Haffner-Luntzer Melanie, Müller-Graf Fabian, Matthys Romano, Hägele Yvonne, Fischer Verena, Jonas René, Abaei Alireza, Gebhard Florian, Rasche Volker, Ignatius Anita
Institute of Orthopedic Research and Biomechanics, University Medical Center Ulm, Ulm, Germany.
Department of Traumatology, Hand-, Plastic-, and Reconstructive Surgery, University Medical Center Ulm, Ulm, Germany.
PLoS One. 2017 Mar 23;12(3):e0174283. doi: 10.1371/journal.pone.0174283. eCollection 2017.
Mice are extensively used for experimental bone-healing studies. However, there are few established nondestructive in vivo techniques for longitudinal fracture-healing analysis in mice, including in vivo micro-computed tomography (μCT) and radiography. Importantly, none of the established methods can discriminate between non-mineralized fibrous tissue and cartilage in the soft fracture callus. Therefore, the objective was to establish high-resolution in vivo magnetic resonance imaging (MRI) for the longitudinal assessment of soft callus formation during bone healing in mice. C57BL/6J mice received a femur osteotomy stabilized using an external fixator and were randomly assigned to five groups. Group 1 mice were scanned three times longitudinally during fracture healing using an optimized MRI scanning protocol to establish an algorithm to characterize the different fracture-callus tissues. Mice of groups 2-4 were scanned once on day 10, 14 or 21, respectively, euthanized after scanning and their femurs subjected to ex vivo μCT and histomorphometric analysis to compare the data assessed by MRI with μCT and histology. Control group 5 mice were not scanned. After 28 days, mice of groups 1 and 5 were euthanized and the fracture-healing outcome was evaluated by bending-test, μCT and histology to determine whether the repeated anesthesia, handling and the MRI measurements themselves influenced fracture healing. The callus-tissue values determined by MRI were mostly comparable to those obtained by μCT and histomorphometric analysis. However, at time points characterized by small relative bone or cartilage areas, MRI measurements were weakly comparable to histomorphometric data, possibly due to the inferior spatial resolution. Importantly, at the early and intermediate phases of healing, cartilage and fibrous-tissue values obtained by MRI were highly accurate. Furthermore, repeated anesthesia, handling and MRI scans did not impact bone healing. Therefore, we demonstrated the feasibility of high-resolution in vivo MRI for longitudinal assessment of soft callus formation during murine endochondral fracture healing.
小鼠被广泛用于实验性骨愈合研究。然而，目前几乎没有成熟的用于小鼠骨折愈合纵向分析的非侵入性体内技术，包括体内微型计算机断层扫描（μCT）和X线摄影。重要的是，现有的方法都无法区分软骨折痂中的非矿化纤维组织和软骨。因此，本研究的目的是建立高分辨率体内磁共振成像（MRI）技术，用于纵向评估小鼠骨愈合过程中软痂的形成情况。C57BL/6J小鼠接受股骨截骨术，并用外固定器固定，然后随机分为五组。第1组小鼠在骨折愈合过程中使用优化的MRI扫描方案进行三次纵向扫描，以建立一种算法来表征不同的骨折痂组织。第2 - 4组小鼠分别在第10、14或21天进行一次扫描，扫描后安乐死，对其股骨进行离体μCT和组织形态计量学分析，以比较MRI评估的数据与μCT和组织学数据。第5组为对照组，小鼠不进行扫描。28天后，对第1组和第5组小鼠实施安乐死，并通过弯曲试验、μCT和组织学评估骨折愈合结果，以确定重复麻醉、处理和MRI测量本身是否会影响骨折愈合。MRI测定的痂组织值大多与μCT和组织形态计量学分析获得的值相当。然而，在相对骨或软骨面积较小的时间点，MRI测量与组织形态计量学数据的可比性较弱，这可能是由于空间分辨率较低所致。重要的是，在愈合的早期和中期，MRI获得的软骨和纤维组织值非常准确。此外，重复麻醉、处理和MRI扫描并未影响骨愈合。因此，我们证明了高分辨率体内MRI用于纵向评估小鼠软骨内骨折愈合过程中软痂形成情况的可行性。
