Digital manipulation of prosthesis data for the introduction of advanced manufacturing techniques

Design stage

• Digitize and carve socket and cosmesis shapes
• Modify socket shape to meet patients demands
• Construct, fit and align trial socket

Manufacture stage

• Merge socket and cosmesis
• Manufacture final prosthesis - by rapid protoyping!!
• Variations using different  file manipulation and construction

Digitize and carve socket and cosmesis shapes

A cast is taken of the amputees residual limb and normal leg. This cast can then be digitized and carved out using the Seattle Digitizer and Seattle Carver from Seattle Limb Systems.

Modify socket shape to meet patients demands

The modification of the socket shape is done using Seattle Shapemaker. Templates that change the shape of certain defined areas can be defined by the user and are a very useful tool in this stage.

Construct, fit and align trial socket

A trial socket can be manufactured by using the Seattle Carver which produces a polyurethan foam socket shape. The foam shape acts as a negative to pull a heated sheet of transparent thermoplastic material over it either in the Seattle ThermoFormer or by hand. A distal adaptor is added and endoskeletal prosthesic components are attached. If the socket fits well on the patient and a suitable alignment has been found, the alignment can be transferred on to the socket shape in the software.

Merge socket and cosmesis

The cosmesis has to be reshaped in such a way that the socket and alignment are incorporated in which the cosmesis looks as natural as possible. A program developed at REHABTech is used to merge both the CAD shapes to one shape. One can think of this as a cosmetic elastic sock that is fitted over the socket (click here to go to presentations).

Manufacture of a Rapid prototyped prosthesis using FDM

Fused Deposition Modelling is a technique of rapid prototype manufacture which involves the depositing of auto-adhering material in specific computer controlled sequence as to build a prototype in space.

The first FDM Fused Deposition Modeling prosthesis has been built by REHABTech. The modified socket, desired cosmesis (can be reverse image of the sound side) and alignment details are used to build a digital image of the prosthesis. This information is then converted using a specifically built software program developed at REHABTech so it can be read by the FDM software. The whole prosthesis, socket, cosmesis and structure are then built as one by the Fused Deposition machine out of ABS.

ABS is an industrial strength plastic that can be coloured easily with automotive paints.

The prosthesis should be modified to avoid high stresses. It is anticipated that a full FEM-analysis on multiple prostheses may provide some basic rules in order to avoid high stresses. Secondly these basic rules can then be applied on new designs. This also could be done for common modifications the prosthetist wants to make such as holes for straps or other attachments.  The wall thickness can also be specified.

Once all of this is ready the prosthesis can be manufactured using, at this stage, rapid 3D prototyping techniques. The techniques to be used in this project is FDM (Fused Deposition Modelling). This part of the project will be performed as part of a collaboration with Swinburn University and Alfred Hospital Plastic Surgical Unit in Melbourne.

Click here to see a video of the making of a trans-tibial socket using FDM (1.6 Mb).
Or you can  download the mpeg version (2.5Mb).

Actual Prosthesis designed,  merged and constructed!!! (7mm wall thickness)

 

ABS - (Acetyl Butyl Styrene - an engineering grade plastic that can be machined, glued, painted and is both strong and light)
The first ABS prosthesis was constructed  with a variable wall thickness and will soon undergo clinical trials and then Finite element analysis combined with destructive strength testing! The weight difference between the ABS and the limb made using "conventional lamination" is only 15 grams.

 

The General Principle of what is done (below)

Variations using different  file manipulation and construction
Also the file information can be used to construct a prosthesis in a "conventional" manner, however the process of manufacturer is much simpler! A lamination is made on an external frame and a lamination is made on the socket BUT they fit inherently together. No shaping, or fitting is required. The same technique can yield a foam cover also.

Think outside the square!!!
By using this technology we can also create some interesting possibilities....
e.g. a  cast has been created so that a single lamination or drape will complete all the components for an entire prosthesis, therefore not requiring "extra" components. This can be an excellent way of making a cheap spare, emergency or shower leg. It can also be a robust prosthesis for rural areas as it removes the complexity of components and the likelihood of things going wrong, particularly in 'outback' or 'third world' type environments.

This proces can also be  used for making cosmeses for more complicated componentry. For instance, it is possible to make a good fitting cosmesis for the Re-Flex VSP Flex Foot. By using the Shapemaker prgram and the Merging software it is actually quite easy.

A simular process is used to make a protective kneecover for the Otto Bock 3R60 knee unit. Because of the possibilities that the Shapemaker program and the Merging Software offer, it is possible to create a protective cover and a cosmesis in one.

Other projects have included making cosmetic covers for complex and difficult shapes both for trans tibial (below knee) and trans femoral (above knee applications)....examples can be found here.

When built as a 3D-Rapid Prototyped project it would save a lot of time but the more importend thing is that every change you want is possible. Just adjust the computer file and create a new model!!! Within a day or even a few hours you could have a new cosmesis/ protection device or prosthesis.