A recently published study showed that a brimless socket design improved prosthetic-related function and quality of life for amputees and was equivalent to an ischial ramus containment socket design in most gait and balance outcome measures.
The ischial ramus containment socket has been the standard of care for several decades, but has posed several problems for amputees, such as a high medial containment wall. With the emergence of an elevated vacuum design, researchers have wondered if, by capitalizing on some of the principles of the elevated vacuum that make the socket interface a more rigid structure, they could lower the trim lines without compromising the biomechanical dimensions and functions of the socket.
“From the mid 1980s, for three decades, [the ischial ramus containment socket] was the mainstay and became the standard of care, and it is the standard of care by most clinicians today. It is a fine system and it certainly addressed a number of issues evolving away from the quad socket system, but it doesn’t solve every problem,” M. Jason Highsmith, PT, DPT, PhD, CP, FAAOP, assistant professor at the School of Physical Therapy and Rehabilitation Sciences at the University of South Florida, told O&P Business News. “We wanted to test the merit of this newer design with a representative sample of typical transfemoral users that are community functioning independently. That was important to us to have high clinical and ecologic validity as opposed to just a confined laboratory experiment that would not have applicability out in society.”
Brimless vs. IRC
Highsmith and colleague, Jason T. Kahle, MSMS, CPO, LPO, FAAOP, of the University of South Florida and chief executive officer of OP Solutions, had an ischial ramus containment (IRC) vacuum-assisted suspension (VAS) interface and a brimless VAS interface designed for 10 unilateral transfemoral amputees. IRC interfaces had a medial wall height of 0.7 cm proximal to the distal-most aspect of the ischial tuberosity, while the brimless design has a medial wall of 3.3 cm more distal than the ischial tuberosity. Main outcome measures included spatiotemporal gait parameters, limits of stability, four square step test and subjective perception using the prosthetic evaluation questionnaire (PEQ).
When calculating degree of asymmetry, study results showed a significantly improved step length toward the IRC. However, researchers also found a significantly narrowed base of support toward the brimless design. Compared with the IRC, researchers found all subjective measures reached statistical significance in favor of improvement with the brimless design.
According to Highsmith, the majority of patients accepted the use of the brimless system over the IRC, which was surprising since most of the patients had a long history with previous technologies.
“It was a little surprising that a lot of these folks had a long history with other socket technologies and then unanimously all of them were accepting of [the brimless] system,” Highsmith, who is also co-director at the Center for Neuromusculoskeletal Research, said. “I expected that someone who had a long history with a previous technology would be hard to change from that. I guess the reduction in pressure on their ischial tuberosity was enough to convince the majority of them.”
“The importance of this study for the amputees is that it creates a more comfortable, better functioning socket, while it gives the prosthetist more alternatives to fill their arsenal with and present to their patients who are experiencing skin breakdown or who are uncomfortable with the ischial containment socket,” Kahle said. “It gives us all a functionally equivalent or superior alternative.”
This is not the first time the researchers had studied differences in brimless and IRC sockets. In a previous study published in the Journal of Rehabilitation Research and Development (JRRD), Kahle and Highsmith analyzed nine transfemoral amputees to test an IRC and brimless socket for vertical and lateral socket movement, coronal hip angle, skin pressure and socket preference.
As with this most recent study, patients preferred the brimless socket to the IRC. When it came to measurement of coronal hip angles and vertical and lateral socket displacement, the researchers found the brimless design was statistically equivalent to IRC. Study results also showed a peak/stance mean pressure in the medial proximal aspect of 322 mmHg in the IRC vs. 190 mmHg in the brimless.
“The nice thing about these recent results were that they have some relationship to the other study that we published in JRRD that showed it is possible that there is some improved skeletal kinematics by lowering the trim line,” Highsmith said. “So essentially think of it as freeing up the hip skeletal structures to be able to move more normally.”
In future studies, Highsmith believes continuous exercise should be used to see if narrower based gait has implications for differences in gait bio energetics. Kahle added that it is also important to compare different types of suspension systems to see which system works best with a brimless socket design.
“While ischial containment sockets are recognized as the standard of care, we firmly believe that in any domain of health care, be it a surgery or a pharmacologic agent or a device like this, the patient should have access to all their options,” Highsmith said. “Elevated vacuum subischial socket technology is here as an option. We think patients should be presented with all the information and that should be one option that they should be given for consideration.” — by Casey Tingle
Disclosures: Highsmith and Kahle have no relevant financial disclosures.