In an athetoid hand, says Starr, the interossei and lumbricales, which flex the metacarpo-phalangeal and extend the phalangeal joints, are affected; rarely are the long extensors and the long flexors affected. Therefore the hand is usually in the so-called interosseal position, with flexion of the proximal and extension of the middle and distal phalanges.
By means of splints, the interphalangeal, metacarpo-phalangeal, and wrist joints should be gradually extended until the deformity is over-corrected (R.
The hand assumes a characteristic attitude: the index and middle fingers are extended at the metacarpo-phalangeal joints owing to paralysis of the interosseous muscles attached to them; the little and ring fingers are hyper-extended at these joints in consequence of the paralysis of the lumbricals; all the fingers are flexed at the inter-phalangeal joints, the flexion being most marked in the little and ring fingers claw-hand or main en griffe.
After division at the elbow, there is impairment of mobility which affects the thumb, and to a less extent the index finger: the terminal phalanx of the thumb cannot be flexed owing to the paralysis of the flexor pollicis longus, and the index can only be flexed at its metacarpo-phalangeal joint by the interosseous muscles attached to it.