Nerve Injuries and Reflexes of the Upper Limb

Nerve injuries of the upper limb are categorized by the location and extent of the lesion.
Symptoms depend on the site and extent of damage.
Motor changes include paralysis of innervated muscles and loss of reflexes.
Sensory changes involve a loss of sensation in the area supplied by the damaged nerve.
Trophic changes from damage to postganglionic sympathetic fibers initially cause redness and heat in the skin; eventually, it becomes blue and colder. Nail growth slows and sweat glands cease to function, resulting in scaly skin.

Biceps brachii reflex: C5, 6, assessed by tapping the tendon of the biceps muscle (flexion of the elbow joint).
Triceps brachii reflex: C6, 7, 8, assessed by tapping the tendon of the triceps muscle (extension of the elbow joint).
Supinator (brachioradialis) reflex: C5, 6, 7, assessed by tapping the tendon of the brachioradialis muscle (supination of the radioulnar joint).

Spinal nerves can be damaged at the level of the roots within the vertebral canal, during passage through the intervertebral foramen, or throughout their peripheral course.
Injuries to levels 1 and 2 may be caused by vertebra fractures or narrowing of the intervertebral foramina.
Herniation and degeneration of the intervertebral disc contribute to nerve damage.

Brachial plexus injuries may affect roots, trunks, divisions, and branches.
Supraclavicular injuries damage the roots and trunks.
Infraclavicular injuries affect divisions and cords.
Causes of brachial plexus injuries include compression, traction, and stab wounds.
Symptoms vary with the area of injury and nerve involvement.

These result from traction and tearing of the fifth and sixth nerve roots of the brachial plexus.
Causes include difficult deliveries and falls in adults.
Affected muscles include abductors (supraspinatus & deltoid), lateral rotators (infraspinatus & teres minor), subclavius, biceps, brachialis, and coracobrachialis.
The affected limb hangs limply down, is medially rotated, and the forearm is pronated and extended.
There is loss of sensation on the lateral side of the arm and forearm.

Excessive abduction of the arm during difficult deliveries or falls can cause these.
Excessive pulling of an arm during delivery or a fall from a height can lead to nerve damage.
Involving the lower part of the brachial plexus (C8 and T1), resulting in paralysis or weakness of the intrinsic muscles of the hand.
The hand often shows a clawing phenomenon because of hyperextension of the metacarpophalangeal joints (and flexion of the interphalangeal joints).

This nerve may be injured by pressure or blows to the posterior triangle of the neck.
Damage is often associated with radical mastectomy procedures.
The serratus anterior muscle is responsible for pulling the scapula's medial border to the posterior thoracic wall and stabilizing it.
Arm elevation above a right angle is affected, leading to a "winged scapula" deformity.

Downward dislocation of the humeral head or fracture of the surgical neck of the humerus can damage the axillary nerve.
Axillary nerve damage results in the paralysis of the deltoid and teres minor muscles.
Abduction of the shoulder is impaired, and the deltoid muscle wastes rapidly.
Sensory loss occurs on the lower half of the deltoid muscle.

Injuries to the radial nerve can be caused by injury in the axilla, radial groove, or to branch injury in the supinator tunnel or superficial branch.
Radial nerve injury in the axilla may be a result of crutch palsy, saturday night palsy or fractures of the humerus.
Wrist drop is a major symptom of radial nerve injury in the axilla because the wrist extensors are paralyzed, and unopposed flexors cause the wrist drop.
Radial nerve injuries in the radial groove can occur due to humeral fractures or pressure from an operating table on the back of unconscious patients. Prolonged tourniquet use can also cause such injuries.
Prolonged tourniquet application can also damage this nerve.
Injuries to its deep and superficial branches lead to motor and sensory deficits, like paralysis of the wrist, hand, and fingers; loss of sensation in areas supplied by the damaged branch

Median nerve damage in the elbow region can occur with supracondylar fractures of the humerus.
This results in weak/absent pronator muscles of the forearm and most wrist and finger flexors.
Motor and sensory changes are seen with the elbow and wrists.
Median nerve injuries at the wrist may result from penetrating wounds or carpal tunnel syndrome.
Carpal tunnel syndrome is a median nerve compression.

Ulnar nerve damage can affect the elbow or wrist due to cuts or stab wounds.
In the elbow, damage mostly paralyzes the flexor carpi ulnaris, medial half of flexor digitorum profundus, and intrinsic muscles of the hand.
At the wrist, cuts or stab wounds can affect the anterior surfaces of the palm and the anterior/posterior surfaces of the medial half of the palm
These results in clawing, sensory loss (anterial surfaces of palm, medial half of palm & fingers), and motor loss, (thumb adductors, interossei and medial lumbricals)