Upper limb nerves and injuries

Ulnar nerve

The ulnar nerve is prone to injury in:

• Fracture of the medial epicondyle of the humerus
• Fracture of the lateral epicondyle of the humerus (see radial nerve also)
• Compression in Guyon canal (medial wrist)
• Fracture of the hook of the hamate

At the wrist, the ulnar nerve passes superficial to the flexor retinaculum, lateral to the pisiform bone.

Motor supply:

• All interossei muscles (palmar and dorsal)
  • Palmar interossei adduct the fingers
  • Dorsal interossei abduct the fingers
• The 3rd and 4th lumbricals
  • Lumbricals flex the metacarpophalangeal (MCP) joints and extend the interphalangeal (IP) joints

The symptoms of peripheral nerve lesions depend on the level of the lesion.

Ulnar nerve injury at the elbow presents with:

• Ulnar claw hand involving the 4th and 5th digits
  • Hyperextension at the MCP joints
  • Flexion at the IP joints
• Loss of hypothenar eminence
• Loss of thumb adduction
• Sensory loss in the ulnar distribution of the hand

Injury at the wrist presents with similar findings, except:

• Claw hand is more pronounced
• Sensory loss affects only palmar areas
• Sensation is intact on the dorsum of the hand in the ulnar distribution

Median nerve

The median nerve is prone to injury in:

• Supracondylar fracture of the humerus (at the elbow)
• Carpal tunnel syndrome

The median nerve is the only nerve that passes through the carpal tunnel.

Key branches and clinical implications:

• Before entering the carpal tunnel, the median nerve has already innervated the forearm muscles.
• The palmar cutaneous branch arises before the carpal tunnel and supplies the thenar eminence and central palm.
  • Therefore, sensation over the palm is intact in carpal tunnel syndrome.
• The palmar digital cutaneous branch supplies the lateral 3.5 digits and travels through the carpal tunnel.
  • Therefore, it is affected in carpal tunnel syndrome.
• The recurrent branch of the median nerve arises in the hand and supplies the thenar muscles:
  • Opponens pollicis
  • Abductor pollicis brevis
  • Superficial part of flexor pollicis brevis
• The 1st and 2nd lumbricals are supplied by the median nerve.

Injury at the elbow (e.g., supracondylar fracture) causes:

• Loss of pronation
• Inability to make a complete fist because the lateral 3 digits can’t be flexed (hand of Benediction deformity)
• Loss of thumb opposition (ape hand deformity)
• Thenar atrophy
• Sensory loss in the median nerve distribution in the hand, including fingertips

Injury at the wrist presents with:

• Loss of thumb opposition (ape hand)
• Benediction sign
• Sensory loss in the entire median nerve distribution in the hand

Carpal tunnel syndrome can be differentiated from median nerve injury at the wrist by:

• Intact sensation in the palm and thenar area in carpal tunnel syndrome

Carpal tunnel syndrome

Carpal tunnel syndrome results from compression of the median nerve in the carpal tunnel. Common associations include:

• Repetitive activities (e.g., long-term typing, construction work)
• Rheumatoid arthritis
• Pregnancy
• Obesity
• Myxoedema

Anatomy:

• The carpal tunnel is on the ventral wrist.
• It is bounded by the carpal bones and the flexor retinaculum.
• Contents:
  • Median nerve
  • Nine tendons:
    • Flexor pollicis longus
    • Four tendons of flexor digitorum superficialis
    • Four tendons of flexor digitorum profundus

Clinical features:

• Tingling, numbness, and pain in the lateral 3.5 fingers
• Symptoms may progress to weakness and thenar atrophy in severe cases
• Wasting and weakness of LOAF muscles:
  • 1st and 2nd lumbricals
  • Opponens pollicis
  • Abductor pollicis brevis
  • Flexor pollicis brevis
• Positive Tinel and Phalen signs

Radial nerve

The radial nerve is prone to injury in:

• Shoulder joint lesions (e.g., inferior dislocation of the humerus)
• Mid-shaft humerus fractures involving the radial groove
• Lateral epicondyle injuries
• Dislocation of the radial head
• Wrist injuries

Injury at the axilla occurs in crutch palsy, Saturday night palsy, and inferior dislocation of the humerus. It presents with:

• Loss of extension at the elbow, wrist, and MCP joints
• Wrist drop
• Sensory loss in the posterior compartments of the upper arm and forearm
• Sensory loss on the dorsum of the hand in the radial nerve distribution

Injury at the mid-shaft humerus (radial groove) presents similarly, except:

• Forearm extension is preserved

Lateral epicondyle injury and radial head dislocation cause similar motor deficits but:

• NO sensory loss

Injury at the wrist level is unique because:

• There is no motor loss
• There is only sensory loss in the radial nerve distribution in the hand, including the first web space

Axillary nerve

The axillary nerve is prone to injury in:

• Fractures of the surgical neck of the humerus
• Inferior or anterior dislocations of the humerus
• Crutch-related palsies

It presents with:

• Loss of shoulder abduction above 30 degrees
• Flat shoulder
• Loss of sensation over the deltoid muscle (lateral arm)

Fall on outstretched hand injuries

These are also called FOOSH injuries. They can lead to fractures in the wrist and forearm, including:

• Colles fracture
• Scaphoid fracture
• Monteggia fracture-dislocation
• Galeazzi fracture-dislocation

Colles fracture:

• Especially common in osteoporosis
• Extra-articular fracture of the distal radius

Scaphoid fracture:

• Presents as pain in the anatomical snuff box
• High risk of avascular necrosis, non-union, and malunion

Monteggia fracture-dislocation:

• Fracture of the ulnar shaft with concomitant dislocation of the radial head
• Most commonly seen in children

Galeazzi fracture-dislocation:

• Fracture of the distal radius with dislocation of the distal radioulnar joint

Shoulder joint and rotator cuff

Also called the glenohumeral joint, the shoulder joint is a highly mobile ball-and-socket joint formed between the head of the humerus and the shallow glenoid cavity of the scapula. This anatomy makes it prone to dislocations.

The rotator cuff muscles stabilize the shoulder joint. The rotator cuff is made of:

• Supraspinatus
• Infraspinatus
• Teres minor
• Subscapularis

Abduction at the shoulder joint is produced by multiple muscles:

• First 15 degrees: supraspinatus
• 15 to 90 degrees: deltoid
• Beyond 90 degrees: serratus anterior and trapezius

Applied anatomy of the shoulder joint

1. Dislocations are common at the shoulder joint.

• Anterior dislocation is the most common, often due to direct trauma.
  • It can damage the axillary artery and nerve or the brachial plexus.
• Posterior dislocation is seen in seizures and electric shock.
• Inferior dislocations are rare.
  • Also called “luxatio erecta” because the arm is held upward in fixed abduction.
  • Caused by hyperabduction injuries.

2. Rotator cuff tear:

• Occurs when one or more tendons or muscles of the rotator cuff are injured due to trauma or long-standing tendinitis
• Presents with shoulder pain and limitation of motion
• Causes weakness in shoulder abduction

3. Adhesive capsulitis (frozen shoulder):

• The joint capsule becomes inflamed and stiff, restricting movement
• Causes severe pain aggravated by cold
• More commonly seen in women with:
  • Connective tissue disorders
  • Thyroid disease
  • Diabetes
  • As a side effect of HAART therapy

Thoracic outlet syndrome (TOS)

Thoracic outlet syndrome results from compression of neurovascular bundles passing through the thoracic outlet, a space bounded by the first rib, clavicle, and scalene muscles. The brachial plexus and/or subclavian vessels are compressed.

Causes include:

• Cervical rib
• Hypertrophied anterior scalene muscle
• Trauma (e.g., traffic accidents)
• Pregnancy
• Repetitive upper limb movements (e.g., athletes)
• Tumors and cysts

It is more common in women.

Diagnosis is suggested by characteristic clinical features that are aggravated by raising the arm above the shoulders. Depending on the structure compressed, it presents as follows:

1. Neurogenic TOS: It presents with paresthesias (pins and needles sensation or numbness) in the fingers and hand, change in hand color, hand coldness, or dull aching pain in the neck, shoulder, and armpit. Gilliat-Sumner hand sign is positive, which is wasting of abductor pollicis brevis in the thenar eminence.
2. Venous TOS: It presents with pallor, a weak or absent pulse in the affected arm, numbness, tingling, aching, swelling of the extremity and fingers, weakness of the neck or arm, the affected limb feels cold to touch and looks paler.
3. Arterial TOS: It presents as change in color and cold sensitivity in the hands and fingers, swelling, heaviness, paresthesias and poor blood circulation in the arms, hands, and fingers. Blood pressure in the affected arm may be less by more than 20mmhg compared to the unaffected arm.

Cubital tunnel syndrome

The cubital tunnel is situated medially and anteriorly at the elbow joint. It is bounded by the cubital tunnel retinaculum extending between the medial epicondyle and olecranon. The ulnar nerve passes through this tunnel.

Repeated elbow flexion predisposes to ulnar nerve compression in the cubital tunnel. It is more common in diabetics, telephone operators, obesity, baseball players, etc.

It presents with:

• Sensory loss, tingling, and numbness in the ring and little fingers
• Muscle wasting of the medial forearm and hypothenar eminence
• Ulnar claw hand (Froment’s sign)
• Abduction of the little finger (Wartenberg’s sign)
• Positive Tinel’s sign

Carpal bones

There are 8 carpal bones arranged in two rows: proximal and distal.

• Proximal row (lateral to medial): scaphoid, lunate, triquetrum, pisiform
• Distal row (lateral to medial): trapezium, trapezoid, capitate, hamate

Key features:

• Scaphoid is boat shaped
• Lunate is crescentic
• Triquetrum is pyramid shaped
• Pisiform is pea shaped
• Trapezoid is the smallest carpal bone
• Capitate is the largest
• Hamate has a hook

Clinical correlations:

• Scaphoid is the most commonly fractured carpal bone and can result in avascular necrosis.
  • Presents as pain in the anatomical snuff box
  • MRI and CT scan are more sensitive than plain X ray in picking up the fracture
• Hook of hamate fractures present with pain in the hypothenar area and ulnar nerve distribution in the hand.
• Anterior displacement of the lunate bone causes median nerve entrapment, leading to acute carpal tunnel syndrome.