5.3 ANÁLISIS ESTADÍSTICO

intimacy of contact of the electrodes to the skin but this time using an adapted version of the standard electrode housing to secure the electrode within the socket but with an adaptation. Ideally, any additional attachment that increased electrode contact security during prosthesis usage would still need to enable the electrode to fit within the socket housing. Consequently, it was decided that the most suitable way to achieve this would be to use a screw-type plunger, housed above the electrode aperture, which could be adjusted to increase the level of pressure over the outer surface of the electrode housed within the socket. The plunger could

135 be unscrewed when necessary to enable the electrode to be positioned within, or removed from the socket housing with minimal disruption to the housing itself.

The initial plunger design consisted of a centrally-threaded aluminium strip, which was 10mm wide, 75mm long and 3mm deep, cranked into a position as shown in figures 4.4 / 4.5, and laminated within the socket walls directly above and around the electrode housing. The screw threaded-plunger consisted of a simple 4mm diameter 2cm long screw with an Allen-key head, which also consisted of a plastic disc, adhered to the distal end of the screw. The plastic disc increased the surface area of the screw plunger as it impacted on the electrode’s outer surface, helping to maintain and improve a secure electrode contact attachment with the skin. The dimensions of the complete plunger design were calculated to allow for the electrode to be inserted within the socket housing relatively easily, but within a structure that would be easily adjusted and would not increase the overall weight of the socket to any significant degree.

The adjustability of the screw plunger allowed for the prosthesis user to select which level of contact was acceptable and comfortable during prosthesis wear. The plunger apparatus would not show the exact pressure between the electrode and the skin; however, it would secure the electrode to the skin more securely than when sited within the electrode housing without the plunger, and would enable the user to determine the level of comfort afforded during usage.

To conclude, the three test conditions therefore used for this study were:

1) Via standard housings, using standard semi-rigid locators inserted into socket holes created by the dummy electrodes (test condition 1, figure 4.5a).

2) Within a socket aperture, not connected to the socket but directly adhered to the skin using double sided tape positioned on plastic extensions built onto the ends of the electrodes (test condition 2, figure 4.5b).

136 3) Within the socket housing but with firmer contact pressure exerted onto the electrode/skin interface via an adjustable plunger located within the superior aspect of the electrode housing (test condition 3, figure 4.5c).

Figure 4.4: View of the myoelectric test prosthesis used in the study and an exploded view of the electrode housing. The electrodes were secured within the socket using standard flexible electrode arms, which slotted into holes created by dummy electrodes during the socket lamination procedure. Test condition 1 simply utilised standard socket housing and standard semi-flexible electrode arms. Test condition 2 used electrodes with no flexible arm attachments but instead was secured to the skin using adhesive tape. Test condition 3 used both the semi-flexible arms and the screw plunger apparatus as shown; the pressure of which was determined by the prosthesis user. (Author’s own illustration)

Interchangeable screw-fit wrist Electrode housing Threshold- controlled ‘Galateya-NPF Reutov’ Myoelectric hand

137 Figure 4.5a: Test condition 1-Electrode arrangement with standard housing

Figure 4.5 b: Test condition 2 - Electrode arrangement within aperture, fastened to skin

Figure 4.5c: Test condition 3 - electrode with plunger attachment located onto electrode but still using semi flexible lateral arms

Aluminium screw- variable plunger housing

Electrode fastened to skin with plastic extensions and tape

Electrode

Contact onto skin

Standard socket /electrode flexible arm housings

138 The screw-variable plunger was located within an aluminium-alloy mounting, which was laminated into the socket around the electrode housing. The plunger could be retracted fully to allow the electrode to be located within the socket aperture for all three conditions.

In test condition 1, (where the electrode was located within the socket wall; figure 4.5a), there was potential for movement to occur between the electrode and the residuum during usage due to overall socket movement. Interface pressure would potentially vary depending on the intimacy of the prosthetic socket fit. In test condition 2, where the electrode was adhered to the skin within an aperture in the socket (figure 4.5b), electrode motion relative to the skin was minimised since the electrode was secured independently from the socket and interface pressure was stabilised. Finally, under condition 3, the electrode interfaced with the skin under intimate contact by means of the screw mechanism (figure 4.5c). This was designed to illustrate the effect of local adjustment upon the efficacy of the electrode/skin interface in improving myoelectric signal performance. Under test condition 3, the electrode was still potentially subject to motion between the socket and the residuum. The intention was to allow the plunger to secure the contact between the electrode and the skin over the length of the electrode, (which has been recommended in the literature to facilitate signal recognition and relaying) (40).

It was not the intention to measure interface pressure directly within this pilot study, but simply to utilise a comfortable interface pressure determined using feedback from the prosthesis user during the testing protocol.

Each prosthesis subject user was assessed for the optimal myoelectric signal position for each electrode site in accordance with recognised best and taught practice (39, 72) (see Appendix C-Clinical and technical methodologies). The selected system was two-site, two- state, which is the standard set up in most clinical myoelectric systems (196) (see also chapter 2).

Each socket was manufactured using a lamination process as outlined in Appendix C- Clinical and technical methodologies. An outer laminate was also attached to each of the sockets, which again was laminated in accordance with the design outlined in figure 4.4 using Otto bock orthocryl laminate resin 617H17. The test prosthesis was able to house the electrode in all three of the test conditions, ensuring that any evident variances in control

139 were not influenced by factors unrelated to the testing conditions themselves (see test prosthesis, figure 4.4). Each socket fitting was adjusted to provide comfort for the prosthesis user. In addition, the gain or amplification setting of each electrode was adjusted to meet the specific requirements of each subject.