Joris ANTHONISSEN, Christian OSSENDORF, Johanna Lisa HOCK, Ulrike RITZ, Alexander HOFMANN, Pol Maria ROMMENS

A new small-animal model for the study of acquired heterotopic ossification after hip surgery

Objective: Heterotopic ossification (HO)--the formation of bone in soft tissues--is a frequent problem after surgery of the hip and pelvis, but little is known about its underlying pathogenic mechanisms. It is vital to study the underlying pathogenesis in animal models to develop and evaluate new prophylactic regimens directed against HO. However, previously developed small-animal models for the study of HO imitate neither surgery nor trauma-mechanisms that potentially cause HO. Hence, the goal of this study was to develop a novel small-animal model imitating hip surgery that can reliably produce HO.Methods: Twenty male Wistar rats were subjected to surgery of the right hip during which the femoral canal was reamed in three steps up to 2 mm, and a muscle lesion was made. Twelve weeks after surgery, the amount of heterotopic bone was assessed using micro-computed tomography.Results: Eighteen of 20 animals showed HO around the hip 12 weeks after surgery. The amount of heterotopic bone varied from very small particles up to near ankylosis.Conclusion: A rat model of hip/pelvic surgery that does not use exogenous osteogenic stimulus and can reliably produce HO was developed

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