Upper limb

Quadrangular space

A gap in posterior wall of axilla where axillary nerve and posterior circumflex humeral artery exit into arm
Borders
- Subscapularis above
- Teres major below
- Long head of biceps medially
- Humerus laterally

Cubital fossa

Triangular space which forms the transition between the arm and forearm
Boundaries
- Superior - imaginary line joining the medial and lateral humeral epicondyles
- Lateral - medial border of brachioradialis
- Medial - lateral border of pronator teres
- Roof - deep fascia of forearm
- Floor - brachialis muscle (medial) and supinator muscle (lateral)
Contents (from medial to lateral)
- Median nerve
- Brachial artery and brachial veins (venae comitantes)
  - Usually bifurcates 1cm distal to elbow skin crease
- Tendon of biceps
- Radial nerve, which divides into posterior interosseous branch and superficial branch
The pronator teres muscle weaves between the contents and is crucial to understanding the layout
- One head arises from common flexor origin at the medial epicondyle, the other arises from the ulna.
- The deep head (ulnar head) separates the median nerve and the ulnar artery
- The median nerve dives down into the cleft produced between the two heads
- Pronator teres then inserts to the lateral border of mid-radius after passing under the radial artery.

Carpal tunnel

Fibro-osseous tunnel at the wrist
Boundaries
- Superficially/roof - flexor retinaculum - runs between medial and lateral structures. Thick connective tissue.
- Deep/floor - deep carpal arch - concave surface
- Laterally - scaphoid and trapezium tubercles
- Medially - hook of hamate and pisiform
Contents: (nine tendons and the median nerve)
- FPL
- Four tendons of FDP
- Four tendons of FDS
- Median nerve
  - At the level of wrist, has three main branches. Palmar cutaneous - take-off proximal to carpal tunnel, supplies skin over thenar eminence. Sensory branch through carpal tunnel. (Recurrent) motor branch which sometimes goes through carpal tunnel (see 'median nerve' below).
Structures that pass superficial to the flexor retinaculum
- Ulnar artery and nerve (in small canal of Guyon)
- Palmaris longus tendon
- Palmar cutaneous branch of median nerve
- Flexor carpi radialis (retinaculum divides laterally to create a separate compartment)
- Superficial palmar arch is more distal to the flexor retinaculum, but superficial

Fascial compartments and muscles

Arm

Anterior compartment

- - Flexors of shoulder and elbow, and biceps supinates
  - Separated from posterior compartment by intermuscular septa medially and laterally
  - All supplied by musculocutaneous nerve
  - Note the bicipital aponeurosis - a broad secondary tendinous expansion from distal biceps brachii, running medially to attach to the deep fascia of the forearm flexors, bridging over the brachial artery and median nerve.
  - Coracobrachialis
  - Biceps brachii
  - Brachialis

Posterior compartment

- Triceps muscle - long head from inferior aspect of glenoid cavity, medial and lateral heads from upper humeral shaft. Inserts to olecranon. The major extensor of the forearm. Supplied by radial nerve.
- Radial and ulnar nerves also pass through compartment

Forearm

- Anterior
  - Superficial
    - All flexors, except for pronator teres - arise from medial epicondyle of the humerus ('common flexor origin') and fan out across the volar forearm.
    - All except FCU are innervated by the median nerve, and half of FDP in the deep compartment.
    - Pronator teres
      - Arises from CFO, humerus above (humeral head) and ulna below (ulnar head)
      - Inserts to shaft of radius
      - Pronates the forearm and flexes the elbow
      - Median nerve enters the forearm between the two heads - possible site of entrapment
    - Flexor carpi radialis
      - Arises from CFO and intermuscular septum
      - Inserts to the base of the second metatarsal
    - Palmaris longus
      - Arises from CFO and intermuscular septum
      - Inserts to the flexor retinaculum
    - Flexor carpi ulnaris
      - Arises from CFO and upper two-thirds of medial margin of ulna (ulnar head)
      - Inserts to the pisiform bone
    - Flexor digitorum superficialis
      - Arises from CFO (upper head) and shaft of radius (lower head)
      - Inserts to the sides of the shafts of the middle phalanges of each of the digits

Deep
- FDP, FDL and pronator quadratus
- All arise from shafts of long bones
- Supplied by median nerve, except for the ulnar half of FDP

Posterior
- Superficial
  - Extensors/supinators - arise from the lateral epicondyle of the humerus and extends towards the dorsum of the wrist
    - Extensor carpi ulnaris
    - Extensor digitorum
    - Extensor digiti minimi
    - Extensor carpi radialis longus and brevis
    - Brachioradialis
  - Supplied by radial nerve

Deep
- Supinator, abductor pollicis longus, extensor pollicis longus, extensor pollicis brevis, extensor indices
- Arise from posterior surfaces of forearm bones and interosseous membrane
- Supplied by posterior interosseous nerve (branch of radial)

Nerves

Musculocutaneous

- Origin
  - C5/C6/C7 - anterior divisions of superior and middle trunks form the lateral cord, then musculocutaneous nerve
- Course
  - Pierces coracobrachialis and passes down anterior compartment of arm beneath biceps muscle
  - Then becomes lateral cutaneous nerve of forearm
- Supplies
  - Sensory - lateral forearm
  - Motor - anterior compartment of arm - BBC (biceps brachii, brachialis, coracobrachialis)
- Injuries
  - Rare - protected by bulk of biceps muscle. Sometimes stab wounds to upper arm.
  - Sensory loss to lateral forearm
  - Weak elbow flexion, forearm supination, absent biceps reflex
- Deformity
  - Wasting of biceps

Axillary

- Origin
  - C5/C6 - posterior division of superior trunk, then posterior cord
- Course
  - Passes beneath shoulder joint, through quadrangular space, into posterior compartment of arm
  - Wraps around SNOH
- Supplies
  - Sensory - sergeant's patch over lower deltoid
  - Motor - deltoid, teres minor
- Injuries
  - Fracture SNOH, stab wounds to posterior shoulder, compression by shoulder dislocation or crutches in armpits
  - Sensory loss - sergeant's patch
  - Motor deficit - very weak shoulder abduction from 15-90 degrees; weak shoulder flexion and extension; weak shoulder external rotation
  - Deformity - wasting of deltoid

Median nerve

- Origin
  - Medial root and lateral root combine to form main nerve
  - C5-T1
- Course
  - Runs down arm with brachial artery
  - Through ACF into forearm, between pronator teres and biceps tendon
  - Central route down forearm. Travels between the layers of FDS and FDP. At the wrist, found ulnar to the tendon of FCR, between the tendons of FPL and FDP.
  - Main branch passes through carpal tunnel and gives off digital nerves. Supplies cutaneous innervation to distal phalanges of index and middle fingers.
  - Branches
    - Palmar cutaneous nerve arises in the mid-forearm. This penetrates the deep fascia at the wrist and supplies the skin over the thenar eminence.
    - Anterior interosseous
    - Deep palmar cutaneous
    - Recurrent muscular branch ('million dollar nerve') - to thenar muscles
      - This nerve is the reason for not straying radially during CTR
      - 50% take-off distal to flexor retinaculum
      - 30% branch within (then still recurrent to thenar muscles)
      - 20% pass through the retinaculum (non-recurrent)
    - Digital cutaneous branch
- Supplies:
  - Most of the flexor muscles of the forearm - all of anterior compartment except FCU and medial parts of FDP
    - Wrist and finger flexors
    - Pronator teres and quadratus
  - LOAF muscles in hand
    - Lateral two lumbricals
    - Opponens pollicis
    - Abductor pollicis brevis
    - Flexor pollicis brevis
  - Cutaneous to the flexor surfaces of 3.5 radial digits and palm
- Injuries
  - Most commonly injured at the wrist - lacerations, compression in carpal tunnel
  - Sensory loss radial 3.5 fingers of palm
  - Weakness and eventually wasting of thenar eminence
  - High lesion
    - Wasting of front of forearm because the long flexors (except FCU and half of FDP) and the pronators are paralysed
    - Hand of benediction - on attempted finger flexion, held with the index/middle finger straight, with all other fingers flexed
    - Test FPL and finger flexors by pinching together pads of thumb and index finger
  - Lesion at the wrist
    - Test abductor pollicis brevis (not flexor because of uncertain nerve supply)

Ulnar nerve

- Origin
  - Direct continuation of the medial cord (C8, T1) but 95% pick up C7 fibres from the lateral cord
- Course
  - Runs down arm with brachial artery
  - Penetrates medial intermuscular septum in mid-arm and passes posteriorly, reaching the groove behind the medial epicondyle of the humerus.
  - In the forearm, lies close to distal ulnar artery.
  - Enters palm of hand via Guyon's canal
  - Main branch gives off digital nerves, and also supplies superficial palmaris brevis.
  - Branches
    - Dorsal branch - arises in the distal forearm 5cm from the wrist flexion crease and passes between FCU and the distal ulna to reach the ulnar side of the dorsum of the hand
- Supplies
  - Flexor muscles of the ulnar side of the forearm - FCP and medial two parts of FDP
  - Most of the intrinsic muscles of the hand - HILA
    - Hypothenar eminence
    - Interossei
    - Lumbricals (medial two)
    - Adductor pollicis
  - Cutaneous to the skin of the ulnar 1.5 digits, and hypothenar eminence
- Injuries:
  - Most commonly injured behind the elbow or at the wrist
  - Low lesion (at the wrist e.g. lacerations)
    - Claw hand on attempted finger extension - hyperextension of the MCPJ of the ring and little fingers, and flexion of IPJ (unopposed action of the extensors and FDP)
    - Sensory loss 1.5 fingers
  - High lesion (elbow or above e.g. fracture, dislocation, damage behind medial epicondyle)
    - Paradoxical straighter fingers because loss of the ulnar half of FDP - can't flex the distal IPJs of the ring and little fingers
    - Sensory loss 1.5 fingers
  - Deformity - wasting of hypothenar eminence and intrinsic muscles of hand

Radial nerve

- Origin
  - Direct continuation of the posterior cord
  - C5-T1
- Course
  - Passes posteriorly below latissimus dorsi tendon and spirals behind the humerus, between the origins of the lateral and medial heads of triceps.
  - Subsequently penetrates the lateral intermuscular septum in mid-arm, through ACF, to reach the forearm extensor compartment, emerging lateral to distal brachialis.
  - Branches into
    - Superficial radial nerve
      - Primarily sensory
      - Lies close to the distal radial artery, then passes under the tendon of brachioradialis and crosses the anatomic snuffbox. It divides over the first extensor compartment into lateral and medial branches.
      - Lateral branch of superficial radial nerve supplies the skin at the radial side of the thenar eminence and dorsal thumb.
      - Medial branch of superficial radial nerve supplies the remainder of the dorsum.
    - Deep radial nerve/posterior interosseous nerve. Primarily motor.
- Supplies:
  - Extensor compartment of the arm and forearm
  - Cutaneous to the skin over them (posterior arm/forearm) and on the lateral half of dorsum of the hand
- Injuries:
  - Most commonly injured by fractures of the shaft of humerus, or transient paralysis due to improper use of crutch of 'Saturday night palsy'
  - Wrist drop - inability to extend the wrist and MCPJ (but the interphalangeal joints can still be straightened by the interossei and lumbricals)
  - Sensory loss minimal overlying the first dorsal interosseous (much overlap from medial and ulnar) - test over dorsum of first web space)
  - Deformity - wasting of triceps and posterior compartment of forearm

Smaller forearm nerves

- Medial antebrachial cutaneous nerve - travels alongside basilic vein to supply skin on medial forearm
- Lateral antebrachial cutaneous nerve - continuation of musculocutaneous nerve - emerges lateral to biceps tendon, supplies lateral arm skin
- Posterior antebrachial cutaneous nerve - arises from radial nerve in the spiral groove

Arteries

Brachial - runs with median nerve in medial side of anterior compartment. Proximal brachial artery first lies posterior to coracobrachialis, close to the humeral shaft, then diagonally crosses the medial part of brachialis belly.
- Branches
  - Profunda branch of brachial joins the radial nerve and follows it through the lateral intermuscular septum, then becoming the radial collateral artery.
  - Superior ulnar collateral artery arises from the mid-point of the brachial artery and accompanies ulnar nerve
  - Major nutrient vessel brachial artery to humeral shaft
  - Bifurcates 1cm distal to the skin crease of the elbow, at the level of the radial tuberosity (and the intersection of brachioradialis and pronator teres muscles), into radial and ulnar arteries.

Radial artery - direct continuation of the brachial artery. In mid-forearm, lies beneath the medial border of brachioradialis. At the wrist, lies between the tendons of brachioradialis (lateral) and FCR (medial). Then across anatomical snuffbox, close to cephalic vein, which is a convenient site for AVF formation.

Ulnar artery - larger branch, takes off nearly at right angles to brachial artery. Becomes superficial in the distal forearm at the lateral border of FDS. Accessible at the wrist on the radial side of the FCU tendon.
- Gives off a very proximal short common interosseous branch, which in turn bifurcates into dorsal and volar interosseous branches and runs along either side of the membrane.
Hand arteries
- Variable circulation
- Forearm arteries terminate in the superficial and deep palmar arches. Usually connected to both radial and ulnar arteries, but some patients have disconnected circulations. Radial artery occlusion/harvest may result in hand ischaemia in 10% of patients.
- Ulnar artery is usually the dominant artery to the hand

Veins

Cephalic vein - superficial along its entire course to the deltopectoral groove
- Forearm - most consistent location of forearm veins - starts along the lateral prominence of the radius. Divides in front of the biceps tendon. Sends a major tributary - median cubital vein - across to the basilic vein
- Continues upwards on lateral side of biceps
- Deltopectoral groove
- Pierces clavipectoral fascia
- Enters axillary vein 1-2cm inferior to clavicle
Median cubital vein - connects cephalic and basilic, running across and superficial to the ACF
Basilic vein - subcutaneous from the antecubital fossa, to the medial aspect of mid-arm, where it penetrates the deep fascia to join one of the brachial veins
Brachial veins - the brachial artery is usually accompanied by two veins, which unite at the level of teres major to form the axillary vein