A failure envelope approach to characterizing strength of an amputated femur with a bone-anchored percutaneous implant

Bone-anchored percutaneous implants, commonly referred to as osseointegrated implants, are gaining popularity as an alternative to sockets for attaching a prosthetic limb to an amputated femur. While these implants have several advantages, femoral fractures are relatively common in these patients, occurring in 6.3% of femurs within 4 years. This study aimed to develop a novel method to quantify femoral strength under all possible external loads acting on the distal implant. Finite element analysis was used to explore combinations of forces and moments that, when applied on the bone-anchored implant, were just sufficient to fracture the femur. The 6-dimensional envelope generated in the current study provided a quantitative description of the strength of the femur-implant construct. All the femoral fractures were predicted in the trochanteric region, corresponding to where most in vivo fractures have been reported. The 6-dimensional envelopes developed in the current study may be useful in the design of fail-safe devices that could reduce femoral fractures in patients with bone-anchored percutaneous femoral implants. The framework presented may also be used for determining patient suitability for bone-anchored percutaneous implants, and for evaluating the functional performance of implant designs.