Peak Stress Reduction in Below-Knee Amputation

Sunil, Priyankha; Bent, Riley; Rios, Gabriella; Leland, William

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Peak Stress Reduction in Below-Knee Amputation

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Transtibial amputation, or below-the-knee amputation, is a surgical procedure performed in the area between the ankle and the knee. Residual limb pain is experienced by 60% of the patients after surgery, often caused by infection, nerve damage (neuromas), and high stresses between the bone-ending and soft tissue due to excessive loading at the amputation site. Our team collaborated with Dr. John J. Wixted, specializing in orthopedic surgery, and Dr. Arthur Graham, specializing in prosthetics, to develop an implant that enhances load distribution and minimizes peak stress on the soft tissue near the bone ending in transtibial amputations. For the weight-bearing end, the team developed four implant designs, flat, turtle, muffin, and mushroom. Each of these designs was tested through the Ansys finite element analysis (FEA) model and Fujifilm Instron Testing to determine the effectiveness of the device designs. This included reducing stress between bone ending and soft tissue, reducing skin irritation, biocompatibility, stable interface, and reducing soft tissue used as a cushion. The outcomes from the FEA analysis presented the mushroom design proved most effective at decreasing the peak muscle ending stresses by 23%, 18%, and 30% for heel strike, standing, and heel-off loading states. The findings from the Fujifilm analysis supported those of the FEA analysis, indicating that the mushroom design was the most effective due to its uniform pressure distribution and consistent low-pressure reading across its surface. Overall, the implant incorporates a mushroom-shaped end structure designed to maximize load distribution, through the increased surface area, resulting in at least a 25% reduction in Peak Von Mises Stress originating from the residual bone near the soft tissues. The mushroom end is connected to a biocompatible Titanium alloy rod through Morse taper, which is then press-fit into the patient’s bone to facilitate osseointegration.

This report represents the work of one or more WPI undergraduate students submitted to the faculty as evidence of completion of a degree requirement. WPI routinely publishes these reports on its website without editorial or peer review.

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