = 0.000; 95% Confidence Interval (CI): 67-118%] compared to SS, and by 39% (p = 0.044; 95% CI: 7-71%) compared to systemic alendronate delivery. Both surface immobilized and systemically delivered alendronate improved implant fixation. Also, locally delivered, that is, surface immobilized alendronate showed a better fixation than systemically delivered. Using sol-gel derived TiO(2) as a platform, it is possible to administer controllable amounts of a variety of BPs.

Effect of locally administered zoledronic acid on injury-induced intramembranous bone regeneration and osseointegration of a titanium implant in rats

BACKGROUND

Intramedullary implantation causes injury-induced stimulation of intramembranous bone regeneration. Intramedullary bone injury along with stress shielding may induce periimplant bone loss and cause early aseptic loosening of an implant. The aim of this study was to determine the effect of locally administered zoledronic acid on periimplant bone and injury-induced stimulation of intramembranous bone regeneration in a rat model.

METHODS

A total of 28 male rats had a titanium implant inserted into their right femur. During the operation, the medullary canal was lavaged using 20 muM zoledronic acid (Zometa 4 mg/5 ml) or sodium chloride. Follow-up times were 4 and 12 weeks, with each follow-up group consisting of seven rats. The femurs with the titanium implants in situ were harvested, and three microscope sections were cut from each femur. The sections were photographed and analyzed with the Analysis computer program.

RESULTS

Between 4 and 12 weeks, the length of fluorescence bone contact increased significantly in both groups (control 15.7% SD and zoledronic acid 18.8% SD), although the difference between the groups was not significant. Periimplant bone volume (thickness) was increased in the 4-week zoledronic acid group compared to the controls (+/-13.4%, P = 0.002) but at 12 weeks the groups no longer differed from each other.

CONCLUSIONS

Our results suggest that zoledronic acid may prevent injury-induced bone loss near an intramedullary implant by inhibiting bone resorption shortly after implantation. This may provide better periimplant bone stock during the early postoperative period.

Alternative indications for bisphosphonate therapy

Bisphosphonates are currently used in the treatment of osteoporosis (postmenopausal and steroid-induced), hypercalcemia of malignancy, Paget's disease of bone, multiple myeloma, and skeletally related events associated with metastatic bone disease in breast, prostate, lung, and other cancers. There are, however, numerous other conditions where a decrease in bone remodeling by bisphosphonates might aid in disease management. The focus of this review will be to discuss a select group of conditions for which bisphosphonate therapy may be efficacious. In this review we present several cases where bisphosphonates have been used as a primary or adjunctive treatment for giant cell lesions of the jaws. Use of bisphosphonate therapy for giant cell tumors of the appendicular skeleton, pediatric osteogenesis imperfecta, fibrous dysplasia, Gaucher's disease, and osteomyelitis will be discussed. Finally, we will review previous in vivo studies on the use of bisphosphonates to augment integration and to treat osteolysis surrounding failing orthopedic implants.

Effect of alendronate and intermittent parathyroid hormone on implant fixation in ovariectomized rats

BACKGROUND

Intermittent administration of parathyroid hormone (PTH) leads to bone formation by increasing osteoblast numbers and activity levels. Animal studies have shown that intermittent PTH administration increases implant fixation in normal rats. The purpose of this study was to analyze the osseous incorporation of an implant in osteoporotic rats while treating them with intermittent PTH (1-34) or alendronate.

METHODS

A total of 36 ovariectomized (OVX) Wistar rats were randomized into three groups. Polymethylmethacrylate cement rods were implanted in one tibia in each rat. The three groups received daily PTH (60 mug/kg body weight [BW]), alendronate (200 mug/kg BW), or saline (0.5 ml/kg BW). A sham-ovariectomized group (n = 12) was treated with saline. After 2 weeks, the area around the implants was analyzed by histomorphometry for bone volume density (BVD) and implant bone contact. Bone mineral density (BMD) was evaluated by dual-energy X-ray absorptiometry.

RESULTS

The BVD was higher in the specimens treated with PTH than in the other groups. PTH improved the BVD, BMD, and implant bone contact. Alendronate doubled the implant bone contact compared to the OVX and sham groups but did not improve BVD or BMD.

CONCLUSIONS

These findings confirm that intermittent PTH enhances implant fixation in osteoporotic bone. The clinical significance of these findings is that application of intermittent PTH may be beneficial for early implant fixation in fractures, nonunions, and prosthetic replacements when bone density is decreased.

Effect of combined local treatment with zoledronic acid and basic fibroblast growth factor on implant fixation in ovariectomized rats

Osteoporosis is a skeletal disorder characterized by low bone mass and deterioration of bone microarchitecture resulting in bone fragility, which impairs fixation of the implants. Zoledronic acid (ZOL) is a potential inhibitor of osteoclast-mediated bone resorption and basic fibroblast growth factor (bFGF) is a growth factor that stimulates osteoblast-mediated bone formation, and these drugs could enhance fixation of implants under osteoporotic conditions. In this study, 40 ovariectomized (OVX) rats were randomly divided into 4 groups (n=10 for each group) and underwent bilateral tibiae implantation using hydroxyapatite (HA)-coated titanium implant: Control group (distilled water immersing before implantation), ZOL group (1 mg/ml of ZOL immersing), bFGF group (20 microg/ml of bFGF immersing), and ZOL+bFGF group (1 mg/ml of ZOL and 20 microg/ml of bFGF immersing). At 3 months after implantation, all animal were sacrificed and the tibiae were harvested for histology, micro-CT examinations and biomechanical testing. Bone area and contact, determined by histomorphometric analysis, were 2.7-fold and 1.8-fold in the ZOL-treated implants, 1.9-fold and 1.8-fold in the bFGF-treated implants, 3.6-fold and 2.3-fold in the both-treated implants compared with controls (p<0.01). Such significant effects were further confirmed by microstructure parameters, the bone volume ratio and the percentage osteointegration were significantly increased by ZOL treatment (3.0-fold and 1.8-fold), bFGF treatment (1.2-fold and 1.9-fold) and ZOL+bFGF treatment (3.3-fold and 2.7-fold) (p<0.001). In addition, push-out test showed that the maximum force and the corresponding interfacial shear strength of the implants treated by ZOL, bFGF and ZOL+bFGF was 8.4-fold and 8.6-fold, 3.8-fold and 3.7-fold, 10.8-fold and 10.7-fold of the control levels, respectively (p<0.05). The combined treatment was better than either treatment alone for force, but was not different from ZOL alone for interfacial strength. The significant correlation between biomechanical and micro-CT parameters demonstrates the role of microstructure assessments in predicting mechanical fixation of implants (p<0.01). Our study suggests that locally applied ZOL or bFGF may improve implant fixation in the ovariectomized rats, and that combined treatment has more beneficial effects on osseointegration, peri-implant bone formation and maximum force than either intervention alone.