ORTHOLETTER

A ten centimetre wide strip of EVA (foam) is rolled into a circle shape, to a diameter almost equal to that measured on the patient's contralateral side (I found two sizes generally fit most patients). The distal uprights are placed inside the roll of EVA, still attached to the caliper jig to maintain alignment as well as the medial-lateral measurement, (Figure 2).

Plaster of Paris (POP) is then poured inside the roll of EVA. Once the plaster has set, the EVA roll and joints are removed from the plaster mould.

The first molding of polypropylene is therefore done with the joints removed from the plaster, using 4mm polypropylene. This should be done with an inner layer of fine stockinette before molding on the positive cast. The stockinette will assist in the vacuum forming process, so that the plastic will follow the contour of the cast exactly (Figure 3).

 Fig.3: first vacuum molding without the joints

Before molding the second layer, the joint stirrup is affixed on top of first layer (this does not require any space between the stirrup and the first layer). The uprights should be fixed, so as not to be displaced during molding, (Figure 4). Once molding is complete, the joints will be sandwiched between two layers of polypropylene. The proximal uprights of the metal joints are then bent to meet the socket.

Assembly of the knee disarticluation component
The objective was to create a knee disarticulation component, designed so that it could easily be incorporated with the polypropylene prosthetic components available from the ICRC. In fact, this component works best when incorporated with the polypropylene components from the ICRC for trans-tibial prosthetics. The distal aspect of the knee component is fixed to a cylindrical cup, which can then be easily incorporated in the ICRC modular system.

Conclusion
This newly designed polyproyplene knee disarticulation joint with metal upright bars has been successful. This type of component can be used for amputations of any cause, regardless of surgical technique used for amputation.

It is easy to adjust a prosthesis made with these components in both static and dynamic alignment. The possible adjustments include anterior and posterior displacements, medial and lateral displacements, extension, and flexion, which can be done in the cup of the component.

The knee disarticulation component like other polypropylene components from the ICRC, can be ready made in different sizes, which hastens the assembly process. Fabrication of the joint as described here consumes only 20 hours of labour.

Advantages of the new component:
- No additional time for correction of joint alignment after the component is mounted and aligned to the foot component as the joints of the polypropylene component are already aligned and parallel before the assembling process.
- The conventional prosthesis requires more time to ensure the joints are parallel during the process of assembling the joint and the shank.
- The weight of a conventional prosthesis is about 3.1kg to 3.3kg, while a prosthesis using the newly designed component is about 2.8kg to 2.9kg.

It should be a great help to many workshops in low-income countries if the ICRC would integrate this prosthetic knee component into component production. This could assure high quality of the material, design and function of the component.