Understanding anatomy of upper limb is crucial for medical students as it forms the foundation for diagnosing and treating upper limb disorders. The upper limb is an intricately structured region of the human body designed for a wide range of complex and precise movements. It consists of bones, joints, muscles, nerves, and vessels that work synergistically to carry out functional tasks.
1. Anatomy of Upper Limb: Osteology
The upper limb includes several bones: the clavicle, scapula, humerus, radius, ulna, and carpal bones.
Clavicle
- S-shaped bone connecting the axial skeleton to the appendicular skeleton.
- Acts as a strut between the sternum and the scapula.
- Fracture is common due to falls on an outstretched hand.
Scapula
- A flat triangular bone on the posterior thoracic wall.
- Provides attachment for numerous muscles including rotator cuff muscles.
- Contains important landmarks: spine, acromion, coracoid process, and glenoid cavity.
Humerus
- Long bone of the upper arm.
- Articulates with the scapula at the shoulder and with the radius and ulna at the elbow.
- Fractures may injure radial or axillary nerves.
Radius and Ulna
- Radius is lateral (thumb side); ulna is medial in anatomical position.
- They articulate with each other at both proximal and distal radioulnar joints, allowing supination and pronation.
Carpal Bones
- Eight small bones arranged in two rows.
- Identified easily in an articulated hand: scaphoid, lunate, triquetrum, pisiform (proximal row), and trapezium, trapezoid, capitate, hamate (distal row).
- The scaphoid is the most frequently fractured carpal bone.
2. Muscles of the Upper Limb
Muscles in the upper limb are grouped according to their location and function.
Pectoral and Scapular Muscles
- Include pectoralis major, pectoralis minor, subclavius, and serratus anterior.
- Deltoid is a key muscle responsible for arm abduction.
- Scapular muscles like the trapezius, levator scapulae, and rhomboids stabilize scapular movements.
Arm Muscles
- Flexor compartment: biceps brachii, brachialis, and coracobrachialis.
- Extensor compartment: triceps brachii and anconeus.
Forearm Muscles
- Flexors and pronators (anterior compartment): flexor carpi radialis, flexor digitorum superficialis, etc.
- Extensors and supinators (posterior compartment): extensor carpi ulnaris, extensor digitorum, etc.
Intrinsic Hand Muscles
- Thenar group: flexor pollicis brevis, abductor pollicis brevis, opponens pollicis.
- Hypothenar group: muscles of the little finger.
- Lumbricals and interossei: assist in fine finger movements.
3. Brachial Plexus
The brachial plexus is a network of nerves that supplies the upper limb.
- Formed by ventral rami of C5 to T1 spinal nerves.
- Divided into: Roots → Trunks → Divisions → Cords → Branches (mnemonic: Randy Travis Drinks Cold Beer).
- Major branches include: musculocutaneous, axillary, radial, median, and ulnar nerves.
- Clinical correlation: Injury to the brachial plexus may cause Erb’s or Klumpke’s palsy.
4. Arteries and Veins of the Upper Limb
Arterial Supply
- Subclavian artery becomes axillary artery, then brachial artery, which bifurcates into radial and ulnar arteries.
- Important branches: deep brachial, radial recurrent, and ulnar recurrent arteries.
Venous Drainage
- Superficial veins: cephalic (lateral) and basilic (medial), connected by the median cubital vein (common for venipuncture).
- Deep veins accompany the arteries as venae comitantes.
5. Venous Drainage and Lymphatics
- Superficial veins like the cephalic and basilic drain into the axillary vein.
- Lymphatic drainage is into the axillary lymph nodes, important in breast cancer spread.
6. Boundaries, Contents, and Clinical Aspects
Axilla
- Pyramidal space between the arm and thorax.
- Contents: axillary artery and vein, cords of brachial plexus, axillary lymph nodes.
- Clinical note: A site for lymph node biopsy and brachial plexus block.
Cubital Fossa
- Triangular depression in front of the elbow.
- Contents: biceps tendon, brachial artery, median nerve (from lateral to medial).
- Clinical significance: Site for venipuncture.
Carpal Tunnel
- Narrow passage in the wrist bounded by the flexor retinaculum.
- Contents: median nerve, flexor tendons.
- Carpal Tunnel Syndrome: Compression of median nerve causing pain and numbness.
7. Joints of the Upper Limb
Shoulder Joint (Glenohumeral Joint)
- Ball-and-socket joint with great mobility but less stability.
- Movements: flexion, extension, abduction, adduction, rotation.
- Muscles involved: deltoid, rotator cuff muscles, pectoralis major.
Elbow Joint
- Hinge joint formed by the humerus, radius, and ulna.
- Movements: flexion and extension.
- Muscles involved: biceps brachii, brachialis (flexion); triceps brachii (extension).
Radioulnar Joints
- Allow pronation and supination.
- Muscles involved: pronator teres, pronator quadratus, supinator, biceps brachii.
Wrist Joint
- Ellipsoid joint for flexion, extension, radial and ulnar deviation.
- Muscles involved: flexor carpi radialis/ulnaris, extensor carpi radialis longus/brevis, etc.
Hand Joints
- Metacarpophalangeal (MCP), proximal and distal interphalangeal joints.
- Muscles involved: intrinsic hand muscles for fine control.
Conclusion
Mastery of the upper limb anatomy for medical students is essential for understanding clinical presentations, surgical procedures, and diagnostic techniques. From the detailed architecture of bones and muscles to the sophisticated neurovascular supply and functional joints, the upper limb exemplifies structural complexity designed for versatility and precision. Future clinicians must develop a clear and thorough understanding of each component to appreciate its functional relevance and pathological variations.