Effect of amputation level on the stress transferred to the femur by an artificial limb directly attached to the bone

Abstract

Attachment of an artificial limb directly to the skeleton has a number of potential benefits and the technique has been implemented for several amputation sites. In this paper the transfer of stress from an external, transfemoral prosthesis to the femur during normal walking activity is investigated. The stress distribution in the femur and at the implant-bone interface is calculated using finite element analysis for the 3D geometry and inhomogeneous, anisotropic material properties obtained from a CT scan of a healthy femur. Attachment of the prosthetic leg at three different levels of amputation is considered. Stress concentrations are found at the distal end of the bone and adjacent to the implant tip and stress shielding is observed adjacent to the implant. It is found that the stress distribution in the femur distal to the epiphysis, where the femur geometry is close to cylindrical, can be predicted from a cylindrical finite element model, using the correct choice of bone diameter as measured from a radiograph. Proximal to the lesser trochanter the stress decreases as the femur geometry diverges significantly from a cylinder. The stress concentration at the distal, resected end of the bone is removed when a collared implant is employed. These findings form the basis for appropriate settings of an external fail-safe device to protect the bone from excessive stress in the event of an undue load.

The effect of bone growth onto massive prostheses collars in protecting the implant from fracture

“…We have shown that ingrowth into the HA Collar alleviates stress concentrations in this region and this is a particularly important finding when using these implants in young patients. Therefore, surgeons and designers must strive to enhance ingrowth no growth 25% growth 50% growth 75% growth 100% growth Table 1: Material properties for implant and PMMA cement used in FE model (according to [26]), cortical bone transversely isotropic material properties (adapted from [28]), porotic bone transversely isotropic material properties (according to [29]). Table 3…”

Load applied on osseointegrated implant by transfemoral bone-anchored prostheses fitted with state-of-the-art prosthetic components

“…Benefits and harms of the osseointegrated implants are confounded, one way or the other, by the fitting of prosthetic components during the rehabilitation and beyond (Helgason et al, 2009;Lee et al, 2008a;Newcombe et al, 2013;Stenlund et al, 2017;Stephenson and Seedhom, 2002;Thesleff et al, 2018). Clinical teams make bespoke recommendations for components considering altogether the regulation, type of implant, manufacturer's instructions, lifestyle and price tag (Morgenroth, 2013).…”

The Micro Topology and Statistical Analysis of the Forces of Walking and Failure of an ITAP in a Femur

“…The A quarter amputation of the femur requires an ITAP with an embedded depth of 160 mm, with a diameter of 14 mm [12]. The femur provided in this study was obtained by CT scanning of a deceased male aged 44 weighing at 85 kg and at a height of 185 cm [17].…”

“…However, the work of Newcombe et al, identified that an ITAP implant was not advisable for an amputation greater than one quarter of the original length of the bone. This was due to the residual σ in the femur housing, known as the anchor, being too great so damage to the cortical bone could occur [12]. Further suggested amendments to the ITAP have been developed to reduces the σ with in both the bone and the ITAP.…”