Adjustable Instantaneous Center & European Alignment musings

Adjustable Instantaneous Center & European Alignment musings

Colleagues,

The instant or rather instantaneous center of rotation on some four bar
knees can be changed as in the 5 bar knees from Teh Lin -DAW and perhaps
other knees.

Have others found this adjustment useful and I would like to know if you have
found a correlation between where the instantaneous center is adjusted, and
the
length and strength of the residuum, (and/or) if its an issue of more
stability initially and reducing stability later. Is or has any gait lab in
the world looked at this or what optimal centrode patterns are?

Furthermore, it has been brought to my attention that single axis knees have
improved toe clearance if aligned in the European alignment system.
It is very possible that I am not understanding this correctly but it seems
that the European alignment starts with bench alignment of the prosthesis
with the foot in dorsiflexion.

This would seem to create improved toe clearance but I wonder if this is
effective with more flexible keels vs. hard sach keels or S/A feet that don't
have front bumpers. Is there a problem with inadequate toe lever?

Additionally, it seems to me that there is toe clearance with a single axis
knee when there is adequate knee AND hip flexion at the appropriate time
which may not happen with the slow or beginning or feeble ambulators

So...it appears that a beginning and or feeble ambulator will have difficulty
clearing the toe
with a single axis knee, would have an easier time with a four bar, but
wouldn't have the safety advantage of the single axis weight activated stance
control type knee.

In which case, we again seem to need, a weight activated stance control 4 bar
knee,
if that is indeed an engineering possibility.

Either that, or as has been suggested to me, a weight activated stance
control knee that is initially shortened for toe clearance until pt has
improved gait with adequate knee and hip flexion and timing...and hopefully
doesn't develop poor gait patterns.

I appreciate the 4 bar knee with stance lock (Total) and use many of them,
but I have pt's that have fallen with these as well. So, I am still waiting
for a light weight 4 bar knee with good stumble resistance. For more active
pts I will explore the other 4 bar knees available including those IC
controlled knees

Ultimately toe clearance can be obtained with all knees under certain
conditions, just more so with 4 bar knees.

All additions, and corrections to my thinking are welcome.

Sincerely,
Mark Benveniste CP
VA MedCtr
Houston, TX