Effect of Modified Visual Information on Postural Balance of Unilateral Transfemoral Amputees during Quiet Standing

Abstract

INTRODUCTION: In the absence of visual information, postural balance is ensured through the integration of sensory inputs from the somatosensory and vestibular systems. Due to the loss of a lower limb, unilateral lower limb amputees cannot effectively use somatosensory inputs from their prosthetic side to control their postural balance. This prosthetic somatosensory state causes them to adopt a different sensory-motor strategy for the maintenance of upright posture. PURPOSE: To assess the effect of modified visual information on the postural balance of unilateral transfemoral amputees (UTFA) during quiet standing. METHODS: A total of 23 UTFA subjects (63.2 ± 7.5 yrs) and 10 healthy subjects (57.4 ± 8.8 yrs) participated in the experiment. Subjects were instructed to stand on dual force plates (Kistler) while center of pressure (COP) displacements from each foot were measured for 30 seconds. They wore display-device eye gear (Olympus Eye-Trek FMD-700), to which a modified image signal, consisting of the tilting of real visual surroundings in the 10th and 20th second, was applied via a personal computer. RESULTS: When the image signal was applied to UTFA, COP increased in the anteroposterior direction under the non-affected limb (0.95 vs. 1.42 cm, p <.01). The overall COP decreased in the anteroposterior direction (1.45 vs. 0.95 cm, p <.05), and the velocity of the overall COP decreased (2.80 vs. 2.32 cm/s, p <.01) during the interval (0-30s) image application. In contrast, the application of the image signal to the healthy subjects induced increased the overall COP in the mediolateral direction (0.31 vs. 0.51 cm, p <.01), increased velocity of the overall COP in the mediolateral (1.06 vs. 1.66 cm/s, p <.01) and anteroposterior (1.28 vs. 2.12 cm/s, p <.05) directions, and increased velocity of the COP (1.85 vs. 3.0 cm/s, p <.05) under the dominant limb. CONCLUSION: The visual signal application had a different effect on the observed sensory-motor strategies of UTFA as compared to healthy subjects. The findings suggest that rehabilitating UTFA using complex balance tasks in challenging environments could help UTFA manage a variety of balance disturbances safely.