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      The effects of nail rigidity on fracture healing in rats with osteoporosis

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          Abstract

          Background and purpose Stress shielding from rigid internal fixation may lead to refracture after removal of the osteosynthesis material. We investigated the effect of a low-rigidity (Ti-24Nb-4Zr-7.9Sn) intramedullary nail regarding stress shielding and bone healing of osteoporotic fractures in the rat.

          Methods 40 female Sprague-Dawley rats, aged 3 months, were divided into the following groups: sham-operation (SHAM) (n = 10), ovariectomized (OVX) (n = 10) and OVX-fracture (n = 20). 10 SHAM rats and 10 OVX rats were killed after 12 weeks to provide biomechanical data. Ovariectomy was performed 12 weeks before fracturing both femurs in 20 rats. The left fracture was stabilized with a high-rigidity titanium alloy pin (Ti-6Al-4V; elastic modulus 110 GPa) and the right with a low-rigidity (Ti-24Nb-4Zr-7.9Sn; elastic modulus 33 GPa). The bony calluses were examined by micro-CT at 6 and 12 weeks after fracture, bone volume (BV) and total volume (TV) were determined at the callus region (ROI1) and the total femur (ROI2). Subsequently, the bones were tested mechanically by a three-point bending test.

          Results In the low-rigidity group, TV (ROI1) increased at 6 weeks, but BV (ROI1), BV (ROI2) were similar but maximum load increased. At 12 weeks, the maximum load and also BV (ROI1, ROI2) were increased in the low-rigidity group.

          Interpretation The low-rigidity nail manufactured from Ti-24Nb-4Zr-7.9Sn showed better external callus formation, seemed to reduce effects of stress shielding, and reduced bone resorption better than the stiffer nail. The low-rigidity nail was strong enough to maintain alignment of the fracture in the osteoporotic rat model without delayed union.

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          Most cited references17

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          Animal models for fracture treatment in osteoporosis.

          Demographic changes in the age structure of occidental populations are giving rise to osteoporosis and associated fractures, which are becoming a major public health burden. Various animal models have been established and used to investigate the pathogenesis of osteoporosis and to facilitate the preclinical testing of new treatment options such as antiresorptive drugs. Although osteoporosis can be induced in animals, spontaneous fractures without adequate trauma were only found in nonhuman primates. An animal model designed to investigate new ways to treat fractures of osteoporotic bone has to fulfill requirements that are very different from those of pharmacological testing. The aspects of major interest in orthopedic applications are bone fragility, efficacy of implant fixation and bone healing. Existing animal models for osteoporosis were critically reviewed focusing on these aspects. The advantages and disadvantages of the models with regard to their application in the testing of new fracture-fixation devices or biological approaches to stimulate bone healing are discussed. Ovariectomy alone does not cause the bone loss seen in osteoporotic human patients. New models to simulate fracture of osteoporotic bone need to be explored and used to address the specific aims of an experiment.
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            Elastic deformation behaviour of Ti-24Nb-4Zr-7.9Sn for biomedical applications.

            In this paper, the elastic deformation behaviour of a recently developed beta-type titanium alloy Ti-24Nb-4Zr-7.9Sn (wt.%) that consists of non-toxic elements and is intended for biomedical applications is described. Tensile tests show that this alloy in the as hot-rolled state exhibits peculiar non-linear elastic behaviour with maximum recoverable strain up to 3.3% and incipient Young's modulus of 42GPa. Solution treatment at high temperature has trivial effect on super-elasticity but decreases strength and slightly increases the incipient Young's modulus. Ageing treatment in the (alpha+beta) two-phase field increases both strength and Young's modulus and results in a combination of high strength and relatively low elastic modulus. In spite of the formation of the alpha phase, short time ageing has no effect on super-elasticity, whereas the non-linear elastic behaviour transforms gradually to normal linear elasticity with the increase of ageing time. We suggest sluggish, partially reversible processes of stress-induced phase transformation and/or incipient kink bands as the origin of the above peculiar elastic behaviour.
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              Refracture of bones of the forearm after the removal of compression plates.

              Of thirty-seven patients who had sixty-two diaphyseal plates removed from the forearm after fixation of a fracture, seven patients had a refracture, two of whom refractured both bones of the forearm. Six of the seven refractures were in patients who initially had had a fracture of both bones, and all were in patients in whom the original fracture had been caused by major trauma. The interval from the time of removal of the plate to refracture ranged from forty-two to 121 days. Only one of the seven patients who had a refracture had had adequate compression of the original fracture. The average interval from the time of the original trauma to internal fixation was two days in six patients who had a refracture and who originally had had primary plating, compared with 8.5 days in the patients who did not have a refracture. One of the seven patients who had a refracture had originally had delayed plating after closed treatment had failed. In retrospect, radiolucency at the site of the original fracture was seen in most patients when the plate was removed.
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                Author and article information

                Journal
                Acta Orthop
                ORT
                Acta Orthopaedica
                Informa Healthcare
                1745-3674
                1745-3682
                26 February 2009
                01 February 2009
                : 80
                : 1
                : 135-138
                Affiliations
                1simpleDepartment of Orthopedics, Xijing Hospital, Fourth Military Medical University Xi'anChina
                2simpleShenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences ShenyangChina
                Author notes
                Article
                SORT_A_380919_O
                10.1080/17453670902807490
                2823242
                19297794
                33c5475c-e538-42e3-9c69-4082d351d201
                Copyright: © Nordic Orthopedic Federation

                This is an open-access article distributed under the terms of the Creative Commons Attribution Noncommercial License which permits any noncommercial use, distribution, and reproduction in any medium, provided the source is credited.

                History
                : 01 March 2008
                : 15 August 2008
                Categories
                Research Article

                Orthopedics
                Orthopedics

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