A team led by Dr Arjan Buis, from the Department of Biomedical Engineering, University of Strathclyde, Glasgow, Scotland, has developed the innovative system, known as Majicast, to manufacture lower limb prosthetic sockets that fit prostheses securely to patients’ residual limbs.
To cast for a new prosthesis, the residual limbs of the amputee are immersed in a tank of water one at a time, with a membrane material wrapped around them. The person’s body weight is then used to load this – similar to loading a prosthesis during gait. This pressure casting deforms the soft tissue, under a uniform load. When a limb is subject to uniform external pressure, there will be an internal equilibrium pressure at which the soft tissue has maximum load-bearing function, and where internal shear stresses are minimized.
Using this casting method, the soft tissue is ideally positioned in its stiffest form for load transfer. This means vertical movement of the limb in the socket – or pistoning – is limited, reducing deep shear stresses and so shear and friction related problems that can cause soft tissue damage and discomfort.
“The method gives uniform loading to the soft tissue,” said Dr Buis. “Normally, taking moulds is done by hand and its success depends on the skill of the person making them. There are also no current socket fit criteria other than that the resulting socket must be comfortable and functional. For an engineer that isn’t very specific, and as a result, we developed a method of both surface and volume matching.”
“The Majicast is a straightforward, fully automated, easy-to-use device that will produce high quality prosthetic sockets,” he added. “The device has been scientifically tested and clinically validated; this method has also been shown to be more repeatable and consistent than traditional methods.”
As the technique does not require a great deal of skill from technicians, it will be easy to train local people to fit prosthetics – something that is important in low income countries where demand is high and money for this is scarce.
The academics are now working with members of Dutch-based social enterprise organization ProPortion to help people in Colombia, offering high-quality artificial legs to people who have lost limbs, often through injuries from landmines.