Article
In vivo MRI findings of Neoangiogenesis in fracture-healing process in an animal model
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Authors
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B. Wieskötter
- Universitätsklinikum Münster, Klinik für Unfall-, Hand- und Wiederherstellungschirurgie, Münster, Germany
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H. Tiggemann
- Universitätsklinikum Münster, Klinik für Unfall-, Hand- und Wiederherstellungschirurgie, Münster, Germany
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M.J. Raschke
- Universitätsklinikum Münster, Klinik für Unfall-, Hand- und Wiederherstellungschirurgie, Münster, Germany
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V. Vieth
- Universitätsklinikum Münster, Institut für klinische Radiologie, Münster, Germany
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W. Heindel
- Universitätsklinikum Münster, Institut für klinische Radiologie, Münster, Germany
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R. Stange
- Universitätsklinikum Münster, Klinik für Unfall-, Hand- und Wiederherstellungschirurgie, Münster, Germany
| Published: | October 21, 2010 |
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Outline
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Objective: In experimental studies, research regarding fracture healing is based on the evaluation of quantity and quality of vascularization and neoangiogenesis in callus- formation. The gold-standard in animal studies are histological and immunohistochemical assays to observe the stages of fracture-healing. An appropriate technique for a non-invasive in vivo measurement of neoangiogenesis during fracture healing has not been established yet.
In this study, a MRI- compatible animal fracture model was developed to determine neovascularization with a special molecular contrast agent for a non- invasive in-vivo analysis of bone healing.
Methods: A standardized femur shaft fracture of eight female Sprague Dawley Rats (20 weeks) was stabilized with an intramedullar PLLA (poly-L-lactideacrylate) nail to avoid electromagnetic interferences during MRI- recording. Radiographs were taken immediately after surgery to examine the quality of fracture and fixation. The MR- Relaxometrie to evaluate neoangiogenesis was performed by dynamic MRI imaging using ultrasmall superparamagnetic iron oxide (USPIO, Supravist®, Bayer Schering Pharma AG, Berlin, Germany, 80 μmol Fe/kg BW) contrast agent. 7, 14, 21 and 28 days postsurgical MR imaging was performed on a 3 Tesla MR system (Intera; Philips, Best, the Netherlands) with a solenoid receive only coil of 70 mm diameter (Philips, Best, the Netherlands). USPIO-induced change in tissue R2* (ΔR2*) was measured with multi echo MR-Relaxometry.
To underline our results, histological and immunohistological assays were performed to quantify and qualify size, structure and neovascularization of fracture callus at day 7, 14, 21 and 28- each with 8 test animals. The microvessel density (MVD) was quantified with digital image analysis (Olympus BX51 Microscope, Olympus Optical Co., Tokyo, Japan and Image-Pro Plus 5.0 software, Media Cybernetics Inc., USA). Differences between MVD and ΔR2* in callus formation were analyzed and correlated using Mann-Whitney U test with significance p<0.05.
Results and conclusions: A significant increase (p<0.05) of neoangiogenesis in callus- formation with a peak after 14 days and subsidence at day 21st recorded with the MRI was observed. Our data matched with results in literature and with our preliminary histological and immunohistochemical data, which show similar characteristics in vascularization and vessel formation in the course of time during fracture healing.
Angiogenesis and vascularization during fracture healing can be determined and monitored using this special MRI technique. The MRI- evaluation of quantity and quality of vessel formation and angiogenesis in the fracture callus might be a new non-invasive method for measurement of results and monitoring of fracture-healing in-vivo in experimental studies and maybe for clinical application in the future.
Furthermore in experimental studies, the amount of rodents sacrificed for evaluation of callus-formation in fracture healing, can be reduced significantly.
