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Direct skeletal attachments for transfemoral amputees have been the subject of clinical trials since the early nineties. This method of attachment allows the amputee an unrestricted range of motion around the hip joint, better sitting comfort, improved sensory feedback through osseoperception, improved limb control and reduced soft tissue problems. However, the length of the rehabilitation period is perceived as a shortcoming by the amputees and the clinicians. The aim of the present study is to estimate the risk of failure during gait, for a patient with direct skeletal attachment of a femoral prosthesis, using finite element analysis (FEA). Material properties and loads were derived from subject-specific data and implant stability assumed secured by bone ingrowth into a porous implant surface. A simplified FEA was used to optimize the implant geometry with respect to load bearing capacity. The resulting geometry was then implemented in a subject-specific FE study. The results indicate that the risk of failure for the implant system is approximately three times greater than what can be expected for an intact femur. The main conclusion, based on the risk of failure factors calculated, is that it is likely that a porous-coated implant could be beneficial for osseointegrated fixation. It is also suggested that the proposed methodology can be used in future studies exploring the mechanical stability of osseointegrated fixation in the view of improving direct skeletal attachments for lower limb amputees.

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Microprocessor-controlled prosthetic knees, which rely on magnetorheological (MR) technology, have the potential to increase the comfort and quality of life of amputees. The focus of this study is on a prosthetic knee which is currently on the market and manufactured by the company Ossur Inc. The knee uses magnetic fields to vary the viscosity of the MR fluid, and thereby its flexion resistance. The torque transmissibility of the knee greatly depends on the magnetic field intensity in the MR fluid. The objective of this study is to investigate the strength of the magnetic field and the braking torque in the knee, for a few selected design parameters, and to determine which changes can be made to the existing design in order to maximize the torque output. The magnetic field in the fluid is evaluated by finite element analysis and the torque is calculated by using a Bingham visco-plastic model. A parametric study is carried out for several design parameters where the effect of variation in each parameter on the braking torque is observed. The results of this study give a valuable insight into which parameters should be prioritized for future changes of the knee, with regard to strength and comfortability.