Rotator drift: A sign of upper motor neuron leg weakness

Objective: There are techniques for eliciting subtle arm weakness (pronator drift), but the accompanying abnormal reflex response (Hoffmann's sign) is of limited value; conversely, in the leg there are no techniques for eliciting subtle weakness equivalent to pronator drift, but there is a robust abnormal reflex response (Babinski's sign). Thus, there is a need to devise a simple and rapid technique for detecting leg weakness capable of being used in either cooperative or comatose patients.

Patients and methods: Using three patient groups (discovery set, training set, test set) a technique for detecting upper motor neuron (UMN) lesion leg weakness was devised.

Results: With the patient supine, the examiner grasps both big toes, pointing them towards the ceiling with the long axis of the foot perpendicular to the bed; the patient is asked to maintain this position for 30 s. People with pyramidal tract weakness show external rotator drift on their weak side: on the normal side the foot is deviated 20-25⁰ from the perpendicular, on the paretic side the foot is deviated more than 30°.

Conclusion: This rotator drift sign is a simple method for detecting subtle UMN leg weakness. When combined with the pronator drift sign, these two signs constitute "pyramidal drift" signs for the bedside detection of UMN hemiparetic weakness.