Upper limb · Forearm
Ulna
The ulna is the medial bone of the forearm, on the little-finger side. Its large hooked upper end grips the trochlea of the humerus to form the main hinge of the elbow, while its small lower head lies beside the radius at the wrist.
- Latin (TA)
- Ulna
- Type
- Long bone: a shaft with two ends
- Side
- Paired — right and left
- Model size
- 25.5 cm longest
Showing a right bone. Rotate it to inspect every surface; switch sides to practise siding.
3D model: Z-Anatomy (CC BY-SA 4.0), derived from BodyParts3D © DBCLS (CC BY-SA 2.1 JP). Adapted by PharmaWallah. Credits & licence
Landmarks
16 of 16 marked on the modelTap a landmark to find it on the bone and read what it is.
The large, curved bony projection at the top of the ulna.
Where: Proximal end, posteriorly; forms the point of the elbow.
Why it matters: Insertion of triceps brachii; fits into the olecranon fossa of the humerus in full extension.
Related: Triceps brachii (insertion)
Viva: What inserts into the olecranon?
Marked on the model at the point Z-Anatomy places this label.
A shelf-like projection from the front of the upper end.
Where: Anterior aspect of the proximal end, below the trochlear notch.
Why it matters: Forms the lower part of the trochlear notch; fits into the coronoid fossa in full flexion; brachialis attaches to its front.
Marked on the model at the point Z-Anatomy places this label.
A large, deep, C-shaped articular notch formed by the olecranon and coronoid process.
Where: Front of the upper end, facing forwards.
Why it matters: Articulates with the trochlea of the humerus at the elbow; its forward-facing position is the key to siding.
Related: Elbow joint (humero-ulnar part)
Viva: What articulates with the trochlear notch?
Marked on the model at the point Z-Anatomy places this label.
A small, shallow articular notch.
Where: Lateral side of the coronoid process.
Why it matters: Articulates with the circumference of the head of the radius; the annular ligament is attached to its front and back margins.
Related: Proximal radioulnar joint
Marked on the model at the point Z-Anatomy places this label.
A rough area on the front of the bone just below the coronoid process.
Where: Anterior surface of the upper end of the shaft.
Why it matters: Insertion of brachialis.
Related: Brachialis (insertion)
Viva: What inserts into the tuberosity of the ulna?
Marked on the model at the point Z-Anatomy places this label.
The shaft, triangular in section and tapering downwards.
Where: Between the upper end and the head.
Why it matters: Its posterior border can be felt under the skin along its whole length, so it is a site of direct-blow fractures.
Marked on the model at the point Z-Anatomy places this label.
The sharp crest on the lateral side of the shaft.
Where: Lateral side of the shaft, facing the radius.
Why it matters: Attachment of the interosseous membrane; its lateral position helps side the bone.
Related: Interosseous membrane
Marked on the model at the point Z-Anatomy places this label.
The rounded border at the back of the shaft.
Where: Back of the shaft, from the olecranon to the styloid process; subcutaneous throughout.
Why it matters: Gives attachment to an aponeurosis shared by flexor carpi ulnaris, flexor digitorum profundus and extensor carpi ulnaris.
Marked on the model at the point Z-Anatomy places this label.
The small rounded lower end of the ulna.
Where: Distal end, forming the bump on the back of the wrist on the little-finger side.
Why it matters: Articulates with the ulnar notch of the radius; separated from the carpus by the articular disc.
Related: Distal radioulnar joint
Viva: Where is the head of the ulna?
Marked on the model at the point Z-Anatomy places this label.
A short, pointed projection from the lower end.
Where: Posteromedial side of the lower end; does not reach as far down as the radial styloid.
Why it matters: The articular disc attaches near its base; the ulnar collateral ligament of the wrist attaches to it.
Marked on the model at the point Z-Anatomy places this label.
Classification & region
Long bone: a shaft with two ends; large above and small below, the opposite of the radius.
- Upper (proximal) end
- Olecranon, coronoid process, trochlear notch, radial notch and tuberosity of ulna.
- Shaft (body)
- Triangular in section, with a sharp lateral interosseous border and a subcutaneous posterior border; tapers downwards.
- Lower (distal) end
- Small rounded head and the ulnar styloid process.
Hold it in the anatomical position
- Hold the bone vertically with the large hooked end (olecranon) at the top.
- Turn it so the trochlear notch faces forwards.
- The radial notch on the side of the coronoid process and the sharp interosseous border then face laterally, towards the radius.
Right or left? Side determination
- Upper end: the large hook-shaped end (olecranon and trochlear notch) is proximal; the small head is distal.
- Anterior: the trochlear notch faces forwards.
- Lateral: the radial notch (on the lateral side of the coronoid process) and the sharp interosseous border face laterally.
- Posterior: the posterior border of the shaft is rounded and subcutaneous; the styloid process at the lower end is posteromedial.
- With the trochlear notch in front and the radial notch lateral, the bone belongs to the side on which the radial notch points away from your midline.
Check yourself: switch the 3D model to “Left bone” and apply the same steps.
Articulations
- With the trochlea of humerus at the Elbow joint (humero-ulnar part) — Trochlear notch..
- With the head of radius at the Proximal radioulnar joint — Radial notch..
- With the ulnar notch of radius at the Distal radioulnar joint — Articular circumference of the head..
Muscle and ligament attachments
| Structure | Type | Where on the bone |
|---|---|---|
| Triceps brachii | insertion | Posterior part of the upper surface of the olecranon. |
| Brachialis | insertion | Tuberosity of ulna and front of the coronoid process. |
| Anconeus | insertion | Lateral side of the olecranon and upper posterior surface. |
| Flexor carpi ulnaris (ulnar head) | origin | Medial side of the olecranon and, by an aponeurosis, the posterior border. |
| Flexor digitorum profundus | origin | Upper anterior and medial surfaces. |
| Flexor digitorum superficialis (humero-ulnar head) and pronator teres (ulnar head) | origin | Medial side of the coronoid process. |
| Supinator | origin | Supinator crest and the hollow in front of it (with the lateral epicondyle and ligaments). |
| Pronator quadratus | origin | Lower part of the anterior surface. |
| Abductor pollicis longus, extensor pollicis longus and extensor indicis | origin | Posterior surface of the shaft. |
| Ulnar collateral ligament of the elbow | ligament | Coronoid process (sublime tubercle) and olecranon. |
| Annular ligament | ligament | Anterior and posterior margins of the radial notch. |
| Interosseous membrane | ligament | Interosseous border. |
| Articular disc (triangular fibrocartilage) | ligament | Near the base of the ulnar styloid process. |
Functions
- Forms the main hinge of the elbow with the trochlea of the humerus.
- Acts as the stable bone around which the radius rotates in pronation and supination.
- Gives attachment to triceps and brachialis (the main elbow extensor and flexor) and to many forearm muscles.
Clinical & practical relevance
- Fracture of the olecranon (from a fall on the point of the elbow) is often pulled apart by triceps.
- Monteggia fracture-dislocation: a fracture of the upper ulnar shaft with dislocation of the radial head.
- Isolated fracture of the ulnar shaft can follow a direct blow to the subcutaneous posterior border, for example when the forearm is raised to protect the head ("nightstick" fracture).
- Posterior dislocation of the elbow may be accompanied by fracture of the coronoid process.
- The ulnar nerve, after passing behind the medial epicondyle of the humerus, enters the forearm close to the medial side of the ulna between the heads of flexor carpi ulnaris.
Identification tips
- Think of the upper end as a spanner: the trochlear notch is the jaw that grips the trochlea, and it faces forwards.
- Radius and ulna are opposites: the ulnar head is at the wrist, the radial head at the elbow.
- The posterior border can be felt along your own forearm from elbow to wrist.
Common student mistakes
- Calling the olecranon the head of the ulna. The head is at the lower end.
- Placing the radial notch on the medial side: it is lateral, facing the radius.
- Saying biceps inserts on the ulna: biceps inserts on the radial tuberosity; brachialis on the ulnar tuberosity.
Common exam questions
How do you side an ulna?Show answer
Hooked end upwards, trochlear notch forwards, radial notch and interosseous border lateral.
What inserts into the olecranon and the tuberosity of the ulna?Show answer
Triceps into the olecranon; brachialis into the tuberosity.
What articulates with the radial notch of the ulna?Show answer
The articular circumference of the head of the radius.
Where is the head of the ulna?Show answer
At its lower (distal) end.
Does the ulna take part in the wrist joint?Show answer
Not directly; its head is separated from the carpal bones by the articular disc.
What is a Monteggia fracture?Show answer
A fracture of the upper third of the ulnar shaft with dislocation of the head of the radius.
What attaches to the margins of the radial notch?Show answer
The annular ligament.
Revision summary
- Medial forearm bone; large hook above, small head below.
- Trochlear notch anterior; radial notch lateral.
- Olecranon: triceps. Tuberosity of ulna: brachialis.
- Radial notch: proximal radioulnar joint; annular ligament on its margins.
- Head: distal radioulnar joint; separated from carpus by the articular disc.
- Styloid posteromedial; shorter than the radial styloid.
- Monteggia: ulnar shaft fracture + radial head dislocation.
Test yourself on the ulna
Spotting questions on bones, sides and landmarks — untimed, with explanations.
Joints of the ulna
References
- Drake RL, Vogl AW, Mitchell AWM. Gray's Anatomy for Students. 5th ed. Philadelphia: Elsevier; 2023.
- Moore KL, Dalley AF, Agur AMR. Moore's Clinically Oriented Anatomy. 9th ed. Philadelphia: Wolters Kluwer; 2023.
- Federative International Programme for Anatomical Terminology (FIPAT). Terminologia Anatomica. 2nd ed. FIPAT.library.dal.ca; 2019. fipat.library.dal.ca/TA2
- Kervyn G, Zielinski M, Vinent L, et al. Z-Anatomy: the libre 3D atlas of anatomy. Models derived from BodyParts3D, The Database Center for Life Science (CC BY-SA 2.1 JP). CC BY-SA 4.0. www.z-anatomy.com/
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