Northwestern University Flexible Subischial Vacuum Socket for persons with transfemoral amputation-Part 1: Description of technique

Abstract

Background: Current transfemoral prosthetic sockets restrict function, lack comfort, and cause residual limb problems. Lower proximal trim lines are an appealing way to address this problem. Development of a more comfortable and possibly functional subischial socket may contribute to improving quality of life of persons with transfemoral amputation.

Objectives: The purpose of this study was to (1) describe the design and fabrication of a new subischial socket and (2) describe efforts to teach this technique.

Study design: Development project.

Methods: Socket development involved defining the following: subject and liner selection, residual limb evaluation, casting, positive mold rectification, check socket fitting, definitive socket fabrication, and troubleshooting of socket fit. Three hands-on workshops to teach the socket were piloted and attended by 30 certified prosthetists and their patient models.

Results: Patient models responded positively to the comfort, range of motion, and stability of the new socket while prosthetists described the technique as "straight forward, reproducible."

Conclusion: To our knowledge, this is the first attempt to create a teachable subischial socket, and while it appears promising, more definitive evaluation is needed. Clinical relevance We developed the Northwestern University Flexible Subischial Vacuum (NU-FlexSIV) Socket as a more comfortable alternative to current transfemoral sockets and demonstrated that it could be taught successfully to prosthetists.

Keywords: Artificial limb; gait; prosthetic socket; transfemoral amputation.

Conflict of interest statement

Declaration of conflicting interests: The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Figures

Figure 1.

(Left) NU-FlexSIV Socket on limb showing sealing sleeve and (right) definitive version of the NU-FlexSIV Socket fabricated by Advanced O&P Solutions (Hickory Hills, IL). Photo courtesy of Michael Angelico.

Figure 2.

Clinical algorithm for NU-FlexSIV Socket. Regarding liner selection, almost all transfemoral limb shapes can be made more cylindrical by fitting an off-the-shelf transtibial liner; custom liners are only required when the limb is heavily scarred or bulbous. The manner in which the liner is customized should ensure that the liner clad limb shape is cylindrical. “Gradated reductions” refer to the reduction of circumferences more proximally than distally. For example, for 6%–4% reductions, the circumferences in the proximal third of the limb are reduced by 6%, the circumferences in the middle third of the limb are reduced by 5%, and the circumferences in the lower third of the limb are reduced by 4%. Source: Reprinted with permission from the authors.

Figure 3.

Example of a symmetrical residual limb shape wherein the area of the residual limb bounded by the reference line and posterior or lateral edges of the limb are approximately the same: this area represents the material to be removed during rectification of the positive model. Cross-sectional diagrams show the plaster removed based on whether the residual limb is considered symmetrical or asymmetrical.

Figure 4.

Quadrant system and exemplar mold rectification map for NU-FlexSIV Socket (M: medial; P: posterior; L: lateral; A: anterior). Color coding on the rectification map indicates depth of plaster removed.

Figure 5.

Flexible check socket fabrication: (a) flexible inner socket with Velcro and sealing ring to hold rigid polyethylene terephthalate glycol (PETG) outer socket in place (distal port hole for air not shown); (b) outer socket sprayed with alcohol to allow it to be pushed onto inner socket; (c) lateral and (d) anterior view of flexible inner socket inserted into outer socket and reinforced with fiberglass tape, black line indicates top of rigid socket; (e) donned socket showing attachment of barb to distal end of outer socket (vacuum is drawn from between the liner and inner socket through port hole and between inner and outer socket via barb); and (f) mid-stance of gait with flexible check socket.

Figure 6.

Still frame from one of the split-screen videos used to visually assess gait in both sockets during the courses.