Musculature of the Upper Limb

Summary

We will cover the following aspects in this section:

Upper arm
1. Anterior compartment
2. Posterior compartment

Forearm
1. Anterior compartment (flexors, pronators)
2. Posterior compartment (extensors, supinators)

Hand
1. Intrinsic hand muscles – LOAF vs ulnar muscles
2. Extensor compartments of the wrist/hand

Upper arm

Anterior compartment

All are innervated by Musculocutaneous nerve (except PT)

Elbow flexion is the main movement done by these muscles
1. Biceps brachii
  - 2 heads
  - Both insert into radial tuberosity
  - Used in elbow flexion and supination

1. Brachialis
  - Also flexes elbow
  - Inserts into ulna unlike biceps brachii
    - Therefore does not supinate but rather semipronates

1. Coracobrachialis
  - Flexes and adducts the arm at shoulder

1. Pronator teres
  - This also has 2 heads
    - One originates at the humerus, and one from the ulna’s medial epicondyle
    - Both insert onto the radius
  - Supplied by the median nerve unlike the other anterior compartment muscles
  - Responsible for pronation & elbow flexion

Posterior compartment

These are all innervated by the Radial Nerve
Responsible for elbow extension
1. Triceps brachii
  - 3 heads (Long, medial, lateral)
  - Insert into olecranon (various origins)
2. Anconeus
  - Lateral epicondyle => olecranon

The Forearm

Remember:
- Wrist flexors attach to medial epicondyle (common flexor origin)
  - Therefore these muscles are anteromedial
  - The main exception is brachioradialis (in extensor compartment)
- Wrist extensors attach to the anterior lateral epicondyle (extensor origin)
  - Extensors therefore lie posterolateral

The anterior compartment of the forearm

Median and ulnar nerve innervation
- All anterior forearm muscles are median except for flexor carpi ulnaris and half of the flexor digitorum profundus

Responsible for wrist flexion + pronation

There are superficial, intermediate, and deep layers to the anterior compartment (3 layers)
- Superficial layer – FCP, PL, FCU, PT,
- Intermediate layer – FDS,
- Deep layer -FDP, FPL, PQ
- REMEMBER – 4 superficial – 1 intermediate = 3 deep

Superficial anterior compartment

A simple mnemonic to remember these superficial muscles is Pass/Fail, Pass/Fail:
- Pass (pronator teres)
- Fail (flexor carpi radialis)
- Pass (palmaris longus)
- Fail (flexor carpi ulnaris)

Pronator teres (See above)
- Two heads
- Median nerve
- Pronation, elbow flexion
Flexor carpi radialis
- CFO => 1st + 2nd metacarpals
- Flexion, radial deviation
Palmaris longus
- CFO => palmar aponeurosis, flexor retinaculum (only one not to go through Carpal tunnel)
- Wrist flexion and abduction
- Tenses palmar aponeurosis
Flexor carpi ulnaris
- CFO => pisiform, hamate, 5th metacarpal
- Flexion, ulnar deviation
- Ulnar nerve innervation

Intermediate anterior compartment

FD superficialis
- 2 heads
- CFO + anterior radius => middle phalanges 2-5
- Therefore flexes the PIP but not the DIPJ
- Only supplied by median nerve

Deep anterior compartment

FD profundus
- Attaches to distal phalanges
- Therefore can also flex the DIPJ
- Supplied half by median n. and half by ulnar n.
Flexor pollicis longus
- Anterior radius => distal phalanx of thumb
- Acts with FPB
Pronator quadratus
- Distal ulna => distal radius
- Pronation

Posterior compartment of forearm

Radial nerve innervation
These are all wrist extensors (except for brachioradialis)
- Originate from the Common extensor origin (CEO) = lateral epicondyle

3 layers – similar pattern to flexors with carpi muscles most superficial:

Brachioradialis
- Lateral supracondylar ridge (LSR) => styloid process of radius
- Elbow flexion, pronation, supination

Superficial muscles of the posterior forearm

NB there are two separate muscles for the radial aspect (ECR longus + ECR brevis unlike the anterior forearm which only has FCR)

Extensor carpi radialis longus
- LSR of humerus => 2nd metacarpal
- Extension, abduction
Extensor carpi radialis brevis
- CEO => 3rd metacarpal
- Extension, abduction
Extensor carpi ulnaris
- CEO => 5th metacarpal
- Extension, adduction
- Posterior interosseous nerve (PIN)

Intermediate muscles of the posterior forearm (supply all digits except index)

Extensor digitorum
- CEO => Distal phalanges 2-4
- Extension of wrist and fingers
- NB this is only one muscle – no profundus/superficialis (reverse to ECR longus + brevis vs FCR)
Extensor digiti minimi
- CEO => 5th digit

Deep muscles of the posterior forearm – thumb + supinator + index

Supinator
- CEO => proximal radius
- Primary supinator
Abductor pollicis longus
- Posterior ulna/radius => 1st metacarpal
Extensor pollicis longus
- Middle of ulna => distal thumb
- Extends distal phalanx
Extensor pollicis brevis
- Posterior radius => Proximal thumb
- Extends proximal phalanx
Extensor indicis
- Posterior ulna => 2nd digit
- Extends index finger

Intrinsic hand muscles

These are mostly ulnar except LOAF
- There are several compartments to know about:
  1. Thenar compartment (LOAF muscles) supplied by the median nerve
  2. Hypothenar compartment supplied by the ulnar nerve
  3. Lumbricals supplied by ulnar, radial, and median nerves
  4. Interossei also supplied by the ulnar nerve
    - These are muscles between the metacarpals that abduct fingers (Dorsal interossei ABduct) and adduct fingers (Palmar interossei ADduct)
    - Remember DAB and PAD
  5. Adductor pollicis (Ulnar n.) – does not fit into any of the above

Thenar Eminence + Lumbricals

Mostly for thumb movement
Attach to the flexor retinaculum, scaphoid, and trapezium
Median nerve innervation

These are also known as the LOAF muscles
- Lumbricals (1st and 2nd median lumbricals – for the index and middle finger)
  - Extend interphalangeals

- Opponens pollicis
  - Medial rotation of 1st metacarpal (cupping hand)
  - Flexor retinaculum =>proximal thumb
- Abductor pollicis brevis
  - Flexor retinaculum => 1st metacarpal
  - Thumb abduction
  - Acts with APL (in posterior compartment)
- Flexor pollicis brevis
  - Thumb flexion
  - Flexor retinaculum =>proximal thumb

Hypothenar muscles

Little finger – innervated by ulnar
- NB these are intrinsic whereas indicis muscles are extrinsic

Abductor digiti minimi
Flexor digiti minimi brevis
Opponens digiti minimi