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19-06-2012 | Physical rehabilitation | Article

Functionality of body-powered prosthetic hands behind the times

Abstract

Free abstract

MedWire News: Research suggests that the functionality of body-powered prosthetic hand and hook devices has not improved for quarter of a century.

"Despite the developments made in electrical prostheses, a significant number of adults and children wear body-powered prostheses," explain Gerwin Smit (Delft University of Technology, the Netherlands) and colleagues.

"These users often prefer the relative benefits of the body-powered prostheses, such as low weight, technical reliability, low cost, and proprioceptive feedback, over the benefits of electrical prostheses, such as grip strength and the fact that a harness is not necessary in most cases."

However, the authors go on to explain that these devices do have a number of drawbacks such as the requirement of a high activation force and frequent failure of the activation cable.

Smit and colleagues carried out an evaluation of the mechanical efficacy of nine currently available body-powered hand (n=5) and hook (n=4) devices and compared the results with those collected for similar devices in 1987.

Pinch forces, activation forces, cable displacements, mass, and opening span were measured for each hand and the work and hysteresis were also calculated.

As reported in the Journal of Rehabilitation Research and Development, the team found that in general the hooks needed lower activation forces and had a higher pinch force than the hands.

They note that a couple of devices required a very high activation force (over 80 N) and also found that the pinch force of all the tested hands was too low (below 20 N) for good functionality.

Of the hooks tested, the researchers judged the Hosmer model 5XA hook with three bands to be the best, and of the hands, the Hosmer Sierra VO hand had the best performance.

Compared with the mechanical functionality results collected in 1987, Smit and co-authors found no significant improvements in the more modern devices.

"Future research should focus on reducing the mass of the cosmetic glove and hand mechanism, determining the comfortable activation force level for shoulder activation, decreasing the required activation force level, and increasing the pinch force of the hands," they conclude.

By Helen Albert

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