The hand of benediction is a pattern of motor deficits that occurs with a proximal injury to the Median nerve when the patient attempts to make a fist.
Pathophysiology
The proximal lesion results in denervation of the motor branches to the long flexors of the fingers in the forearm:
M. flexor digitorum superficialis: Flexion at the PIP joints (proximal interphalangeal joints) of all fingers is absent.
M. flexor digitorum profundus: Flexion at the DIP joints (distal interphalangeal joints) of the index finger (Dig. II) and middle finger (Dig. III) is absent.
M. flexor pollicis longus: Flexion of the distal phalanx of the thumb is absent.
The ulnar portion of the M. flexor digitorum profundus for Dig. IV and V is innervated by the Ulnar nerve and remains intact.
The hand of benediction is a dynamic phenomenon and only becomes apparent during movement. It must not be confused with the claw hand seen in an ulnar nerve lesion, which is already present as a deformity at rest.