Strategies adopted by cerebellar ataxia patients to perform U-turns

Cerebellar ataxia is associated with unsteady, stumbling gait, and affected patients report a high rate of falls, particularly during locomotor tasks. U-turns (180° turns while walking) require a high level of coordination in order to completely reverse the body trajectory during ongoing motion, and they are particularly challenging for patients with cerebellar ataxia. The aim of this study was to investigate the kinematic strategies adopted by ataxic patients when performing U-turns. Nine ataxic patients and ten controls were analysed as they performed 180° turns to the right while walking. We evaluated the following aspects: centre of mass velocity, body rotation, number of steps needed to complete the task, step length and step width, lower limb joint kinematics and segmental reorientation. Compared with controls, the ataxic patients showed slower deceleration and re-acceleration of the body, needed more steps to complete the U-turn, showed markedly reduced step length and were unable to modulate step width between steps. Furthermore, the patients adopted an extended joint rather than a flexed joint turning strategy, and the degree of knee flexion was found to be negatively correlated with the number of falls. Ataxic patients show an abnormal U-turn in comparison to age-matched healthy subjects. Some of the observed alterations are indicative of a primary deficit in limb-joint coordination, whereas others suggest that patients choose a compensatory strategy aimed at reducing the instability.