Tissue differentiation around a short stemmed metaphyseal loading implant employing a modified mechanoregulatory algorithm: A finite element study

Short stemmed cementless implants are being used increasingly to avoid problems associated with their long stemmed counterparts such as size, stiffness, and bulky nature, which can contribute to stress shielding, fractures, and hence loosening. They are also thought to enhance physiological loading of the femur. We performed a computational investigation of the possible tissue differentiation and bone ingrowth processes for a specific type of stemless implant using a mechanoregulatory hypothesis, with modifications to simulate tissue differentiation, and simplified loading conditions. The peak forces during stair climbing and normal walking were investigated to evaluate their influence on the process. The results were compared to clinical studies for relevance and corroboration. The majority of the tissue type formed was fibrous, occupying the proximal regions of the implant. The lateral flare design feature of the implant was predicted to enhance bone and cartilage formation in regions beneath it compared to the same design without a flare. The percentage of bone formed increased through the iterations and accounted for nearly 35% of the tissue at the end of the iterations in Gruen zones 2 and 6, replacing cartilage tissue as differentiation progressed. This agreed well with clinical data showing similar regions of bone formation and suggests that the distal regions of the implant under the lateral flare, resting in the metaphyseal region of the bone, promoted implant stability.