Ulnar nerve entrapment
Left, drawing of the ulnar nerve of the upper extremities and right, area of sensory innervation

Definition

The ulnar nerve entrapment is a common condition caused by compression of the ulnar nerve. It results in numbness and pain in the hand, particularly in the ulnar aspect of the ring and little fingers and the medial side of the wrist.

Anatomy of the radial nerve and location of the Guyon's canal at the wrist (palmar side)

Pathology

The ulnar nerve begins at the cervical spine, travels across the arm, forearm and wrist to innervate the outer hand. It is enclosed in a tunnel of connective tissue that lies under the medial epicondyle. The ulnar nerve regulates sensation to the little finger and outer side of the ring finger (ulnar side) on both the palmar and dorsal sides of the hand. It also innervates the muscle of the forearm and hand to allow the flexion of the fingers and forearm during a grip. When hit, this nerve triggers an electric shock type of reaction. The tunnel of the ulnar nerve located in the hand is called Guyon’s canal. The constriction, or entrapment, of the nerve is caused by swelling of the surrounding soft tissue, resulting in neuropathy. This can occur at the neck, collarbone and wrist but it is mostly observed at the posterior side of the elbow. In this case it is named cubital tunnel syndrome. Depending on the entrapment point, there are different regional locations of neurological symptoms.

Classification

Fractures of the humerus shaft can display various patterns: transverse, oblique, spiral, and comminuted. In addition they are differentiated depending on whether the fracture is displaced or undisplaced, relative to the loss of bone alignment and closed or open fracture. The AO (Arbeitsgemeinschaft für Osteosynthesefragen) Foundation, an international organisation founded in Switzerland, focussing on research and education for the management of orthopaedic injuries), is one of most used systems available to characterise humerus shaft fractures. According to the AO humerus shaft fractures are divided into their level of comminution:

Type A - No comminution

Type B - Presence of butterfly fragment (wedge-shaped fragment of bone

Type C - Comminution

Elbow fracture dislocation can cause ulnar nerve entrapment

Causes

The aetiology of ulnar nerve entrapment also called cubital tunnel syndrome or sulcus ulnaris syndrome at the elbow is unknown. Due to the restricted space and the different anatomical locations the ulnar nerve can be easily compressed. The pathology is thought to origin from of the following causes:

Degeneration of the cervical spine

Fracture and dislocation to the elbow, causing nerve compression, or cubital tunnel syndrome

Pressure on the ulnar nerve caused by long periods of leaning on the elbows direct blow to the elbow at the “funny bone”

Repetitive and prolonged bending of the elbow

Cyst in the elbow

Fracture and dislocation to the wrist causing nerve compression at the Guyon’s canal, or Guyon’s canal syndrome.

Prolonged leaning on the elbows can lead to ulnar nerve entrapment

Risk factors

There are various risk factors thought to predispose for ulnar nerve entrapment at the elbow:

History of fracture or dislocation of the elbow

Arthritis and bone spur growth at the elbow

Swelling of the elbow joint

Physical activities or postures involving prolonged bending/leaning on the elbow

Diabetes increasing risk of neuropathy

Hand claw is a symptom of severe nerve entrapment at the wrist

Symptoms

The symptoms of ulnar nerve entrapment depend on the location where the nerve compression occurs. The symptoms usually begin gradually and increase over time. With cubital tunnel syndrome at the elbow symptoms include numbness at:

Small finger

 Along outer side of the ring finger

Outer half of the dorsal hand

When the nerve is severely damaged the fingers remain partially bent (ulnar claw). Hand claw is more severe when the ulnar entrapment is located at the wrist (Guyon’s canal syndrome) but the sensation on the dorsal hand remains preserved.

Other symptoms are:

Sleepy sensation of the little and ring fingers particularly when the elbow is bent

Pain radiating to the forearm

Weakening of grip strength

Failure in coordinating fine finger movement

Examination of the ulnar nerve (Tinel sign) is critical for the diagnosis of entrapment

Diagnosis

Medical history will be discussed with the patient. During the clinical evaluation the doctor will examine:

Both hands, arms, shoulders and neck to identify the area of nerve compression based on symptoms arising following movement and palpation

Reaction to the small and ring fingers when the funny bone is tapped (Tinel’s sign)

Ulnar nerve displacement when bending the elbow

Changes in the sensation of fingers and muscle strength during grip

X-rays to examine the bone quality and rule out fractures, arthritis

Electrodiagnostic tests to monitor nerve conduction when stimuli are applied to electrodes placed on the nerve

Electromyography to test nerve activity directly of the muscle using a needle placed in the muscle

Blood tests to exclude the existence of other medical conditions (diabetes, hypothyroidism).

Treatment

Local steroid injection reduces inflammation and pain

Nonoperative treatment

Early conservative treatment is key for reducing the symptoms of ulnar nerve entrapment. If diabetes, injury and arthritis are present they are given medical priority.

Specific measures for conservative treatment are:

Immobilisation of the arm with a splint (especially at night) is the first remedy to reduce symptoms

Application of cool pads and administration of NSAIDs in case of concomitant swelling and inflammation

Local steroid injections around the ulnar nerve with more severe symptoms

Physical therapy such as ‘nerve gliding’

Exercise directed to the ulnar nerve by stretching and strengthening elbow and wrist

Surgery for ulnar nerve transposition. Note the arrows showing the nerve transfer upwards to reduce friction

Surgical treatment

In case of prolonged or worsening of symptoms despite conservative treatment, surgery is necessary. This aims to release the entrapped ulnar nerve.

Two surgical approaches are available:

1. Cubital tunnel release or nerve decompression

This procedure is used in mild forms of ulnar nerve entrapment at the elbow. Following an incision along the inner side of the elbow, the ligamentous roof of the cubital tunnel is severed and separated. The cut ligament will repair spontaneously and provide more room for the ulnar nerve and release the symptoms.

2. Anterior transposition of the ulnar nerve

With an incision at the elbow the ulnar nerve is transferred from behind the elbow to the anterior area of the elbow. The nerve is moved under the skin and fat, either under or above the muscle. These procedures are named subcutaneous transposition or submuscular transposition of the ulnar nerve, respectively. The post-operative recovery takes longer with this approach.

Elbow stretch is part of rehabilitation

Rehabilitation

After surgery the initial care includes:

Elbow immobilisation for a few weeks with a bandage or splint to prevent joint bending

Treatment with analgesics and NSAIDs 

Ice pads to reduce inflammation and swelling

Elbow rehabilitation soon after surgery possibly with the support of a brace.

Exercises guided by a physiotherapist will assist in gaining strength of the operated elbow. Minor symptoms may persist for a few months after surgery. Although strength in grasping activity may return after 4 weeks post-surgery full recovery can take up to 1 year.

A correct posture while working at desk can prevent numerous pathologies of the hand, wrist and elbow

Prevention

The causality of manual work and the ulnar nerve entrapment syndrome remains unclear, however a number of measures, including occupational health and safety rules at workplace, should be implemented to reduce the risk of the condition. These recommendations include:

Ergonometric education for correct posture during manual activities to avoid longer periods in which the elbow is kept bent

Wear splint at night if symptoms arise

Regular stretching exercises

Frequent rests when involved in heavy industrial manual work