Gait initiation by patients with lower-half parkinsonism.

Patients with multiple deep cerebral infarcts and white matter degeneration commonly exhibit a hesitant, shuffling gait, with preserved arm swing. This pattern of walking is called lower-half or lower-body parkinsonism. Gait initiation and turning consist of one or more short, hesitant steps in which the feet shuffle across the floor. This abnormality of gait initiation was studied with quantitative motion analysis in five patients, ages 74-87 years. Five men and five women with normal mobility and comparable ages exhibited three key events of gait initiation: (i) activation of tibialis anterior and inactivation of triceps surae produced bilateral ankle dorsiflexion and a sagittal moment of force that propelled the body anteriorly; (ii) abduction of the swing hip occurred simultaneously with event (i); and (iii) abrupt 3-10 degrees flexion of the support hip and knee occurred nearly simultaneously with events (i) and (ii) and produced a transient reduction in vertical force beneath the support foot. Events (ii) and (iii) produced a coronal moment of force about the ankles that propelled the body toward the support foot. Thus, in normal gait initiation, a smooth sequence of postural shifts propels the body anterolaterally toward the support limb, culminating in a forward step. The patients, by comparison, exhibited errant deviations in their postural shifts of gait initiation, and one or more aborted steps frequently preceded the first complete step. Nevertheless, all patients employed the usual three key events in their initial attempt at stepping, consistent with a normal motor strategy of gait initiation. These results and previous clinical observations suggest that the principal locomotor deficit is an impaired generation of postural shifts that mediate changes from one steady-state posture or movement to another.