INFLUENCE OF VISION ON STANDING STABILITY OF BELOW KNEE AMPUTEES

Human stability is controlled by various parts of neuromuscular, visual and
vestibular systems. It depends upon integration of afferent information from the visual, vestibular and
proprioception systems. Below knee amputees miss the ankle strategy and do not have the
mechanoreceptors and sensory inputs from ankle and sole of the foot and should use other
mechanisms to improve their standing balance. There is not enough evidence in literature regarding
stability of below knee amputees. Moreover, it is not cleared weather the dependency of these subjects
on vision to compensate lack of sensory input is more than normal subjects or not. Therefore, the aim
of this study was to evaluate the stability of below knee amputees and also to determine the influence
of vision on stability.
Materials & Method: Two groups of normal and amputees (20 amputee subject and 20 normal
subjects) participated in this research study. The stability of subjects was evaluated using a Kistler
force plate. The difference between the stability of subjects was determined by two sample t-test.
Results: The mean values of COP excursion of the amputees were 23.71±7.8 and 13.49±5.3 mm in the
anteroposterior and mediolateral directions, respectively compared to 24.21±9.76 and 14.55±8.06 mm
for normal subjects under open eyes condition (P>0.05). The results showed that there was no
difference between stability of amputees and normal subjects. Moreover, there was no difference
between stability parameters between two test conditions.
Conclusion: There was no difference between stability of amputees and normal subjects. It can be
concluded that although the amputees missed the ankle strategy and foot and ankle sensory inputs,
they could enhance their standing stability by other mechanisms such as internal mechanism and the
information obtained from the skin in contact with socket and also external mechanism such as
alignment of prosthesis. The stability of the amputees during quiet standing with open eyes is the same
as that of closed eyes. It means that the amputees do not depend upon vision to restore their standing
stability