A Successful Collaboration To Improve Transfemoral Sockets

April 1, 2015

A Successful Collaboration To Improve Transfemoral Sockets

Transfemoral (TF) amputees face numerous disadvantages compared to those with a transtibial (TT) amputation. In addition to the issues that are common to all lower limb amputees, such as volume changes and perspiration, TF amputees also experience reduced comfort and range of motion due to existing designs in which a rigid plastic socket extends high on the limb. Adequate suspension of these sockets is also difficult to achieve due to the lack of space available on the thigh for accommodating the external seals that are used successfully in TT suspension.

Faced with these challenges, transfemoral amputees can be forgiven for having low expectations when offered the opportunity to test a new design. However, amputees who have been fit with a new transfemoral socket concept from WillowWood have made statements such as “The day I got this, I ran for the first time in three years;” “For the first time in 35 years, I can vertically jump;” and “I’m living again.” What new technology has caused such a reaction, and how did it come about?

The project began in early 2011 when the U.S. Department of Veterans Affairs announced an Innovation Initiative (VAi2) to improve the fit, function, and comfort of prosthetic sockets for transfemoral amputees. Because WillowWood’s engineering team had already been working on some concepts that coincided with this goal, it made sense to apply for this grant; but to make the proposal even stronger, WillowWood approached The Ohio State University (OSU) and The University of Akron (UA) to join the project as collaborators. Ohio State is a world leader in wound healing and tissue health; UA has extensive experience with polymers. Together, these three entities submitted a concept paper in April 2011 that described a 4-pronged approach:

1) Development of an internal seal for a TF socket.
2) Improvement and adaptation of WillowWood’s LimbLogic® vacuum suspension system to TF applications.
3) Stabilizing the temperature inside of the prosthetic socket through the use of new thermally enhanced materials and structures.
4) Research to establish the optimal integration of these new technologies and their efficacy.

In August of 2012, WillowWood was selected to receive the VAi2 grant, and work began in earnest. UA evaluated existing liner and socket materials, and OSU conducted outcomes research on various existing socket designs. WillowWood used their findings in the development of the socket system, after which OSU and UA evaluated the new design. Additional collaborators from industry, such as Outlast Technologies, were brought in along the way.

Throughout the process, the internal WillowWood team met weekly, an Outcomes Measures group held a weekly teleconference with OSU, and a Cooling System group held a weekly teleconference with UA. WillowWood’s team also visited OSU and UA to participate in some of the testing efforts. The team published monthly reports and shared documents using BaseCamp, a web-based project management and collaboration tool. Face-to-face meetings between collaborators, VA personnel, and amputee test patients were held each quarter.

The resulting system incorporates the following elements:

• An internal socket sealing system featuring a flexible polymeric sealing membrane attached to a flexible inner brim. This system accommodates proximal limb motion while maintaining a secure, comfortable seal that is protected from punctures.
• A vacuum system that allows better positioning of the knee components for optimized knee center height; easier release of vacuum; reduced noise; adaptive pressure regulation based on socket conditions; and tracking of socket conditions and system usage.
• A liner that regulates skin temperature by incorporating Outlast®, a Phase Change Material (PCM) that stores and releases thermal energy as it transforms from a solid to liquid and back to a solid.
• A lower trim line that increases comfort for the user without sacrificing suspension.

The system has been worn by dozens of test patients, all of whom provided valuable feedback to help refine the design along the way. Users report that they no longer have to remove the socket during the day to wipe away sweat; they participate in activities that their previous prostheses did not allow them to do; and all of their daily activities, including something as simple as sitting in a chair, are much more comfortable.

There were many challenges along the way, such as contract negotiations, gel formulations, socket fabrication, sensor accommodation for in-socket testing, and thermoconductivity test methods. The key to successful completion of the project was for all parties to remain flexible as they worked to solve each issue. Each entity contributed key achievements in their areas of expertise to produce a significant step forward in transfemoral socket technology.

WillowWood, located in Mt. Sterling, Ohio, is an industry leader in the design, manufacturing, and distribution of prosthetic products, including the Alpha® family of liners, the Pathfinder® II foot, and the LimbLogic® vacuum system. For more information about WillowWood and its products, please call 1.800.848.4930 or visit the company’s website at www.willowwoodco.com.