Yu, Chung-huang; (1999) New Method for Restoring Standing to Paraplegics : Control of Leg Muscle Stimulation by the Handle Support Reactions. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

It is highly desirable to restore standing to paraplegics using functional electrical stimulation (FES) because of its potential therapeutic and functional benefits. However, FES standing is not widely successful yet. Among the reasons are that the stimulation intensity is not regulated so the muscles fatigue quickly or that the artificial controllers only allow predefined motions. This study started with an aim to design body-worn sensors which measure net moments about leg joints to make the controller robust. However, it is found that even with the best technologies, the errors of the yet-to-make sensors are far too large. Therefore we conclude that a hands-free FES standing system with leg moment feedback is not practicable. However, paraplegics do stand with arm supports. Therefore, an FES system should be considered in the context of supported standing. Our kinematic analysis suggests that if arm supports are used, theoretically, paraplegics can control their leg posture by positioning their pelvis. Our kinetic analysis shows that (1) moments at all leg joints must be coordinated for standing to be possible, and (2) the co-ordinating moments in fact come from the upper-body while using imperfect controllers. These new understandings lead to our novel control principle - CHRELMS (Control by Handle Reactions of Leg Muscle Stimulation). With CHRELMS stimulation intensity is controlled by the upper-body, therefore the stimulation controller follows the subject's want in real time, not a pre-stored task. As our experiments with a T6 paraplegic volunteer demonstrated, the CHRELMS allows him to actively vary his standing motions and enables him to perform a controlled sitting-down manoeuvre. It is also shown that he applies we-named "quick-knee-locking" and "knee- moment-reduction" strategies for standing up and sitting down respectively. It is quite clear now how the paraplegic controls his leg motions by his upper-body with the help of FES.

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