Inversion or pronation of the foot following thalamotomy for Parkinson's disease

The author has observed inward turning of the foot of 2 parkinsonian patients following thalamotomy on the contralateral side. In one instance, the surgery was unilateral and in the other bilateral. The anatomical position of the involved lesions was in the region of the complex of the ventrocaudal nuclei (ventralis posterolateralis). It appears that three elements are present whenever such pronation of the foot occurs, namely, paresis, hypertonicity, and impairment of sensory modalities such as localization, two-point discrimination and vibration.