Re: Adjustable Instantaneous Center & European Alignment musings

Re: Adjustable Instantaneous Center & European Alignment musings

A couple of comments on Euopean alignment and stance brake knees.
The increased toe clearance for the Euro alignment over the TKA alignment is
due to the relative anterior placement of the knee. The foot is not
dorsiflexed. In fact, if the bench alignment is done with a safety factor
lift under the heel, the foot is plantarflexed. As pointed out by Radcliffe,
this does not cause the leg to be too long or the toe to catch in swing
because the distance from the ball of the foot to the hip is the same in both
systems.

Safety knees. In my opinion, they should be used much less than they are.
Why, They cause the amputee to walk with an unnatural gait because they
can't begin to flex the knee in late stance, while still in double support.
If a good walker is fitted with a safety knee, they will likely complain of a
popping when the knee begins to bend. This is because the brake is
resisting knee flexion, the amputee is producing a knee flexion moment with
active hip muscle action and when enough weight is transferred off of the
prosthesis and the brake releases, they get that annoying pop.
I prefer to fit all AK's who have adequate hip musculature with a knee that
will allow and even encourage voluntary controlled knee flexion while still
in double support.

Hope this is useful and that this brief explanation gets my thoughts across.
I would be happy to continue this if anyone likes.

Regards,
Jack Uellendahl, CPO

In a message dated 2/9/01 6:45:44 AM Central Standard Time, <Email Address Redacted>
writes:

<< 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. >>