Attn researchers, mfgrs, prosthetists-

Attn researchers, mfgrs, prosthetists-

Dear Colleagues:

Is anyone else interested in this? Should we be?
I would like to have 4 bar knees characterized by the amount of toe
clearance provided, the distance and posterior displacement of the virtual
center of rotation, and perhaps the path of the centroid. For those that are
interested, this information may help to eventually determine the choice of
polycentric knee used (along with price and weight)

A limited study was done by Gard, Childress, &Uellendahl and published in Vol.
8 Number 2/Spring 1996 of JPO. I think this was an excellent topic and
would like to see an expanded version to include all 4-5-6 bar knees
currently available. As I understand it, this was done with computer
modeling so perhaps it would be possible for new knees
to be assessed and thus characterized.

It seem relatively simple to determine the position of virtual center of
rotation and I would like to see it in the specs of a knee unit. Toe
clearance and other parameters are more difficult to determine.

Its an interesting article. An advantage of the polycentric knee that I
believe is not mentioned in the article, is the greater ease of generating a
flexion moment. My presumption is that with a higher virtual center of
rotation, the short residuum has less of a lever arm to lift, thus reducing
torque on the limb and making it easier to initiate flexion. Am I correct?

In principle I would think we would want to choose a virtual center
of rotation inversely proportional to the length of the limb. (the shorter
the Limb, the higher the virtual center of rotation) Or, perhaps we always
want it as high as possible? Or do we want the virtual center of rotation to
be located at some optimal point along the residual limb? (Of course there is
always the anterior-posterior positioning to be considered for stability.)

Do you think these issues are relevant or a needless attempt at precision
that is unnecessary?

Mark Benveniste CP.