Transtibial Prosthesis Material Management
November 2020 Issue
Throughout my career I have lamented the lack of research and empirical data demonstrating which modification techniques for transtibial patients are effective based on patient presentation. I have struggled with determining exactly which casting and modification techniques will give my patients the best results and limit complications within their sockets. I believe that the O&P philosophy of "let's try this and see if it works," is doing a disservice to our patients. This trial and error philosophy results in more check sockets, frustrated patients, and frustrated practitioners.
To create my own criteria chart for the best treatment methodologies, I gathered research from Össur, WillowWood, Ottobock, the Steeper Group, Coyote Design, and ALPS, and my own clinical experience. I found that the industry leaders each have a different perspective on modification of molds and casting techniques based on tissue density, limb shape, and other patient presentations.
After piecing together the data from each group, I determined that to develop a personal best practices guideline, I needed to develop patient presentation criteria of my own. I broke down patient presentations into the following: soft tissue density; medium tissue density; firm tissue density; gastroc prominence upon muscle activation; redundant tissue presence; volume control issues; adhesions; perspiration; invaginations; distal sensitivity; bony prominence presence/spurs; skin grafts; and allergies to liner materials.
After narrowing down presentation, I then looked at materials: liner materials; suspension methods; casting methods; socket styles; flexible inner liner options; the use of fabric materials against the skin; custom liner use; and distal end pads.
Using the data from the industry sources, I created a chart linking the use of different materials to the different presentation criteria. I was fascinated to find that a lot of my assumptions about materials were wrong. For example, Ottobock only recommends using TPE for suction sockets. I have used TPE for everything except vacuum sockets. I suspect Ottobock's recommendation is because of flow properties and durometer. Their preference for pin suspension sockets is silicone, which tends to be stiffer and have lower flow properties, and makes sense because it would prevent elongation of the limb and thus prevent pistoning.
I was also surprised to find that fleshier limbs seem to have a better fit when total contact modification techniques were used. My reasoning is that the hydrostatic compression of the soft tissues would solidify the tissue better within the socket and prevent motion. Conversely, a patient with a more solid and bony presentation would tend to do better with a PTB or Stable Flex design. The Stable Flex, by Coyote Design, although a total contact design, focuses on removal of material at weigh-tolerant areas to create a total contact uneven surface bearing socket.
The chart that I developed isn't the last word for prosthetists, but I have found it helpful for narrowing down the materials and techniques I should use given the vast number of options. I hope that future research will be conducted to help O&P better serve our patients and remove much of the guesswork that we are faced with. I am interested to hear other practitioners' opinions on what I have developed.
Matthew Harris, CPO, is a practitioner at Horizon Prosthetics, Colorado Springs, Colorado. He can be contacted at firstname.lastname@example.org.