What is the detailed anatomy of the upper limb?

Detailed Anatomy of the Upper Limb

The upper limb is a complex anatomical structure comprising bones, joints, muscles, blood vessels, and nerves that work together to provide exceptional functionality and mobility for various daily activities.

Bony Anatomy

Shoulder Girdle

• Clavicle: Forms the anterior portion of the shoulder girdle, articulating with the sternum medially and acromion laterally
• Scapula: Triangular flat bone with important processes:
  • Acromion process
  • Coracoid process
  • Glenoid fossa (articulates with humeral head)
  • Spine of scapula

Arm (Brachium)

• Humerus: Long bone with:
  • Proximal end: head, anatomical neck, surgical neck, greater and lesser tubercles
  • Shaft: deltoid tuberosity
  • Distal end: medial and lateral epicondyles, trochlea, capitulum

Forearm (Antebrachium)

• Radius: Lateral bone with:
  • Proximal end: head, neck, radial tuberosity
  • Shaft: narrower proximally, wider distally
  • Distal end: styloid process, ulnar notch
• Ulna: Medial bone with:
  • Proximal end: olecranon process, coronoid process, trochlear notch
  • Shaft: narrower distally
  • Distal end: head, styloid process

Wrist and Hand

• Carpals: 8 bones arranged in proximal and distal rows
  • Proximal row: scaphoid, lunate, triquetrum, pisiform
  • Distal row: trapezium, trapezoid, capitate, hamate
• Metacarpals: 5 bones forming the palm
• Phalanges: 14 bones forming the digits
  • 2 in thumb (proximal and distal)
  • 3 in each finger (proximal, middle, distal)

Joints

Shoulder Complex

• Sternoclavicular joint: Saddle-type synovial joint between sternum and clavicle
• Acromioclavicular joint: Plane synovial joint between acromion and clavicle
• Glenohumeral joint: Ball-and-socket synovial joint between glenoid fossa and humeral head
  • Stabilized by: glenoid labrum, rotator cuff muscles, glenohumeral ligaments
• Scapulothoracic articulation: Functional joint between scapula and thoracic wall

Elbow Complex

• Humeroulnar joint: Hinge joint between trochlea and ulnar trochlear notch
• Humeroradial joint: Ball-and-socket joint between capitulum and radial head
• Proximal radioulnar joint: Pivot joint between radial head and radial notch of ulna

Wrist and Hand

• Distal radioulnar joint: Pivot joint between radius and ulna
• Radiocarpal joint: Condyloid joint between radius and proximal row of carpals
• Midcarpal joint: Between proximal and distal rows of carpals
• Carpometacarpal joints: Between carpals and metacarpals
  • Thumb CMC: Saddle joint with wide range of motion
• Metacarpophalangeal joints: Condyloid joints allowing flexion/extension and abduction/adduction
• Interphalangeal joints: Hinge joints allowing flexion/extension

Muscular Anatomy

Shoulder Muscles (52.5% of upper limb muscle volume) 1

• Rotator cuff:
  • Supraspinatus: Abducts arm, stabilizes humeral head
  • Infraspinatus: External rotation, stabilization
  • Teres minor: External rotation, stabilization
  • Subscapularis: Internal rotation, stabilization
• Deltoid: Largest volume fraction (15.2%) 1, primary abductor with three parts:
  • Anterior: Flexion, internal rotation
  • Middle: Abduction
  • Posterior: Extension, external rotation
• Other shoulder muscles:
  • Pectoralis major: Adduction, internal rotation
  • Latissimus dorsi: Extension, adduction, internal rotation
  • Teres major: Extension, adduction, internal rotation

Arm Muscles

• Anterior compartment:
  • Biceps brachii: Elbow flexion, supination
  • Brachialis: Primary elbow flexor
  • Coracobrachialis: Adduction, flexion of shoulder
• Posterior compartment:
  • Triceps brachii: Primary elbow extensor

Forearm Muscles (31.4% of upper limb muscle volume) 1

• Anterior compartment (flexors):
  • Superficial layer: Pronator teres, flexor carpi radialis, palmaris longus, flexor carpi ulnaris
  • Intermediate layer: Flexor digitorum superficialis
  • Deep layer: Flexor digitorum profundus, flexor pollicis longus, pronator quadratus
• Posterior compartment (extensors):
  • Superficial layer: Brachioradialis, extensor carpi radialis longus/brevis, extensor digitorum, extensor digiti minimi, extensor carpi ulnaris
  • Deep layer: Supinator, abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, extensor indicis

Hand Muscles (16.0% of upper limb muscle volume) 1

• Thenar muscles: Abductor pollicis brevis, flexor pollicis brevis, opponens pollicis
• Hypothenar muscles: Abductor digiti minimi, flexor digiti minimi brevis, opponens digiti minimi
• Midpalmar muscles: Lumbricals (4), dorsal interossei (4), palmar interossei (3)

Vascular Supply

Arterial Supply

• Subclavian artery: Gives rise to axillary artery
• Axillary artery: Continues as brachial artery at lower border of teres major
  • Branches: Superior thoracic, thoracoacromial, lateral thoracic, subscapular, anterior/posterior circumflex humeral
• Brachial artery: Main artery of arm
  • Branches: Profunda brachii, superior/inferior ulnar collateral
  • Bifurcates into radial and ulnar arteries at cubital fossa
• Radial artery: Lateral forearm, forms deep palmar arch
• Ulnar artery: Medial forearm, forms superficial palmar arch
• Palmar arches: Anastomoses between radial and ulnar arteries
  • Superficial palmar arch: Primarily from ulnar artery
  • Deep palmar arch: Primarily from radial artery

Venous Drainage

• Superficial veins:
  • Cephalic vein: Lateral aspect, drains into axillary vein
  • Basilic vein: Medial aspect, joins brachial veins to form axillary vein
  • Median cubital vein: Connects basilic and cephalic veins at cubital fossa
• Deep veins: Generally paired, accompany corresponding arteries
  • Radial veins
  • Ulnar veins
  • Brachial veins
  • Axillary vein
  • Subclavian vein

Nerve Supply

Brachial Plexus

• Roots: C5-T1
• Trunks: Upper (C5-C6), Middle (C7), Lower (C8-T1)
• Divisions: Anterior and posterior divisions of each trunk
• Cords: Lateral, Posterior, Medial (named by relationship to axillary artery)

Major Terminal Branches

• Musculocutaneous nerve: Supplies anterior arm muscles
• Median nerve: Supplies most anterior forearm muscles and thenar muscles
• Ulnar nerve: Supplies flexor carpi ulnaris, medial half of flexor digitorum profundus, most intrinsic hand muscles
• Radial nerve: Supplies posterior compartments of arm and forearm
• Axillary nerve: Supplies deltoid and teres minor

Clinical Significance

• Thoracic outlet syndrome: Compression of neurovascular structures at the thoracic outlet, affecting upper limb function 2
• Upper limb deep vein thrombosis: Can occur in axillary or subclavian veins, requiring prompt diagnosis 2
• Rehabilitation after stroke: Upper limb function is critical for activities of daily living; various therapeutic approaches can improve outcomes 2
• Wrist injuries: Common in upper limb trauma, requiring appropriate imaging and management 3

Imaging Considerations

• MRI: Excellent for soft tissue evaluation, including muscles, tendons, and ligaments 2
• CT: Provides detailed bone imaging, useful for fracture evaluation 2
• Ultrasound: Valuable for examining tendons, guiding injections 3
• CTA/MRA: For vascular assessment in suspected arterial or venous pathology 2

Understanding the detailed anatomy of the upper limb is essential for clinicians to accurately diagnose and treat various musculoskeletal, neurovascular, and traumatic conditions affecting this complex structure.