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Introduction
The bones of the upper limb enable a wide range of movements essential for daily activities and tasks. These bones can be divided into four functional components: the shoulder girdle, arm, forearm and hand.
The skeletal structure consists of the clavicle and scapula in the shoulder girdle, the humerus in the arm, the radius and ulna in the forearm, and the intricate bones of the wrist and hand.
The shoulder girdle
The shoulder girdle plays a crucial role in connecting the upper limb to the axial skeleton. It comprises two bones: the clavicle and the scapula.
The primary function of the shoulder girdle is to facilitate actions such as lifting, pushing, pulling, and rotating the upper limb. It achieves this through articulation with the sternum at the sternoclavicular joint and with the humerus at the glenohumeral joint.
Clavicle
The clavicle is a S-shaped bone positioned horizontally across the top of the thorax, connecting the sternum at its medial end to the scapula at its lateral end. The clavicle acts as a strut, maintaining the shoulder’s position away from the thorax.
It serves as an attachment point for several muscles whilst also protecting neurovascular structures that pass beneath it.
The clavicle can be divided into three main anatomical areas: the sternal end, shaft and acromial end.
The sternal end
The sternal end of the clavicle is the medial third of the bone and is characterised by its broader, roughly triangular shape.
The sternal end features a concave, oval-shaped facet that articulates with the clavicular notch of the manubrium and the first costal cartilage, forming the sternoclavicular joint. The articular surface is covered with hyaline cartilage.
Inferiorly, the sternal end has a roughened area known as the costal tuberosity, where the costoclavicular ligament attaches. This ligament stabilises the joint by anchoring the clavicle to the first rib.
The shaft
The shaft of the clavicle constitutes the middle third of the bone, connecting the two ends and accounting for the majority of the bone’s length. Several muscles attach to the shaft of the clavicle: sternocleidomastoid, pectoralis major, subclavius, deltoid, trapezius, and sternohyoid.
The superior surface is palpable subcutaneously and provides the attachment site for the platysma muscle.
The inferior surface is marked by the subclavian groove, a shallow depression where the subclavius muscle inserts.
The acromial end
The acromial end of the clavicle constitutes the lateral third of the bone, articulating with the acromion process of the scapula to form the acromioclavicular (AC) joint.
The acromial end of the clavicle is broader and flatter compared to the medial third.
The inferior surface features the conoid tubercle, a roughened area for the attachment of the conoid ligament. The trapezoid ligament attaches laterally to this at the trapezoid line; together, these ligaments form the coracoclavicular ligament.
The acromioclavicular ligament attaches to the convex distal clavicle.
Clinical relevance: clavicular fractures
Fractures typically occur in the middle third (the shaft) of the clavicle, where the bone’s curvature and the absence of ligamentous reinforcement create a biomechanical weak point.
Scapula
The scapula, commonly known as the shoulder blade, is a flat, triangular-shaped bone located on the posterior aspect of the thoracic cage.
The scapula articulates with the humerus at the glenohumeral joint and with the clavicle at the acromioclavicular joint.
The scapula can be divided into three main anatomical areas: the costal surface, the lateral surface and the posterior surface.
The medial border of the scapula runs parallel to the vertebral column and serves as an attachment point for muscles such as the serratus anterior and rhomboids. The lateral (axillary) border leads toward the glenoid cavity, providing attachment points for the teres major and minor muscles. The superior border features the scapular notch, which allows the suprascapular nerve to pass through.
The costal surface
The costal surface of the scapula is smooth and concave in shape, facilitating a gliding movement over the thoracic wall anteriorly.
It is characterised by a large, shallow depression known as the subscapular fossa, which serves as the origin for the subscapularis muscle, one of the four rotator cuff muscles.
The coracoid process is a hook-shaped bony projection arising from the superolateral aspect of the costal surface, and acts as the attachment for coracobrachialis, the short head of the biceps brachii and pectoralis minor.
The lateral surface
The lateral surface plays a pivotal role in facilitating shoulder joint articulation.
The glenoid fossa is positioned at the superior part of the lateral surface. It is a shallow, pear-shaped depression that articulates with the humeral head, forming the ball-and-socket glenohumeral joint.
The infraglenoid tubercle is located inferior to the glenoid fossa and is the origin of the long head of the triceps brachii muscle.
The supraglenoid tubercle is located superior to the glenoid fossa, and it provides attachment for the long head of the biceps brachii muscle.
The posterior surface
Central to this surface is the spine of the scapula, a ridge-like structure that divides the posterior surface into two distinct regions: the supraspinous fossa superiorly and the infraspinous fossa inferiorly.
The supraspinous fossa serves as the origin for the supraspinatus muscle, a rotator cuff muscle.
The larger infraspinous fossa provides attachment for the infraspinatus muscle, another rotator cuff muscle.
Laterally, the spine culminates in the acromion process, a bony projection that articulates with the clavicle at the acromioclavicular joint, forming the superior aspect of the shoulder.1
The arm
Humerus
The humerus is the long bone of the upper arm, extending from the shoulder to the elbow. It can be divided into three main anatomical areas: the proximal end, shaft and distal end.
The proximal end
The proximal end of the humerus, together with the scapula, forms the shoulder joint.
The proximal head of the humerus consists of a head, greater and lesser tuberosities, intertubercular sulcus, anatomical neck and surgical neck.
Head of humerus
The head of the humerus is a smooth, hemispherical surface located at the proximal end of the humerus and articulates with the glenoid fossa to form the glenohumeral joint.
The greater tuberosity
The greater tuberosity is a palpable projection situated on the lateral aspect of the humeral head. It serves as the attachment site for three of the four rotator cuff muscles: supraspinatus (attaches to the superior facet), infraspinatus (attaches to the middle facet) and teres minor (attaches to the inferior facet).
The lesser tuberosity
The lesser tuberosity is an anteriorly positioned prominence located on the humerus and provides the attachment for the subscapularis muscle.
The intertubercular sulcus
Separating the greater and lesser tuberosities is the intertubercular groove. This groove accommodates the tendon of the long head of the biceps brachii muscle as it travels from the shoulder to its insertion point on the radial bone.
The anatomical neck
The anatomical neck of the humerus is located immediately distal to the head of the humerus. It forms a subtle groove encircling the articular surface of the humeral head and is the attachment site for the fibrous capsule of the shoulder joint.
The surgical neck
The surgical neck of the humerus is located distal to the tubercles. The surgical neck marks the transition between the humeral head and the shaft.
Clinical relevance: humerus fracture
The surgical neck of the humerus is more prone to fractures than the anatomical neck. It is narrower and structurally vulnerable to the mechanical forces exerted during trauma. Fractures at the surgical neck are clinically significant because of the nearby axillary nerve and the posterior circumflex humeral artery, both of which can be compromised.
The shaft
The shaft of the humerus is cylindrical in shape.
The deltoid tuberosity is located laterally and is the insertion point of the deltoid muscle.
The radial groove runs obliquely along the posterior aspect of the shaft. This shallow groove accommodates the radial nerve and the deep brachial artery.
The distal end
The distal end of the humerus articulates with the bones of the forearm, the radius and ulna, at the elbow joint.
The distal anterior humerus comprises two prominent condylar structures: the capitulum and the trochlea. The capitulum, located laterally, articulates with the head of the radius. The trochlea, positioned medially, articulates with the trochlear notch of the ulna. The coronoid fossa is an anterior depression that lies superior to the trochlea, which receives the coronoid process of the ulna during flexion of the elbow.
The radial fossa lies superior to the capitulum, allowing space for the radial head during elbow flexion.
Flanking the articulating surfaces are the medial and lateral epicondyles, bony prominences that serve as attachment sites for muscles and ligaments of the forearm. The medial epicondyle is more pronounced and provides attachment for the flexor muscles of the forearm, whereas the lateral epicondyle serves as the origin for extensor muscles.2
The distal humerus also features the olecranon fossa, a posterior depression that accommodates the olecranon process of the ulna during elbow extension.
The forearm
The forearm contains two parallel bones: the radius and the ulna. These bones articulate proximally with the humerus at the elbow and distally with the carpal bones of the wrist.
Radius
The radius is the lateral bone of the two long bones of the forearm. It can be divided into three anatomical areas: the proximal end, the shaft and the distal end.
The proximal end
The proximal end of the radius plays a crucial role in the complex movements of the forearm and elbow joint, contributing to both flexion, extension, pronation and supination.
The radial head is the most superior part of the proximal radius. It is a disc-shaped structure with a concave superior articular surface. This surface articulates with the capitulum of the humerus to form the radiocapitellar joint and also with the radial notch of the ulna to form the proximal radioulnar joint.
Distal to the head is the neck of the radius.
On the medial aspect of the radius, distal to the radial neck, the radial tuberosity serves as the insertion point for the biceps brachii muscle.
The shaft
The shaft of the radius is cylindrical in its upper third and becomes more triangular in its middle and distal thirds. The bone’s surface exhibits three distinct borders (anterior, posterior, and interosseous) and three surfaces (anterior, posterior, and lateral), each serving as attachment sites for muscles and ligaments.3
The distal end
At the distal end, the radius widens and flattens, featuring a concave, smooth surface that articulates with the scaphoid and lunate bones of the carpus to form the radiocarpal joint.
The styloid process is a bony projection on the lateral aspect of the distal radius.
The ulnar notch is located on the medial side of the distal radius. Its concave surface articulates with the head of the ulna, forming the distal radioulnar joint, allowing for supination and pronation of the forearm.
Clinical relevance: distal radius fracture
The distal radius is prone to fractures, especially from falls onto an outstretched hand (FOOSH). Patients typically experience wrist pain, swelling, deformity, and reduced hand function. In some cases, median nerve compression may cause numbness in the thumb and fingers.
A Colles’ fracture is a break in the distal radius, occurring 2–3 cm from the wrist joint. It is characterised by the dorsal displacement of the distal fragment of the radius, creating a ‘dinner fork’ deformity.
Ulna
The ulna is the medial bone of the two long bones of the forearm. It can be divided into three anatomical areas: the proximal end, the shaft and the distal end.
The proximal end
The proximal end of the ulna plays an essential role in elbow articulation, and is characterised by several distinct anatomical features:
- Olecranon process: a curved bony projection forms the posterior aspect of the elbow, which serves as the insertion point for the triceps brachii muscle
- Coronoid process: a triangular eminence projecting anteriorly, providing attachment for the brachialis muscle
- Trochlear notch: a C-shaped concavity that lies between the olecranon and coronoid processes, and articulates with the trochlea of the humerus, allowing hinge-like flexion and extension of the elbow joint
- Radial notch: situated on the lateral aspect of the coronoid process and accommodates the head of the radius, forming the proximal radioulnar joint
- Ulnar tuberosity: distal to the coronoid process and serves as the attachment site for the brachialis muscle
- Supinator crest: on the lateral surface and provides attachment for the supinator muscle
The shaft
The shaft of the ulna is slender and triangular. The bone’s surface exhibits three distinct borders (anterior, posterior, and interosseous) and three surfaces (anterior, posterior, and medial), each serving as attachment sites for muscles and ligaments.
The distal end
The ulnar head articulates with the ulnar notch of the radius and contributes to the distal radioulnar joint.
Extending from the ulnar head is the ulnar styloid process, a slender bony projection located posteromedially. The styloid process serves as an attachment site for the ulnar collateral ligament of the wrist, which provides medial stability to the wrist joint.
Clinical relevance: distal ulnar fracture
The ulna is prone to fractures, especially from falls onto an outstretched hand (FOOSH), causing forced pronation. These include:
- Nightstick fractures: an isolated ulnar diaphysis (shaft) fracture pattern caused by direct trauma to the forearm. Typically, a defensive injury when a person raises their forearm to protect themselves. The name originates from the action of blocking a nightstick (a weapon).
- Monteggia fracture-dislocations: where the proximal ulna is fractured, and the radial head dislocates. Radial head dislocations can cause injury to the posterior interosseous nerve (deep branch of the radial nerve).4
Editor
Dr Jamie Scriven
References
- Betts JG, Young KA, Wise JA, et al. 8.1 The Pectoral Girdle.Anatomy and Physiology 2e. Openstax. 2022. Available from: [LINK].
- Jones J, Yap J, Knipe H, et al. Humerus. Radiopedia. 2024. Available from: [LINK].
- Drake RL, Vogl AW, Mitchell AWM. Regional Anatomy: Forearm. Gray’s Anatomy for Students 3e. Churchill Livingstone. 2015.
- Hansen JT. Upper Limb. Netter’s Clinical Anatomy 4e. Elsevier. 2017.
Image references
- Figure 1. Betts JG, Young KA, Wise JA, et al. Figure 8.3 Pectoral Girdle. Anatomy and Physiology 2e. OpenStax. Adapted by Geeky Medics. Available from: [LINK]. Licence: [CC BY 4.0].
- Figure 2. Gaillard F. Clavicle fracture. Radiopaedia. Adapted by Geeky Medics. Available from: [LINK]. Licence: [CC BY-NC-SA 3.0].
- Figure 3. Betts JG, Young KA, Wise JA, et al. Figure 8.4 Scapula. Anatomy and Physiology 2e. OpenStax. Adapted by Geeky Medics. Available from: [LINK]. Licence: [CC BY 4.0].
- Figure 4. Betts JG, Young KA, Wise JA, et al. Figure 8.5 Humerus and Elbow Joint. Anatomy and Physiology 2e. OpenStax. Available from: [LINK]. Licence: [CC BY 4.0].
- Figure 5. Gaillard F. Surgical neck of humerus fracture. Radiopaedia. Available from: [LINK]. Licence: [CC BY-NC-SA 3.0].
- Figure 6. Betts JG, Young KA, Wise JA, et al. Figure 8.6 Ulna and Radius. Anatomy and Physiology 2e. OpenStax. Available from: [LINK]. Licence: [CC BY 4.0].
- Figure 7. Mackenzie R. Colles fracture. Radiopaedia. Available from: [LINK]. Licence: [CC BY-NC-SA 3.0].
- Figure 8. Botz B. Nightstick fracture. Radiopaedia. Available from: [LINK]. Licence: [CC BY-NC-SA 3.0].
- Figure 9. Radswiki T. Monteggia fracture dislocation. Radiopaedia. Available from: [LINK]. Licence: [CC BY-NC-SA 3.0].
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