Model and measurement studies on stages of prosthetic gait.   

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Clinical consequences

The predictions, outcomes and insights gained from our model and measurement studies contributed to the development of our theory about asymmetry, funcional ability and learning. Based on our findings, we concluded that it is impossible to walk symmetrically with a mechanical prosthetic limb, unless additional efforts are made to compensate for the shortcomings in the prosthetic limb. We expect that improving functional ability, instead of minimizing asymmetry, will contribute to the improvement of the patients satisfaction. According to the principles of Discovery Learning and learning as a function of attentional focus, improving the functional ability can best be achieved by training in environments which enable the TF amputee to find individual optimal performance patterns for complex motor skills.

Asymmetry and functional ability

For high functioning individuals with lower-limb amputation, gait deviation does not significantly correlate to patient satisfaction 10. Kark and Simmons (2011) suggested that improving self-percieved functional ability and attitudes toward the prosthesis, rather than minimizing gait deviation, will improve patient satisfaction. To improve functional ability we have to understand the principles of prosthetic limb use and compensation strategies. Studies by Vrieling et al. (2009) showed that ’an important source for the creation of adjustment strategies in amputees was the non-affected limb’. This last finding is also confirmed by some of the studies in the current thesis. The observed real world phenomena and predictions of our models of the conceptual world show that this sound limb dependency is an important strategy, which contributes to functional ability.
Both experienced and recently TF amputated subjects, tested during gait initiation and termination and during obstacle crossing, in a motion analysis laboratory 1, showed a decrease in CoP motion under the prosthetic limb, with more weight bearing of the non affected limb. During gait initiation they were able to produce less forward velocity of the CoM during gait initiation compared to AB subjects. The TF amputee showed less braking force under the prosthetic limb during gait termination compared to the sound limb. This shortcoming when using the prosthetic limb, has consequences for the gait initiation and termination strategy. During gait initiation, subjects preferred to lead with the prosthetic limb. During gait termination, subjects preferred to lead with the sound limb. These findings suggest that the subjects prefer to use the sound limb to produce the necessary impulse. However, our gait termination model study showed that not only the leading limb influenced the magnitude of the impulse during the single limb stance phase, but also the trailing limb accelerations influenced the impulse. This finding suggest that also the moving trailing limb, and probably other moving segments, can be used in a CoM velocity control strategy. We found a relation between the mass of the trailing limb and the magnitude of the impulse. The accelerations of a relatively heavier trailing sound limb influenced the ground reaction force more than a lighter prosthetic limb. This asymmetrical mass distribution within the TF amputee and the consequences for the outcome of limb motions contribute to our theory that the prosthetic limb user has to control the inequality between the two limbs that take part in the teamwork and the idea that symmetry can only be achieved when additional efforts are made to compensate for this mass inequality. Not only during gait initiation and termination the TF amputee has to make additional effort to compensate for the inequality when pursuing symmetry, but also during obstacle crossing. Vrieling et al. (2009) showed that when crossing an obstacle, TF subjects preferred to lead with the sound limb. Their trailing prosthetic limb showed a decrease in flexion compared to a sound knee, which was compensated with a circumduction movement and an increase in the plantar flexion of the sound ankle in the stance phase. According to our model study it should be feasible to counteract this asymmetrical motion of the prosthetic limb by using ground friction and fast hip motions. When using this strategy, TF subjects should be able to cross the obstacle with a flexed knee. The disadvantage of this strategy is that it costs more energy compared to the knee extension strategy.
Based on the findings in the laboratory and the model studies, which show that compensation strategies mainly depend on the active control possibilities of the sound limb and that more energy is needed when trying to counteract the asymmetrical motions, it seems an unattainable goal to pursue full symmetry during prosthetic gait. We expect, in accordance with Kark and Simmons, that improving functional ability will probably contribute to the improvement of the patients satisfaction. Please notice that we removed the words ’self-percieved’ and ’attitude towards the prosthesis’ from the sentence used by Kark and Simmons, and added ’probably’ as these parameters were not included in the current thesis, which focusses on specific elements of functional ability during gait from a biomechanical perspective.

Learning

Traditionally, TF amputee who learn to walk with a prosthetic limb with an artificial knee, perform poorly during the initial gait training, hence the use of parallel bars, support by therapists and other safety measures. Our studies showed that AB subjects learned within 100 steps how to use the prosthetic limb in a safe way, provided that they were paying attention to how they placed their device on the floor. Their training was only limited, no therapists were involved and the only safety measure provided was the wall next to the subjects. To learn the subjects how to use the prosthesis, we created an environment in which our subjects were allowed to move around and to do and use whatever they thought was necessary. Although it seemed a rather unorganized environment, we made sure that there were sufficient objects that could be of help to understand how the prosthetic device behaves when in use. We placed some balls (to kick) and boxes (to step on and off) in a room that challenged the subjects. This training concept was based on the principles of Discovery Learning 11 and learning as a function of attentional focus 12. Discovery Learning takes place in problem solving situations where the subjects draw on their own experience and prior knowledge and is a method of instruction through which subjects interact with their environment by exploring and manipulating objects, wrestling with questions and controversies, or performing experiments. Using the objects, we directed the subjects’ attention to the effects of their movements (external focus), in contrast to attention to the movement itself (internal focus) 12. The self-initiated noisy training sessions featured a variety of between-exercises differences, which would help the subjects to learn motor skills that were adapted better to their own physical needs and skills and enabled them to find individual optimal performance patterns for given complex motor skills. Even though an occasional fall occurred, based on the short learning time (100 steps) of our subjects, we feel that this type of training and the concepts of the underlying theories have relevance for the development of improved rehabilitation programs.
In this Discovery Learning concept, rehabilitation professionals working with TF amputee do have an important role. They have to deploy their practical and theoretical skills to create safe environments in which patients are offered the opportunity to explore all the possibilities of their prosthetic limbs without physical assistance. In these environments, TF amputee are allowed to make errors within certain limits 13. Domingo and Ferris (2009) reported that physical assistance can hinder motor learning of walking balance, as it does not allow for error detection and correction. Only for more difficult tasks assistance appears less detrimental. Of course, it should be taken into account that freezing situations, in which the TF amputee reduces his Degrees of Freedom during skill acquisition as described by Bernstein (1967) in too difficult tasks must be limited, as it might narrow the range of possibilites.
When creating these environments, therapists should take into account that TF amputees have to use the aforementioned strategies to compensate shortcomings 15. Therefore, it seems advisable that the therapists create situations in which their patients experience the benefits of initiating gait with the prosthetic limb leading and terminating gait with their sound limb leading. Also, patients should experience that by using ground friction, fast hip motions and maintaining distance between the obstacle and the prosthetic foot during obstacle crossing it is possible to create foot clearance over an obstacle.

 

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