Paralysis

Upper Limb Anatomy

The upper limb is a complex and highly mobile part of the human body, designed for a wide range of movements and functions such as grasping, holding, and manipulating objects. It consists of bones, muscles, nerves, blood vessels, and lymphatics that work in harmony to perform these functions. A thorough understanding of upper limb anatomy is essential for medical students, clinicians, and surgeons to diagnose and manage various musculoskeletal and neurovascular conditions.

Introduction

The upper limb extends from the shoulder girdle to the fingertips. It is divided into four major parts:

• Shoulder (pectoral girdle)
• Arm (brachium)
• Forearm (antebrachium)
• Hand (manus)

This section will focus primarily on the bones, muscles, nerves, arteries, and lymphatics of the upper limb, with special emphasis on their anatomical relationships, functions, and clinical relevance.

Bones of the Upper Limb

Clavicle

The clavicle, also known as the collarbone, is a long bone that serves as a strut between the sternum and the scapula. It is S-shaped and palpable subcutaneously along its entire length.

• Function: Provides support to the shoulder, transmits shocks from the upper limb to the axial skeleton.
• Articulations: Sternoclavicular joint medially, acromioclavicular joint laterally.

Scapula

The scapula (shoulder blade) is a flat, triangular bone that articulates with the clavicle and humerus. It lies on the posterior thoracic wall, over ribs 2-7.

• Features: Spine, acromion, coracoid process, glenoid cavity, subscapular fossa.
• Function: Serves as an attachment site for muscles and facilitates shoulder movements.

Humerus

The humerus is the long bone of the arm. It extends from the shoulder to the elbow joint.

• Features: Head (articulates with glenoid cavity), greater and lesser tubercles, deltoid tuberosity, medial and lateral epicondyles.
• Function: Facilitates arm movements and provides attachment points for muscles.

Forearm Bones

The forearm consists of two long bones:

• Ulna: Medial (ulnar) side, larger proximally, forms the elbow joint with the humerus.
• Radius: Lateral (radial) side, involved in wrist movements.

Both bones are connected by the interosseous membrane, allowing for forearm rotation.

Hand (Carpus, Metacarpus, Phalanges)

The hand comprises:

• Carpal bones: 8 small bones forming the wrist.
• Metacarpal bones: 5 bones forming the palm.
• Phalanges: 14 bones forming the fingers (proximal, middle, distal; except thumb which has only proximal and distal).

Muscles of the Upper Limb

Superficial Muscles

Superficial muscles are primarily responsible for movements of the shoulder, arm, and forearm. They include:

• Deltoid: Abducts, flexes, and extends the shoulder.
• Pectoralis Major: Adducts and medially rotates the humerus.
• Pectoralis Minor: Stabilizes the scapula.
• Latissimus Dorsi: Extends, adducts, and medially rotates the shoulder.
• Teres Major: Assists in adduction and medial rotation.
• Supraspinatus, Infraspinatus, Teres Minor, Subscapularis: Rotator cuff muscles involved in stabilizing the shoulder joint and rotating the humerus.

Deep Muscles

Deep muscles include the intrinsic muscles of the hand, flexors, extensors, and muscles involved in finer movements.

• Biceps Brachii: Flexes the elbow and supinates the forearm.
• Brachialis: Primary flexor of the elbow.
• Triceps Brachii: Extends the elbow.
• Flexor and Extensor Groups: Responsible for wrist and finger movements.

Nerves of the Upper Limb

Brachial Plexus

The brachial plexus is a network of nerves originating from spinal nerve roots C5 to T1, providing motor and sensory innervation to the upper limb.

• Roots and Trunks: C5-T1 roots combine to form upper, middle, and lower trunks.
• Divisions and Cords: Trunks divide into anterior and posterior divisions, which form lateral, posterior, and medial cords.
• Branches: Major terminal branches include the musculocutaneous, axillary, median, radial, and ulnar nerves.

Major Nerves and Their Functions

• Musculocutaneous Nerve: Flexes the elbow, supplies lateral forearm skin.
• Axillary Nerve: Supplies deltoid and teres minor muscles, shoulder skin.
• Radial Nerve: Extends the wrist and fingers, supplies posterior arm and forearm.
• Median Nerve: Flexor muscles of the forearm, thenar muscles, lateral palm skin.
• Ulnar Nerve: Medial hand muscles, sensation over medial hand.

Blood Supply of the Upper Limb

Subclavian Artery

The subclavian artery becomes the axillary artery at the lateral border of the first rib.

Axillary Artery

Continuing from the subclavian, it supplies the shoulder and chest wall. It gives off several branches including the thoracoacromial and lateral thoracic arteries.

Brachial Artery

Continuation of the axillary artery at the lower border of teres major. It supplies the arm and divides at the elbow into radial and ulnar arteries.

Radial and Ulnar Arteries

Supply the forearm and hand, forming the superficial and deep palmar arches.

Lymphatic Drainage

The lymphatic system drains the upper limb primarily into the axillary lymph nodes, which are grouped into humeral, pectoral, subscapular, central, and apical nodes. These nodes are vital in immune response and metastatic pathways in cancers.

Joint Articulations

Glenohumeral Joint

Ball-and-socket joint between the head of the humerus and the glenoid cavity of the scapula. It allows wide range of movements but is inherently unstable.

Elbow Joint

Hinge joint formed by the humerus, radius, and ulna, permitting flexion and extension.

Wrist Joint

Ellipsoid joint between the radius and carpal bones, allowing flexion, extension, abduction, and adduction.

Carpometacarpal and Interphalangeal Joints

Allow movements of the fingers and thumb essential for grasping and manipulation.

Clinical Correlations

• Fractures of the Clavicle: Common in falls, may damage underlying neurovascular structures.
• Rotator Cuff Injuries: Tendon tears, impingement syndromes affecting shoulder stability and movement.
• Deltoid Muscle Paralysis: Due to axillary nerve injury, resulting in inability to abduct the arm.
• Crush Injuries to the Brachial Plexus: Leading to varying degrees of motor and sensory deficits.
• Vascular Injuries: Such as axillary artery damage causing ischemia.
• Nerve Compression Syndromes: Carpal tunnel syndrome involving median nerve compression.

Summary

The anatomy of the upper limb is intricate and functionally significant. Knowledge of the bones, muscles, nerves, blood vessels, and joints is essential for understanding both normal movements and pathological conditions. Mastery of this anatomy aids in clinical diagnosis, surgical interventions, and rehabilitation practices.