Contractures and dynamic splinting in Duchenne Muscular Dystrophy:
Effects on gait economy.

In 1981, Sutherland et al. described gait patterns in Duchenne Muscular
Dystrophy (=DMD) patients. They found that lumbar lordosis is the earliest
postural change observed in gait and that this was probably a compensation to
keep the force line behind the hip after weakness of the m. gluteus maximus.
They also described the necessity of equinus posture for knee stability. This
is a provoking pose for shortening of the Achilles tendon.
Armand et al (2005) compared gait of 2 SMA patients with 2 DMD and concluded
that DMD children use hip and circumduction of the leg to move body forward.
Furthermore, maintenance of stance seemed to be achieved through equinus and
lordosis. The main difference observed in gait was less pelvic instability in
DMD children, despite their weak abductor muscle strength. They proposed that
this could be caused by contracture of the tibio-iliac tract or the higher
abductor moment because of toe-standing. This leads to the assumption that
contractures can also have positive effects in gait instead of only
deteriorating the process of wheelchair dependence.

An evaluation of plantar flexion contractures in DMD was performed by
Gaudreault et al. in 2009. They measured passive ankle plantar flexion moments
by hand held dynamometer and net moments by gait analysis in 11 DMD boys and 14
controls and concluded that the relative passive moment contribution to the net
plantar flexion moments was higher in boys with DMD compared to controls. The
higher rigidity coefficient in contractures seems to lead to energy storage in
the ankle and a higher plantar flexion moment in the end of the lengthening
phase in gait.
The fact that ankle contractures can contribute positively to gait is supported
by a study in stroke patients (Lamontagne et al. in 2000), but is also seen in
healthy runners: Scholz et al. (2008) found that in healthy runners, the amount
of stored energy in Achilles tendon increases as moment arm gets smaller,
leading to better running economics.
In Duchenne Muscular Dystrophy due to Achilles tendon contractures the moment
arm gets smaller, thus hypothetically leading to better gait economics. In
other words ankle contractures can be beneficial as an energy storing mechanism
in the pre-swing phase of the walking cycle and release of this energy in the
toe-off (foot clearance of the floor) in the initial swing phase.

In the management of DMD much emphasis is put on controlling contractures.
However, contractures of the Achilles tendon could be a very useful adaptation
of the body. A frequently seen problem however with these contractures is
stumbling in swing phase by balance problems and the need for more pelvic tilt
for moving forward. This can be a cause of fatigue. Thus there seems to be a
precarious balance between walking ability and extent of contractures, but also
between standing ability and extent of contractures. For walking ankle
contractures causing equinus seem to be preferable as an energy storing
mechanism and as a good lining for the lumbar lordosis, while for standing and
the swing phase during walking a minimal equinus is preferable.

There are dynamic orthoses that can mimic energy storing at the pre-swing
phase, can help lifting the foot (toe off), and clearing the foot during swing
phase (no stumbling). One of the most promising is the Spring Swing, because
this orthosis can be adjusted in force (by means of a spring) needed to get a
good foot clearance by using different springs. In stance, this orthosis could
give additional stabilization and correction of flaccid equinovarus (often seen
in boys with DMD), while plantar flexion and balance movements in the sagittal
axis are still possible. By using this dynamic orthosis the minimal contracture
in the ankle can be accepted for a good standing position, while during walking
the energy storing mechanism of the orthosis can help toe-off and good foot
clearance.

This study will consist of two parts. In the primary observational part we will
assess kinematic and kinetic walking patterns in Duchenne Muscular Dystrophy.
Goal is to asses the correlation between progressive contractures and gait
patterns. This will be compared with the findings of Gaudreault (2007) to
confirm their hypothesis that contractures of the ankle have a positive effect
on gait in DMD.

Secondary, in an intervention study using the same subjects as their own
controls (repeated N=1 study), the effects of a dynamic ankle-foot orthosis
(AFO) in gait will be evaluated. This to point out whether this AFO leads to a
better performance in timed motor performance and fatigue, due to better foot
clearance during swing.

If the hypothesis of Gaudreault et al. is correct, we expect to find the Spring
Swing having a positive effect on gait economy (meaning better gait
characteristics, longer walking distance, and less fatigue). Wearing the AFO's
could then lead to a longer ambulation period for boys with DMD.

The patients will each be tested once without braces, e.g. the observational
study, T0. Four weeks later they are studied again with dynamic AFO*s, the
intervention study, T1. In between the two sessions the Spring Swing will be
custom made by the orthopedic technician, and the boys will be allowed to walk
for 2 weeks at home with the orthosis before the second session in the movement
laboratory.

In the observational study, clinical and functional tests are run, together
with an extended gait analysis in the gait laboratory. In the intervention
study, measurements are repeated after using the spring swing for 2 weeks. The
spring of the dynamic brace is adjusted to reach zero degrees dorsal flexion in
resting position.

In the intervention study a dynamic ankle-foot orthosis of OIM (Orthopedische
Instrumentmakerij, type *spring swing*) will be used. This brace is made of
polypropylene and has a spring attached on the back of the AFO near the
Achilles tendon. It is designed to give an active dorsoflexion moment in swing
phase, thus leading to foot clearance. Polypropylene is flexible, allowing
small movements in the sagittal axis, as needed for balancing and allowing
plantar flexion as seen in toe-walking. The spring can be adjusted to change
the external dorsal flexion moment on the ankle created by the orthosis. The
orthosis will be custom made and the spring is adjusted to reach zero degrees
dorsal flexion in resting position.

Burden associated with participation will be limited, since measurements are
non-invasive. In addition, it is expected that the interventions are beneficial
and may help to gain functional abilities or preserve them for a longer period.
If the results are positive, the principles of this training may be applicable
to other neuromuscular disorders.*The participants can keep the custom made
orthosis if regarded as benificial.