Case of the Week 26-4-97: What people said...

There is a small absorptive extensor power burst immediately after a flat-foot left initial contact, which is rightly attributed to clonus of the gastrocs (confirmed in the EMG - by the way the blue blocks indicate the normal muscle "on" periods). However, it's of interest that her left ankle is dorsiflexed throughout (with a flat moment curve), which seems to go against the gastrocs being spastic. Moreover, the left knee is hyperflexed throughout (and by the way, the frontal and transverse plane abnormalities at the knee are therefore likley to be measurement artefacts).

Since the knee is affected in swing as well as stance, there must be hamstring and rectus spasticity, since the knee achieves neither late stance extension nor full swing flexion. Given this, and the fact that her ankle is not in equinus, I would have to say her major problem is at the knee - the flat-foot contact being a compensation for the flexed knee.

Now to the reduced right-sided hip abduction moment... Normally, of course, the function of this moment (gluteus medius contraction) is to support the pelvis & trunk over the stance leg whilst the swing leg advances - a lack of moment causing the Trendelenberg sign. However, the reduced moment occurs on her better side (the right). A glance at the frontal plane movie and trunk kinematics tells us why - she is using lateral trunk flexion instead of gluteus to produce a passive hip abduction moment, to increase clearance on her poor left side (i.e. compensate for lack of knee flexion - note that her left hemipelvis is always higher than the right). There's plenty of emg in the right gluteus medius, suggesting it is functioning fine.

Why does she use lateral trunk flexion instead of hip abductors? I confess I don't know - but you certainly see this a lot. Anybody any ideas?

Chris Kirtley

Dept. of Rehabilitation Sciences

The Hong Kong Polytechnic University

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