Trans Tibial

Suspension:

This is the means by which any prosthesis is held on. There are 5 main types of suspension: 


• Straps: This includes anything that is attached at specific points on the prostheses and then attached to a higher point on the body. These can be made of anything from leather to cotton and rely on their tightness in order to keep the prostheses from slipping off. (e.g. PTB Strap) 



• Sleeves: These rely on constriction on the prostheses and the limb above the prostheses and depending on the material of the sleeve, it can even seal the prosthesis to the limb and create suspension with suction. 



• Suction: By creating an air lock between the residual limb and the socket a very strong suspension is created. This can be done by sealing the socket with a sleeve or having a very intimate fitting socket with a valve in the end. 

  

• Supracondular: This is when a portion of the socket is 'pinched' in above the bony protrusions that are present at most joints.

• Liner Suspension: By incorporating a nut into the bottom of a form fitting gel liner, a mechanical locking mechanism can the be incorporated into the leg so when the amputee steps into the socket the locking mechanism engages with the liner and suspends the limb. A release mechanism is then incorporated so that the patient can remove the socket.
  

Interface:

An interface is anything placed between the skin of the residual limb and the hard inner surface of the laminated socket. It is used in order to absorb some of the forces that would otherwise be transferred to the skin from the socket or to take up volume that the residual limb has lost. Included in this are:

• Socks: These can be made of cotton, wool, spandex or any combination of these or other materials. The primary use for socks is to counter fluctuations in residual limb volumes. The thickness of prosthetic socks is measured in 'ply' therefore as the residual limb shrinks, the # of ply of sock the patient wears increases.

• Foam liners: There are a number of different types of foam that are used in prosthetics, but the main ones are plastizote and pelite. The foam performs three functions: 1) it absorbs a greater amount of forces than just socks alone 2) it can be used to accommodate shapes of residual limb that would be difficult to pass into the rigid socket of the prosthesis and 3) it can be easily modified to accommodate large fluctuations in shape of the stump.

• Gel liners: This is the newest form of interface and comes in three specific materials, urethane, thermoplastic polymer, and silicone. Each have different characteristics but the goal is that the intimate fitting liner absorbs not only some of the direct pressure forces but also the shear forces that occur between the socket and the skin. In some cases by using a method of attaching the liner to the prostheses we take advantage of the suction between the liner and the leg and use it to suspend the socket.

Components:

This includes anything from the socket to the floor. There are the obvious components such as feet and knees but there are also specialized components that can be used to increase the function.



 

Foot:

Feet will initially be separated into two types: articulating and non-articulating. (i.e.: with or without an ankle.)

• Articulating: This includes both single axis and multiple-axis ankles. They increase shock absorption at heel strike, promote knee stability and, especially with the multiple-axis ankles, allow the foot to conform to uneven surfaces. This motion will reduce any energy storing capabilities of the foot.

• Non-articulating: These can be separated into energy storing and non-energy storing (SACH) feet.

• Energy Storing: The keel for this type of foot is made of a very stiff material that when flexed, stores this energy until pressure is taken off and it 'springs' back to its original shape releasing its stored energy. By storing and then releasing energy throughout the gait cycle the foot can decrease the energy it takes for the patient to ambulate.

• Non-Energy Storing (SACH): In these feet, the compression of the foam heel simulates plantar flexion at heel strike. This foam absorbs much of the energy or shock at heel strike and can give a smooth transfer onto the soft keel section of the foot. These feet are very reliable and durable and because they don't rely on a stiff internal keel, they tend to have slightly better cosmetics.