MusculoskeletalEstablishment of a femoral critical-size bone defect model in immunodeficient mice
Introduction
Localized bone loss associated with trauma, tumor, infection, periprosthetic osteolysis, or congenital musculoskeletal disorders, with all of these conditions requiring surgical intervention, is a major worldwide socioeconomic problem. Immunodeficient small-animal models are of particular interest for translational research strategies, as they allow for the use of human cells—a critical step on the path from bench to bedside.
So far, both tibial and femoral murine segmental bone defect models have been used. The tibial fracture model was first described by Hiltunen et al. in 1993 [1]. The disadvantages of this model are the triangular, distally declining caliber of the tibia and the bent longitudinal axis. Additionally, the close proximity of the fibula can influence the fracture repair process [2]. In contrast to the tibia, the murine femur is a tubular bone with a relatively consistent inner and outer diameter and a straight longitudinal axis [2].
In order to develop cell-based tissue engineering strategies for bone repair, there is a need for high-quality bone defect models in small animals. The small dimensions of the murine femur make it difficult to achieve proper stabilization of a critical-size bone defect. The aim of this study was to find the optimal defect size for a murine critical-size bone defect using external bony fixation method. The defect size has to be large enough to get reliable nonunions, while at the same time being small enough to achieve proper stabilization when using an external fixation device. Our hypothesis was that a segmental osseous defect size of a minimum of 2 mm would be required to generate a reliable nonunion.
Section snippets
Experimental procedure
Mice were randomized to three groups. One surgeon implanted the external fixation device (Fig. 1A, MouseExFix, RISystem; AO Research Institute, Davos, Switzerland) onto the right femur of each mouse. A defect of 1 mm, 2 mm, and 3 mm was created in groups 1 (n = 10), 2 (n = 10), and 3 (n = 10), respectively. After wound closure no additional treatment was provided in an effort to avoid influencing the natural pattern of bone regeneration. All of the operations were performed within a 12-d
Results
All of the animals survived the operation. Twenty-four out of 30 animals reached the 12th postoperative week. Six out of 30 animals (n = 2 per each group) died before the end of the observation period due to severe anemia (n = 1), infection (n = 1), pin loosening necessitating euthanasia (n = 2), and anesthetic complications during follow-up radiographs (n = 2).
Discussion
The aim of this study was to establish a murine femoral critical-size bone defect model using external fixation technique. Our main finding was that a 3-mm defect is needed to achieve a bony segmental nonunion rate of 100% after a 12-wk observation period.
Other investigators have previously used custom-made femoral external fixators for similar purposes. Cheung et al. developed an external fixation device composed of two aluminum blocks that were interconnected by two rods [4]. The femur was
Conclusions
A segmental osseous nonunion was reliably produced in nude mice by creating a 3-mm segmental femoral bone defect maintained by external fixation. This mouse model allows translational evaluation of tissue engineering concepts for site-specific bone regeneration, including strategies using allogeneic and xenogeneic cell types and tissues.
Acknowledgment
This work was supported by the AO Foundation (Start up Grant S-10-67) and the German Academic Exchange Service/Federal Ministry of Education and Research (grant no. D/09/04774). The authors are grateful to Suzanne Manthey for assistance during histology; Stephan Kirschner, MD, for help with in statistical analysis; and Christine Hamann, MD, and Volker Betz, MD, for assistance during the study design. Zhenyu Yao, MD is thanked for assistance during graphical formatting, and Dr. Ralf Bergmann for
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