Article

Facioscapulohumeral muscular dystrophy is a slowly progressive hereditary
disorder resulting in fatty infiltration of eventually most skeletal muscles.
Weakness of trunk and leg muscles causes problems with postural balance and gait,
and is associated with an increased fall risk. Although drop foot and related
tripping are common problems in FSHD, gait impairments are poorly documented. The
effect of ankle plantarflexor involvement on gait propulsion has never been
addressed. In addition to ankle plantarflexion, gait propulsion is generated
through hip flexion and hip extension. Compensatory shifts between these
propulsion sources occur when specific muscles are affected. Such a shift may be
expected in patients with FSHD since the calves may show early fatty
infiltration, whereas iliopsoas and gluteus maximus muscles are often spared for
a longer time. In the current study, magnetic resonance imaging was used to
assess the percentage of unaffected calf, iliopsoas and gluteus maximus muscles.
Joint powers were analyzed in 10 patients with FSHD at comfortable and maximum
walking speed to determine the contribution of ankle plantarflexor, hip flexor
and hip extensor power to propulsion. Associations between muscle morphology,
power generation and gait speed were assessed. Based on multivariate regression
analysis, ankle plantarflexor power was the only factor that uniquely contributed
to the explained variance of comfortable (R(2)=80%) and maximum (R(2)=86%)
walking speed. Although the iliopsoas muscles were largely unaffected, they
appeared to be sub-maximally recruited. This submaximal recruitment may be
related to poor trunk stability, resulting in a disproportionate effect of calf
muscle affliction on gait speed in patients with FSHD.
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