Fracture forces in femurs implanted with PMMA

With increasing numbers of hip fractures each year in the US, it is important to develop preventive treatment options including prophylactic reinforcements and tools to assess treatment efficacy. Thirteen cadaver femurs including five normal, two osteopenic and six osteoporotic pairs, were selected from a larger sample and were tested to fracture in a materials testing machine. Three osteoporotic femurs were injected with PMMA in the neck region while the contralateral femurs were used as controls. Photographs from two orthogonal directions captured the geometry of the femur and system prior to testing. Fracture forces and moments were measured using three load cells. The load cells were attached to a custom fixture that was designed to characterize all forces and moments during testing. A total of eight force and moment signals, along with machine head displacement and time were recorded simultaneously. A detailed biomechanical analysis of the forces and moments at fracture was performed using the measured loads and the geometry of bones in the test fixture. The analysis confirmed that the PMMA implanted osteoporotic femurs fractured at higher forces than their contralaterals. The reinforced femurs' fracture forces were similar to those of normal bones. Their fracture patterns more closely resembled normal femurs than osteoporotic femurs.