Numerical analysis of an osseointegrated prosthesis fixation with reduced bone failure risk and periprosthetic bone loss

Abstract

Currently available implants for direct attachment of prosthesis to the skeletal system after transfemoral amputation (OPRA system, Integrum AB, Sweden and ISP Endo/Exo prosthesis, ESKA Implants AG, Germany) show many advantages over the conventional socket fixation. However, restraining biomechanical issues such as considerable bone loss around the stem and peri-prosthetic bone fractures are present. To overcome these limiting issues a new concept of the direct intramedullary fixation was developed. We hypothesize that the new design will reduce the peri-prosthetic bone failure risk and adverse bone remodeling by restoring the natural load transfer in the femur. Generic CT-based finite element models of an intact femur and amputated bones implanted with 3 analyzed implants were created and loaded with a normal walking and a forward fall load. The strain adaptive bone remodeling theory was used to predict long-term bone changes around the implants and the periprosthetic bone failure risk was evaluated by the von Mises stress criterion. The results show that the new design provides close to physiological distribution of stresses in the bone and lower bone failure risk for the normal walking as compared to the OPRA and the ISP implants. The bone remodeling simulations did not reveal any overall bone loss around the new design, as opposed to the OPRA and the ISP implants, which induce considerable bone loss in the distal end of the femur. This positive outcome shows that the presented concept has a potential to considerably improve safety of the rehabilitation with the direct fixation implants.

Design features of implants for direct skeletal attachment of limb prostheses

“…The longevity of the bone‐device bond is also an important issue considering the relatively short hosting bone of the residuum and the high loads associated with operating limb prostheses . An additional concern for longevity of the bone‐device bond is that after replacement surgery, the porosity of the cortical bone hosting the femur implant increases compared to the ipsilateral bone, potentially reducing cortical bone strength …”

“…22,24,87,92 An additional concern for longevity of the bone-device bond is that after replacement surgery, the porosity of the cortical bone hosting the femur implant increases compared to the ipsilateral bone, potentially reducing cortical bone strength. 93,94 To meet the existing challenges faced by DSA, the development of new designs and methodologies for reducing the associated risks 95,96 continues. New challenges may arise with the promising use of the transcutaneous implants for neuromuscular control of the limb prostheses.…”

Experimental Validation of an ITAP Numerical Model and the Effect of Implant Stem Stiffness on Bone Strain Energy

“…Before reliance on an in silico model can be established its accuracy must be assessed. 1,41,42 Validated FE proximal femur models 12 and SAAP FE models in proximal femurs 39,44 are described in the literature, however at the time of writing, there is no study describing a validated in silico model of an ITAP in a proximal femur.…”

New method of fixation of in-bone implanted prosthesis

“…This effect, called stress shielding, increases the porosity of the cortical bone that hosts the implant, relative to the ipsilateral bone [15]. The outcomes of stress shielding are reduction in hosting bone strength [16–17] and cortical thinning in the distal zones, which increases with time [18]. The weaking and thinning increase the risk of failure, especially among young patients who are involved in more active locomotion [19–20].…”