This section of the chapter discusses quiet-stance postural control in children with CP, and
addresses both issues of alignment of body segments and characteristics of body sway
during quiet stance and the effect these may have on other aspects of balance. Alignment
of the body refers to the relationship of body segments to one another, as well as to the
position of the body with reference to gravity and the base of support (Shumway-Cook and
Horak 1992). Alignment of body segments over the base of support determines to a great
extent the effort required to support the body against gravity. In addition, alignment
determines the type of movement strategies that will be effective in controlling posture.
Changes in resting stance position or alignment are often characteristic of the child with CP.
Abnormalities in alignment can reflect changes in the alignment of one body part to another
or in alignment of the centre of mass (COM) relative to the base of support.
Children with CP often experience reduced range of motion in joints of the ankle, knee,
and hip. In addition, contractures of the hip, knee, and ankle muscles may contribute to
atypical postures in sitting and standing. These include excessive posterior tilt of the pelvis
during sitting due to shortened hamstrings muscles, toe standing due to shortening of the
gastrocnemius muscle, and flexion of the knee during stance due to hip-flexor tightness.
These constraints often result in a crouched posture during stance. Atypical alignment can
also be expressed as a change in the position of the body with reference to gravity and the
base of support. For example, asymmetric alignment in standing is often characteristic of
children with a unilateral neural lesion, such as unilateral spastic CP (spastic hemiplegia).
Children with this type of lesion tend to stand with weight displaced toward the non-involved
side. This asymmetric alignment is a strategy that typically develops to compensate for
weakness in the hemiparetic leg (Shumway-Cook and Horak 1992).
One way of measuring postural stability during quiet stance is to ask the child to stand
on a force plate and to measure their centre of pressure (COP) displacement and velocity
characteristics during spontaneous sway. A number of laboratories have explored the
differences in these characteristics for children with CP versus typically developing children
(Ferdjallah et al. 2002, Rose et al. 2002). Rose et al. (2002) measured COP during quiet
stance under eyes-open and eyes-closed conditions for a group of children with bilateral
spastic CP (spastic diplegia), aged 5–18 years, and compared the results to typically
developing children of the same age range. They noted that 33% showed significantly higher
mean values for COP in at least two of the parameters, path length and average radial
displacement of the COP. Values for frequency of sway were lower for the participants with
CP than for the typically developing children. Values did not become more abnormal with
eyes closed, which suggests that the children with CP had normal dependence on visual
feedback for balance during quiet stance.