Characterisation and Development of an Experimental Mechanical Model of Avascular Necrosis of the Femoral Head

Avascular necrosis (AVN) of the femoral head is a debilitating disease of the bone that may result from a variety of aetiologies, and progresses to the death of the bone and collapse of the femoral head, and ultimately to deformation of the hip joint. In vitro models of AVN have been previously developed in live animals; however none of these models produce the mechanical failures that are observed in AVN femoral heads. The aim of this study was to produce a mechanical simulation model of AVN in vitro. To achieve this, a series of preliminary studies were carried out. First, femoral heads from AVN patients undergoing total hip arthroplasty were studied to understand the effects of the disease on the mechanical and structural properties of the bone. The findings were compared with mechanical and structural properties of bone from nonpathological control femoral heads, and the results demonstrated mean reductions in the mechanical properties of bone with AVN. Methods of reducing mechanical properties of bone were analysed to develop a mechanical simulation model of AVN in vitro. For this, chemical methods were analysed which either demineralised or dissolved the collagen matrix in the bone. The effects of treatment time were analysed on mechanical properties of bone, and it was found that demineralising bone plugs in hydrochloric acid was the most effective method of reducing the mechanical properties of bone. In order to develop a model of AVN, porcine bone sections were treated with hydrochloric acid and returned to the femoral heads to simulate lesions in AVN. The resultant change in the structural mechanical properties of the femoral heads were analysed to determine the most suitable method of simulating AVN in porcine bone, and to provide recommendations for achieving a mechanical bone model representing the structural and mechanical properties of AVN femoral heads.