Pectoral Girdle and Upper Limb: Bones and Markings

Pectoral Girdle and Upper Limb: Overview

The pectoral girdle and upper limb are essential components of the human appendicular skeleton, providing support and mobility for the arms. This section covers the major bones of the shoulder and arm, including the scapula, clavicle, humerus, radius, and ulna, along with their key anatomical features.

Scapula

Structure and Key Features

• Scapula (shoulder blade) is a flat, triangular bone located on the posterior side of the ribcage.

• It connects the humerus (upper arm bone) with the clavicle (collarbone).

• Major landmarks include:

  • Spine: A prominent ridge running across the posterior surface.

  • Acromion: Lateral extension of the spine, forms the highest point of the shoulder.

  • Coracoid process: Anterior projection for muscle attachment.

  • Glenoid cavity: Shallow socket that articulates with the head of the humerus to form the shoulder joint.

  • Supraspinous and infraspinous fossae: Depressions above and below the spine for muscle attachment.

  • Medial, lateral, and superior borders: Edges of the scapula.

Example: The glenoid cavity is crucial for the ball-and-socket movement of the shoulder joint.

Clavicle

Structure and Key Features

• Clavicle (collarbone) is an S-shaped bone that connects the sternum (breastbone) to the scapula.

• It acts as a strut to keep the upper limb away from the thorax, allowing for maximum range of motion.

• Major landmarks include:

  • Acromial end: Lateral, articulates with the acromion of the scapula.

  • Sternal end: Medial, articulates with the manubrium of the sternum.

  • Conoid tubercle: Inferior surface, attachment for the conoid ligament.

  • Superior and inferior surfaces: Provide attachment sites for muscles and ligaments.

Example: The clavicle is often fractured due to its subcutaneous position and role in force transmission from the upper limb to the trunk.

Humerus

Structure and Key Features

• Humerus is the long bone of the upper arm, extending from the shoulder to the elbow.

• It articulates proximally with the scapula and distally with the radius and ulna.

• Major landmarks include:

  • Head: Rounded, fits into the glenoid cavity of the scapula.

  • Anatomical and surgical necks: Sites of common fractures.

  • Greater and lesser tubercles: Muscle attachment points.

  • Deltoid tuberosity: Lateral surface, attachment for the deltoid muscle.

  • Medial and lateral epicondyles: Distal projections for muscle attachment.

  • Trochlea and capitulum: Articulate with the ulna and radius, respectively.

  • Olecranon fossa: Posterior depression for the olecranon of the ulna.

Example: The humerus is involved in both the shoulder and elbow joints, allowing for a wide range of arm movements.

Radius and Ulna

Structure and Key Features

• Radius and ulna are the two long bones of the forearm.

• The radius is lateral (thumb side), and the ulna is medial (little finger side) in the anatomical position.

• Major landmarks include:

  • Head of radius: Disc-shaped, articulates with the capitulum of the humerus.

  • Radial tuberosity: Attachment for the biceps brachii muscle.

  • Styloid process of radius: Lateral distal projection.

  • Olecranon: Proximal end of ulna, forms the point of the elbow.

  • Trochlear notch: Articulates with the trochlea of the humerus.

  • Coronoid process: Anterior projection of the ulna.

  • Ulnar tuberosity: Muscle attachment site.

  • Interosseous membrane: Connects the radius and ulna along their lengths.

Example: The radius rotates around the ulna during pronation and supination of the forearm, allowing the palm to turn up or down.

Summary Table: Major Bones and Key Markings

Bone	Key Markings	Function/Significance
Scapula	Spine, acromion, coracoid process, glenoid cavity, fossae	Muscle attachment, shoulder joint formation
Clavicle	Acromial end, sternal end, conoid tubercle	Connects upper limb to trunk, transmits force
Humerus	Head, tubercles, deltoid tuberosity, epicondyles, trochlea, capitulum	Arm movement, joint articulation
Radius	Head, radial tuberosity, styloid process	Forearm rotation, muscle attachment
Ulna	Olecranon, trochlear notch, coronoid process, ulnar tuberosity	Elbow joint formation, muscle attachment

Additional info: The pectoral girdle provides the only direct bony attachment of the upper limb to the axial skeleton, allowing for a high degree of mobility but less stability compared to the pelvic girdle.