Abstract: Objective To develop a knee joint impact device to produce animal model of subchondral bone micro-fracture in rabbits.Methods A knee joint impact device was designed. 12 New Zealand rabbits were divided into group A (n=6) and Group B (n=6). In the group A, 6 patellar-femoral joints of the 6 rabbits were impacted (1.74 kg from height of 30 cm). In the group B, 6 femoral condyles of the 6 rabbits were impacted (1.14 kg from height of 28 cm). All the rabbits were evaluated with X-ray and MRI post injury. The femora of all the rabbits were observed with HE staining. Results No fracture line was found in all the animals with X-rays. The MRI of the 6 knee joints in the group A showed low signal intensities on T1 weighted, T2 weighted and fat suppression images. Histopathology demonstrated integrated cartilage and sunchondral bone plate, micro-fractures of cancellous and bleeding in marrow. The MRI of the 5 knee joints in the group B showed low signal intensities on T1 weighted images and high signal intensities on T2 weighted and fat suppression images. Histopathology demonstrated integrated cartilage and sunchondral bone plate, micro-fractures of cancellous and bleeding in marrow. No disorder was found with MRI and histology in the contral sides. Conclusion The impact device of the knee joint can produce controllable and reproducible subchondral bone micro-fracture in rabbits.

Key words: subchondral bone, micro-fracture, animal model, impactor, imaging, histopathology, knee, rabbits