Ulnar Nerve: What is it? Functions, Physiological Variants, Clinical Significance and Surgical Considerations

It supplies motor and sensory innervation to the upper limb.

The ulnar nerve, also known as the ulnar nerve , is one of the 5 terminal branches of the brachial plexus, arising from the medial cord.

The ulnar nerve originates from the contributions of the ventral branches of the C8 and T1 nerve roots. The nerve runs through the medial arm and forearm, and then passes to the wrist, hand, and fingers.

The ulnar nerve is a major peripheral nerve in the upper limb. In the forearm, the ulnar nerve pierces the two heads of the flexor carpi ulnaris and travels along the ulna. Three branches arise on the forearm:

  • Rama muscular.
  • Palmar cutaneous branch.
  • Dorsal cutaneous branch.

Function

The ulnar nerve provides motor innervation to part of the forearm and most of the hand. Provides sensory cutaneous innervation to the medial forearm, the medial wrist, and the medial and middle halves.

The ulnar nerve and its branches send motor innervation to the flexor carpi ulnaris and deep flexor digits in the forearm, and the hypothenary muscles (opponens digiti minimi, abductor digiti minimi, and flexor digiti minimi brevis).

In the hand, the ulnar nerve provides motor innervation to the third and fourth lumbrical muscles, dorsal interossei, palmar interossei, adductor pollicis, flexor pollicis brevis, and palmaris brevis.

This nerve is responsible for sensory innervations on the palm side of the fifth finger and the adjacent half of the fourth finger, as well as the anterior and posterior part of the fingertips.

The ulnar nerve also controls most of the small muscles in the hands that are crucial for fine finger movement, in addition to some of the larger muscles in the forearm that are critical for strengthening grip.

Motor function

The ulnar nerve innervates the muscles in the anterior compartment of the forearm and in the hand.

The anterior forearm

In the anterior forearm, the muscular branch of the ulnar nerve supplies two muscles:

Flexor carpi ulnaris : flexes and holds the hand at the wrist.

Deep flexor digitorum (medial half) : flex the fingers.

The remaining muscles in the anterior forearm are innervated by the median nerve.

Hand

Most of the muscles of the intrinsic hand are innervated by the deep branch of the ulnar nerve.

The hypothenary muscles (a group of muscles associated with the little finger) are innervated by the ulnar nerve. It also innervates other muscles in the hand:

  • Lumbrical muscles of the hand.
  • Adductor pollicis / adductor pollicis muscle.
  • Interossei of the hand / dorsal interosseous muscles of the hand.
  • Palmaris brevis / short palmar muscle.

The other muscles of the hand (such as the thenar eminence) are innervated by the median nerve.

Sensory function

There are three branches of the ulnar nerve that are responsible for its cutaneous innervation.

Two of these branches arise in the forearm and travel to the hand:

Palmar cutaneous branch : innervates the skin of the medial half of the palm.

Dorsal cutaneous branch : innervates the skin of the middle and middle fingers and the associated dorsal hand area.

The last branch arises in the hand itself:

Superficial branch : innervates the palmar surface of the middle and middle finger.

Nerves

The ulnar nerve carries sensory and motor fibers from the C8 and T1 dorsal rami. The nerve runs along the medial arm from the anterior to the posterior compartment, through the internal intermuscular septum, called the arch of Struthers.

The arch is made up of the medial head of the biceps, the medial intermuscular septum, and the medial brachial ligament. It then passes behind the medial epicondyle of the humerus, emitting its first branch that provides proprioception to the elbow joint.

At the distal elbow, the ulnar nerve passes under Osbourne’s ligament (retinaculum between the two heads of the flexor carpi ulnaris muscle). It continues through the flexor and pronator muscles of the forearm and onto the wrist, superficially to the flexor retinaculum.

The ulnar nerve enters the hand through Guyon’s canal, a fibroosseous tunnel formed by the pisiform and the hook of the hamate. In the hand, the ulnar nerve branches to form a palmar cutaneous section (Henle’s nerve) and a dorsal cutaneous branch.

The dorsal cutaneous nerve branches further into the radial and ulnar branches providing sensation to the dorsal hand.

Muscles

The ulnar nerve innervates the flexor muscles of the forearm, including the flexor carpi ulnaris and flexor digitorum deep. It also innervates the intrinsic muscles of the hand, including the palmaris brevis, lumbrical, hypothenar, and interosseus muscles.

In the hand, the superficial branch of the ulnar nerve supplies the palmaris brevis and sensory muscles for the hypothenar muscles, the fourth common digital nerve, and the proper ulnar nerve.

The deep branch innervates the hypothenar muscles, opponens digiti minimi, interosseous muscles, third and fourth lumbrical muscles, adductor pollicis, and medial head of flexor pollicus brevis.

Physiological variants

It is important to identify anatomical variants to quickly and correctly diagnose nerve dysfunction to avoid delays in treatment. Two nerve variations include the Martin-Gruber and Riche-Cannieu anastomoses.

The Martin-Gruber anastomosis is a communication between the median and ulnar nerves in the forearm anywhere distal to the medial epicondyle.

With this anatomical variant, the motor nerves supplying the intrinsic ulnar muscles are carried by the anterior interosseous branch of the median nerve.

In the middle forearm, these fibers exit the anterior interosseous nerve to join the ulnar nerve. Therefore, with this variant, patients may have functional intrinsic hand muscles despite ulnar nerve dysfunction.

The Riche-Cannieu anastomosis occurs when the median and ulnar nerves connect in the palm. This variant is shown as motor fibers that are normally carried by the median nerve, which now carries the ulnar nerve to the hand and then intersects in the palm.

This is clinically significant in the context of carpal tunnel syndrome. Patients with advanced median nerve pathology may have normal function of the standard median nerve distribution.

Surgical Considerations

The most common site of ulnar nerve entrapment is at the elbow in the ulnar tunnel. Ulnar tunnel decompression with possible ulnar nerve transposition is a relatively common orthopedic procedure.

The ulnar tunnel is made up of Osbourne’s ligament (ulnar tunnel retinaculum) and the deep layer of the aponeurosis of the 2 heads of the flexor carpi ulnaris muscle.

Osbourne’s ligament is the proximal roof of the ulnar tunnel and prevents subluxation of the nerve with flexion of the elbow. Surgical decompression for ulnar tunnel syndrome, Osbourne’s fascia is performed to relieve pain and paresthesia caused by nerve injury.

Transposition of the nerve from the arch of Struthers to the flexor carpi ulnaris is also one of the recommended surgical treatments.

The arch of Struthers is made up of the medial brachial ligament, the medial head of the triceps, and the medial intermuscular septum, just in the vicinity of the medial epicondyle of the humerus. This is another possible site of ulnar nerve compression.

Another surgical consideration includes incidental ulnar nerve damage during carpal tunnel release surgery. During surgery for carpal tunnel syndrome, a small incision is made near the crease of the wrist.

The surgeon will dissect through the soft tissues of the wrist at the transverse carpal ligament to relieve compression of the median nerve.

Damage to the deep motor branch of the ulnar nerve may occur during this dissection, as the bifurcation runs just medial to the carpal tunnel along the hamate carpal bone.

Although ulnar nerve damage is a rare complication of carpal tunnel release surgery, it is important that the incision is kept in line with the radial border of the ring finger.

Clinical significance

Ulnar nerve injury can be caused by a number of reasons based on the location of the injury along the nerve, most commonly at the elbow.

Injury proximal to the lower trunk of the brachial plexus can cause Klumpke’s palsy, an injury to the elbow can cause ulnar tunnel syndrome, and compression in the Guyon’s wrist canal can manifest as a sensory and sensory deficit in the hand.

Klumpke’s palsy is the manifestation of a lesion of the lower trunk in the brachial plexus. Most commonly, lower trunk injuries are the result of an upward force on an infant’s arm, or an upward pull on an adult’s arm.

The injury can also be the result of traumatic vaginal delivery with traction on the abducted arm of a baby due to a high birth weight child or a small birth canal.

Klumpke’s palsy has a functional deficit of the intrinsic muscles of the hand that presents clinically with a complete claw. This syndrome is also known as suspension strap syndrome.

Horner syndrome (ptosis, miosis, and anhidrosis) can occur due to loss of sympathetic T1 input. Pupil constriction is the result of unopposed parasympathetic entry into the eye.

The most common site of injury to the ulnar nerve is near the elbow. Nerve pathology can be caused by anatomical damage from medial epicondyle fracture, osteophyte infection, soft tissue mass, or synovitis in the elbow joint.

The nerve can also be damaged by compression from prolonged periods of flexion of the elbow, such as sleeping, exercising, driving, writing, or talking on the phone.

Ulnar tunnel syndrome is a peripheral neuropathy due to chronic compression or repetitive trauma of the ulnar nerve in the elbow between the medial epicondyle of the humerus and the olecranon process of the ulna.

Congenital laxity of the ulnar tunnel retinaculum can be seen, resulting in hypermobility of the ulnar nerve. This can lead to repetitive subluxation and possible anterior dislocation when the elbow is flexed.

Repetitive trauma to this location can cause recurrent frictional inflammation over the medial epicondyle .

Ulnar nerve compression can also occur at the wrist due to compression through Guyon’s canal, local trauma, ganglion cysts, and compression of the external nerve.

The ulnar nerve and artery enter Guyon’s canal, a fibroosseous tunnel formed by the pisiform and the hook of the hamate.

The ulnar nerve bifurcates within the canal into superficial and deep branches. Nerve compression in the wrist can also be caused by riders with excessive handlebar pressure and prolonged compression while typing at a desk.

The diagnosis of ulnar nerve injury can be made with a complete medical history, musculoskeletal and neurological physical examination.

However, electromyography (EMG) and nerve conduction studies can be used as an adjunct to diagnose and localize the lesion.

Ulnar nerve damage

The ulnar nerve is one of the three main nerves in the arm, and also one of the most commonly compressed nerves.

This compression can occur in a variety of places, affecting where and how ulnar pain manifests and which ulnar nerve compression treatment is used.

The ulnar nerve runs from the neck through the arm and forearm to the tips of the ring and ring fingers. As it passes through the body, it passes through a series of tunnels and bone structures where it can become compressed, irritated, or trapped.

For example, it can get caught under the clavicle, behind the elbow, exiting the spinal cord causing pain in the neck of the ulnar nerve or in the wrist.

Some women with large breasts may even experience ulnar nerve shoulder pain due to the pressure that the bra strap can put on the ulnar nerve. The ulnar nerve is most susceptible to injury to the elbow and wrist.

Damage to the elbow

The most common source of pain in ulnar nerve compression is in the elbow; in fact, this injury is the second most common entrapment disorder after carpal tunnel syndrome.

The ulnar nerve is often compressed on its way through the ulnar tunnel on the outside of the elbow, which is why it is also called ulnar tunnel syndrome. Here, it passes through a very narrow space with little protective cover.

Think about the last time you hit your “funny bone.” What actually caused the strange elbow pain sensation: ulnar nerve compression. This gives you an idea of ​​the symptoms and causes of this condition.

Symptoms of the ulnar nerve in the elbow

But the symptoms of compression ulnar nerve pain are not limited to ulnar nerve pain in the elbow.

In addition to a sore pain in the inner part of the elbow, an ulnar nerve type of hand pain and numbness in the fourth and fifth fingers as well as the back of the hand may also be experienced.

This, in turn, can compromise the fine motor skills of the hand and weaken the grip. Usually, the symptoms of ulnar tunnel syndrome are aggravated in the middle of the night or early in the morning.

But if treatment of the ulnar nerve injury is not pursued, the discomfort and debilitating side effects could become chronic and result in muscle atrophy or development of the finger deformity known as “Ulnar Claw” or “Spinter’s Claw.” .

Flexor carpi ulnaris and medial half of the deep flexor of the paralyzed fingers. Flexion of the wrist can still occur, but is accompanied by abduction. The interossei are paralyzed, so abduction and adduction of the fingers cannot occur.

Movement of the little and ring fingers is greatly reduced due to paralysis of the two medial lumbricals.

All sensory branches are affected, so there will be a loss of sensation in the areas that innervate the ulnar nerve. The patient cannot grasp the paper placed between the fingers.

Treatment of the ulnar nerve in the elbow

Many ulnar nerve pain treatment options involve addressing the cause and fortunately, most cases are relatively mild. The ulnar nerve can be compressed at the elbow for repeated or prolonged periods when one has strongly bent arms.

A common cause, for example, is sleeping with your arms bent and your elbows bent sharply. An elbow brace that compresses the ulnar nerve can be helpful in keeping one from bending the arms at night.

Leaning on your elbows, especially against a hard surface, can also be problematic. This can happen when you lean against a counter or table, or it can happen when you rest your elbow on an armrest.

One must be careful to avoid this kind of pressure as much as possible.

Again, wearing an ulnar nerve elbow brace may provide some protection and / or a reminder to exercise better posture. Anti-inflammatory medications can also be helpful.

Injuries to the elbow or ulnar tunnel region or conditions that cause joint inflammation, such as rheumatism, infection, alcoholism, diabetes, hypothyroidism, or tumors, can also cause ulnar pain in the wrist, elbow, or hand.

In such cases, the underlying problem may need to be addressed to achieve ulnar nerve pain relief. Meanwhile, an elbow ulnar nerve support may be helpful to minimize discomfort.

Wrist damage

Another place that is often the site of ulnar nerve compression is the wrist. Here, the ulnar nerve can be pressed as it passes through what is known as Guyon’s Canal.

Therefore, this type of pain on the ulnar side of the wrist is known as Guyon’s canal syndrome or Guyon’s tunnel syndrome.

It is quite similar to the carpal tunnel in terms of causes and symptoms; it just involves a different nerve. Therefore, these two conditions can occur together.

This ulnar wrist injury can be due to a number of causes that put acute or repetitive force on the wrists.

Pain on the ulnar side of the wrist is common among riders, for example, as some riders spend long periods of time with the palm / wrist area pressed against the handlebars of their bike.

Therefore, this condition is sometimes also known as handlebar paralysis or rider’s neuropathy.

Other sports where this injury is common are golf, tennis, and baseball. In these sports, grasping the golf club, tennis racket, or baseball bat causes repetitive stress on the ulnar nerve.

And the oscillating action of a player can fracture the hamate bone, which can cause ulnar nerve wrist pain as it can make it difficult for the nerve to pass through Guyon’s canal.

Weight lifting can also compromise Guyon’s canal and cause ulnar wrist pain. Or one could compress the ulnar nerve simply by pressing the wrist against a hard surface when clicking the mouse, for example.

The use of vibrating tools is also considered a causative factor for pain on the wrist, the ulnar side.

Similarly, those who frequently compete on motorcycles or cars, combining vibration and pressure on the wrist, often suffer from ulnar side wrist pain.

Ulnar nerve compression in the wrist can also be due to internal causes such as cysts, arthritis, deformities, or injuries in the wrist area.

Symptoms of the ulnar nerve in the wrist

The symptoms of Guyon’s canal syndrome are largely the same as those of ulnar tunnel syndrome with a few exceptions.

Like ulnar nerve compression at the elbow, this ulnar nerve wrist injury causes tingling and tingling in the little finger and ring finger and / or palm, burning sensation in the wrist and / or numbness and clumsiness.

But unlike ulnar tunnel syndrome, its type of ulnar nerve compression does not affect the back of the hand. Additionally, ulnar claw development is typically more pronounced with this type of injury.

Treatment of the ulnar nerve in the wrist

The first step in treating a pinched ulnar nerve is to stop or avoid tasks that irritate the wrist as much as possible.

When that’s not an option, be sure to take frequent breaks from activity and restrict the amount of time one spends doing it.

Taking anti-inflammatory medications can help with the resulting inflammation and ulnar side wrist pain.

An ulnar orthodontic appliance can help by reducing pressure on the wrist and stimulating blood flow to reduce inflammation and promote healing.

An ulnar brace can also provide protective padding for the wrist, which is helpful in treating and preventing ulnar wrist pain.

There are also ulnar nerve supports to avoid stress on the wrist at night.

There are also a number of ergonomic aids that reduce problematic strain on the wrists, such as wrist bands, special computer mice, keyboard wrist rests, or can openers.

Unfortunately, conservative modes of treatment are not always successful in treating ulnar nerve pain. In such cases, surgery to transpose or decompress the nerve (or some combination of both) may be necessary.

The main risks of ulnar neuropathy surgery are infection or bleeding, although there is the possibility of persistent numbness or pain after ulnar nerve surgery if the procedure is ineffective.

You can also find wrist and elbow braces to support these areas after surgery or after cast removal.