Ambroise UTX-FS Manuel - Page 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:

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.

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

Figure 7

Influence of the step size on the knee load.

With increasing step size, the knee load is

more strongly flexing.