Development and validation of rabbit models of acetabular posterior wall fractures

Objective To validate the rationality of establishing an animal model to simulate acetabular fractures in human patients so as to develop invivo studies about conditions involving acetabular fractures. Methods Thirty mature New Zealand rabbits (60 hips) were submitted to extended non-weight-bearing radiography of the hip, and obvious deformity and dislocation were excluded. Lateral center-edge angle (LCEA) and acetabular-head index (AHI) of the hip were measured by picture archiving and communication systems (PACS), and the results were compared with normal adults. Another 24 mature New Zealand rabbits collected were divided into three groups according to the random number table: group A, served as normal controls and groups B and C, subjected to high-energy fractures of the acetabular posterior wall by using heavy impact method. Load between femoral head and acetabulum was measured by pressure transducer. Acetabular fractures in group C were fixed with a plate-screw system, but not in group B. After 3 months, radiography of the hip was implemented. A semi-quantitative scoring system about osteoarthritis (OA) was applied to each radiographic image. Cartilage tissues of the acetabular posterior wall were resected for histological study, and was rated using the Mankin histologic rating system. Results LCEA and AHI of the rabbit hip were (29.9±3.6)°(95%CI 29.12-30.75) and (84.6±1.6)% (95%CI 84.18-84.99) respectively, and all were in the normal reference ranges of adult human (P>0.05). Contact stress delivered to the acetabulum was 45 MPa. After 3 months, radiography and histology of the hip exhibited obvious differences among the groups. Hip joint with post-traumatic osteoarthritis combined with subluxation and cartilage with irregular surface, fibrous tissue and osteophyte were seen in group B. Decreased thickness of the articular cartilage and malalignment and proliferation of cartilaginous cells on acetabulum posterior wall were seen in group C. Hip OA semi-quantitative score and Mankin score in groups B and C were better than group A, but the results were the best in group B (P<0.05). Conclusions Rabbit hip joint presents good matching with the acetabulum and is suitable for animal studies simulating human hip conditions. The rabbit model of acetabular fractures developed in this study simulates human posterior wall acetabular fractures availably, and is suitable for animal studies about pathophysiology, treatment and intervention of human conditions involving acetabular fractures. Key words: Acetabulum; Hip fractures; Models, animal