**7. Ulnar nerve**

#### **7.1. Anatomy**

The ulnar nerve contains fibers from C8 and T1 and is the largest terminal branch of the medial cord of the brachial plexus. The nerve enters the arm with the axillary artery and courses medially to the brachial artery before piercing the intermuscular septum approaching the elbow. It then travels along the border of the medial head of the triceps and enters the postcondylar groove lateral to the medial epicondyle [22]. At the elbow, the ulnar nerve enters the forearm between the medial epicondyle and the olecranon through the cubital tunnel. The roof of the cubital tunnel is a fibrous aponeurosis that thickens to form the cubital tunnel retinaculum or arcuate ligament of Osborne. This retinaculum connects the tendinous origin of the humeral and ulnar heads of the flexor carpi ulnaris, giving off branches to the elbow joint [23] (Figure 4).

**Figure 4.** Ulnar nerve anatomy at the elbow.

Exiting the tunnel, the ulnar nerve pierces the flexor pronator aponeurosis, innervating the flexor digitorum muscles before entering Guyon's canal at the wrist. The terminal branches of the ulnar nerve supply motor innervation to the adductor pollicis, the flexor pollicis brevis, the hypothenar muscles, the third and fourth lumbricalis, and all of the interosseous muscles. The sensory distribution of the nerve includes the palmar and dorsal medial aspects of the hand, often including half of the ring finger (Figure 5).

will compensate by flexing the flexor pollicis longus of the thumb to maintain grip pressure. Clinically, this compensation manifests as flexion of the interphalangeal joint of the thumb.

Compression Neuropathies http://dx.doi.org/10.5772/55316 115

**Figure 5.** Ulnar nerve anatomy in the hand.

#### **7.2. Ulnar nerve entrapment**

The ulnar nerve, like the median nerve, is susceptible to compression neuropathies at proximal and distal levels. Proximally, the most common site of compression is the cubital tunnel as the ulnar nerve enters the forearm between the medial epicondyle and the olecranon. Other potential sites of compression at the elbow, are between the humeral and ulnar heads of the flexor carpi ulnaris muscle and 3cm distal to the cubital tunnel, when the ulnar nerve pierces the flexor pronator aponeurosis. Distally, the ulnar nerve can be compressed at the Guyon's canal at the wrist. Each one of these sites of compression present with different signs and symptoms which will be described next.

#### **7.3. Cubital tunnel syndrome (Ulnar nerve compression at the elbow)**

#### *7.3.1. Etiology*

The majority of cases occur spontaneously with no documented history of trauma, caused by adhesions that prevent the nerve's gliding with elbow flexion, stretching the nerve behind the epicondyle that impairs nerve conduction. Other causes include direct pressure either by tumors, external swelling-synovium, lipomas or osteophytes, subluxation over the medial epicondyle or just by inadequate space in the cubital tunnel and over the potential sites of compression mentioned above [24].

#### *7.3.2. Diagnosis*

The patient may present both motor and sensory disturbances, including pain at the medial portion of the proximal third of the forearm, parestesias or anesthesia of palmar and dorsal surfaces of the ring and small fingers, and ulnar innervated intrinsic muscles weakness, which can present atrophy in late stages. During physical exam, the acute flexion of the elbow for 30 seconds usually accentuates the sensory symptoms and also may cause tingling in the little and ring finger, promptly relieved by extending the elbow. A positive Tinel's sign at the posterior elbow will be referred to the small finger.

We may also find a positive Froment's sign and a positive Wartenburg's sign (Figure 6). Froment's sign tests for the action of adductor pollicis, which is weak with an ulnar nerve compression. A patient is asked to hold an object, usually a flat object such as a piece of paper, between their thumb and index finger. The examines then attempts to pull the object out of the patient's hands. A normal individual will be able to maintain a hold on the object without difficulty. With ulnar nerve palsy, the patient will experience difficulty maintaining a hold and will compensate by flexing the flexor pollicis longus of the thumb to maintain grip pressure. Clinically, this compensation manifests as flexion of the interphalangeal joint of the thumb.

**Figure 5.** Ulnar nerve anatomy in the hand.

Exiting the tunnel, the ulnar nerve pierces the flexor pronator aponeurosis, innervating the flexor digitorum muscles before entering Guyon's canal at the wrist. The terminal branches of the ulnar nerve supply motor innervation to the adductor pollicis, the flexor pollicis brevis, the hypothenar muscles, the third and fourth lumbricalis, and all of the interosseous muscles. The sensory distribution of the nerve includes the palmar and dorsal medial aspects of the

114 Peripheral Neuropathy - A New Insight into the Mechanism, Evaluation and Management of a Complex Disorder

The ulnar nerve, like the median nerve, is susceptible to compression neuropathies at proximal and distal levels. Proximally, the most common site of compression is the cubital tunnel as the ulnar nerve enters the forearm between the medial epicondyle and the olecranon. Other potential sites of compression at the elbow, are between the humeral and ulnar heads of the flexor carpi ulnaris muscle and 3cm distal to the cubital tunnel, when the ulnar nerve pierces the flexor pronator aponeurosis. Distally, the ulnar nerve can be compressed at the Guyon's canal at the wrist. Each one of these sites of compression present with different signs and

The majority of cases occur spontaneously with no documented history of trauma, caused by adhesions that prevent the nerve's gliding with elbow flexion, stretching the nerve behind the epicondyle that impairs nerve conduction. Other causes include direct pressure either by tumors, external swelling-synovium, lipomas or osteophytes, subluxation over the medial epicondyle or just by inadequate space in the cubital tunnel and over the potential sites of

The patient may present both motor and sensory disturbances, including pain at the medial portion of the proximal third of the forearm, parestesias or anesthesia of palmar and dorsal surfaces of the ring and small fingers, and ulnar innervated intrinsic muscles weakness, which can present atrophy in late stages. During physical exam, the acute flexion of the elbow for 30 seconds usually accentuates the sensory symptoms and also may cause tingling in the little and ring finger, promptly relieved by extending the elbow. A positive Tinel's sign at the

We may also find a positive Froment's sign and a positive Wartenburg's sign (Figure 6). Froment's sign tests for the action of adductor pollicis, which is weak with an ulnar nerve compression. A patient is asked to hold an object, usually a flat object such as a piece of paper, between their thumb and index finger. The examines then attempts to pull the object out of the patient's hands. A normal individual will be able to maintain a hold on the object without difficulty. With ulnar nerve palsy, the patient will experience difficulty maintaining a hold and

**7.3. Cubital tunnel syndrome (Ulnar nerve compression at the elbow)**

hand, often including half of the ring finger (Figure 5).

**7.2. Ulnar nerve entrapment**

*7.3.1. Etiology*

*7.3.2. Diagnosis*

symptoms which will be described next.

compression mentioned above [24].

posterior elbow will be referred to the small finger.

Simultaneous hyperextension of the thumb metacarpophalangeal joint is indicative of ulnar nerve compromise.

*7.3.3. Treatment*

muscle atrophy.

*7.3.4. Complications*

complications.

*7.4.1. Guyon's canal*

*7.4.2. Zones of nerve*

transposition, and medial epicondylectomy.

**7.4. Ulnar nerve compression at the wrist**

described in this chapter (Figure 7).

It is divided in non-operative and operative options. The non-operative treatment is advised in patients with mainly postural symptoms by avoiding flexing the elbow or leaning on the inner side of the elbow, and by splinting the elbow at 45º extension at night, changing the patient's sleeping posture. One may consider surgery in more advanced stages, if the patient refers numbness or weakness in the hand, which may represent axonal demyelination and

Compression Neuropathies http://dx.doi.org/10.5772/55316 117

Surgical management of the ulnar nerve entrapment at the elbow is determined by the patient's preoperative symptoms and intraoperative findings. It includes transposition of the nerve anterior to the axis of rotation of the elbow so that elbow flexion relaxes rather than stretches the nerve. Commonly performed procedures include simple decompression by unroofing the cubital tunnel, anterior subcutaneous transposition, intramuscular transposition, submuscular

In selected cases, simple decompression of the cubital tunnel and the anterior subcutaneous transposition may be effective, but the ulnar nerve may be more susceptible to trauma injuries as it becomes more superficial. The submuscular anterior transposition is the best operation for cubital tunnel syndrome when an adequate distal mobilization is performed. Other options include a percutaneous and endoscopic release being both technically possible but not generally recommended because of poor results and a high incidence of recurrence [25].

Complications are rare but they include haematoma, infection, neuroma, damage to medial cutaneous nerve of forearm and devascularization of the ulnar nerve, which is the worst of the

At the wrist, the ulnar nerve and artery enter Guyon's canal, which is a fibro-osseous tunnel formed between the pisiform and hamate hook. The floor of the canal is formed by the pisohamate ligamento and the flexor retinaculum, and the roof is the palmaris brevis and the

Within Guyon's canal, the ulnar nerve bifurcates into superficial and deep branches giving off sensory and motor branches, which innervate intrinsic muscles of the hand previously

As the ulnar nerve enters the wrist through Guyon's canal, it is divided in 3 zones:

**i.** Proximal to bifurcation of nerve into deep and superficial branches.

superficial volar carpal ligament (continuation of distal forearm fascia).

**Figure 6.** Positive Froment's sign.

On the other hand we have Wartenburg's sign. The patient is placed with wrist in neutral position and forearm fully pronated and instructed to perform full extension of all the fingers. Once digits are extended, patient is asked to fully abduct all fingers and then adduct all fingers. A positive signs is indicated with the observation of abduction of the 5th digit, with inability to adduct the 5th finger when extended. The inability to perform adducted digital extension is due to weakness in ulnar innervated intrinsic muscles.

Electromyography and nerve conduction may reveal a drop in speed conduction or alterations in the sensitive latency, but these studies may be normal, specially in postural conditions, requiring complementary studies like X-rays or an MRI if a space occupying lesion is suspected or if there is a conduction block with established compression but the site is not clear.

### *7.3.3. Treatment*

Simultaneous hyperextension of the thumb metacarpophalangeal joint is indicative of ulnar

116 Peripheral Neuropathy - A New Insight into the Mechanism, Evaluation and Management of a Complex Disorder

On the other hand we have Wartenburg's sign. The patient is placed with wrist in neutral position and forearm fully pronated and instructed to perform full extension of all the fingers. Once digits are extended, patient is asked to fully abduct all fingers and then adduct all fingers. A positive signs is indicated with the observation of abduction of the 5th digit, with inability to adduct the 5th finger when extended. The inability to perform adducted digital extension is

Electromyography and nerve conduction may reveal a drop in speed conduction or alterations in the sensitive latency, but these studies may be normal, specially in postural conditions, requiring complementary studies like X-rays or an MRI if a space occupying lesion is suspected

or if there is a conduction block with established compression but the site is not clear.

nerve compromise.

**Figure 6.** Positive Froment's sign.

due to weakness in ulnar innervated intrinsic muscles.

It is divided in non-operative and operative options. The non-operative treatment is advised in patients with mainly postural symptoms by avoiding flexing the elbow or leaning on the inner side of the elbow, and by splinting the elbow at 45º extension at night, changing the patient's sleeping posture. One may consider surgery in more advanced stages, if the patient refers numbness or weakness in the hand, which may represent axonal demyelination and muscle atrophy.

Surgical management of the ulnar nerve entrapment at the elbow is determined by the patient's preoperative symptoms and intraoperative findings. It includes transposition of the nerve anterior to the axis of rotation of the elbow so that elbow flexion relaxes rather than stretches the nerve. Commonly performed procedures include simple decompression by unroofing the cubital tunnel, anterior subcutaneous transposition, intramuscular transposition, submuscular transposition, and medial epicondylectomy.

In selected cases, simple decompression of the cubital tunnel and the anterior subcutaneous transposition may be effective, but the ulnar nerve may be more susceptible to trauma injuries as it becomes more superficial. The submuscular anterior transposition is the best operation for cubital tunnel syndrome when an adequate distal mobilization is performed. Other options include a percutaneous and endoscopic release being both technically possible but not generally recommended because of poor results and a high incidence of recurrence [25].

#### *7.3.4. Complications*

Complications are rare but they include haematoma, infection, neuroma, damage to medial cutaneous nerve of forearm and devascularization of the ulnar nerve, which is the worst of the complications.

#### **7.4. Ulnar nerve compression at the wrist**

#### *7.4.1. Guyon's canal*

At the wrist, the ulnar nerve and artery enter Guyon's canal, which is a fibro-osseous tunnel formed between the pisiform and hamate hook. The floor of the canal is formed by the pisohamate ligamento and the flexor retinaculum, and the roof is the palmaris brevis and the superficial volar carpal ligament (continuation of distal forearm fascia).

Within Guyon's canal, the ulnar nerve bifurcates into superficial and deep branches giving off sensory and motor branches, which innervate intrinsic muscles of the hand previously described in this chapter (Figure 7).

#### *7.4.2. Zones of nerve*

As the ulnar nerve enters the wrist through Guyon's canal, it is divided in 3 zones:

**i.** Proximal to bifurcation of nerve into deep and superficial branches.


#### *7.4.3. Etiology*

The most common cause of Guyon's canal entrapment is a carpal ganglion. The next most common etiology is repeated trauma to the hypothenar area usually related to occupation. Finally, other less frequent causes include osteophytes from pisotriquetral joint, fracture of the hook of hamate, and pseudoaneurysms of the ulnar artery.

ed, MRI if precise location of tumours needs to be addressed, and finally electromyography

Compression Neuropathies http://dx.doi.org/10.5772/55316 119

It consists in surgical decompression of the canal with special care to avoid injury to the dorsal division, which does not pass through the canal. The safest way to decompress the canal is finding the nerve proximal to pisiform and tracing the branches of the nerve distally, progres‐ sively unroofing the canal. Once it is open we must treat any pathology we identify like a

The radial nerve receives innervation form C5-C8 and T1 roots, being the terminal branch of the posterior cord. It enters the arm behind the brachial artery, medial to the humerus and anterior to the long head of the triceps muscle running through the radial groove at the humerus, giving off branches for both heads of the triceps muscle. It descends distally along the border of the brachialis muscle and approximately 2cm distal to the elbow, the radial nerve divides into the posterior interosseous nerve and the superficial sensory divisions. The posterior interosseous nerve passes beneath the fibrous proximal margin of the supinator muscle, known as the arcade of Frohse, and bifurcates to innervate the extensor carpi ulnaris muscle and the digital extensor muscles. The

and nerve conduction to confirm the level of conduction block.

radial nerve does not innervate any hand muscle [26] (Figure 8).

**Figure 8.** Radial nerve anatomy showing its divisions at the forearm.

*7.4.5. Treatment*

**8. Radial nerve**

**8.1. Anatomy**

ganglion or a pseudoanerysm.

#### *7.4.4. Diagnosis*

The patient will present with some similar symptoms as in the cubital tunnel syndrome, with some specific differences. In low ulnar neuropathy, the symptoms will not be related to position of the elbow. Also, the sensation at the dorsal aspect of the ulnar border will be preserved, as the dorsal sensory branch of the ulnar nerve has taken off 5 to 10cm proximal to Guyon's canal. The function of flexor carpi ulnaris and flexor digitorium profundus muscles will be preserved. The motor affection will be exclusive of the intrinsic muscles of the hand, which can be measured with lateral pinch between thumb and side of index finger.

The diagnosis is mainly clinic but some other studies may be needed in order to complete our investigation. X-rays are necessary to evaluate the integrity of the osseous components of the canal, ultrasound if we suspect of a ganglion, arteriogram if ulnar artery aneurysm is suspect‐

**Figure 7.** Guyon's canal anatomy.

ed, MRI if precise location of tumours needs to be addressed, and finally electromyography and nerve conduction to confirm the level of conduction block.

#### *7.4.5. Treatment*

**ii.** Around deep motor branch.

*7.4.3. Etiology*

*7.4.4. Diagnosis*

**Figure 7.** Guyon's canal anatomy.

**iii.** Around superficial sensory branch.

hook of hamate, and pseudoaneurysms of the ulnar artery.

The most common cause of Guyon's canal entrapment is a carpal ganglion. The next most common etiology is repeated trauma to the hypothenar area usually related to occupation. Finally, other less frequent causes include osteophytes from pisotriquetral joint, fracture of the

118 Peripheral Neuropathy - A New Insight into the Mechanism, Evaluation and Management of a Complex Disorder

The patient will present with some similar symptoms as in the cubital tunnel syndrome, with some specific differences. In low ulnar neuropathy, the symptoms will not be related to position of the elbow. Also, the sensation at the dorsal aspect of the ulnar border will be preserved, as the dorsal sensory branch of the ulnar nerve has taken off 5 to 10cm proximal to Guyon's canal. The function of flexor carpi ulnaris and flexor digitorium profundus muscles will be preserved. The motor affection will be exclusive of the intrinsic muscles of the hand,

The diagnosis is mainly clinic but some other studies may be needed in order to complete our investigation. X-rays are necessary to evaluate the integrity of the osseous components of the canal, ultrasound if we suspect of a ganglion, arteriogram if ulnar artery aneurysm is suspect‐

which can be measured with lateral pinch between thumb and side of index finger.

It consists in surgical decompression of the canal with special care to avoid injury to the dorsal division, which does not pass through the canal. The safest way to decompress the canal is finding the nerve proximal to pisiform and tracing the branches of the nerve distally, progres‐ sively unroofing the canal. Once it is open we must treat any pathology we identify like a ganglion or a pseudoanerysm.
