The Rabbit Model of Femoral Bone Defects: Steps to Overcome Potential Pitfalls

Aims: To identify the potential pitfalls and indicate procedures to prevent them, during the evaluation of biomaterials for orthopaedic and craniofacial research in the New Zealand White (NZW) rabbit animal model of femoral bone defects.

Place and Duration of Study: Laboratory for Research of the Musculoskeletal System, School of Medicine, University of Athens, between June 2014 and July 2015.

Materials and Methods: Pre-emptive analgesia (carprofen 2.2 mg/kg sc), chemoprophylaxis (enrofloxacin 10 mg/kg sc) and anaesthesia (ketamine/xylazine 30/5 mg/kg im) were administered to NZW rabbits (body weight 3.3±0.2 kg, mean ± SD) for the aseptic surgical creation of drilled bone defects of 6 mm diameter (“critical size defect”) in the external femoral condyle of the left limb. All rabbits recovered without post-surgical complications from the first postoperative day.

Results and Discussion: Although the research group consisted of Veterinarians and Orthopaedic Surgeons with experience in this model, they were challenged with potential pitfalls which were overcome step by step. Among them is the precise localization of the defect to be drilled. Intra-operative palpation of the external femoral condyle assists in determining the site, and post-operative X-ray evaluation confirms it. Additionally the correct width and depth of the bone defect are important to adhere to, which was achieved by using a 5.5 mm diameter bone drill and observing its depth marks. Another challenge is to have the specific amount of biomaterial implanted confined to the defect. Its potential distribution in the femoral shaft, diffusion in the metaphysial trabecular bone or excessive covering of the bone surface, are also pitfalls to be avoided.

Conclusions: The increased use of this animal model in the evaluation of biomaterials in orthopaedic and craniofacial research requires knowledge, skills, surgical accuracy and attention to a sequence of steps, in order to achieve homogenous results and high repeatability of the implantation technique. With the fulfillment of these conditions, the extraction of valid scientific results and reduction of the number of animals used are possible.