The present disclosure describes a method for determining vertebral instability and more specifically describes a method for quantifying the type and extent of spinal instability in a standardized manner. The present disclosure also relates to measuring the intervertebral rotation and the intervertebral space between vertebral pairs using simple images and from these measurements one or more vertebral pairs of the spine are unstable And determining if there is any. Finally, the present disclosure describes software that can be used to quantify the type and extent of vertebral instability.