NU-FlexSIV Prosthetic Subischial Socket

NU-FlexSIV Prosthetic Socket

Northwestern University Flexible Subischial Vacuum (NU-FlexSIV) Socket System

Meet Katie Gazola, above knee amputee and recipient of a NU-FlexSIV Socket System

NU-FlexSIV Prosthetic Socket


Transfemoral (above-the-knee) prosthetic socket technology has changed significantly over the past 10 years. Yet, the most common issue shared by above-knee prosthetic socket users is discomfort in the groin or at the “seat” (where the socket cradles the pelvis). A new socket design, the NU-FlexSIV socket, is trying to resolve these issues to improve patient comfort.

The NU-FlexSIV socket utilizes a subischial design, which eliminates the need for the socket to contact the pelvis without compromise of stability. The socket was created by Scheck & Siress prosthetist Ryan Caldwell, CP/LP, FAAOP, who has been fitting the NU-FlexSIV socket on many different types of patients for the past 14 years. The NU-FlexSIV socket gained global recognition after presentations and courses on the socket were taught around the world since 2015. Currently, several Scheck & Siress locations offer the NU-FlexSIV socket.

How the NU-FlexIV Works

The NU-FlexSIV socket uses a combination of compressive silicone liners, flexible socket materials, vacuum suspension, and impression techniques. The lower trimlines improve the patient’s hip range of motion and comfort level, which are experienced in both walking, sitting and other activities. A prosthesis is a highly customized medical device that should always meet the patient’s needs. The NU-FlexSIV socket is trying to solve everyday problems and improve patient’s functional ability post-amputation.


Since 2010, Northwestern University has partnered with Scheck & Siress to continue development of the NU-FlexSIV socket through support of the Department of Defense (DoD). Given the clinical success of the technology, the DoD provided additional funding to compare its effectiveness to the standard of care socket technology. Early indications show that the NU-FlexSIV socket is performing at an equivalent functional level with improved comfort.

Read more on the NU-FlexSIV Socket Design.

For questions, email Ryan Caldwell, CP/LP, FAAOP at [email protected]