The ulnar nerve is a major peripheral nerve of the upper limb. In this article, we shall look at the anatomy of the ulnar nerve – its anatomical course, motor and sensory functions, and its clinical correlations. The ulnar nerve arises from the brachial plexus within the axilla region, and is a continuation of the medial cord that contains fibres from spinal roots C8 and T1.
The nerve descends in a plane between the axillary artery (lateral) and the axillary vein (medial), as it proceeds down the medial aspect of the arm with the brachial artery located lateral. At the midpoint of the arm, the ulnar nerve penetrates the medial fascial septum to enter the posterior compartment of the arm. It passes posterior to the elbow through the ulnar tunnel (small space between the medial epicondyle and olecranon), and gives arise to an articular branch which supplies the elbow joint.
In the forearm, the ulnar nerve pierces the two heads of the flexor carpi ulnaris, and travels deep to the muscle, alongside the ulna. Three main branches arise in the forearm- the muscular branch, the palmar cutaneous branch, and the dorsal cutaneous branch.
The ulnar nerve innervates two muscles in the anterior compartment of the forearm, and the majority of the intrinsic hand muscles. In the anterior forearm, the muscular branch of the ulnar nerve supplies the flexor carpi ulnaris and the medial half of the flexor digitorum profundus – both muscles responsible for the flexion and adduction of the hand at the wrist. The remaining muscles in the anterior forearm are innervated by the median nerve.
In the hand, the majority of the intrinsic muscles (excluding the thenar muscles and two lateral lumbricals) are innervated by the deep branch of the ulnar nerve – including the hypothenar muscles (flexor digiti minimi brevis, abductor digiti minimi, opposens digiti minimi), the medial two lumbricals, the adductor pollicis, and the palmar and dorsal interossei of the hand. The palmaris brevis is an exception to this rule and is innervated by the superficial branch of the ulnar nerve. The remaining muscles of the hand (the lateral two lumbricals and thenar eminence) are innervated by the median nerve.
Froment’s sign is a test for ulnar nerve palsy – specifically paralysis of the adductor pollicis. The patient is asked to hold a piece of paper between the thumb and index finger, as the paper is pulled away. They should be able to hold the paper there with no difficulty (via adduction of the thumb). A positive test is when the patient is unable to adduct the thumb. Instead, they flex the thumb at the interphalangeal joint to try to maintain a hold on the paper.
There are three branches of the ulnar nerve that are responsible for its sensory innervation. Two of these branches arise in the forearm, and travel into the hand - the palmar cutaneous branch and the dorsal cutaneous branch.
The palmar cutaneous branch of the ulnar nerve innervates the medial half of the palm, while the dorsal cutaneous branch supplies the sensory innervation to the dorsal surface of the medial one and a half fingers, and the associated dorsal hand area.
At the wrist, the ulnar nerve travels superficially to the flexor retinaculum, and is medial to the ulnar artery. It enters the hand via the ulnar canal (Guyon’s canal) and terminates by giving rise to superficial and deep branches.
In conclusion, the ulnar nerve is a major peripheral nerve of the upper limb with a range of motor and sensory functions. Anatomically, it arises from the brachial plexus within the axilla region, and proceeds down the medial aspect of the arm before passing posterior to the elbow through the ulnar tunnel. Three main branches arise in the forearm – the muscular branch, the palmar cutaneous branch, and the dorsal cutaneous branch. In the anterior forearm, it supplies two muscles, and in the hand it supplies most of the intrinsic muscles - excluding the thenar muscles and two lateral lumbricals. Clinically, its palsy is assessed via Froment’s test, which is positive if the patient is unable to adduct the thumb, and instead flexes the thumb at the interphalangeal joint. Sensory wise, it innervates the medial half of the palm and the dorsal surface of the medial one and a half fingers.
The ulnar nerve is a nerve that runs along the medial aspect of the upper limb, connecting to muscles in the arm, forearm, wrist and hand. At the midpoint of the arm, the ulnar nerve penetrates the medial fascial septum to enter the posterior compartment of the arm. It passes posterior to the elbow through the ulnar tunnel (small space between the medial epicondyle and olecranon) and also gives rise to an articular branch which supplies the elbow joint.
In the forearm, the ulnar nerve pierces the two heads of the flexor carpi ulnaris, and travels deep to the muscle, alongside the ulna. From here, three main branches arise in the forearm-
At the wrist, the ulnar nerve travels superficially to the flexor retinaculum and is medial to the ulnar artery. It then enters the hand via the ulnar canal (Guyon’s canal). In the hand, the nerve terminates by giving rise to superficial and deep branches.
Damage of the ulnar nerve can occur at the elbow or the wrist. Common mechanisms of injury include trauma at the level of the medial epicondyle (e.g. isolated medial epicondyle fracture, supracondylar fracture), and lacerations to the anterior wrist. The damage caused by ulnar nerve palsy results in a loss of motor and sensory function.
The ulnar nerve innervates muscles in the anterior compartment of the forearm, and in the hand. In the anterior forearm, the muscular branch of the ulnar nerve supplies two muscles- flexor carpi ulnaris which flexes and adducts the hand at the wrist, and the medial half of the flexor digitorum profundus which flexes the ring and little fingers at the distal interphalangeal joint.
In the hand, the majority of the intrinsic hand muscles are innervated by the deep branch of the ulnar nerve. This includes the hypothenar muscles (flexor digiti minimi brevis, abductor digiti minimi, opponens digiti minimi), the medial two lumbricals, adductor pollicis and palmar and dorsal interossei of the hand. The palmaris brevis is an exception to this rule and is innervated by the superficial branch of the ulnar nerve. The other muscles of the hand (lateral two lumbricals and the thenar eminence) are innervated by the median nerve.
All sensory branches of the ulnar nerve are affected by palsy, resulting in a loss of sensation over the areas that the ulnar nerve innervates. Where the damage occurs at the wrist, the palmar and superficial branches are usually severed, but the dorsal branch is unaffected. This results in sensory loss over the palmar side of the medial one and a half fingers only.
Ulnar nerve palsy can be identified in patients who demonstrate the following signs- an inability to grip paper placed between their fingers, a positive Froment’s sign (described below) and wasting of the hypothenar eminence.
Froment's sign is a test for ulnar nerve palsy, specifically paralysis of the adductor pollicis. To perform the test, the patient is asked to hold a piece of paper between the thumb and index finger, as the paper is pulled away. In a healthy person, the patient should be able to hold the paper there with no difficulty, via adduction of the thumb. A positive test is when the patient is unable to adduct the thumb, instead flexing the thumb at the interphalangeal joint to try to maintain a hold on the paper.
The Ulnar Nerve is a nerve which affects the motor functions of the flexor carpi ulnaris and the flexor digitorum profundus. It is also responsible for the sensation of the ulnar side of the hand, which includes the ring finger and the small finger. Therefore, it is important to assess the integrity of the nerve in a clinical setting in order to detect any potential issues as early as possible. In order to do this, two tests are often performed - Froment’s sign and the Ulnar Claw. Froment’s sign assesses thumb adduction, while the Ulnar Claw checks for the extention of the little finger. If the ulnar nerve is injured, it could lead to a loss of sensation and permanent paralysis of the hand.
Damage to the ulnar nerve can occur at the level of the elbow due to certain traumas or compressions in the cubital tunnel. Traumas most commonly associated with ulnar nerve damage include isolated medial epicondyle fractures and supracondylar fractures. If the ulnar nerve is affected, then all of the muscles that it innervates will be affected. Specifically, the patient will find it difficult to flex their wrist, as the flexors of the wrist (flexor carpi ulnaris and the medial half of the flexor digitorum profundus) are unable to move due to paralysis. Additionally, the interossei muscles won’t be able to abduct or adduct the fingers, and the movement of the 4th and 5th digits will be impaired due to paralysis of the medial two lumbricals and hypothenar muscles. Furthermore, the adduction of the thumb and the patient will display a positive Froment’s sign as the adductor pollicis muscle is paralysed. The patient will also be unable to grip paper placed between their fingers as the hypothenar eminence will begin to waste away.
The damage caused to the ulnar nerve at the elbow has an effect on the sensory functions of the hand. All the sensory branches of the ulnar nerve are affected which will result in a loss of sensation over the areas that it innervates.
Ulnar nerve damage can also occur at the wrist due to lacerations to the anterior part of the wrist. Similar to damage at the elbow, only the intrinsic muscles of the hand are affected. Therefore, the patient will find it difficult to abduct and adduct their fingers due to paralysis of the interossei muscles. Additionally, the movement of the 4th and 5th digits will be impaired due to paralysis of the medial two lumbricals and hypothenar muscles. Furthermore, the adduction of the thumb will be impaired and the patient will have a positive Froment’s sign as the adductor pollicis muscle is paralysed. The patient will also be unable to grip paper placed between their fingers as the hypothenar eminence will begin to waste away.
The damage to the ulnar nerve at the wrist will cause similar effects on the sensory functions as damage to the elbow. The palmar branch and superficial branch are usually severed, but the dorsal branch is left unaffected. This results in a sensory loss over the palmar side of the medial 1.5 fingers only.
Following damage to the ulnar nerve at either the wrist or the elbow, patients will display several signs that suggest the damage of the nerve. These include an inability to grip paper placed between the fingers, a positive Froment’s sign and some wasting of the hypothenar eminence.
