Ischial containment sockets are the current standard of care for military service members with transfemoral amputation. However, they fit intimately with the ischium, which may limit hip motion and contribute to proximal socket discomfort, a common complaint among prosthesis users. Subischial sockets, such as the newly described Northwestern University Flexible Subischial Vacuum (NU-FlexSIV) Socket technique, do not interact with the ischium, potentially increasing hip motion and improving comfort.
Purpose: To transfer the NU-FlexSIV Socket technique to military prosthetists and evaluate performance among military service members with transfemoral amputation.
Study design: case series.
Methods: Four of the 11 enrolled subjects completed the study protocol comparing the NU-FlexSIV Socket to the ischial containment socket. Gait kinematics (over ground and on stairs), physical performance measures (Four-Square Step Test, T-test of Agility, and an obstacle course), limb-socket motion, and socket comfort were assessed after accommodation time in each socket.
Results: While wearing the NU-FlexSIV Socket, sagittal plane hip motion generally increased while coronal plane trunk motion and walking speed remained largely unaffected during over ground walking. During stair ascent, sagittal plane hip motion increased while wearing the NU-FlexSIV Socket, with minimal changes in walking speed for all subjects. Pre- and post-walking fluoroscopy measures suggest fit of the NU-FlexSIV Socket was less affected by activity. Most subjects reported that the NU-FlexSIV Socket was more comfortable for sitting but some found it less comfortable for walking and running. Performance measure results were mixed. Although attempts were made to consistently implement the NU-FlexSIV Socket technique, some challenges were experienced.
Conclusions: The NU-FlexSIV Socket provided greater hip motion across a variety of tasks without adversely affecting other movement mechanics but did not consistently improve socket comfort. Variability in the liners and socket materials used may have contributed to variability in results. Overall, the design was a viable alternative to traditional ischial containment sockets for some individuals with transfemoral amputation.