Table of Contents
Median Nerve Lesions
The median nerve originates from C5 to T1 nerve roots and emerges from the medial and lateral cords of the brachial plexus. It is the only nerve that passes through the carpal tunnel of the wrist.
The median nerve innervates all the flexors in the forearm except the flexor carpi ulnaris and the ulnar portion of the flexor digitorum profundus. In the hand, the nerve supplies the lumbricales 1 and 2, abductor pollicis brevis, opponens pollicis, and the superficial head of the flexor pollicis brevis. It provides cutaneous innervation for the palmar surface of the hand, thumb, index, and middle fingers.
The causes of the median nerve lesion are diverse, depending on the lesion location:
|Location of lesions:||Lesions:|
|Lesions in the axilla||Median nerve palsy by arterial punctures|
|Lesions in the upper arm||Fracture of a supracondylar process; bone spur; a supracondylar process can cause irritation of the nerve without trauma.|
|Lesions in the elbow area||Fractures of the distal humerus; puncture and injection|
|Lesions in the forearm||Due to chronic irritation, it can cause pain and spasms in the volar forearm and paresthesias of the radial fingers.|
|Lesions in the wrist||Cut injuries; rare distal radius fractures; tumors such as schwannoma or fibrolipoma; compression within the carpal tunnel.|
The common symptoms are:
- Oath or monkey hand
- Atrophy of the thenar muscles (thenar atrophy): depression in the lateral side of a thenar eminence; thenar atrophy is generally diagnosed with a carpal tunnel syndrome
- Sensory disturbance
- A positive ‘bottle sign’ test – the patient cannot close the hand around a bottle
- Trophic-vegetative disorder: edematous changes in the hand and fingers, pain and hyperpathia, failure of the sweat glands, and moisturizing of the respective skin areas
- Inability to flex the thumb and forefinger – a patient fails to make an ‘O’ with the thumb and forefinger.
Note: An oath or a monkey hand arises due to the failure of muscles innervated by the median nerve so that a patient cannot make a full fist. The index finger and part of the middle finger cannot be bent. There is no flexion of the thumb in the metacarpophalangeal and terminal joints. Ring and little fingers, however, can be flexed because they are innervated by the ulnar nerve.
Median nerve palsy can be diagnosed by testing the muscles innervated by it.
The muscles innervated by the median nerve are:
- Pronator teres and pronator quadratus
- Flexor carpi radialis
- Palmaris longus
- Flexor digitorum superficialis
- Flexor digitorum profundus of fingers 1 and 3
- Flexor pollicis longus
- Lumbricals 1 and 2
- Opponens pollicis
- Abductor pollicis brevis
- Flexor pollicis brevis
Electrophysiological findings can be helpful but are not always reliable.
Rupture/injury of muscles or tendons resulting in symptoms similar to median nerve palsy.
Carpal tunnel syndrome – conservative treatment such as wrist splinting and rest. Surgical treatment such as carpal tunnel release.
Carpal Tunnel Syndrome
The carpal tunnel is formed anteriorly by the flexor retinaculum and posteriorly by the carpal bones. The median nerve and the tendons of the flexor digitorum longus travel to the fingers through the carpal tunnel. Carpal tunnel syndrome occurs from the narrowing of the tunnel and subsequent compression of the structures within it.
The causes of carpal tunnel syndrome include:
- The inflammatory response in the tendon sheaths
- Fluid retention
- Repetitive movements that bend the hand (e.g. typing on a keyboard)
On the lateral side of the hand, compression of the median nerve may cause sensory disturbances and lead to thenar muscle atrophy. Symptoms also include pain, numbness, and/or tingling of the affected fingers.
Carpal tunnel syndrome can be diagnosed by physical exam. Two tests include:
- Tinel’s sign: In this test, the examiner lightly taps the carpal canal of the patient. If this elicits a sensation of tingling or ‘pins and needles’ in the distribution of the nerve, Tinel’s sign is ‘positive’.
- Phalen’s maneuver: The examiner flexes the patient’s wrist for 30–60 seconds. The examiner makes sure that fingers are kept straight. The test is positive if the patient feels burning, tingling, or numbness over the thumb, index, middle, and/or ring fingers.
Electrophysiological tests can also be done. These are focused on the extension of the motor latency to the thenar muscles and the delay of the sensory conduction velocity in the distal segment.
Conservative treatment includes nonsteroidal anti-inflammatory drugs (NSAIDs), wrist splinting, handrails, and corticosteroid injections.
If conservative treatment fails, carpal tunnel release surgery can be done.
Ulnar Nerve Lesions
The ulnar nerve originates from C8–T1 spinal nerve roots. It emerges from the medial cord of the brachial plexus. It contains both the motor and sensory nerve fibers.
It descends the arm at the posteromedial aspect of the humerus and enters the forearm under the flexor carpi ulnaris aponeurosis posterior to the medial epicondyle of the humerus.
The ulnar nerve innervates the following muscles:
- Flexor carpi ulnaris
- Flexor digitorum profundus (ulnar portion)
- Hypothenar muscles
- Opponens digiti minimi
- Abductor digiti minimi
- Flexor digiti minimi brevis
- Part of the thenar muscles
- Adductor pollicis
- Lumbricals 3 and 4
The ulnar nerve innervates the skin over the little finger and the corresponding region on the ulnar side of the back of the hand. It also completely innervates the little finger and the ulnar half of the ring finger.
Common causes of lesions/injury differ according to their location.
Lesions in the Axilla and Upper Arm
Usually from direct trauma.
Lesions in the elbow area
- Direct trauma to the medial elbow
- Fractures of the medial condyle
- Fracture of the trochlea
- Supracondylar fracture
- Secondary paresis
- Pressure lesions: they are the most common cause of the ulnar paresis in the elbow. Approximately 10–25% of all the ulnar paresis occur after general anesthesia.
Dislocation of the ulnar nerve from the sulcus
An ulnar subluxation usually resolves. The symptoms include:
- Paresthesia over the ulnar dermatome
- Dupuytren’s contracture
- Small finger deformities
- Knuckle pads or ‘heloderma’
Lesions in the forearm
Lesions of the dorsal branch of the ulnar nerve can be caused by:
- Surgical procedures of the distal forearm such as shunt operations
- Tight watches or handcuffs
Lesions in the wrist
Wrist lesions may occur due to the following reasons:
- Direct trauma such as blunt force
- Penetrating trauma
- Guyon’s cyst
- Chronic stress of the wrist from manual labor
Digital nerves lesions
Digital nerves lesions usually result from trauma or external compression.
The following symptoms characterize ulnar nerve lesions:
- ‘Claw hand’
- Atrophy of the little finger
- Restricted ulnar deviation of the hand and an incomplete fist: the 4th and the 5th fingers do not fully flex because of failure of the ulnar part of the flexor digitorum profundus
- Lack of adduction of the thumb – Froment’s sign
- Loss of sensation in the small finger
Fourth and 5th finger hyperextension at metacarpophalangeal joints and flexion of the interphalangeal joints. Also known as the ‘hand of benediction’.
The tests include:
- Asking the patient to adduct the thumb – Froment’s sign
- Asking the patient to spread his fingers to test the dorsal interossei
- Brachial plexus injury
- Nerve root damage to C8–T1
- Damage to the brachial plexus
- Spinal cord injury
- Chronic spinal muscular atrophy of the Aran-Duchenne type
- Amyotrophic lateral sclerosis
Ulnar nerve palsy
Surgery involves shifting the ulnar nerve to the anterior aspect of the elbow joint.
Ulnar nerve dislocations
Ulnar nerve dislocations can usually be treated conservatively, aimed at avoiding compression. This includes wearing padding at the elbow and reducing elbow flexion. Rarely, in the case of recurrent dislocation, the nerve is surgically relocated to the volar side.
Radial Nerve Lesions
The radial nerve originates from C5–T1 nerve roots and emerges from the posterior cord. It has a motor and sensory nerve fibers and innervates the extensors of the arm and hand. In the upper arm, it innervates the triceps brachii and the anconeus. In the lower arm, it innervates the brachioradialis, the extensor indicis, and the supinator muscle.
The nerve provides sensory innervation of the skin on the extensor surfaces of the upper and lower arm and dorsal side of the proximal and middle phalanges of the radial 2½ fingers. The sensory innervation takes place via the dorsal antebrachial cutaneous nerve, the inferior lateral brachial cutaneous nerve, and the dorsal antebrachial cutaneous nerve.
The common causes of radial nerve lesions are:
- Use of crutches: paralysis occurs due to the pressure of crutches at the axilla
- Humeral shaft fracture
- Reduction of the humeral shaft fracture
- ‘Drop hand’: loss of dorsiflexion of the wrist
- Loss of extension of all the fingers except the thumb
- Loss of extension of the thumb at the metacarpophalangeal joint
- Loss of reflexes at the triceps brachii and/or brachioradialis
- Magnetic resonance imaging (MRI)
- Triceps and/or brachioradialis reflex or muscle strength
- Strength testing of:
- Extensors carpi (radial and ulnar)
- Extensor digitorum communis and extensor indicis
- Abductor pollicis longus
- Extensor pollicis brevis
Nerve palsies from humeral shaft fractures usually resolve so no treatment is needed.
Axillary Nerve Lesions
The axillary nerve originates from C5 and C6 and originates from the posterior cord of the brachial plexus.
It innervates the deltoid and teres minor. It innervates the skin at the upper lateral and dorsal area of the upper arm through the superior lateral brachial cutaneous nerve.
The common causes are:
- Shoulder dislocation
- A fracture of the surgical neck of the humerus
- A scapular fracture
- External compression, i.e. from sleeping on the stomach with arms folded over the head
Assessment after shoulder dislocation can be difficult because the arm cannot be moved before it is reduced. Approximately 10–15% of axillary nerve lesions occur as a result of a shoulder dislocation.
The following symptoms are typical of the axillary nerve lesion:
- Deltoid atrophy and damage to the nerve trunk (a protruding edged shoulder and visible contours on the acromion and humeral head)
- Failure of the deltoid (loss of elevation of the arm from 0–15° of abduction)
If you suspect the axillary nerve lesion, the examiner may use the following measures:
- Nerve conduction velocity measurements
- Muscle function testing
Physical Examination of the deltoid muscle
The deltoid abducts the arm from 0–15°. With your hand on the patient’s shoulder, ask him to try abducting his arm and feel if the deltoid muscle twitches.
- Muscular dystrophy – bilateral deltoid muscles affected
- Spinal muscular atrophy – unilateral deltoid atrophy
- Rotator cuff tear – causing pain or loss of arm abduction
Conservative management includes physiotherapy exercises.
Surgical nerve transplantation is possible in cases of isolated axillary nerve lesions from blunt trauma.