A Conventional Method to Make a Prosthetic Limb - ( BK Prosthetic Leg )

Introduction.

A prosthesis (also called a prosthetic limb, artificial limb, or limb "replacement" though natural limbs are irreplaceable) is an artificially made substitute for a limb lost through a congenital defect (present at birth), accident, illness, or wartime injury. 

When someone loses a limb due to injury or disease, the rich functionality once offered by that limb is lost as well. An upper extremity amputation, involving the loss of all or part of an arm, might mean the loss of the ability to perform job skills or normal activities of daily living. For a lower extremity amputee, someone missing portions of one or more legs, this could mean the loss of the ability to walk or run.

Prosthetic limbs are incredibly valuable to amputees because a prosthesis can help restore some of the capabilities lost with the amputated limb. Although prosthetic limbs have still not advanced to the point where they can rival the functionality provided by biological limbs, the capabilities they do provide can be significant. Great strides are being made each day in the field of prosthetics  and while great technological challenges remain, artificial limbs are becoming increasingly similar to real limbs.

In this article, a conventional method of making a Patellar - Tendon - Bearing (PTB) socket/stump for a below knee, transtibial amputated patient is described and the same ideas can be applicable for making other prosthetics as well.

PTB Socket.

Transtibial Sockets.

Types of Prosthesis:

Generally, a type of prosthesis called a cosmesis is designed to be purely cosmetic and has little or no function; artificial hands often fall into this category. Other prostheses are highly functional and have little or no cosmetic disguise; artificial legs, designed to be covered by pants (trousers), are sometimes little more than metal rods and wires.

In theory, any part of the body from ear or nose to the finger or toe could be replaced by a prosthesis. In practice, there are four common types of prosthetic limb, which replace either a partial or complete loss of an arm or leg:

1. Below the knee (BK, transtibial): An prosthetic lower leg attached to an intact upper leg.
2. Above the knee (AK, transfemoral): A prosthetic lower and upper leg, including a prosthetic knee.
3. Below the elbow (BE, transradial): A prosthetic forearm.
4. Above the elbow (AE, transhumeral): A prosthetic lower and upper arm, including a prosthetic elbow. 

Human limbs that can be replaced

Above images show (Left)Prosthesis structure & (Right) stump and liner.

Collecting patient data and starting the procedure:

• Assessment of the patient was carried out, which means collecting the history and all the relevant data for the procedures by the clinician.

• Since the amputee is a trans-tibia amputated patient, the respective measurement form was used to collect the data.

Below knee prosthesis measurement form.

Casting room:

• This is the place where the created prosthetic limbs are attached to the patient and providing the alterations (if needed for the artificial limbs) and providing the useful training to the amputee in order to get trained with the new limbs.

• Once the patient’s limb is fitted with the socket, patient is asked to stand on a laser light platform for alignment checking which means the laser light is expected to come to the center of the patient’s body to denote that the body’s weight is equally distributed to both legs. If not, the alterations must be carried out in the prosthetic limb till the laser ends in the middle line (Median Plane) to the body which will ensure that the amputee will walk properly maintaining the equilibrium of the body weight by both legs.

• Then once these steps are completed, the training session for the patient to train the muscles to synchronize with the artificial limb will begin. These training also will be carried out into different sessions. The first session is the amputee will be asked to walk in the plain platform by holding the attached bars in both sides.

• Second sessions is amputee must walk on the plain platform by holding one side of the bar at a time and repeat this to both directions.

• Then as the third session the patient should walk on different types of platforms (from soft to hard and stony) and inclined platforms by both directions in order to get trained to receive the support of the limbs in different types of planes to walk  in his / her day to day life.

• Once the patient passes these steps then the amputee is allowed to go home with the attached limb but needs to follow up some regular visits to make sure that the limb is fully supportive.

• In any case if the amputee feels any problems with the limb, according to the needs of him / her the limb can be altered to serve well.  

Modification Room:

• Clinicians enter this room with the collected data of the patient (measurement form) to create a prosthetic limb.

• Plaster of Paris (PoP) bandage is used to create the negative cast which is important to make the replica of the limb. Then the replica is made which is considered as the positive cast.

• Cell phone blades are used to shape the replica.

• Then the positive cast is covered with some certain materials which are heated in the oven in order to create the socket along with the liner.

• Heating and molding are taken place in this stage.

• Once this process is done the PoP casts will be discarded and for further designing the newly created molds will be kept.

• Then the new molds will be shaped properly by many types of machinery.

• Then they fit together with the pylon and the foot as the final design.

• Once the final design is over then the patient’s training with the newly created prosthetics will be started over in the casting room.

Procedure:

• Patient was interviewed and his amputation history recorded in first part of the Below Knee Prosthesis measurement form.

• Patient’s stump is measured with soft tape. These measurements are recorded in the second part of the Below Knee Prosthesis measurement form.

• Patient’s stump wrapped with clear wrapping plastic.

Stump wrapped from top to bottom of stump

• Pressure points (pressure tolerance and release point) marked with marker pen.

Stump marking

• Patient’s stump re-wrapped with second layer of clear wrapping plastic.

• Pressure and release point marker transferred to the second layer.

• Plaster of Paris (POP) dipped into the water for 5 seconds and squeezed.

• POP wrapped around the stump from the top to bottom. During this process, second layer of clear wrapping plastic end rolled to ease the POP removal process.

POP wrapped on stump

• Patient’s stump massaged and pressure applied at marked points to shape the POP.

• Once POP hardens, using the reference of the rolled end of the clear wrapping plastic, POP is removed. This is the negative cast.

The negative cast

• It will be noticed that the marks have been transferred to the Inner Diameter, ID of the negative cast.

Visible transferred marks inside the negative cast

• Negative cast filled with POP to create a positive cast. The positive cast kept for natural drying in the lab.

• Once the PoP is dried enough, then the negative cast is removed from the positive cast with a knife.

Negative cast removal process

• Marks transferred back to the positive cast so that they appear clearer. 

• If not clearly visible then the marks are redrawn using an indelible pencil, so that when the positive cats is trimmed and smoothed, they can be used as reference lines. 

• The indelible pencil is used to highlight the bony prominence, protrusions and ends of the bone.

Marks are redrawn on positive cast

• In the next step, the blades are used to trim and sharpen the positive cast at specific locations. 

• The smoothing process should start at the patella tendon bearing region and usually this area is trimmed down to a depth of 1cm. This region is a weight bearing area. 

• While trimming, the blade should not touch the patella. 

Trimming the positive cast

• The area between the fibula head and the tibia is also trimmed down slightly. These areas are marked on the cast and the bony prominence should not be touched while trimming. 

• This area should be trimmed down to a 3 mm depth. If these are trimmed they will cause patient discomfort in the future when the socket is fabricated and used. 

• Below the pressure point regions are given which should consider while trimming:

Pressure point regions.

• The depth of trimming depends greatly on the shape and features of the patient’s stump. 

• It is necessary to make sure that the positive cast will allow us to fabricate the socket that provides balanced pressure and reduce patient discomfort. 

• The plaster of Paris is then going to be applied to the bony protrusions such as the fibula head to reinforce those regions. The application should be smooth and cover the bony prominence to ensure better fitting. 

• Lastly, the posterior channels are made using the trimming blades. This is done to give relief to the hamstring tendons. The plaster of Paris is added to the medial and lateral sides of the hamstrings to define the shape.

• Wearing the stockings on the positive cast and then applying powder on those stockings are the techniques to remove the mold easily from the positive cast.

• Polyethylene – PE (orange in color) and Polypropylene – PP (yellow in color) are the source materials for the molds.

Polypropylene blocks

• Apply Vaseline on the holding frames where the molding materials are kept and put into the oven for melting (deform). 

• So these Vaseline help the materials not to stick with the frames.

Placing the polypropylene in the oven after fixing the frame

• After fixing the materials, placing them in the oven which ill heat them at 180 ℃ for 15 minutes.

• While this takes place the positive cast is attached with the suction pump.

• Once the materials are ready from the oven, then the materials is kept on the positive cast and pressed gradually by hands from top to bottom in order to make the shape of the positive cast.

• Meanwhile the suction pump applies the suction over the material in order to get shaped according to the surface where it was kept and pressed by hands.

• Then the unwanted edges are cut and removed and wait for a couple of minutes to make sure that the material is completely got rigid.

The polypropylene plastic is cut to fit the shape of the positive cast

• Then it will be removed by just pulling it, where the stockings and the applied powder will help really a lot to remove the mold by reducing the frictions between the positive cast and the molded shape.

The shape of the mould after the plastic cools

• Then the edges are shaped nicely by different equipment.

• At last the bottom of the mold is attached with a 3 slandered hinge connector which will later attached with the pylon and the foot to fulfill the prosthetic limb.  

Final Product

Note that according to the patient's desires and budget the materials and the textures which are used here, can be changed in this process. 

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Reference:

• Explain that Stuff. 2018. Prosthetics: A simple introduction to artificial limbs. [ONLINE] Available at: https://www.explainthatstuff.com/prosthetic-artificial-limbs.html. [Accessed 08 June 2018].
• HowStuffWorks. 2018. How Prosthetic Limbs Work | HowStuffWorks. [ONLINE] Available at: https://science.howstuffworks.com/prosthetic-limb.htm. [Accessed 08 June 2018].