Ambroise UTX-FS Handmatig - Pagina 10
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The user must learn to properly complete the swing of the orthosis leg. If he / she doesn't do
this, then the next stance phase can begin without a locked knee.
In that case the user can only provide a safe situation by pressing the knee in extension from
the hip. If even this does not happen, an unsafe situation might occur. The user will transfer
his body weight on the supporting leg with an unlocked knee. Practice luckily shows that
users, after some training, generally have no difficulty in extending the knee for the next
stance phase.
Unlocking
The ankle hinge is connected to the knee hinge with control wire. For unlocking the knee
hinge of the UTX-SWING, two conditions must be simultaneously satisfied:
1.
First, the ankle should be in sufficient dorsiflexion. Only a small amount of degrees is
required. About 5° is enough to trigger the hinge. Also, without active muscles, dorsal
flexion still occurs naturally at the end of the stance phase when the supporting leg
rotate forward over the foot.
2.
In addition to dorsiflexion there must also, simultaneously, occur extension of the knee.
The knee hinge of the UTX-SWING has a lock in both flexion and extension. The knee
hinge can only be unlocked when it is pressed against the extension lock, that is to say, if
around the knee an extension moment is present. Releasing the flexion lock is safe in this
situation. If on the other hand the knee would be unlocked when it momentarily tends
to flex (is loaded with flexing moment of force) an unsafe situation would occur, leading
to possible falling. With the UTX-SWING this is not possible, because an extension is
needed for release.
This compelling double condition: dorsiflexion of the ankle ánd knee extension askes
for extra attention mainly during training of users. Especially the extension of the knee at
the end of the stance phase is tricky for some because it requires residual control over
the hip movements. Hip muscles are not necessarily required for this. Residual function of
still partially active knee extensors, but also an existing hyperextension of the knee may be
sufficient to stretch the knee.
There are a number of gait elements that need special attention during the training of UTX
SWING-users.
Step size
First, the step size matters.
When taking too small a step, it is possible that the upper body is insufficiently placed in
front of the supporting leg at the end of the stance phase. As a consequence, no or insufficient
dorsiflexion of the ankle will occur (Figure 6). The release of the knee hinge will not occur.
When taking too big a step, the other condition (knee extension) at the end of the stance
phase can be a problem. In very large strides it is difficult to make the floor reaction force
vector to run in front of the knee, in other words: to get the knee in extension. (Figure 7).
Timing
The requirement of getting the knee in extension at the end of the stance phase makes,
the users timing important. For some users, the required unlocking procedure seems
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UTX.2018.01
small step
normal step
dorsiflexion too small
dorsiflexion suffucient
Figure 6
Influence of the step size on the occurring
dorsiflexion at the end of the stance
phase. At small steps, there is insufficient
dorsiflexion in order to allow unlocking the
hinge.
normal step
big step
floor reaction vector
floor reaction vector
Figure 7
Influence of the step size on the knee load.
With increasing step size, the knee load is
more strongly flexing.
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