Abstract
The hybrid FES using the Walkabout device that links the knee-ankle-foot-orthoses (KAFO) and C-posture provides lateral stability, however it had little effect on anteroposterior stability. The purpose of this study was to determine the influence that the foot position and FES provides to the quiet standing balance. A force platform was used to measure center of pressure (COP) while quite standing. Measurements were made as follows, 1) C-posture, 2) Unilateral foot forward, 3) Using the triangular stand, 4) Using the FES. In this study, to improve the balance in the anteroposterior direction, the unilateral lower extremity was contacted forward using a triangular stand with the FES. We concluded that the hybrid FES using the triangular stand provides standing stability on the anteroposterior for paraplegics.
1.
Introduction
Balance is a generic term
describing the dynamics of body posture used to prevent falling. Winter [1]
reported that balance is related to the inertial forces acting on the body and
the inertial characteristics of body segments. The slightest sway can unbalance
every segment in the quiet standing [2]. Though paraplegic patients have
insufficient muscle activity (which equals output source) and the somatosensory
(which equals equilibrium maintenance function), they could maintain standing
by FES and use of the several orthoses. The hybrid FES was conducted using the
Walkabout (fig 1) to prevent muscle fatigue, reduce energy consumption, and
enable better stability [3]. The medially linked knee-ankle-foot orthoses
(KAFO) seemed to have many merits in the functions of standing and walking,
wheelchair compatibility, cosmetics, and easy don-doff [4]. The first advantage
of the medially linked KAFO is that it provides better lateral stability while
standing, and it is rare to fall towards the mediolateral direction. However,
the main problem is poor stability towards the anteroposterior direction, this
can cause problems during activity of daily living while in the standing
position. The purpose of this study was to determine the influence that the
foot position and FES provides to the quiet standing balance.
2.
Methods
Subjects
Subjects were 6 men with established
traumatic paraplegia and a woman with paraplegia by neuroblastoma. Subjects had
lesions between T4 and T12 levels, all patients had complete sensorimotor loss
Fig 2. Total length of the COP
Fig 3. The
length of the COP on the X-axis and on the Y-axis
(American Spinal
Injury Association impairment scale grade A)(table 1). Two individuals were
implanted with the electrodes for applying FES to the lower limb and trunk and given
training for ambulation with the KAFO using FES 8 years and 2 years ago,
respectively. The percutaneous intramuscular electrodes were implanted into the
motor points of the paravertebral muscle, psoas major, vastus lateralis, vastus
medialis, sartorius, tensor fasciae latae, gluteus maximus, gluteus medius,
biceps femoris, adductor magnus and implanted near the femoral nerve and
peroneal nerve.
FES system
The Akita stimulator III (BIOTEC, LTD, Japan)
was used to restore the function of standing-up, standing and walking. The
stimulator had 12 channels. The pulse amplitude was modulated from 0 to –15V.
Rectangular pulse trains were used with a 200 microseconds pulse width and a
pulse interval of 50ms.
Procedure
A force platform (9281B, Kistler)
was used to measure center of pressure (COP) while quite standing in four
methods. 1) C-posture: Usual standing position with hip hyperextension. 2) Forward:
Unilateral foot was put forward 10cm. 3) Triangular stand: Unilateral foot was
put forward 10cm and a triangular stand inserted between sole and floor. 4)
FES: A quite standing using FES with a triangular stand. During the quiet
standing, subjects were instructed to look straight ahead and stand as quietly
as possible with arms by their side, not touching either their thighs or
orthoses with their hands. During the quiet standing on a force platform, the COP
digitized at a rate of 35Hz for 30 seconds. The total length of COP, the length
of COP on the x-axis, and the length of COP on the y-axis were calculated from
measured value variables.
3.
Results
All
measurements were performed satisfactorily. The standing with a triangle stand
using FES was shortest in total length. The average total length is 5.89m/min
in the C-posture, 2.98m/min in the forward, 0.57m/min using the triangular
stand, and 0.39m/min using the triangular stand with FES (fig 2). There were no
significant differences in the length on the x-axis between all measurements. The
length on the y-axis was 5.20m/min in the C-posture, 1.86m/min in the forward,
0.98m/min using the triangular stand, 0.59m/min using the triangular stand with
FES (fig 3).
4.
Discussions
The
equilibrium function is controlled by vision, the vestibular system, and the
somatosensory. The complete paraplegic patient has to maintain the equilibrium
function with the loss of muscle activities in the lower extremities and the
somatosensory loss. According to
Andrews and associates [5], if a subject leans slightly forward with hips and
knees fully extended during standing, the floor reaction force passes in front
of the knee joint and the leg is mechanically stable. This posture is often
referred to as the C-posture which allows the patient to stand stably. While standing in the C-posture
using the medially linked KAFO, the patient could maintain the standing
position for long time. Middleton [6] described how the Walkabout device links
the KAFO and C-posture, because the abduction foot position in the Walkabout,
while increasing lateral stability, had little effect on anteroposterior
stability. When his patients were moving in the standing position, they not
only increased their C-posture, but often used contralateral arm movements, as
well. They were necessary to prevent overbalancing forwards or backwards
because of their inherent instability in the anteroposterior direction. Winter
et al. [1] described that the relation between the COP and the center of
gravity (COG) is important in the anteroposterior direction at quiet standing,
it is controlled using an “ankle-strategy”. It is described how the position of
COP and COG is sensed, and it is controlled by the muscle activity in the ankle
due to changes in the position of COP. However, the paraplegic patient while in
the standing position keeps the anteroposterior balance by using only the trunk
and the upper extremity and they have to try to control their balance while
maintaining the hip hyperextension. So, maintaining the balance in the anteroposterior direction is extremely difficult.
In this study, to improve the balance in the anteroposterior direction, the
unilateral lower extremity was contacted forward. However, the base of support
becomes a triangle, instead of a parallelogram, because the ankle joint is
fixed by orthoses and this only allows heel contact to occur with the
unilateral lower extremity. This makes it difficult to provide adequate support
using both lower extremities. The base of support becomes a parallelogram again
by using a triangular stand under the sole and it is possible to recreate support
by bilateral lower extremities. In addition, falling forward was decreased by
the combination of a triangular stand and the rigidity of the ankle part of the
posterior unilateral orthoses. However, it is necessary to realize that
instability appears in the mediolateral direction when unilateral lower
extremity contact is too far forward. Using FES, standing stability was
improved. The reason for the improvement of the standing balance is that the
stability of the lower trunk and the hip joint improved. Shimada et al [7]
reported that the hybrid FES was superior in stability, reducing muscle
fatigue, energy consumption. We concluded that hybrid FES, using the unilateral
foot forward with the triangular stand, provided quiet standing stability for
paraplegics. Finally, if the standing balance of paraplegic patients improves,
their activity of daily living in the standing position will progress. However,
not only the quiet standing evaluation but also dynamic standing evaluation
should be further examined.
References
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