Anatomy of the Upper Limb: Pectoral Girdle and Upper Extremity Bones & Joints

Upper Limb: Pectoral Girdle and Upper Extremity

Overview of the Pectoral Girdle

The pectoral girdle connects the upper limb to the axial skeleton and consists of the clavicle and scapula. It provides structural support and facilitates a wide range of movements for the arm.

• Clavicle: S-shaped bone that acts as a strut between the sternum and scapula.

• Scapula: Flat, triangular bone located on the posterior thoracic wall.

• Function: Stabilizes the shoulder and allows for arm mobility.

• Articulations: Sternoclavicular joint (clavicle-sternum), acromioclavicular joint (clavicle-scapula).

Clavicle Anatomy

The clavicle is easily palpable and serves as an attachment site for several muscles and ligaments.

• Medial (sternal) end: Articulates with the manubrium of the sternum.

• Lateral (acromial) end: Articulates with the acromion of the scapula.

• Functions: Transmits mechanical force from the upper limb to the axial skeleton; protects neurovascular structures.

• Common injuries: Fractures often occur at the junction of the middle and lateral thirds.

Scapula Anatomy

The scapula is a flat bone with several important landmarks for muscle attachment and articulation.

• Spine: Prominent ridge on the posterior surface.

• Acromion: Lateral extension of the spine; articulates with the clavicle.

• Coracoid process: Projects anteriorly; attachment for muscles and ligaments.

• Glenoid cavity: Shallow socket for the head of the humerus, forming the shoulder joint.

Bones of the Upper Limb

Humerus

The humerus is the largest bone of the upper limb, forming the arm between the shoulder and elbow.

• Head: Articulates with the glenoid cavity of the scapula.

• Greater and lesser tubercles: Sites for muscle attachment.

• Shaft: Contains the deltoid tuberosity for deltoid muscle attachment.

• Distal end: Forms the elbow joint with the ulna and radius.

Radius and Ulna

The radius and ulna are the two bones of the forearm, running parallel to each other.

• Radius: Located laterally (thumb side); rotates around the ulna during pronation/supination.

• Ulna: Located medially (little finger side); forms the major part of the elbow joint.

• Proximal ends: Head of radius articulates with the capitulum of the humerus; olecranon of ulna forms the elbow prominence.

• Distal ends: Radius articulates with carpal bones at the wrist; ulna has a smaller role in wrist articulation.

Carpal Bones

The wrist contains eight carpal bones arranged in two rows, allowing for flexibility and movement.

• Proximal row: Scaphoid, lunate, triquetrum, pisiform.

• Distal row: Trapezium, trapezoid, capitate, hamate.

• Function: Facilitate wrist movement and stability.

• Clinical relevance: Scaphoid is commonly fractured due to falls on an outstretched hand.

Metacarpals and Phalanges

The hand consists of five metacarpal bones and fourteen phalanges (finger bones).

• Metacarpals: Numbered I-V from thumb to little finger.

• Phalanges: Each finger has three (proximal, middle, distal) except the thumb, which has two.

Joints of the Upper Limb

Shoulder (Glenohumeral) Joint

The shoulder joint is a ball-and-socket synovial joint, allowing for a wide range of motion.

• Articulating surfaces: Head of humerus and glenoid cavity of scapula.

• Ligaments: Glenohumeral, coracohumeral, and transverse humeral ligaments stabilize the joint.

• Movements: Flexion, extension, abduction, adduction, rotation, circumduction.

• Clinical relevance: Prone to dislocation due to shallow glenoid cavity.

Elbow Joint

The elbow is a hinge-type synovial joint formed by the humerus, radius, and ulna.

• Articulations: Trochlea of humerus with trochlear notch of ulna; capitulum of humerus with head of radius.

• Ligaments: Ulnar collateral, radial collateral, and annular ligaments.

• Movements: Flexion and extension; pronation and supination of the forearm.

Wrist (Radiocarpal) Joint

The wrist joint is formed by the distal end of the radius and the proximal row of carpal bones (except the pisiform).

• Type: Condyloid synovial joint.

• Movements: Flexion, extension, abduction (radial deviation), adduction (ulnar deviation), circumduction.

Ligaments of the Upper Limb

Shoulder Ligaments

Ligaments stabilize the shoulder joint and prevent excessive movement.

• Glenohumeral ligaments: Reinforce the anterior aspect of the joint capsule.

• Coracohumeral ligament: Strengthens the superior part of the capsule.

• Transverse humeral ligament: Holds the tendon of the long head of the biceps brachii in place.

Elbow Ligaments

The elbow joint is stabilized by strong collateral ligaments.

• Ulnar collateral ligament: Medial support.

• Radial collateral ligament: Lateral support.

• Annular ligament: Encircles the head of the radius, allowing rotation.

Comparative Table: Bones of the Upper Limb

Bone	Location	Main Features	Articulations
Clavicle	Pectoral girdle	S-shaped, palpable, strut function	Sternum, scapula
Scapula	Pectoral girdle	Spine, acromion, coracoid process, glenoid cavity	Clavicle, humerus
Humerus	Arm	Head, tubercles, shaft, condyles	Scapula, radius, ulna
Radius	Forearm (lateral)	Head, neck, shaft, styloid process	Humerus, ulna, carpal bones
Ulna	Forearm (medial)	Olecranon, shaft, head, styloid process	Humerus, radius, carpal bones
Carpals	Wrist	Eight small bones, two rows	Radius, metacarpals
Metacarpals	Palm	Five bones, numbered I-V	Carpals, phalanges
Phalanges	Fingers	Proximal, middle, distal (except thumb)	Metacarpals

Key Terms and Definitions

• Pectoral girdle: Set of bones connecting the upper limb to the axial skeleton.

• Glenoid cavity: Shallow socket in the scapula for the humerus.

• Olecranon: Prominent projection of the ulna forming the elbow.

• Annular ligament: Ligament encircling the head of the radius.

• Pronation/Supination: Rotational movements of the forearm.

Examples and Clinical Applications

• Clavicle fracture: Commonly occurs from falls on the shoulder; may affect neurovascular structures beneath.

• Shoulder dislocation: Occurs when the humeral head is displaced from the glenoid cavity.

• Scaphoid fracture: May lead to avascular necrosis due to poor blood supply.

Formulas and Equations

While anatomy is primarily descriptive, biomechanics of the upper limb may use force equations:

• Torque (moment of force):

$\tau = F \times r$

• Where: $\tau$ = torque, $F$ = force, $r$ = distance from axis of rotation.

Additional info: Biomechanical equations are included for context, as upper limb movement involves force and lever principles.