Experimental assessment of a new direct fixation implant for artificial limbs

An alternative to prosthetic socket rehabilitation of patients with transfemoral amputation is realized by means of direct skeletal fixation devices. offering significant improvements in mobility and comfort. However, strain shielding due to high stiffness of these metal-based implants causes considerable and progressive bone loss. To overcome this phenomenon a new concept of a direct fixation implant, in form of a collared metallic pin articulating inside a polymer intramedullary part, was developed. In this study we used experimental and finite element techniques to assess whether the novel concept produced a more physiological strain distribution in the bone as compared to a standard titanium implant. Cortical strains were measured experimentally on seven human cadaver femora, both intact and implanted with a generic standard implant and the new implant. Three load configurations were considered, simulating: heel strike, toe off and one leg stance. A finite element model derived from computed tomography data was used to calculate strains in intact bone and bone with generic models of the two implant types. Significant strain shielding occurred around both implant types, albeit that for the novel design strain shielding was generally less (p