Above Knee Prosthesis

An above knee prosthesis or transfemoral prosthesis is custom made for a person who has had an above knee or transfemoral amputation. The prosthesis consists of a custom made socket, liner, knee, pylon, and foot. Sometimes the prosthesis may consist of a sleeve or other harness, depending on the suspension system used for that patient.

Beginning the Process

Liners and Cast/Scan

The next step in the process is to have the patient fit with a liner. The liner is a soft interface that the patient wears over the skin. It is donned before the socket. The main function of the liner is to absorb the forces created when ambulating in your prosthesis, to keep your residual limb healthy, and to allow you to wear the prosthesis for longer.

There are many different liners on the market and your prosthetist will pick the best liner for you. This is based on many factors, including suspension type, activity level, skin issues, hand dexterity, boney prominences , shape, etc. There are off-the-shelf (OTS) and custom liners. If the residual limb is an uncommon shape or very boney,  custom liners may be used. These are made by taking an impression of the patient’s limb via a plaster cast or scan using our several different scanners/software. The process of obtaining a custom liner takes longer than obtaining an OTS liner. If the shape of the limb is common, measurements are taken to order the proper sized OTS liner.

Once the liner is ready to be fit on the patient, they are called to come back into the office for a casting appointment. The liner will be donned onto the patient’s limb and the fit will be assessed. If the fit is well, measurements and a cast of the limb will be taken over the liner. Different casting methods will be used based upon the suspension style that was previously decided upon by the prosthetist and patient. From here, the cast will be filled and modified appropriately to make your custom AK diagnostic prosthetic socket.

Diagnostic sockets

The first prosthetic socket you will receive will be called a diagnostic socket. This socket will be made of a clear plastic, utilizing the appropriate suspension method (pin/locking, elevated vacuum, suction). The socket will be donned while the patient stands and puts weight onto the residual limb. Usually, these sockets are made to not be taken home by the patient at this time, but can be made to walk on to check alignment at the second diagnostic fitting appointment. A plastic diagnostic socket is used to start with as parts of the socket may need to be modified to appropriately contour to your limb. This can be easily done by heated and flaring the plastic.

A second diagnostic socket may be needed to adjust the first diagnostic socket to give the patient a better/more appropriate fitting socket. The better the fit of the socket for AK prosthesis, the higher the rate of success is in ambulating with one.

Laminated/Final socket

Once we have confirmed the diagnostic prosthetic socket fits the patient well, we can move on to the laminated socket. The laminated socket is fabricated using carbon fiber, which means it is much lighter than the plastic socket and has a higher tensile strength. Carbon fiber is also more durable, son the socket will be able to last up to a few years, depending on activity level and any limb changes. The patient can choose to have the socket custom designed/colored to meet their personality, which may to have the socket color match their skin tone or have their favorite sports team logo on the socket. Depending on the style of suspension, there may be an inner socket may of Proflex, which is a softer plastic inside the outer carbon shell.

The prosthesis will be donned with the patient several times, allowing the patient to be able to don/doff it themselves. Height and alignment will be adjusted accordingly. Gait training will be performed to help the patient get use to using the limb. Physical therapy will play an important part of gait training and strengthening their lower limb muscles outside of appointments with your prosthetist.

Prosthetic Knees

There are many different types of knees to choose from in the market today. When you are coming up with a plan for your prosthesis, your practitioner will ask you about your lifestyle and  activities you participate in. This will include how far you walk, what sport(s) you play, are you on uneven terrain for camping, hiking, hunting, and how often you are on your feet. All these different activities you do every day play a crucial role in deciding what foot will be best for you. Each knee offers different benefits to different activities from having stance stability to a Microprocessor Otto Bock C-leg 4 that can swing and flex the knee during the gait cycle. The different types of knees are as follows:

Single Axis

A simple hinge, usually with adjustable friction for swing phase damping. Most reliable alternative available, especially suitable for those living in remote areas. An example of this is the S.A.F.K. by Hosmer.

Manual Locking

This knee is the most stable knee used in prosthetics. The knee is locked during gait and the patient releases the lock mechanism in order to sit down. Manual locking knees are primarily used with patients who have very short residual limbs and/or poor hip strength and are unable to control the knee.  This is the knee of last resort. An example of this knee is the 3R33 by Otto Bock.

Stance Control

This knee is very stable and is often prescribed for a first prosthesis. When weight is placed on the prosthesis, the knee will not bend until the weight is displaced. This system functions as a constant-friction knee during leg swing but is held in extension by a braking mechanism as weight is applied during stance phase. This knee is a common choice for older or less active amputees. An example of this is the 3R49 by Otto Bock.

Polycentric

These knees have multiple centers of rotation, which can provide a number of unique functional capabilities. These are designed to offer enhanced knee stability in early stance phase, combined with the ability to flex under weight bearing, just prior to swing phase. This is highly advantageous for the more active individual. Very useful for longer TF limbs and knee disarticulations. An example of this knee is the Total knee by Ossur.

Fluid Controlled: Hydraulic/Pneumatic

These knees have chambers in them filled with either gases, such as air, or oils, such as silicone. These allow a variable speed swing phase. Due to the properties of a fluid-filled cylinder, the amputee is able to increase and decrease walking cadence with the knee automatically compensating. Pneumatic are mainly for a normal speed cadence while hydraulic control units are used for more moderate to higher cadences. An example of this would be the Mauch Knee by Ossur.

Microprocessor

These knees improve mobility and reduce the risk of injury from falls, which leads to better overall health and well-being for wearers. All computerized knees include a microprocessor, software, sensors, a hydraulic or pneumatic resistance system and a battery. Sensors monitor and detect changes in the environment, such as walking on a different surface, going up or down a slope or walking at a different speed. Based on that feedback, the microprocessor adjusts the resistance to knee flexion (bending) and extension (straightening) to accommodate walking speed and terrain. This enhances stability and security for the user. Other features are typically included such as stumble recovery, controlled descent of ramps and controlled recline into a seated position.​ The technology continues to evolve, offering prosthetic wearers even smarter knees with improved sensors and longer battery life. There are MCP systems now that connect the knee to the foot so they can communicate throughout the gait cycle. When the foot detects that it is going down a ramp, it sends a signal to the knee to increase knee flexion resistance to make it safer to walk down the ramp. Examples of the MCP knee is the C-leg 4 by Otto Bock and the MCP system is the LINX system by Endolite.