FINITE-ELEMENT ANALYSIS OF THE IMPLANTED PROXIMAL TIBIA - A RELATIONSHIP BETWEEN THE INITIAL CANCELLOUS BONE STRESSES AND IMPLANT MIGRATION

The cancellous bone stresses within the implanted proximal tibia were examined using a three-dimensional anatomical finite element model. Th ree versions of a proximal tibial prosthesis were examined: an all pol yethylene press-fit design; a metal backed, stemmed press-fit design a nd a (horizontally) cemented metal backed, stemmed design. All three d esigns had published migration and survivorship data. The objectives o f the study were (i) to compare the stresses generated by each of the tibial components, (ii) examine the influence of the resected surface morphology and (iii) compare the initial cancellous bone stresses with the published migration and survivorship data. The all polyethylene p rosthesis generated the highest cancellous bone stresses. Addition of a metal backing and a stem reduced the stresses, but the cemented devi ce produced the lowest cancellous bone stresses. The surface morpholog y had a significant effect on the cancellous bone stresses generated b y press-fit prostheses. As the bone-prosthesis contact area decreased, the peak cancellous bone stresses increased by as much as 243%. The s urface morphology had no effect on the cancellous bone stresses genera ted by the cemented implant. Good correlation was found between the pr edicted cancellous bone stresses and the migration and survivorship da ta, with the implant generating the highest cancellous bone stresses m igrating the most and having the poorest survival rates at 5 year. The results support the hypothesis that the progressive failure of cancel lous bone is a mechanism of implant migration regardless of the method of fixation and the implantation site. (C) 1998 Elsevier Science Ltd. All rights reserved.