[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Anatomy](https://durgical.com/en/anatomy/) › [Upper limb](https://durgical.com/en/anatomy/region/upper-limb/) › Ulna [Skeletal system](https://durgical.com/en/anatomy/system/skeletal-system/) · [Upper limb](https://durgical.com/en/anatomy/region/upper-limb/) # Ulna The ulna is the forearm bone on the little-finger side; it forms the elbow hinge and is the fixed post the radius turns around. [See in 3D →](https://durgical.app/?from=durgipedia&lang=en#region=upper_limb&select=ulna&side=r) Opens in the Durgical app, no sign-up needed. ## What it is The forearm bone on the little-finger side; its hook (olecranon) is the point of the elbow. ## What it does Forms the hinge of the elbow with the humerus and is the fixed post the radius turns around. ## Key points - Monteggia fracture: a proximal ulnar fracture with dislocation of the radial head; the dislocation is easily missed if the radiocapitellar line is not checked - Terrible triad of the elbow: posterior dislocation plus a radial head fracture and a coronoid process fracture, a very unstable injury - Ulnar variance (ulnar head length compared with the radius): positive variance is linked to ulnocarpal impaction and [TFCC](https://durgical.com/en/anatomy/triangular-fibrocartilage-complex/) wear, negative variance to Kienböck disease ## Key facts **Joints with** Humerus (trochlea), radius (proximal and distal radio-ulnar joints); separated from the carpus by the TFCC **Landmarks** Olecranon, coronoid process, trochlear and radial notches, ulnar tuberosity, head, styloid process ## Relations **Above** Olecranon with the [triceps tendon](https://durgical.com/en/anatomy/triceps-tendon/) and the [olecranon bursa](https://durgical.com/en/anatomy/olecranon-bursa/) over it; the trochlear notch wraps the trochlea of the [humerus](https://durgical.com/en/anatomy/humerus/) **In front** Coronoid process with the [brachialis](https://durgical.com/en/anatomy/brachialis/) on the ulnar tuberosity; FDP and [pronator quadratus](https://durgical.com/en/anatomy/pronator-quadratus/) on the front of the shaft; the [ulnar artery](https://durgical.com/en/anatomy/ulnar-artery/) and [ulnar nerve](https://durgical.com/en/anatomy/ulnar-nerve/) descend under the [flexor carpi ulnaris](https://durgical.com/en/anatomy/flexor-carpi-ulnaris/) **Medial** [UCL (elbow)](https://durgical.com/en/anatomy/ulnar-collateral-ligament-of-the-elbow/) on the sublime tubercle of the coronoid; the ulnar nerve passes into the forearm through the gap between the humeral and ulnar heads of flexor carpi ulnaris **Lateral** Radial notch for the radial head, held by the [annular ligament](https://durgical.com/en/anatomy/annular-ligament-of-the-radius/); the interosseous membrane to the [radius](https://durgical.com/en/anatomy/radius/); the [supinator](https://durgical.com/en/anatomy/supinator/) from the supinator crest **Behind** Subcutaneous posterior border along its whole length; [anconeus](https://durgical.com/en/anatomy/anconeus/) beside the olecranon; ECU in its groove next to the styloid process ## How to find it The olecranon is the point of the elbow, and the posterior border is followed under the [skin](https://durgical.com/en/anatomy/skin/) all the way to the wrist. The ulnar head is the rounded bump on the back of the little-finger side of the wrist with the forearm pronated; the styloid process lies just behind and distal to it. ## On imaging A true lateral of the elbow shows olecranon and coronoid fractures; forearm films include both the elbow and the wrist. Ulnar variance is measured on a PA wrist view taken in neutral rotation (shoulder abducted, elbow flexed to 90°), because pronation and grip make the ulna look longer. ## Common problems - Olecranon (elbow tip) fracture from a fall on the elbow. - Shaft fracture from a direct blow when raising the arm to protect the head ('nightstick' fracture). - Ulnar styloid fracture alongside a distal radius fracture. ## How it is diagnosed X-rays of the elbow, forearm and wrist (both forearm joints are always checked). ## Treatment - Cast or splint for stable, undisplaced fractures. - Surgery (wires, plate or screws) for displaced olecranon or shaft fractures. ## Clinical notes - Displaced olecranon fractures are pulled apart by the triceps and lose active elbow extension; the ulnar nerve lies close to the fixation - Fractures at the base of the ulnar styloid can involve the TFCC attachment at the fovea and destabilise the distal radio-ulnar joint - Coronoid fractures are a marker of a recent elbow dislocation or instability, even when the joint has gone back into place ## Anatomical variants - Ulnar variance differs between people and between ethnic groups, and changes with forearm rotation and grip - Congenital radio-ulnar synostosis is rare and often bilateral ## Development The olecranon centre appears around age 9–10 (the O of CRITOE) and may ossify from more than one piece; before it fuses in adolescence, the physis can be mistaken for a fracture, and a comparison view of the other elbow helps. ## Related conditions - [Forearm fractures (both-bone, Monteggia, Galeazzi)](https://durgical.com/en/conditions/forearm-fractures/) - [Elbow dislocation](https://durgical.com/en/conditions/elbow-dislocation/) - [Olecranon bursitis](https://durgical.com/en/conditions/olecranon-bursitis/) ## Test yourself Think of the answer, then tap the question to see it. ## What is a Monteggia fracture of the ulna, and what is easily missed? A proximal ulnar fracture with dislocation of the radial head; the dislocation is missed if the radiocapitellar line is not checked. ## What makes up the terrible triad of the elbow? Posterior elbow dislocation plus a radial head fracture and a coronoid process fracture of the ulna: a very unstable injury. ## Which conditions are linked to positive and to negative ulnar variance? Positive variance: ulnocarpal impaction and TFCC wear. Negative variance: Kienböck disease. ## Why do displaced olecranon fractures of the ulna lose active elbow extension? The triceps, which inserts on the olecranon, pulls the fragments apart. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/anatomy/ulna/) Educational information, not medical advice. For any symptom, see a health professional. ## Its names **Official Latin (TA2)** ulna TA2 1230 **Official Spanish (DeCS)** Ulna **English (TA2)** Ulna ## Related - [Interosseous arteries](https://durgical.com/en/anatomy/interosseous-arteries-of-the-forearm/) - [Anconeus](https://durgical.com/en/anatomy/anconeus/) - [Annular ligament](https://durgical.com/en/anatomy/annular-ligament-of-the-radius/) - [APL](https://durgical.com/en/anatomy/abductor-pollicis-longus/) - [Brachialis](https://durgical.com/en/anatomy/brachialis/) - [Elbow cartilage (humerus)](https://durgical.com/en/anatomy/cartilage-of-the-capitulum-and-trochlea/) - [Radial head cartilage](https://durgical.com/en/anatomy/cartilage-of-the-radial-head/) - [Ulnar notch cartilage](https://durgical.com/en/anatomy/cartilage-of-the-trochlear-notch/) Sources: Terminologia Anatomica (TA2); [Anatomy, Shoulder and Upper Limb, Forearm Ulna](https://www.ncbi.nlm.nih.gov/books/NBK547749/); [Anatomy, Shoulder and Upper Limb, Forearm Bones](https://www.ncbi.nlm.nih.gov/books/NBK545260/). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/anatomy/ulna/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/anatomy/ulna/