RESUMEN
BACKGROUND: The rising incidence of acetabular fractures in the elderly presents an increasing surgical challenge due to patient co-morbidities, complex fracture patterns' and osteoporotic bone. Of interest in this study are those of the quadrilateral plate, which are more common in elderly patients with osteoporosis. Following such injuries, the weight-bearing surface of the femoral head moves medially. Non-operative management of these fractures can lead to the acetabulum articulating on the femoral neck increasing the risk of subsequent femoral neck fracture as a result of the altered biomechanics.Using finite element analysis (FEA) this study seeks to understand the changing biomechanics of the proximal femur in such instances and to determine if there is a threshold of femoral head medialisation that can predict probability of femoral neck fracture. METHODS: A femoral neck FEA model was created from the CT and MRI scans of a healthy hip. Using FEA, the model was used to apply point loading to the femoral head at the anatomical weight bearing area and subsequent lateralization of this point down to the femoral neck-shaft junction. This simulates the changing forces acting on the femur as the head medialises into a fractured acetabulum. RESULTS: As the point of contact moved laterally the stress levels within the proximal femur increased steadily, particularly along the superior neck. Bending moment at the medial neck shaft junction also increased. This increase in stress levels can be seen as a corollary for risk of fracture within the femur. CONCLUSION: With medialisation of the femur into a fractured acetabulum there is a significant change in the stress distribution within the femoral neck. Clinically, this is indicates that patients with such injuries are at an increased risk of femoral neck fractures once they begin to mobilise after the initial injury, a devastating result. This model may be of use to treating surgeons in predicting the risk of femoral neck fracture.