Multi-purpose gel liners are the primary suspension choice for the majority of lower limb amputees, according to Gerald Stark, CPO, FAAOP, vice president of product development and education for Fillauer Inc. Stark presented at the American Orthotic and Prosthetic Association (AOPA) National Assembly in Seattle.
According to Stark, 60% of lower limb amputees report skin conditions that can be characterized as moderate to severe enough to limit prosthetic wear. He also noted that nearly 80% of amputees claim to have chronic skin conditions including irritations, ulcers, cysts and verrucous hyperplasia. While gel liners are the choice for the majority of the amputees, Stark pointed out that prosthetists tend to have two or three favorite liners for their patients, as opposed to one dominant liner given to all.
“Not all gel liners are the same and they are actually intentionally designed to have different properties,” Stark said at the assembly.
Flexible gel liners serve multiple purposes such as suspension, shear relief and cushioning. The design of gel liners has evolved to include many different designs. Gel liners can be broken down into clinical classifications based on material type, softness, construction matrix and suspension and surface matching. According to Stark, there are three major types of gel liners – thermoplastic elastomer (TPE), silicone and urethane. Stark mentioned how TPE, a nanostructure of plastic and rubber, was not a viable liner option for prosthetics until an outer fabric coating was added to the liner. Without the added fabric, compression and shear caused an immediate breakdown on the liner.
Athletes tend to favor custom and stiffer designs to reduce energy loss. Conversely, geriatric patients tend to prefer softer designs and can tolerate more generic interface shapes, according to Stark. Custom molded liners can be made with urethane or silicone as long as they are reinforced with a pin construction. According to Stark, vacuum suspension may maximize the durability of a liner and minimize any volume changes. Each manufacturer can change the softness of the material based on their proprietary formula, Stark said.
Stark described the balance prosthetists and orthotists need to find between softness and durability.
“Durability is usually the converse of softness depending on the construction matrix,” Stark said at the assembly.
If the gel liner is too soft, the shear force resistance will be poor. Severe skin conditions could limit or ultimately eliminate a patient’s ability to wear a prosthesis. Understanding and controlling this balance is vital, according to Stark. — Anthony Calabro
Gel liners have become widely used, though they still have issues. As mentioned, skin condition may be adversely affected when gel liners are used, possibly due to material interaction with the skin or by a lack of careful attention to hygiene. As research continues in the development of new products, we are likely to see materials that are less resistant to developing odor or harboring bacteria. A better understanding is needed of how the liner materials are interacting with the skin and socket, especially when variables such as active vacuum are added. The material interaction may be even more important as the number of individuals with limited circulation or neuropathy who utilize gel liner technology increases.
— Laura Miller, PhD, CP
Rehabilitation Institute of Chicago