Role of visual, vestibular and somatosensory systems in the neural regulation of head position and body posture in young women with idiopathic scoliosis

Idiopathic scoliosis (IS) occurs with a prevalence of 1-3 % in the population,
and is the most common spinal deformity in adolescents. This type of scoliosis
usually develops during the period of rapid growth as a three-dimensional
deformity of both translational and rotational asymmetry. Apart from the spinal
deformity, other features are posterior chest wall prominence and overall
postural imbalance in the coronal plane. Morphological changes associated with
IS alter the relative position of the head, the shoulders, the shoulder blades,
and the pelvis in all planes. Although several possible causative factors have
been suggested and examined, there is no generally accepted theory for the
aetiology of idiopathic scoliosis. A systematic literature research of the
aetiology of IS conducted earlier this year, has given reason to belief that
integration of the three perceptual systems - visual, somatosensory and
vestibular - at the brainstem level possibly plays a part in the development of
IS. With this information, healthy people are able to establish the true
vertical and horizontal without any problems. Even if the head or body is
tilted, the person is still able to establish upright. The sensory information
is redundant that orientation and balance are guided by simultaneous reafferent
cues. The functional ranges of the systems overlap, thus permitting them to
compensate in part for each other*s deficiencies. Therefore, when visual
information is absent, healthy people are still able to closely estimate the
true vertical. They are able to make a fairly accurate estimation of
verticality of their bodies. Several findings give reason to assume that
patients with idiopathic scoliosis are less capable of doing so. The assumption
on which this study is based, is that patients with IS have a different neural
regulation of head position and body posture than healthy people do.

The goal of this study is to establish differences and agreements in the
integration of vestibular, visual and somatosensory information and in the
neural regulation of head position between girls with idiopathic scoliosis,
woth congenital scoliosis and healthy girls. Results should provide more
information about the pathology of idiopathic scoliosis and possibly about the
aetiology.

Measurements take place in the CAREN laboratory (Computer Assisted
Rehabilitation Environment; a virtual reality system for research and
rehabilitation of the Institute of Human Movement Sciences) of the University
of Groningen. Using the laboratory*s camera system, we can track the position
in space of a marker that is placed on the subject*s body in real-time. The lab
has a platform which will be used to roll-tilt subjects and/or a box. The box
consists of black, wooden pergolas and white Chinese paper. The backside of the
box is open; this way the subject will not feel trapped and we can videotape
her movements.
There are four experimental conditions:
1.Inbox: Subject is standing inside the box with her eyes open (the box and
subject*s support surface are tilting along with the platform)
2.Inbox sit: subject is sitting on the table inside the box with her eyes open
(the box is tilting along with the platform, but the subject*s support surface
is not)
3.Outbox open: Subject is standing on the platform without the box with her
eyes open (subject*s support surface is tilting along with the platform)
4.Outbox closed Subject is standing on the platform without the box with her
eyes closed (subject*s support surface is tilting along with the platform)

Not applicable