📚 Question Bank

The axillary nerve or surgeon's nerve is frequently injured during inadvertent intramuscular (IM)

injections.

The course of axillary nerve:

• It is a branch of the posterior cord of the brachial plexus in the axilla
• It exits the axilla through the quadrangular space to enter the arm
• In the arm, it winds around the surgical neck of the humerus and gives cutaneous supply to the lower part of the deltoid (upper lateral cutaneous nerve of the arm)

Injuries to the axillary nerve can be caused by:

• Fracture of surgical neck of humerus
• Inferior dislocation of the humerus
• Inadvertent IM injection

Test for axillary nerve involves testing sensations of skin over the lower part of the deltoid. In the case of axillary nerve lesions, there is a loss of sensations over this region. It is called regimental badge anesthesia.

Named nerves of the upper limb are:

• Laborer’s nerve - median nerve
• Musician’s nerve - ulnar nerve
• Surgeon’s nerve - axillary nerve
• Nerve of Bell - long thoracic nerve

The median nerve is not directly related to the humerus. Nerves related to the humerus:

• Axillary nerve is at the surgical neck
• Ulnar nerve is at the medial epicondyle
• Radial nerve is at the spiral groove of the shaft of the humerus.
• Median nerve course:
• Origin: Lateral and medial cords of the brachial plexus
• Axilla and arm: No muscle supply from the median nerve
• Forearm (flexor compartment): It supplies most superficial flexors. It leaves the cubital fossa between the 2 heads of Pronator teres and gives off the anterior interosseous nerve
• Before entering deep into the flexor retinaculum gives off a palmar cutaneous branch. At the distal end of the flexor retinaculum, it divides into a recurrent branch and palmar digital nerves

Injury to the median nerve at the wrist is tested by contraction of the abductor pollicis brevis. Loss of thumb mobility and opposition (abductor pollicis brevis) is tested by pen test.

Option A: Paralysis of flexor pollicis brevis can occur in median nerve injury at the arm and elbow. Benediction hand sign (attempt to make a fist gives pointed index and middle finger) and Ochsner's clasping test (attempt to clasp both hands show pointing index finger) are used to test such injuries.

The images below show the Benediction hand sign and Ochsner's clasping test.

Option B: The lateral 1/2 of the palm is supplied by the palmar cutaneous branch of the median nerve. It is usually spared in median nerve injury to the wrist as it does not pass through the carpal tunnel.

Option D: The loss of sensation over ring finger cannot be tested for median nerve injury as it supplies:

• Lateral half of palmar aspect
• Medial half of distal 1/3 of dorsal aspect

Note: Out of three muscles in the thenar eminence only abductor pollicis brevis and opponens pollicis can be tested for isolated action. Flexor pollicis brevis cannot be tested for isolated action.

The nerve supply of the region marked in the image is the median nerve. The ape-thumb deformity is seen in the median nerve lesion irrespective of the site of the lesion, as it is a defect of the end of the nerve. It is caused by non-use atrophy of the muscles of the thenar eminence (except adductor pollicis).

Median nerve supply:

The sensory nerve supply to hand by median nerve is given below.

Branch Median nerve

Anterior interosseous nerv e

Recurrent branch

Palmar cutaneous branch Palmar digital nerves

Muscles/ region

Superficial flexors (pronator t eres, flexor carpi radialis, pal maris longus, flexor digitoru m superficialis)Exceptions: fl exor carpi ulnaris, medial hal f of flexor digitorum profund us

2 ½ muscles:Flexor pollicis lo ngus, pronator quadratus, lat eral half of FDP (medial half by ulnar nerve)

Thenarmuscles(except adduc tor pollicis)

Lateral 2/3rd of palm

Lateral 2 lumbricalsSkin over the lateral 3 ½ digits

Option A: Adductor pollicis is innervated by the ulnar nerve.

Option B: Median nerve innervates lateral half of flexor digitorum profundus. Ulnar nerve innervates medial half of flexor digitorum profundus.

Option D: Wrist drop is seen in radial nerve palsy.

Note: Thenar muscles include abductor pollicis, adductor pollicis, opponens pollicis, and flexor pollicis brevis. Adductor pollicis is called the graveyard of the ulnar nerve because after supplying all other muscles medially it ends laterally in adductor pollicis.

The ulnar nerve supplies the palmar interossei. The course of the ulnar nerve:

• A branch of the medial cord of the brachial plexus
• No muscle supply in the axilla and arm
• Up to midarm, it passes medial to the brachial artery
• After midarm, it inclines posteromedially to perforate the medial intermuscular septum and passes through a fibrous canal called arcade of Struthers (not to be confused with supinator arch or arcade of Frohse which is over radial nerve deep branch).
• In the upper forearm, it passes between the 2 heads of FCU and gives off some branches
• In the distal forearm, it gives off a dorsal cutaneous branch
• In the wrist, it passes superficial to flexor retinaculum but under a fascial band lateral to pisiform called Guyon's ulnar tunnel
• Distal to pisiform it gives 2 terminal branches. One superficial terminal and another deep terminal

Ulnar nerve supply:

The image given below shows the cutaneous innervation of the hand by the ulnar nerve.

Branches

Upper forearm branches

Dorsal cutaneous branch (dis tal forearm)

Palmar cutaneous branch (ne ar the wrist)

Superficial terminal branch Deep terminal branch

Muscles/ region

Flexor carpi ulnarisMedial ha lf of flexor digitorum profund us

Dorsum of medial 1/3 of han d and medial 1 1/2 fingers

Hypothenar eminence

Palmaris brevisPalmar surfac e of medial 1 1/2 fingers

All intrinsic muscles of the h and (except first 2 lumbricals and thenar eminence)

The given clinical scenario is suggestive of an injury to the ulnar nerve lesion before its division into a superficial and deep branch, as the function of both branches is affected.

The ulnar nerve after passing distal to pisiform bone gives 2 terminal branches:

• Superficial branch which supplies
• Palmaris brevis
• Skin on the palmar surface of medial 1½ fingers
• Deep branch runs within the concavity of deep palmar arch. It supplies all intrinsic muscles of the hand (except first 2 lumbricals and thenar muscles)

Injury to the ulnar nerve:

Given below is the Froment test used to test adductor pollicis.

Site of injury Causes

High lesion(Elbow)

Fracture/dislocation of theme dial epicondyleCubital tunnel syndromeCompression betw een the two heads of FCUTar dy ulnar nerve palsy (Valgus deformity)

Low lesion(Wrist)

Wrist laceration/ slashingGuy on's canalsyndrome

Site of injury High lesion(Elbow) Low lesion(Wrist)

Motor loss

Sensory loss

Claw-handdeformityHypothe nar interosseous wastingLo ss of:• Abduction adduction of fingers(Card test- Positive)

• Adduction of thumb(Frome nt sign-Positive)• Flexion of MCP jointsWeakness of wrist flexion (radial deviation)

Over dorso-ulnar aspect of th e palm

Claw-handdeformity(more pr onounced)Hypothenar inte rosseous wastingLoss of:• Ab duction adduction of finger s(Card test- Positive)• Adduct ion of thumb(Froment sign-P ositive)

Over palmar aspect of theme dial 11/2fingers

Given below is the course of the ulnar nerve.

Note: Wartenberg's sign is used to assess the weakness of palmar interossei.

Loss of adduction points toward the deep ulnar nerve injury. The hypothenar injury could have caused downstream loss of innervation of the deep ulnar nerve which innervates adductor pollicis in thenar eminence.

The course of deep ulnar nerve:

• At its origin, it innervates the hypothenar muscles.
• As it crosses the deep part of the hand, it innervates all the interosseous muscles and the third and fourth lumbricals.
• It ends by innervating the adductor pollicis and the medial (deep) head of the flexor pollicis brevis.
• It also sends articular filaments to the wrist joint following Hilton's law.
• Given below is the course of the ulnar nerve.

Paralysis of all interossei is seen in injury to the ulnar nerve in the elbow. All interossei (dorsal and palmar) are supplied by ulnar nerve.

• Dorsal Interossei - Abduction (DAB)
• Palmar Interossei - Adduction (PAD)

Note: Median nerve and ulnar nerve injury lead to a total claw hand.

The radial nerve, ulnar nerve, and median nerve can be tested using the thumb. The muscles of thumb that are affected in the different nerve injuries are:

Nerve inju ry

Median ne rve

Ulnar ner ve

Radial ner ve

Thumb muscle affected Opponens pollicis

Adductor pollicisPalmar inter ossei

Abductor pollicis longus (AP L)Extensor pollicis brevis (EP B)Extensor pollicis longus (E PL)

Thumb movement lost

Thumb opposition

Adduction of thu mb

Thumb extension

The lower lateral part of the arm is innervated by the lower lateral cutaneous nerve of the arm. It is one of the 5 branches of the radial nerve in the spiral groove.

The course of the radial nerve:

• It is the largest branch of the brachial plexus (C5, 6, 7,8, T1).
• It leaves the axilla by passing through the lower triangular space.
• It enters the arm and runs along the radial groove with profunda brachii artery. It gives the following branches:
• Lower lateral cutaneous nerve of arm
• Posterior cutaneous nerve of forearm
• Branch to lateral head of triceps
• Branch to medial head of triceps
• Branch to anconeus
• In the forearm, it divides in to 2 branches superficial (sensory) and deep (motor) branch at the cubital fossa.
• Superficial branch crosses the tendon of brachioradialis and goes posterior to supply dorsum of the hand.
• Deep branch/ posterior interroseous nerve pierces the supinator and supplies the extensors in the forearm.

In the given clinical scenario, there is a likely injury to the posterior interosseous nerve.

It is prone to be injured in radial head fractures as the nerve winds around the radial neck to go into the posterior compartment of the forearm. There is no cutaneous sensory loss in lesions confined to the posterior interosseous nerve.

The radial nerve divides into 2 branches, namely superficial (sensory) and deep (motor) branches at the cubital fossa.

Deep radial nerve after supplying extensor carpi radialis brevis (ECRB) and supinator, continues as posterior interosseous nerve (PIN). From the posterior compartment, the supinator muscle wraps around the upper 1/3rd of the radius to reach the anterior compartment.

PIN arches and winds around the radial neck along with the supinator muscle, into the posterior compartment of the forearm. Hence, it is in close relation with the radial head and neck, and the supinator arch or arcade of Froese.

There is no cutaneous innervation by the posterior interosseous nerve.

Sensations over the thumb and index finger are lost in C6, C7 nerve root injuries.

The palmar pad of the thumb is innervated by C6 and the pad of the index finger is innervated by C7.

A tap on the tendon of the triceps posterior to the elbow mainly tests for C7.

A tap on the tendon of the biceps in the cubital fossa tests mainly for spinal cord level C6.

The lateral head of the triceps is paralyzed in a lesion of the radial nerve in the lower spiral groove.

Spiral groove injuries could be upper or lower (proximal or distal). The following muscles are affected:

• Lateral head of triceps - as branching happens in the lower spiral groove
• Anconeus - as branching happens from the upper spiral groove

Option A: Radial nerve branches from the posterior cord of the brachial plexus. It leaves the axilla by passing through the lower triangular space.

Option C: Anconeus is supplied by a branch arising in the spiral groove.

Option D: In the arm, it runs along the radial groove with the profunda brachii artery.

Paresthesia over the skin of thenar eminence is not seen in carpal tunnel syndrome. As the median nerve gives off the palmar cutaneous branch, that supplies the thenar eminence before it enters the carpal tunnel.

Carpal tunnel syndrome is due to compression of the median nerve due to:

• Reduced size of the osseofibrous carpal tunnel
• Inflammation or thickening of the synovial sheaths of the flexors tendons (tenosynovitis) due to stress injury (eg., occupational)
• Inflammation of the flexor retinaculum
• Arthritic changes in the carpal bones (particularly rheumatoid arthritis)
• The pain and paresthesia are worse at night and on gripping objects.
• Structures passing through the carpal tunnel:
• Tendons of FDS (flexor digitorum superficialis), FDP (flexor digitorum profundus), FPL (flexor pollicis long)
• Median nerve

No artery passes through the carpal tunnel.

The median nerve is likely to be injured in case of deep laceration of the radial side of the wrist, whereas the radial nerve is least likely to be injured.

Wrist slash injuries:

A deep laceration on the radial side of the wrist may injure the following structures:

• Radial artery
• Median nerve
• Flexor carpi radialis tendon
• Palmaris longus tendon

A deep laceration on the ulnar side of the wrist may injure the following structures:

• Ulnar artery
• Ulnar nerve
• Flexor carpi ulnaris tendon

The structure marked in the image is the Guyon's canal. The roof of Guyon's canal is formed by the palmar carpal ligament and palmaris brevis.

Guyon's canal is a 4 cm long canal formed by splitting of the flexor retinaculum along the anteromedial side of the wrist.

Boundaries:

• Ulnar/Medial side - Pisiform bone, flexor carpi ulnaris, and abductor digiti minimi
• Lateral - Hook of hamate, extrinsic flexor tendons, and the transverse carpal ligaments
• Floor - Flexor retinaculum and pisohamate ligaments
• Roof - Palmar carpal ligament and palmaris brevis
• Contents:
• Ulnar nerve
• Ulnar artery

Injury to the medial epicondyle injures the ulnar nerve. Since flexor digitorum superficialis (supplied by median nerve) and extensor digitorum (supplied by the radial nerve) are still functional, complete paralysis of the third and fourth digits is not seen.

Injury to the medial epicondyle damages the ulnar nerve. This causes:

• Paralysis of:
• Flexor carpi ulnaris (FCU) - loss of ulnar deviation
• Medial half of flexor digitorum profundus (FDP) - loss of distal interphalangeal joint flexion
• Hypothenar paralysis - lead to atrophy
• Sensory loss over medial 1/3 of hand and medial 1 1/2 fingers

Injury to the long thoracic nerve during radical mastectomy paralyzes the serratus anterior muscle. This can be tested by raising the arm above the head on the affected side.

Shrugging of the shoulders is mainly carried out by the trapezius, which is supplied by the spinal accessory nerve. This muscle works with the serratus anterior for overhead abduction.

Pectoralis major, supplied mainly by medial and lateral pectoral nerves, causes flexion at the shoulder joint. It is involved in touching the opposite shoulder.

The anterior axial line extends till the wrist joint.

The axial line is the junction between two dermatomes supplied by discontinuous spinal nerves.

• The anterior axial line starts from the sternal angle (second rib) and extends to the wrist joint level.
• The posterior axial line begins at the shoulder and reaches the elbow joint level.

The images given below show the dermatomes of the upper limb with a dark green line indicating the axial line.

Extension at the metacarpophalangeal joint and flexion at interphalangeal joints due to ulnar nerve injury produces claw hand (main en griffe).

The ulnar nerve supplies medial two lumbricals in the hand. The lumbricals have a combined action on metacarpophalangeal (MCP) joint flexion and interphalangeal (IP) joint extension (glass holding posture).

In ulnar nerve injury, since the medial lumbricals are not functional, the forearm muscles are unopposed. MCP joint goes into hyperextension (unopposed activity of extensor digitorum, posterior forearm) and IP joints go into flexion (unopposed activity of flexor digitorum muscles, anterior forearm) and they bring about the claw hand deformity.

The image given below shows the ulnar claw hand (main en griffe). Note the hyperextension at MCP joints and flexion at IP joints.

The structure marked in the image is the radial nerve demonstrated in the cubital fossa. A lesion of the radial nerve leads to a wrist drop.

Ape thumb deformity is seen in a lesion of the median nerve. Claw hand deformity is seen in a lesion of the ulnar nerve.

The drooping of the shoulder is due to the paralysis of the trapezius muscle. The trapezius is innervated by the spinal accessory nerve (CN XI). It causes:

• Retraction of scapula
• Shrugging of the shoulder
• Overhead abduction (along with serratus anterior)

Paralysis of the trapezius causes drooping of the shoulder and slight winging of the scapula (the superior angle of the scapula becomes more prominent).

The thoracodorsal nerve does not cause winging of the scapula. It supplies latissimus dorsi muscle and if injured, the patient will not be able to extend, adduct, or medially rotate the arm.

Nerves causing winging of scapula:

Nerves

Spinal accessory nerv e

Long thoracic nerve

Dorsal scapular nerve

Muscles

Trapezius and sternocleidom astoid

Serratus anterior

Levator scapulae, rhomboid major, and rhomboid minor

Type of winging

The superior angle of the sca pula becomes more promine nt (lateral winging)

The scapula is pulled upward s and towards the spine by th e unopposed action of the tra pezius (medial winging)

Similar to serratus anterior b ut mild winging

Injury to the spinal accessory nerve can cause both drooping of the shoulder and winging of the scapula.

The trapezius is innervated by the spinal accessory nerve (CN XI). It causes:

• Retraction of scapula
• Shrugging of the shoulder
• Overhead abduction (along with serratus anterior)
• Nerves causing winging of the scapula:

Nerves

Spinal accessory nerv e

Long thoracic nerve

Dorsal scapular nerve

Muscles

Trapezius and sternocleidom astoid

Serratus anterior

Levator scapulae, rhomboid major, and rhomboid minor

Type of winging

The superior angle of the sca pula becomes more promine nt (lateral winging)

The scapula is pulled upward s and towards the spine by th e unopposed action of the tra pezius (medial winging)

Similar to serratus anterior b ut mild winging