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Stainless steel screws coated with bisphosphonates gave stronger fixation and more surrounding bone. Histomorphometry in rats
Linköping University, Department of Clinical and Experimental Medicine, Orthopaedics and Sports Medicine . Linköping University, Faculty of Health Sciences.
Department of Biomaterials, Inst. of Surgical Sciences, Sahlgrenska Academy at Göteborg University, Box 412, SE-405 30 Göteborg, Sweden.
Linköping University, Department of Physics, Chemistry and Biology, Applied Physics . Linköping University, The Institute of Technology.
Department of Biomaterials, Inst. of Surgical Sciences, Sahlgrenska Academy at Göteborg University, Box 412, SE-405 30 Göteborg, Sweden.
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2008 (English)In: Bone, ISSN 8756-3282, Vol. 42, no 2, 365-371 p.Article in journal (Refereed) Published
Abstract [en]

Coating of stainless steel screws with bisphosphonate in a fibrinogen matrix leads to an enhancement of the pullout strength 2 weeks after insertion in rat tibiae. This effect then increases over time until at least 8 weeks. The pullout force reflects the mechanical properties of the bone within the threads, which acts as a screw nut. The aim of the present study was to find descriptive and morphometric histological correlates to the increased pullout strength. Because the bisphosphonates are applied via the implant surface, we also measured bone to implant contact and how far away from the surface any effects could be seen.

Stainless steel screws underwent one of three treatments: uncoated control, controls coated with a layer of cross-linked fibrinogen, or screws further modified with bisphosphonates covalently linked and physically adsorbed to the fibrinogen layer. At 1 (n = 33) and 8 (n = 27) weeks, bone to implant contact and bone area density in the threads were measured, as well as bone area density at 250 and 500 μm from the outer edge of the threads. Additionally, removal torque for each screw treatment was measured at 2 weeks (n = 28).

At 8 weeks, the part of the bisphosphonate screw that was located in the marrow cavity had become surrounded with bone, whereas there was almost no bone surrounding the controls. The bone area density in the threads along the entire bisphosphonate screw was increased by 40% compared with uncoated controls, and at 250 μm distance it was more than doubled. At 1 week, coated screws had less implant–bone contact, but at 8 weeks there was no difference between uncoated and bisphosphonate-coated screws. The bisphosphonate screws had 50% increased removal torque at 2 weeks compared to uncoated screws. Howship's lacunae and osteoclasts were found near the screws with bisphosphonates at 8 weeks, suggesting that some bone remodeling took place near the implant, in spite of the presence of bisphosphonates.

Place, publisher, year, edition, pages
Elsevier/ScienceDirect , 2008. Vol. 42, no 2, 365-371 p.
Keyword [en]
Histomorphometry; Stainless steel; Torque removal; Bisphosphonate; Implant fixation
National Category
URN: urn:nbn:se:liu:diva-15308DOI: 10.1016/j.bone.2007.10.013OAI: diva2:113872
Available from: 2008-10-30 Created: 2008-10-30 Last updated: 2009-08-21Bibliographically approved
In thesis
1. Surface bound bisphosphonate for implant fixation in bone
Open this publication in new window or tab >>Surface bound bisphosphonate for implant fixation in bone
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Läkemedel bundet till implantatytan förbättrar implantatets förankring i ben
Abstract [en]

During the surgical preparation of bone, prior to insertion of an implant, bone will be traumatized which leads to local resorption. Consequently, early implant fixation might be reduced. Impaired early fixation, as evidenced by radiostereometry, has been associated with increased risk of late loosening. Bisphosphonates are known to inhibit bone resorption by osteoclasts and have shown to increase implant fixation when administered systemically or locally directly at the bone prior to implant insertion.

A method to bind bisphosphonates directly to the implant was developed. Stainless steel screws were coated with crosslinked fibrinogen, serving as an anchor for bisphosphonate attachment. The screws were inserted in the tibial metaphysis in rats and implant fixation was analyzed with pullout measurements. Bisphosphonate coated screws turned out to have 28 % higher pullout force at 2 weeks compared to control screws with the fibrinogen coating only. The next experiment was designed to measure at what stage in the healing process the strongest bisphosphonate effect was gained. Bisphosphonate coated screws were expected to reduce the resorption of the traumatized bone. However, no decreased fixation was found in the control group. Instead, the fixation increased with time, and so did the effect of the bisphosphonates. At 8 weeks, the pullout force was twice as high for screws with bisphosphonate compared to control screws. By histology at 8 weeks, a bone envelope was found around bisphosphonate coated screws but absent around control screws. Thus, the anti catabolic action of the bisphosphonate resulted in an increased amount of bone surrounding the bisphosphonate screws.

Titanium is generally considered to be better fixated in bone compared to stainless steel. The coating technique was found to be applicable on titanium as well, again with improved fixation.

A majority of fractures occur in osteoporotic bone. Despite the relatively low amount of bisphosphonates at the screws, the bisphosphonate coating improved implant fixation at 2 weeks also in rats made osteoporotic by ovariectomy.

In conclusion, bisphosphonates bound to titanium or stainless steel screws coated with fibrinogen increased fixation in bone, in rats. These results suggest that the bisphosphonate and fibrinogen coating might improve the fixation of screw shaped implants and possibly also arthroplasties, in humans.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2008. 49 p.
Linköping University Medical Dissertations, ISSN 0345-0082 ; 1059
National Category
urn:nbn:se:liu:diva-15310 (URN)978-91-7393-919-5 (ISBN)
Public defence
2008-05-21, Elsa Brännströms sal, Campus US, Hälsouniversitetet, Linköpings universitet, Linköping, 13:00 (English)
Available from: 2008-10-30 Created: 2008-10-30 Last updated: 2012-01-19Bibliographically approved

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Wermelin, KarinTengvall, PenttiAspenberg, Per
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Orthopaedics and Sports Medicine Faculty of Health SciencesApplied Physics The Institute of TechnologyDepartment of Orthopaedics Linköping
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