1st Joint ESMAC-GCMAS Meeting - Análise de Marcha

O-41
AN EXPLORATION OF THE FUNCTION OF THE TRICEPS SURAE DURING
NORMAL GAIT USING FUNCTIONAL ELECTRICAL STIMULATION
Stewart, Caroline Dr 1 , Postans, Neil Dr 1 , Schwartz, Michael Dr 2,3 , Rozumalski, Adam Mr 2 ,
Roberts, Andrew Mr 1
1 ORLAU, RJAH Orthopaedic Hospital, Oswestry, UK
2 Gillette Children’s Specialty Healthcare, St Paul, USA
3 University of Minnesota, Minneapolis, USA
Summary/conclusions
This study uses random bursts of functional electrical stimulation (FES) to perturb normal gait.
The results are used as an indicator of the normal function of the calf muscles and also to
provide supporting evidence for predictions based on induced acceleration analysis (IAA).
Gastrocnemius and soleus are shown to have opposing actions at the knee and ankle during
second rocker. These counterintuitive results correlate with published predictions from IAA.
Introduction
The triceps surae muscle comprises soleus and the two heads of gastrocnemius. All cross the
ankle and subtalar joints, having plantarflexing moment arms. Only gastrocnemius crosses the
knee, where it has a flexing moment arm. Manual muscle testing produces a predictable
response and, intuitively, the common tendon suggests a similar action at the ankle.
Computer simulation techniques have been used to investigate the role of particular muscles
during gait. Recent work using IAA has yielded some surprising results for the calf muscles,
demonstrating that gastrocnemius and soleus sometimes have opposing functions [1] [2]. IAA
models, results, presentation and interpretation vary and the approach is not without its critics
[3]. There is a clear need for additional practical validation.
The aim of this study was to investigate the dynamic action of the triceps surae muscles, during
normal gait, using discrete bursts of FES. IAA can also be considered to be a perturbation
away from the existing dynamics, hence the FES results can be compared directly with IAA
predictions.
Statement of clinical significance
The triceps surae muscles are frequently implicated in the development of pathological gait
patterns in conditions such as cerebral palsy. Many different treatments are recommended,
including surgery, Botulinum toxin injection and stretching programmes. In order to treat the
muscles appropriately it is important to understand their function during normal walking.
Computer simulation is becoming a clinically important tool in the decision making process
following gait analysis. If a direct link can be demonstrated between the response of subjects
in the gait laboratory and the results of the models then researchers and clinicians will have
much greater confidence in using this kind of information.
Methods
5 adult male subjects volunteered to take part in the study. No subject had any pathology
affecting their walking. Each had one lower limb tested, selected at random. One pair of FES
electrodes was placed over the lateral head of the gastrocnemius muscle and a second over
soleus. The timing of the stimulation was controlled using foot switches. The pulse width of
the stimulation was altered to elicit as strong a contraction as was tolerable.
A full body marker set was used and gait data collected using a Vicon 612 system in
conjunction with a single Kistler force plate. Six different stimulation conditions were tested,
the two muscles with three different timings - first, second and third rockers. The order of the
testing was randomized. In each case a series of walking trials was collected, with each trial
randomly assigned for stimulation or no stimulation. For the stimulation trials only the stance
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