biodex 950-440 - Page 126

126 Biodex Medical Systems, Inc. © 2017
Resulting in:
∅! = !
1
𝑛
𝑥
!
− 𝜎
!
!
!
!!!
+ 𝑦
!
− 𝜎
!
!
Where:
Ø = resulting Sway Index (score).
𝑛 = number of samples.
Stability Index (SI): The Stability Index is the average position from center, in degrees. It is
important the patient has a COG (Center Of Gravity) centered before starting. The score ranges
from 0.0 to 20.0, where each ring on the screen represents 5.0 degrees.
Stability Index with dynamic platform motion represents the variance of platform displacement
in degrees, from level, in all motions during a test. A high number is indicative of a lot of
movement during a dynamic test. With static measures, it is the angular excursion of the
patient's Center Of Gravity.
Use as a starting point for a perfectly balanced state.
𝑆𝐼! = !
1
𝑛
𝑋
!
!
+ 𝑌
!
!
!
!!!
Where 𝑛 = number of samples.
Forward/Backward (Anterior/Posterior) Stability Index: Represents the variance of platform
displacement in degrees, from level, for motion in the sagittal plane.
𝑆𝐼
!
! = !!
1
𝑛
𝑌
!
!
!
!!!
Left/Right (Medial/Lateral) Stability Index: Represents the variance of foot platform
displacement in degrees, from level, for motion in the frontal plane.
𝑆𝐼
!
! = !
1
𝑛
𝑋
!
!
!
!!!
Angle: The sway angle, Angle (°), is derived from the position of the patient’s center of gravity
(COG) from a center position of zero and the estimated height of the patient’s COG.