Design and Fabrication of a New Expandable Transtibial Liner with Manual Volume Control: A Prototype

Abstract

Diurnal volume changes is one of the main factors influencing socket fit in transtibial prosthesis and causing pressure problem issues. Embedded bladder liners have been recently a potential approach to deal with this problem. The aim of this technical note was to introduce a new transtibial silicone liner designed based on hybrid socket theory. To make expandability in the liner, an integrated wax structure was constructed over the selected areas of the positive model and then removed after lamination process. In addition, a mechanical system with manual control was designed to fit the liner with the residual limb volume by pumping the water in or out of the liner through connective tubes. The results showed that this new design had high reliability in maintaining identical surface pressures after volume changes in laboratory trials. Therefore, it seems that selective expandability of this liner would accommodate residual limb volume fluctuations without disturbing effect on preliminary pressure pattern.

Keywords: Amputation Stumps; Bladder; Liner; Lower Extremity; Silicones; Transtibial; Volume Fluctuation.

Figure 1

Process of making expandable liner. Wax structure formed over the positive. Medial and Anterior view (A). The liner and its socket after lamination. Tubes were passed through a hole into the pyramid (B)

Figure 2

Volume adjustment system. SolidWorks design (A): expandable liner (1), connective tubes (2), water injection channel (3), pumping piston (4), water container (5), tube clamp (6), one-way valve (7), air evacuation valve (8), track for silicone tubes (9), water evacuation valve (10). Pumping system assembled between foot unit and socket (B).

Figure 3

Reliability test measurement. Sensor locations on the limb (A), new liner in experimental trial. Black array shows force applied on the prosthesis, which was controlled by a bathroom scale beneath it (B).