The ulnar nerve originates as a terminal branch of the medial cord of the brachial plexus with nerve root fibers from C8-T1.
In the arm, the ulnar nerve runs medial to the axillary artery and subsequently the brachial artery on the coracobrachialis muscle in the anterior compartment. The nerve passes to the posterior compartment through the medial intermuscular septum distally running with the superior ulnar collateral artery. Further on, it runs between medial head of triceps brachii muscle and the medial intermuscular septum to pass posterior to the medial humeral epicondyle in the superficial condylar groove (cubital tunnel).
The ulnar nerve enters the forearm from the arm via the two heads of flexor carpi ulnaris (FCU) muscle. It subsequently lies superficial to flexor digitorum profundus and deep to FCU and medial to the ulnar artery. At the wrist, the ulnar nerve runs lateral to the tendon of FCU.
Prior to passing the flexor retinaculum at the wrist, the ulnar nerve gives off the dorsal cutaneous branch.
- dorsal cutaneous branch
- palmar cutaneous branch
- branch to palmaris brevis
- superficial terminal branch
- deep terminal branch
The ulnar nerve has both sensory and motor supply:
- articular innervation to elbow, wrist, carpal and phalangeal joints
- cutaneous innervation to ulnar aspect of the hand, specifically the 5 digit and the medial half of the 4 digit.
- may arise from the 7th and/or 8th cervical nerve roots only
- may pass in front of the medial epicondyle of the distal humerus
- Riche-Cannieu anastomosis: communication between the recurrent branch of median nerve and deep branch of ulnar nerve in hand
- Martin-Gruber anastomosis: communicating nerve branch between the median nerve and the ulnar nerve in the forearm
- may supply all the thenar muscles
- branch to the dorsum may be absent