Prosthetic Socket Design

Socket design – Areas of attention:

Residual limb control
Flexibility in the Socket
Volume management
Interactive Socket

Socket design – Shapes that sockets can take:

The Socket Design is usually a mixture of:
NSNA - Normal Shape Normal Alignment of Ivan Long.
CAD-CAM - Contoured Adducted Trochanteric – Controlled Alignment Method, John Sabolich and Tom Guth.
UCLA CAT-CAM – Christopher Hoyt.
MAS Marlo Anatomical Socket.
ISNY Otto Bock.
Hoyt UCLA - IC Socket.

RIAS -The Responsive Interactive Anatomical Socket

Amputees are comfortable if?

Flexible systems are truly flexible.
Can adapt to volume changes.
Can adapt to shape changes.

What is needed?

Truly flexible socket
Ability to accommodate volume changes
Ability to re-direct and accommodate forces

Ideal Socket Design:

The shape or socket should not expand outside it’s volume only allow for shape changes that are wanted and limit the shape changes that are not.
Introduce shape changes to assist the comfort level and control of prosthesis, for example contouring around the hamstrings on heel contact and the femur to assist the weight bearing area and to give more control to the femur.
Control of forces on one side might require release of force/ pressure in another area (not necessarily the opposite side)
Circumferential shape changes but not the size. The circumferential measurement should stay the same even of the shape of the circumference changes!

Many ways to achieve this:

The RAIS System is designed around what is simple, affordable and available.
Pre-Pregs, lamination/ infusion, silicone extruded and Laminated.

Advantages:

Closely mimics the muscle? / Soft tissues / firm structures.
Can accommodate movement and shape changes.
Can be firm in required areas (Control) and flexible (cushioning) in other, able to fluctuate as the residual limb shape changes.

To RIAS System can achieve this by –

Use all available parts of the anatomy for suspension.
Take weight on weight bearing surfaces.
To give as much control to the prosthesis as is possible.
To give as much feedback.
To improved proprioception
Improve suspension of the prosthesis to the residual limb.

In all amputation levels there is a degree of instability caused by the amount of soft tissue in the residual limb and by the conditioning of the soft tissue (muscle groups).

The greater the soft tissue and the lower the conditioning, the lower the control available to the sockets and therefore to the residual limb.

However even in the residual limb with low soft tissue volume (example a Symes amputation) where there are larger areas with low tolerance or are intolerable to pressure. The greater the need for cushioning and suspension.

Tissue Loading – Damage can occur at 8kpa - Daly CH et al

                The Effect of pressure loading on the blood flow rate in human skin 1976

Therefore, pressure areas need to be designed specifically to spread the required pressure over the required area. Example, to control the femur/ tibia/ fibula.

Suspension – improved.
Volume control – dynamic.
Comfort – in donning, doffing, sitting, stance and swing phase.
Stance & Swing phase – areas of pressure change during the gait cycle to the optimum levels.
Dynamic control – at all times, during the gait cycle and sitting.
Static control – standing & sitting.
All amputation levels – Hemi pelvectomy to Symes level.