From its origin, the ulnar nerve courses distally through the axilla, arm and forearm into the hand. It is a mixed nerve and provides motor innervation to various muscles of the forearm and hand as well as sensory supply to the skin of the hand.
The ulnar nerve can broadly be described as the nerve of the hand, as it innervates the vast majority of the intrinsic hand muscles. It is one of the most clinically relevant nerves of the upper limb, due to its superficial course and clinically apparent role in hand function.
This article will discuss the anatomy and function of the ulnar nerve, as well as its clinical relevance.
|Origin||Brachial plexus (C8-T1)|
|Branches||Muscular branches, articular branches, palmer cutaneous branch, dorsal cutaneous branch, superficial branch, deep branch
- Flexor carpi ulnaris and medial half of flexor digitorum profundus
- Most of the intrinsic hand muscles
- Anterior aspect of the ulnar 1½ fingers (little finger and half of the ring finger) and medial palmar skin
- Dorsal aspect of the ulnar 1½ fingers and medial aspect of dorsum of hand
Ulnar nerve supplies all intrinsic muscles of the hand except the LOAF muscles.
(standing for: Lateral two lumbricals, Opponens pollicis, Abductor pollicis brevis, Flexor pollicis brevis)
- Origin and course
- Branches and innervation
- Clinical relations
Origin and course
The ulnar nerve is the distal continuation of the medial cord of the brachial plexus, from the nerve roots of C8 and T1. It often carries fibers from C7 via a communicating branch from the lateral cord.
From the medial cord, the ulnar nerve passes distally through the axilla, medial to the axillary artery. It descends on the medial aspect of the arm, medial to the brachial artery and the biceps brachii muscle. In the mid-portion of the arm, the nerve pierces the medial intermuscular septum to enter the posterior compartment. Here, the nerve runs anterior to the medial head of triceps barchii muscle and in 70-80% of people, this nerve passes under the arcade of Struthers. This is a thin, aponeurotic band, that extends from the medial head of triceps to the medial intermuscular septum.
The ulnar nerve then passes between the medial epicondyle and olecranon in the groove for ulnar nerve to enter the anterior compartment of the forearm. Posterior to the medial epicondyle, the ulnar nerve is subcutaneous and easily palpable. It is commonly referred to as the "funny bone" in this region. The ulna nerve typically has no branches in the arm.
From the arm, the ulnar nerve runs through the cubital tunnel, superficial to the posterior and oblique bands of the ulnar collateral ligament. This cubital tunnel is bordered by the medial epicondyle, the olecranon and a fibrous band (arcuate ligament) which joins the two heads of flexor carpi ulnaris muscle. Here, the nerve gives off articular branches to the elbow joint. The ulnar nerve continues into the anterior compartment of the forearm by passing between the humeral and ulnar heads of the of flexor carpi ulnaris.
The ulnar nerve descends on the medial aspect of the forearm, over the flexor digitorum profundus muscle and deep to the flexor carpi ulnaris muscle. Close to the wrist, the nerve emerges lateral to flexor carpi ulnaris with the accompanying ulnar artery, which lies lateral to it. Both structures run superficial to the flexor retinaculum (transverse carpal ligament) to enter the hand just lateral to the pisiform bone and are only covered by fascia and skin.
In the forearm, the ulnar nerve gives rise to two muscular branches: one to the flexor carpi ulnaris and the second to the ulnar (medial) part of the flexor digitorum profundus. The lateral half of the flexor digitorum profundus muscle and the remaining muscles of the anterior compartment of the forearm are supplied by the median nerve. Additionally, the ulna nerve gives rise to two cutaneous branches in the forearm: palmar cutaneous nerve and dorsal cutaneous nerve. These nerves pass into the hand to provide sensory innervation.
At the wrist, the ulnar nerve and artery enter the hand by coursing through the Guyon’s canal (ulnar canal), a groove between the pisiform and the hook of the hamate, bridged by the palmar carpal ligament.
Here, the nerve divides into superficial and deep branches to provide both sensory and motor innervation to the hand.
Branches and innervation
The ulnar nerve usually does not have any major branches in the arm. In the forearm the nerve gives rise to articular branches, muscular branches, and the palmar and dorsal cutaneous branches. In the hand, the nerve provides two terminal branches: superficial branch of ulnar nerve and deep branch of ulnar nerve.
As the ulnar nerve passes between the medial epicondyle and olecranon and through the cubital tunnel, it gives rise to articular branches that provide innervation to the elbow joint.
Two muscular branches emerge from the ulnar nerve in the proximal forearm. These supply motor innervation to the flexor carpi ulnaris and the medial half of the flexor digitorum profundus.
Palmar cutaneous branch
The palmar cutaneous branch arises from the ulnar nerve around the mid-portion of the forearm. This nerve runs along the ulnar artery to the distal forearm, where it perforates the deep fascia. It provides sensory innervation to the skin at base of the medial palm, which overlies the medial carpal bones.
Dorsal cutaneous branch
The dorsal cutaneous branch of the ulnar nerve emerges in the distal forearm, proximal to the wrist. This nerve courses posteriorly, deep to the flexor carpi ulnaris and perforates the deep fascia to enter the medial aspect of the dorsum of hand. Here, it divides into two or three dorsal digital nerves to supply sensation to the skin on the medial side of the dorsum of hand as well as the proximal regions of the medial 1½ digits (little finger and half of the ring finger).
Superficial branch of ulnar nerve
The superficial branch of the ulnar nerve supplies sensory innervation to the anterior aspect of the ulnar 1½ digits (little finger and half of the ring finger) and medial palmar skin. Additionally, it provides motor innervation to the palmaris brevis muscle in the hypothenar region of the hand. It arises from the ulnar nerve just distal to the pisiform bone and often divides into two palmar digital nerves.
Deep branch of ulnar nerve
The deep branch of the ulnar nerve emerges from the same region of the nerve as the superficial branch. It courses between the muscles of the hypothenar region into the deep aspect of the plam, alongside the deep palmar branch of the ulnar artery. This nerve provides motor innervation to the vast majority of hand muscles. These include: the hypothenar muscles (abductor, flexor, and opponens digiti minimi muscles), all the interossei (3 palmar and 4 dorsal), the medial two lumbricals, the deep head of flexor pollicis brevis and adductor pollicis.
Looking for strategies to improve your anatomical knowledge? Learn more about the importance of active recall in learning anatomy.
To summarize, the ulnar nerve supplies motor innervation to the flexor carpi ulnaris, the medial half of the flexor digitorum profundus and all the intrinsic hand muscles with the exception of the LOAF muscles (lateral two lumbricals, opponens pollicis, abductor pollicis brevis and flexor pollicis brevis).
The ulnar nerve provides sensory supply to the following areas of the hand:
- The skin of the palmar and dorsal aspects of the medial 1½ digits and adjacent palm.
- The skin on the medial side of the dorsum of hand.
Learn more about the ulnar nerve and other major nerves in the upper limb with our video tutorials and quizzes:
It is very easy to remember the innervation provided by the ulnar nerve if you use the following mnemonic:
Ulnar nerve supplies all intrinsic muscles of the hand except the LOAF muscles
- Lateral two lumbricals
- Opponens pollicis
- Abductor pollicis brevis
- Flexor pollicis brevi
Ulnar nerve injury
Ulnar nerve injures are quite common and can occur at various sites along its course through the upper limb. The common sites of injury or compression include posterior to the medial epicondyle, the cubital tunnel and Guyon’s canal. Injures to the ulnar nerve are characterized by paresthesia (tingling), numbness and depending on the severity may result in considerable impairment of both motor and sensory functioning in the hand.
The characteristic presentation of an ulnar nerve injury is the "claw hand". Individuals with this deformity have hyperextension of the metacarpophalangeal joints (due to the lack of innervation to the medial two lumbricals and the unopposed action of the extensors of this joint) and flexion of the interphalangeal joints of 4th and 5th fingers (due to the unopposed action of the flexor digitorum profundus). The severity of this deformity, however, depends on the location of the injury. Higher (proximal) injuries, such as at the elbow, may denervate the ulnar part of flexor digitorum profundus such that the flexed appearance may not be apparent.
Sensory loss following an ulnar nerve injury also depends on the site of injury. This is normally determined by assessing the function of the dorsal cutaneous branch which arises in the distal forearm and supplies the medial side of the dorsum of hand.
Usually, the more proximal a nerve injury, the worse it is. The opposite is true when we consider the ulnar nerve. This is because the flexor digitorum profundus (in the forearm) that flexes the fingers is partially innervated by the nerve. A proximal injury removes innervation to both the forearm muscles and hand muscles. A distal injury, on the other hand, only denervates the hand muscles; hence the still functioning finger flexors give the patient a pronounced clawed appearance in the ring and little fingers. With a proximal injury leading to an open palm, there is more capacity for hand function. This phenomenon is called the ulnar paradox.
Proximal ulnar nerve compression often occurs when a person rests their elbow on the table for a long time, or on a window (for long distance drivers). It can also occur as an athletic injury, particularly in throwing athletes e.g. baseball pitchers, cricketers, and javelin throwers. The rapid movement of the elbow joint from flexion into whip-like extension can results in compression of the nerve.
Cyclists often suffer ulnar nerve problems as they rest the medial border of their hand on their handlebars, resulting in hamate and therefore distal ulnar nerve compression (handlebar neuropathy).
To help you remember the hand sign associated with an ulnar nerve injury, use the following mnemonic.
- Drop = Radial nerve
- Claw = Ulnar nerve
- Median nerve = Ape (Apostle's) hand