Upper limb nerves and injuries

Ulnar nerve

It is prone to injury in fracture medial epicondyle of the humerus, fracture of the lateral epicondyle of the humerus (see radial nerve also), compression in the Guyon canal located in the medial wrist and fracture hook of the hamate. It passes superficial to the flexor retinaculum of the hand, lateral to the pisiform bone. All interossei muscles, palmar and dorsal, are supplied by the ulnar nerve. Palmar interossei adduct while dorsal interossei abduct the fingers. The third and fourth lumbricals are supplied by the ulnar nerve. The lumbricals flex the metacarpophalangeal joint and extend the interphalangeal joint.

The presenting symptoms in peripheral nerve lesions depend on the level of lesion. Ulnar nerve injury at the elbow will present with ulnar claw hand involving 4th and 5th digits with hyperextension at the MCP joints and flexion at the interphalangeal joints, loss of hypothenar eminence with loss of thumb adduction and sensory loss on ulnar distribution of hand.

Injury at the wrist presents with similar symptoms as above except more pronounced claw hand and sensory loss only affecting palmar areas with sensations being intact on the dorsum of hand in ulnar distribution.

Median nerve

It is prone to injury in supracondylar fracture of the humerus at the elbow and carpal tunnel syndrome. It is the only nerve that passes through the carpal tunnel. Before the median nerve enters the carpal tunnel, it has already innervated muscles of the forearm. Palmar cutaneous branch of the median nerve , which provides sensory supply to the thenar eminence and central palm, arises before entry into the carpal tunnel, so sensation to the palm is intact in carpal tunnel syndrome. But the palmar digital cutaneous branch which supplies lateral 3.5 digits travels through the carpal tunnel and is affected in carpal tunnel syndrome. Recurrent branch of median nerve, origins in the hand, supplies thenar muscles opponens pollicis, abductor pollicis brevis and superficial part of flexor pollicis brevis. The first and second lumbricals are also supplied by the median nerve.

Injury at the elbow/ supracondylar fracture humerus causes loss of pronation, inability to make a complete fist as lateral 3 digits cannot be flexed (Hand of Benediction deformity), loss of opposition of thumb (Ape Hand deformity), thenar atrophy and sensory loss in the median nerve distribution in hand including fingertips.

Injury at the wrist presents with loss of thumb opposition ( ape hand), Benediction sign is present with sensory loss in the entire median nerve distribution in the hand.

Carpal tunnel syndrome can be differentiated from median nerve injuries at the wrist by intact sensations in the palm and thenar area in carpal tunnel syndrome.

Carpal Tunnel Syndrome

It results from compression of the median nerve in the carpal tunnel from repetitive activities like occupations involving long term use of typing on a computer etc, construction workers, entrapment of the median nerve in rheumatoid arthritis, pregnancy, obesity, myxoedema etc. The carpal tunnel is present ventrally on the wrist bounded by the carpal bones and flexor retinaculum. The median nerve and nine tendons -flexor pollicis longus, four each of flexor digitorum superficialis and flexor digitorum profundus pass through the carpal tunnel. Patients present with tingling, numbness and pain in lateral 3.5 fingers gradually progressing to weakness and atrophy of the thenar eminence in severe cases. Wasting and weakness of LOAF muscles- first and second lumbricals, opponens pollicis, abductor pollicis brevis and flexor pollicis brevis. Tinel and Phalen signs are positive.

Radial nerve

Prone to injury in shoulder joint lesions like inferior dislocation of humerus; mid shaft humerus fractures involving the radial groove, lateral epicondyle injuries, dislocation of the radial head and wrist injuries.

Injury at the axilla occurs in crutch palsy ,Saturday night palsy and in inferior dislocation of humerus. It presents with loss of extension at elbow, wrist and MCP joints, wrist drop, sensory loss in posterior compartments of upper arm and forearm and dorsum of hand in radial nerve distribution.

Injury at mid shaft humerus or at the radial groove presents similarly as above except with preserved forearm extension. While lateral epicondyle injury and radial head dislocation causes similar motor deficits but NO sensory loss.

Injury at wrist level is unique in that there is no motor loss, only loss of sensation in radial nerve distribution in the hand including the first web space.

Axillary nerve

Prone to injury in fractures of surgical neck of the humerus, inferior or anterior dislocations of the humerus and crutch related palsies. It presents with loss of abduction of shoulder above 30 degrees with a flat shoulder and loss of sensation over deltoid muscle (lateral arm).

Fall on outstretched hand injuries

Also called FOOSH injuries. It can lead to fractures in the wrist and forearm area including Colles fracture, scaphoid fracture, Monteggia fracture dislocation and Galeazzi fracture dislocation. Colles fracture is especially common in osteoporosis, it involves extra articular fracture of the distal radius. Scaphoid fracture presents as a pain in the anatomical snuff box with a high risk of avascular necrosis, non-union and malunion. Monteggia fracture-dislocation involves fracture of the ulnar shaft with concomitant dislocation of the radial head, most commonly seen in children. Galeazzi fracture-dislocation involves fracture of distal radius with dislocation of the distal radioulnar joint.

Shoulder joint and Rotator cuff

Also called as 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, making it prone to dislocations. The rotator cuff muscles provide stability to the shoulder joint. It is made of supraspinatus, infraspinatus, teres minor and subscapularis muscles. Abduction at the shoulder joint is a function of multiple muscles - first 15 degrees is by supraspinatus; 15 to 90 degrees is by the deltoid and beyond 90 degrees is by the serratus anterior and trapezius.

Applied anatomy of the shoulder joint

1. Dislocations are common at the shoulder joint. Anterior type is the most common, often due to direct trauma. It can damage the axillary artery and nerve or the brachial plexus. Posterior type is seen in seizures and electric shock. Inferior dislocations are rare. It is also called “luxatio erecta” as the arm is held upward in fixed abduction. It is caused by hyperabduction injuries.

2. Rotator cuff tear: It occurs when one or more tendons or muscles of the rotator cuff are injured as a result of trauma or long standing tendinitis. It presents as shoulder pain and limitation of motion with weakness in abduction at the shoulder joint.

3. Adhesive capsulitis or frozen shoulder: The joint capsule gets inflamed and stiff, restricting movement and resulting in severe pain aggravated by cold. It is more commonly seen in women with connective tissue disorders, thyroid disease, diabetes and as a side effect of HAART therapy.

Thoracic outlet syndrome (TOS)

This syndrome results from the compression of neurovascular bundles passing through the thoracic outlet which is a space bounded by the first rib, clavicle and scalene muscles. Brachial plexus and/or subclavian vessels are compressed. Causes include cervical rib, hypertrophied anterior scalene muscle, trauma like traffic accidents, pregnancy, repetitive upper limb movements like in athletes, tumors and cysts etc. It is more common in women. Presence of characteristic clinical features which are aggravated by raising the arm above the shoulders are diagnostic of TOS. Depending upon 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 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 on the elbow joint, and is bounded by the cubital tunnel retinaculum extending between the medial epicondyle and olecranon. The ulnar nerve passes through this tunnel. Repeated flexion at the elbow predisposes to ulnar nerve compression in the cubital tunnel. It is more common in diabetics, in telephone operators, obesity, baseball players etc. It presents with sensory loss, tingling and numbness in the ring and little fingers, muscle wasting of medial forearm and hypothenar eminence, ulnar claw hand called Froment’s sign, abduction of little finger called Wartenberg’s sign and positive Tinel’s sign.

Carpal bones

There are 8 carpal bones arranged in two rows - proximal and distal. The proximal row comprises of, from lateral to medial, scaphoid, lunate, triquetrum and pisiform. The distal row comprises of, from lateral to medial, trapezium, trapezoid, capitate and hamate. 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 while hamate has a hook. Scaphoid is the most commonly fractured carpal bone and can result in avascular necrosis. It presents as pain in the anatomical snuff box, MRI and CT scan being more sensitive than palin X ray in picking up the fracture. Hook of hamate fractures present with pain in the hypothenar area and ulnar nerve distribution in hand. Anterior displacement of the lunate bone causes median nerve entrapment leading to acute carpal tunnel syndrome.