Depending on the site of compression, the patient may demonstrate motor, sensory or a mixed picture.

Yellow: zone 1

Proximal to bifurcation of the ulnar nerve, compression causes a mixed loss. This is commonly caused by a fractured hook of hamate or a ganglion.

Green: zone 2

Motor branch after bifurcation, compression causes loss of motor supply to muscles innervated by ulnar nerve in the hand. A fracture of the hook of hamate is the most common cause.

Blue: zone 3

Sensory branch after bifurcation, compression causes sensory loss to hypothenar eminence (the little finger and lateral side of ring finger). The most common causes are an aneurysm of the ulnar artery, thrombosis and synovial inflammation.