Plantar pressure in relation to hindfoot varus in people with unilateral upper motor neuron syndrome.

Introduction: Hindfoot varus deformity is common in people with unilateral upper motor neuron syndrome (UMNS) and can be dynamic or persistent. The aims of this study were (1) to gain insight into plantar pressure characteristics of people with chronic UMNS in relation to hindfoot varus and (2) to propose a quantitative outcome measure, based on plantar pressure, for the scientific evaluation of surgical interventions.

Methods: In this retrospective study, a cohort comprising plantar pressure data of 49 people with UMNS (22 "no hindfoot varus", 18 "dynamic hindfoot varus", and 9 "persistent hindfoot varus"), and 586 healthy controls was analyzed. As an indication of plantigrade foot contact, the ratio between the plantar contact area of the affected and the non-affected foot was calculated. To investigate spatial and temporal aspects of plantar pressure, normalized plantar pressure patterns and center of pressure trajectories were computed.

Results: People with UMNS had lower plantar pressure area ratios compared to healthy controls. Additionally, increased plantar pressure underneath the lateral foot was found in people with a persistent hindfoot varus. Center of pressure trajectories were more lateral during the first 26% of the stance phase in people with a dynamic hindfoot varus and during the first 82% of the stance phase in people with a persistent hindfoot varus compared to healthy controls.

Conclusion: Spatial and temporal differences in plantar pressure were found in people with dynamic or persistent hindfoot varus deformity. We propose to primarily use the medio-lateral center of pressure trajectory as outcome measure for the scientific evaluation of surgical interventions targeting hindfoot varus.