New Voluntary Opening Prosthetic Devices Offer no Improvement Over Old Devices

Researchers have found no improvements in new voluntary opening
prosthetic devices when compared with data from devices in 1987, according to a
recent study.

“The first measurements of voluntary closing devices were published
in Prosthetics and Orthotics International in 2010,” Gerwin
Smit, MSc,
Delft University of Technology, Netherlands, told O&P
Business News
. “We were surprised by the poor mechanical performance
of most voluntary closing devices. We wanted to know if this was also the case
in voluntary opening devices.”

According to Smit and colleagues, no recent data are available on the
mechanical efficiency of voluntary opening devices. The latest study on a broad
range of adult- and child-sized voluntary opening devices was published by
Corin and colleagues in 1987. By comparing their study findings with those of
Corin and colleagues, researchers could “give an objective view of how
voluntary opening terminal devices have improved during the past decades,”
according to Smit.

New vs. old

Smit and colleagues quantitatively tested nine voluntary opening
prosthetic devices — four hooks and five hands— measuring the pinch
forces, activation forces, cable displacements, mass and opening span and
calculated the work and hysteresis. The results were compared with the 1987
data on prosthetic devices.

Study results showed that the hooks were lighter than a human hand and
the gloved hands were the same weight as the human hand. The opening span of
the hooks was wider than the span of the gloved hands, and the hooks had a
longer maximum cable excursion range. Activation forces and pinch forces were
higher in hooks, according to the researchers. However, activation forces of
several devices were very high and pinch forces were too low in all tested

When study results were compared with data from 1987, researchers found
no significant difference for the required work or pinch forces for the hooks
or for the hands. However, the activation force required for new hooks and
hands was significantly higher compared with the older devices of the 1987
data, which suggests they actually performed worse.

“It can therefore be concluded that, despite all technologic
advantages in other fields, [voluntary opening] prosthetic devices have not
improved since 1987,” the researchers wrote. “This study also shows
that some newer devices had a poorer performance than devices tested in

“Various user studies indicate that there is a need for improvement
of body powered terminal devices,” Smit said. “This is especially the
case for body powered prosthetic hands, which show high rejection rates.”

Room for improvement

The results indicated that more research is needed on prosthetics to
find improvements. Some improvement opportunities include reducing the mass of
the hands and activation force to enable comfortable wearing; increasing pinch
force to an acceptable level; and developing more flexible cosmetic gloves, as
well as either a more flexible or no inner glove. The researchers suggested
further study should be performed to determine the comfortable activation force
level and examine optimal shoulder movement for the most efficient force.

“Currently we are developing a body-powered prosthetic hand, which
provides sufficient pinch force and which requires activation force that is
comfortable to the user,” Smit said. “Surprisingly, there is no data
available in literature on what level of activation force of the shoulder
harness is comfortable or acceptable to the user. Therefore, we are also
conducting a study to determine the optimal activation force level.”

Smit and colleagues concluded that it is not only desirable to improve
body-powered prostheses, but necessary so that prosthesis users could be
“offered a prosthesis that is optimized to their needs and demands.”
by Casey Murphy


Smit G. Efficiency of voluntary opening hand and hook devices: 24 years
of development.

J Rehabil Res Dev. 2012;49:523-534.

Disclosure: Smit received financial support from OIM Stichting.

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