Hands Free Hydro Cast – Optimising Trans-femoral Socket Design and Maximising Rehabilitation Potential

Buis AWP, McGarry A, Kamyab M, Murray KD, Hillman S

Biomedical Engineering, University of Strathclyde, Glasgow, UK

Introduction

• Statement of problem (Why)

• Implementation of a “good” fit

• Methodology (What & How)

• Results

• conclusion

Statement of problem

• The purpose of a socket is to provide a mechanical connection between the skeleton and the rigid structure of the prosthesis.

• The dominating concepts are the Quad and Ischial cont.

• How stabilising are those sockets?

• Are they reproducible?

• Can we do better?

Implementation of a “good” fit• Socket fit criteria:

o As “stiff” as possible couplingo No tissue damageo Minimum discomfort

Implementation tools;o Surface matchingo Volume matching

• Is it possible to distribute the load to the different transmission elements in a controlled

way?

• Yes, if the force flow distributes itself proportionally to the stiffness of the available path!

Implementation of a “good” fit

Rubber Block Metal Block Rubber Block

“Let nature deform the soft tissues in such a way that the

stiffest path principle is achieved”

• Copy of the existing Ischial containment socket.

• Pressure cast socket according the Hydro cast principle.

Methodology

Methodology (work packages)

1. Dynamic interface pressure (ideally shear)

2. Femoral stability

3. User performance outcome measures• Kinetic (forces)

• Kinematic (position in space and time)

Methodology

• Dynamic interface pressure

• Validated Tekscan™ pressure measurement system

Methodology• Femoral stability

Methodology• User performance outcome measures

• Kinetic (forces)

• Kinematic (position in space and time)

• Dynamic interface pressure

Hydro

Ischialcontainment

A M P L

Results

Video

Ultra sound

X section socketMedial

Anterior

Sensor

Results

Results

A

Medial

Hydro Cast

Lateral

P

Ischial Containment

A

Medial

Lateral

P

• User performance outcome measuresSummary

• Speed slightly higher with the old socket, but it was noted that the subject’s speed increased as she became more accustomed to the new socket.

• Stride length slightly longer with the old socket, effected via increased step length bilaterally.

• Cadence and double support time much the same for both conditions.• Single support time on the right a little decreased with the new socket.• Clear differences between pistoning and gapping were observed.

Indicating that the Hydro concept is more stable.

Results

Conclusion• No significant pressure distribution differences.

• Shear should be investigated!

• No significant Kinetic and kinematic differences.

• Significant stability differences in direction,

pistoning and gapping in favour of the Hydro concept

prosthesis.

Thank you!