Interventions

Apart from walking on the level surface of the gait lab floor, subjects were asked to absolve a circular walking path on some irregular walking surfaces as well. A foldable 10-yard gravel path

had been set up so that it can be used within the regular laboratory capture volume. The principle is similar to a custom made irregular surface that has been used for a recently

published study on amputee gait (Curtze, Hof, Postema, & Otten, 2011). The main advantage of having the gravel path cover the force plates is that subjects could use the safety harness that is connected to a rail on the ceiling. Force plate data were not deemed dependable, due to the irregular size and distribution of stones.

After the gravel path, subjects were asked to walk along the hallway and to climb a flight of stairs, in order to reach the outdoor parking lot, cross the parking lot, and return to the lab on a different route through the building (figure 31). While those walking trials were mainly intended to serve as a fatiguing exercise to reach the desired level of exertion, they also yielded data that promise to be interesting for subsequent analysis in possible follow-up studies⁶.

Stair walking has been investigated before, mostly to describe the functionality of the used prosthetic components (Powers, Boyd, Torburn, & Perry, 1997; Schmalz, Blumentritt, & Marx, 2007), or develop better ones (Au et al., 2008). Experimental setups may feature a small stair that can be climbed in the gait lab while using one of the floor force plates to capture the kinetics of one foot during landing from the step or pushing up to climb the step. More elaborate structures have instrumented steps integrated in the stairs, which allows a more

6Although members of the research team accompanied the subjects while doing so, this condition

could be considered walking in a real-life environment. Data was solely collected by means of the mobile iPecs systems, and could be used to compare walking in and outside the lab. A more diverse selection of walking surfaces might seem desirable in order to provoke more significant differences in the data.

However, it may be already a considerably different condition to just walk outside of the controlled confinements of the laboratory, away from the critically observing eyes of the technician, and on the way to a destination (for instance the stairwell) instead of just “aimlessly” walking up and down.

natural motion pattern during ascend and descent alike. A setup like this, although desirable, did not fit in the scope of our study at this time. Stair ambulation mechanics are too complex for an in-depth investigation in our context. Instead, the iPecs readings could be used to merely compare step-by-step and inter-leg symmetry, similarly than for all other interventions (see manuscripts in Appendix D).

With respect to prosthetic alignment, two levels of perturbation have been included:

Optimal alignment, which we assumed to be the original alignment that was found when the subject arrives, and a by 2 degrees increased ankle plantar flexion, which was considered a subtle misalignment. This was easily realized by adjusting the setscrews of the standard modular adapters in the prostheses (figure 30). Connections between prosthetic components in the standard modular system (Naeder & Naeder, 2000) are realized by adapters with a four faced inverted pyramid structure on a spherical base (male adapter), and respectively with four set screws around an opening that accommodates the pyramid structure (female adapter). The magnitude of alignment changes followed respective examples from the literature. A range of six degrees of socket tilt in anterior-posterior direction has been reported to be on the brink of acceptability for most amputees (Chow et al., 2006). Three and six degrees respectively have been used as typical perturbations to demonstrate changed kinetics (Boone, 2005). Even a ten degree change as an intervention has been used before (Pinzur et al., 1995), which indicates that our selected perturbation is indeed subtle in comparison.

Figure 29: Alignment mechanism of prosthesis modular adapter

In order to simulate the real-life occurrence of the prosthesis user being fatigued, a respective intervention was included. As already discussed in the respective paragraphs of the literature review section earlier, the definition of an appropriate fatigue protocol is not trivial.

The most influential muscle group for trans-tibial gait seems to be the hip-extensors. However, an exercise that targets fatiguing of those particular muscles will require the prosthesis be worn for leverage or support, which in turn increases the risk of friction-induced skin breakdown and further inconvenience. Unilateral fatiguing of the sound leg would result in a condition too far off of the actually expected situation that is supposed to be simulated. Instead of applying a standardized fatigue protocol, the fatigue level was monitored as an uncontrolled variable. After the first two walking trials in the lab (one with the original alignment, one with the increased ankle plantar flexion), subjects were asked to continuously walk along the path (figure 31) while

frequently reporting their perceived exertion on the Borg RPE scale (Borg, 1998). The data captured during the repetition where the perceived exertion reached 5 on the CR10 scale was used for the evaluation. Immediately following, the ankle alignment was returned to its

misaligned state, and subjects were asked to complete one last walking trial, during which data was captured as well.

Figure 30: Schematic of the walking path in and outside the laboratory building. Total length of the loop is 210 meters, 40 of which are outdoors