Axial forces and bending moments in the loaded rabbit tibia in vivo

A minifixateur system with 4 force sensors was developed and attached to rabbit tibia (n = 4), which were subsequently ostectomised. Axial forces, bending moments and bending angles were calculated telemetrically during weight bearing in motion between 6 and 42 days post operation.Highest single values were 201% body weight [% bw] for axial forces and 409% bw cm for bending moments. Whereas there was a continous decrease in axial forces over time after day 10 (P = 0.03 on day 15), a decrease in bending moments was inconsistent (P = 0.03 on day 27). High values for bending moments were frequently, but not consistently, associated with high values for axial forces.Axial forces in rabbit tibia exceeded axial forces in sheep, and differed from indirectly calculated data. The rabbit is an appropriate fracture model because axial loads and bending moments in rabbit tibia were more closely to human conditions than in sheep tibia as an animal model.There are various animal models for musculoskeletal research. Some laboratory species, e.g. mice and rats, are too small for the investigation of implant materials (e.g. orthopaedic plates and screws) in weight-bearing bones. Therefore, in addition to sheep and dogs, rabbits are a commonly used model [1,2]. Studies using rabbit tibia were done to assess fracture healing following internal fixation with screws and plates [2,3], external fixation [4,5], and intramedullary nailing [6-8]. Although bone microstructure, bone remodelling, gait, and consequently, the biomechanical forces acting on the bones differ presumably from those of humans, screening of newly developed implant materials is common in animal models. As additional evaluation method, in vivo μ-computed tomography can be performed in rabbits to examine bone and implant alteration during the post operative follow-up period [9]. In contrast, this method cannot be used in larger animals due to their size. To decide, whether the rabbit or a large animal model is the appropr