Virtual time-to-contact identifies balance deficits better than traditional metrics in people with multiple sclerosis

Multiple sclerosis (MS) is a neurodegenerative disease that negatively affects the quality of electrical signaling throughout the central nervous system. Although impaired postural control is one of the most common symptoms in people with MS (PwMS), commonly reported metrics such as center of pressure (CoP) path length and velocity have not been great predictors of fall risk. A relatively new metric, known as virtual time-to-contact (VTC), is a measurement that uses the instantaneous position, velocity and acceleration of the CoP, to predict how long it would take the CoP to reach the boundary of the base of support for every data point in a trial. While the VTC metric has shown promising results in PwMS, there are still inconsistencies in how VTC is reported. Thus, the purpose of this work was to compare VTC to commonly reported measures of postural balance control to identify the most appropriate metric(s) for assessing balance impairments unique to PwMS. A group of patients with MS and a group of neurologically healthy controls performed a static balance task with both eyes open and eyes closed. The VTC minimum values (minima) were the best at detecting balance performance differences between conditions and between study groups. In addition, VTC minima was the best at detecting proprioceptive weaknesses in PwMS, assessed via the Romberg ratio. These results suggest that the VTC minima may be better than traditional metrics at detecting balance impairments unique to PwMS as well as proprioceptive deficits within this population.