Osteology of the Upper Limb: Clavicle Overview

Osteology of the Upper Limb

• The clavicle is a long bone with no medullary (bone marrow) cavity.
• It serves as a rigid support for the scapula and free upper limb, transmits forces from the upper limb to the axial skeleton, and provides attachment for muscles.
• The clavicle has two ends: the medial (sternal) end is enlarged and triangular, while the lateral (acromial) end is flattened.
• The medial 2/3 of the shaft is convex forward, while the lateral 1/3 is concave forward.
• The clavicle has two surfaces: the superior surface is smooth, and the inferior surface is rough due to attachment of ligaments and muscles.
• The clavicle articulates with two bones: the sternum forming the sternoclavicular joint and the acromion of the scapula forming the acromioclavicular joint.
• Fractures of the clavicle are relatively more common, especially in slender children.
• The weakest part of the clavicle is the junction between the middle and lateral one-thirds, which is the site for most fractures of the clavicle.
• Fractures of the clavicle can also occur during childbirth, especially in babies with broad shoulders. However, these fractures heal quickly.
• The scapula is a large triangular flat bone that overlies between the 2nd and 7th ribs.
• The scapula gives attachment to muscles and allows for a considerable degree of movement on the thoracic wall to enable the arm to move freely.
• The scapula has two surfaces: the costal (concave anterior) surface forms the large subscapular fossa, and the posterior surface is divided by the spine of the scapula into the smaller supraspinous fossa above the spine and the larger infraspinous fossa below the spine.
• The scapula also includes a head and neck, a glenoid fossa with a tubercle above and below it, and three processes: the coracoid process, acromion, and spine.
• The scapula has three borders: the medial (vertebral) border, lateral (axillary) border, and superior border.
• The scapula has three angles: the superior angle, inferior angle, and lateral angle.
• The scapula has four fossae: subscapular fossa, supraspinous fossa, infraspinous fossa, and glenoid fossa/cavity.
• The scapula articulates with two bones: the clavicle and humerus.
• The acromion of the scapula articulates with the lateral end of the clavicle forming the acromioclavicular joint.
• The glenoid fossa (cavity) articulates with the head of the humerus forming the gleno-humeral joint.
• Fractures of the scapula are uncommon because it is well protected by muscles and the thoracic wall.
• Most fractures involve the protruding acromion, the most subcutaneous part of the scapula.
• The humerus is a long bone that allows for a wide range of movement, transmits forces down to other parts of the upper limb, and provides attachment for muscles.
• The humerus has two ends: proximal and distal ends (epiphysis) and a shaft (diaphysis).
• The proximal end of the humerus is composed of the head, two necks (anatomical and surgical necks), and two tubercles (greater and lesser tubercles).
• The head of the humerus is hemispherical, smooth, and rounded.
• The anatomical neck is formed by a groove separating the head from the tubercles.
• The surgical neck is the narrow part distal to the tubercles.
• The greater tubercle of the humerus is large and projects on the lateral margin of the humerus.
• The lesser tubercle is small and projects anteriorly.
• The radius is the lateral and shorter bone of the forearm.
• The radius stabilizes the forearm and provides attachment for muscles.
• The radius has a head proximally, a shaft (diaphysis) in the middle, and a styloid process distally.
• The head of the radius is small and circular with an upper surface that’s concave for articulation with the capitulum.
• The neck of the radius is narrowed and connects the head with the shaft.
• The shaft of the radius is cylindrical, narrow superiorly, and widens inferiorly.
• The shaft has three surfaces: anterior, posterior, and lateral.
• The radial tuberosity is medially directed and separates the proximal end from the body.
• The distal radius is expanded and has four distinct surfaces: lateral, medial, posterior, and anterior.
• The radial styloid process projects from the lateral side of the distal end.
• The radius articulates with the humerus proximally, the ulna, and the carpal bones distally.
• The radius articulates with the humerus to form the elbow joint. The head of the radius enters into the radial fossa of the humerus on full flexion.
• The radius articulates with the ulna at proximal and distal radio-ulna joints, allowing for the pronation and supination movement.
• The radius articulates with the carpal bones (scaphoid and lunate) forming part of the wrist joint.
• The ulna is the medial and longer bone of the forearm.
• The ulna stabilizes the forearm and provides attachment for muscles.
• The ulna has a proximal part, shaft (diaphysis), and head distally.
• The proximal end of the ulna has two prominent projections (processes): the coronoid and olecranon processes.
• The olecranon process projects proximally from the posterior aspect. It’s large and has two surfaces: the posterior surface, which is smooth and subcutaneous, and the anterior surface, which is concave.
• The coronoid process is small and projects anteriorly. It forms the inferior part of the trochlear notch.
• The proximal end of the ulna has two notches: the trochlear and radial notch.
• The trochlear notch articulates with the trochlea of the humerus.
• The radial notch is a smooth rounded concavity lateral to the coronoid process, which articulates with the head of the radius to form the proximal radio-ulna joint.
• The shaft of the ulna is cylindrical, broad superiorly, and narrow inferiorly.
• The shaft has three surfaces: anterior, posterior, and medial.
• The distal end of the ulna has a small rounded head connected to the shaft by the neck.
• The ulna styloid process projects from the medial side of the head.
• The ulna articulates with the humerus, the trochlea of the humerus articulates with the trochlea notch of the ulna to form the elbow joint.
• The ulna articulates with the radius at proximal and distal radio-ulna joints, allowing for the pronation and supination movement.
• The ulna articulates with the carpal bones forming part of the wrist joint.
• At the elbow joint, the coronoid process of the ulna enters into the coronoid fossa of the humerus on full flexion, while the olecranon process of the ulna enters into the olecranon fossa of the humerus on full extension.
• The articulations between the ulna and humerus at the elbow joint allow primarily only flexion and extension, but a small amount of abduction and adduction occurs.
• Colle’s fracture is a transverse fracture within the distal 2 cm of the radius and is the most common fracture of the forearm.
• The radial styloid process is longer than that of the ulna, but in Colle’s fracture, it is reversed due to shortening of the radius.
• The hand is composed of the carpals (wrist), metacarpals (palm), and phalanges (fingers).
• The carpal bones are the bones of the wrist and are eight in number, arranged into two rows of four bones each.
• The metacarpals are the bones of the palm and each has a base proximally, a shaft (body), and a rounded head distally.
• The shape of the bases of the metacarpals varies and is distinct in all metacarpal bones.
• The shaft of the metacarpals is slightly curved with a longitudinal palmar concavity.
• The head of the metacarpals is smooth and rounded, articulating with the concavity on the base of the proximal phalanx forming metacarpophalangeal joints.
• The head of the first metacarpal is wider than the others.
• The metacarpals articulate with carpal bones forming the carpometacarpal joint and with the proximal phalanx forming the metacarpophalangeal joints.
• The phalanges are long bones, 14 in number in each hand, with three for each finger (2nd to 5th digits) and two for the thumb (1st digit).
• The phalanges of the thumb are shorter and broader than those of the fingers.
• Each phalanx has a base, shaft (body), and head.
• The base of the phalanx is large, proximal, and concave oval, articulating with the rounded head of the metacarpal.
• The shaft of the phalanx is curved along its length and is convex dorsally.
• The head of the phalanx is rounded and articulates with the base of the next phalanx.
• Boxer’s fracture is a fracture of the neck of the 1st and 2nd metacarpals, which heals rapidly due to good blood supply.
• Crushing injuries of the hand can lead to multiple metacarpal fractures, causing instability of the hand.
• Crushing injuries to the phalanges can be extremely painful due to developed sensation from nerves.
• Fractures of the distal phalanx are usually commuted and painful with a painful hematoma developing.

This quiz explores the osteology of the clavicle, detailing its structure, functions, and articulations. Understand the significance of this bone in the upper limb's anatomy and its role in common fractures. Test your knowledge on the clavicle's unique features and its connection to surrounding bones and muscles.