trans-femoral amputee using the non-adaptive, mechanical knee (top plot, filled diamonds) and the patient-adaptive knee (bottom plot, filled diamonds). In both plots, the subject's sound side leg is shown (open squares), along with reference data from unimpaired walkers (standard error bars). For the amputee participant, the non-adaptive, mechanical knee produced a maximum flexion angle that increased with increasing speed, far exceeding 70 degrees at the fastest forward walking speed, whereas the patient-adaptive knee gave a maximum flexion angle that was less than 70 degrees and agreed well with the unimpaired, biologic data. These results indicate that a patient-adaptive control scheme and local mechanical sensing are all that is required for amputees to walk with an increased level of biologic realism compared to mechanically passive prosthetic systems.

New horizons for lower-limb prosthetic technology: merging body and machine

Society is at the threshold of a new age when prosthe-ses will no longer be separate, lifeless mechanisms, but will instead be intimate extensions of the human body, structurally, neurologically, and dynamically. Such a merging of body and machine will not only increase the acceptance of the physically challenged into society, but will also enable individuals suffering from leg amputation to more readily accept their new artificial appendage as part of their own body. Several scientific and technological advances will accelerate this mergence. An area of research of considerable importance is the development of improved power supplies and more efficient prosthetic actuator designs where both joint impedance and mechanical power generation can be effectively controlled in the context of a low-mass, high cycle-life, commercially viable prosthesis. Another critical area of research will be to combine local mechanical sensing about an external prosthetic joint with peripheral and/or central neural sensors positioned within the body. Neural prostheses such as the Bion (Loeb, 2001, see Chapter 32 of Volume I), combined with external biomimetic prosthetic systems, may offer important functional advantages to amputees. The fact that only EMG

or local mechanical sensors were employed in pros-thetics imposes dramatic limitations in the system's ability to assess user intent. In the advancement of prosthetic systems, we feel that distributed sensory architectures are research areas of critical importance.

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