# Radius and Ulna Anatomy > Radius and ulna anatomy for MBBS Anatomy: biceps insertion, annular ligament, Colles fracture and growing ends of both bones. - Canonical URL: https://prepelephant.com/topics/mbbs/anatomy/radius-and-ulna-anatomy - Exam / course: MBBS · Subject: Anatomy - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-02 - Last updated: 2026-10-02 - How to cite: "Radius and Ulna Anatomy", PrepElephant, https://prepelephant.com/topics/mbbs/anatomy/radius-and-ulna-anatomy ## Direct answer Pronation and supination work because the radius spins around a relatively fixed ulna, its disc-shaped head rotating within the annular ligament at the top and its lower end swinging round the ulnar notch at the bottom. The radius carries about four-fifths of axial load across the wrist, which is why the osteoporotic elderly fracture it — Colles fracture, two to three centimetres above the distal end, with the classic dinner-fork deformity. The ulna anchors the elbow: triceps on the olecranon, brachialis on the coronoid, and the trochlear notch gripping the humerus like a wrench. Their nutrient arteries both arise from the anterior interosseous artery, their foramina pointing in opposite directions — upwards in the radius, downwards in the ulna — because each grows mainly at the end its foramen runs away from. ## What you must remember - **Radius, top to bottom:** head with its articular disc, neck, radial tuberosity for biceps (rough behind where a bursa separates tendon from bone), interosseous border, and distally the styloid process, ulnar notch and dorsal (Lister's) tubercle for the extensor pollicis longus. - **Ulna, top to bottom:** olecranon, trochlear notch, coronoid process with the radial notch on its side, supinator crest, and the styloid process whose tip normally sits about a centimetre proximal to the radial styloid. - **Radio-ulnar joints:** proximal — head inside the annular ligament, a fibrous ring attached at the radial notch; distal — triangular fibrocartilage complex; between them, the interosseous membrane transmits force from the radius upwards to the ulna. - **Growing ends, reversed:** the radius grows chiefly at its distal end, so its nutrient foramen points upwards; the ulna grows at its proximal end, so its foramen points downwards — the standard one-mark reversal pair. - **Colles versus Smith:** a fall on the outstretched hand dorsally displaces the distal radius (dinner fork); a fall on the flexed wrist or a direct blow volarly displaces it in reverse (Smith, garden-spade). - **Pulled elbow:** in a child under five, sudden longitudinal traction tears the cuff of the annular ligament at its distal attachment; the radial head slips out, and the child holds the arm pronated and refuses to move it. - **Nerve relations:** the posterior interosseal nerve (radial) winds through the two heads of supinator onto the neck of the radius — at risk in radial neck fractures and careless surgical approaches. ## A grandmother, a toddler and the same bone An elderly woman slips on a wet bathroom floor and lands on her palm: the distal radius breaks two to three centimetres above the joint, the fragment tilting dorsally with radial shortening and often an accompanying ulnar styloid avulsion, so the wrist and forearm silhouette from the side resembles a dinner fork. Reduction restores length and tilt; the distal radius is cancellous bone, and quality decides the fracture. Three years later the same family returns with a two-year-old swung by the arms at a fair, now cradling a motionless, pronated limb. Nothing is broken: in a young child the annular ligament's distal attachment gives way and the radial head subluxates. The manoeuvre that cures — supinating and flexing the elbow while pressing over the radial head — is anatomy used as therapy, and the click is felt more than heard. ## How the viva frames these bones Side determination comes first — radius styloid lateral, tuberosity medial; ulna olecranon posterior — then the attachment grid: biceps to the radial tuberosity (supination, which is why biceps reflex tests C5-C6 at this exact site), brachialis to the coronoid and ulnar tuberosity, and pronator teres placed so that its two heads embrace the median nerve's passage into the forearm. The reversal of nutrient foramina is the favourite trick question, and the candidate who explains the rule — the foramen points away from the growing end — rather than reciting directions for each bone passes twice. ## Frequently asked questions ### What is a Colles fracture and what produces the deformity? A fracture of the distal radius two to three centimetres above the wrist with dorsal and radial displacement of the distal fragment, from a fall on the outstretched hand. The silhouette resembles a dinner fork, and the ulnar styloid is often avulsed with it. ### How is a pulled elbow produced and reduced? Sudden longitudinal traction in a child under five tears the distal attachment of the annular ligament, allowing the radial head to subluxate. Supination with elbow flexion, often with pressure over the radial head, reduces it with a palpable click. ### Why does the radius fracture distally in the elderly while children fracture the shaft? The distal radius is cancellous bone, and postmenopausal bone loss makes it the commonest fracture site in older women. Children's bones bend, buckle and greenstick instead under the same load. ### Where does biceps insert and what is its action there? Onto the radial tuberosity, with a bursa against its rough posterior half. It is the prime supinator of the forearm, strongest with the elbow flexed, and its reflex tests the C5-C6 segment. ### Which way do the nutrient foramina of the radius and ulna point? The radius's points upwards (distal growing end) and the ulna's downwards (proximal growing end).