Radio ulnar joint easiest
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Here is a concise, exam-ready summary of the radio-ulnar joints:
Radio-Ulnar Joints
There are two radio-ulnar joints - proximal and distal - that act as a functional pair to produce forearm rotation (pronation/supination). They are linked by the interosseous membrane, so movement of one always accompanies movement of the other.
1. Proximal Radio-Ulnar Joint (PRUJ)
| Feature | Detail |
|---|---|
| Type | Synovial pivot joint (uniaxial) |
| Articulation | Articular circumference of the radial head rotating within the radial notch of the ulna |
| Key stabilizer | Anular ligament of the radius - wraps around the radial head, holding it against the radial notch |
| Location | Inside the elbow joint capsule (part of the cubital joint complex) |
The radial head is slightly oval, so the pronation/supination axis shifts ~2 mm radially during pronation - this clears space for the radial tuberosity within the interosseous space.
The proximal radioulnar joint is NOT a simple hinge but is more like a ball-and-socket type articulation, giving it excellent stability. - Imaging Anatomy: Bones, Joints, Vessels and Nerves
2. Distal Radio-Ulnar Joint (DRUJ)
| Feature | Detail |
|---|---|
| Type | Synovial pivot joint (uniaxial) |
| Articulation | Ulnar notch of the radius articulating with the convex head of the ulna |
| Key stabilizer | Triangular fibrocartilage complex (TFCC) / articular disc - separates the DRUJ from the wrist joint |
| Disc attachment | Apex attaches to ulnar styloid; base to the margin of the radius between the ulnar notch and carpal surface |
During pronation, the ulnar notch of the radius slides anteriorly (anteriorly) over the convex head of the ulna.
During supination, it returns to the neutral position.
Pronation and Supination
The movement occurs entirely in the forearm and involves:
- The radial head spinning at the PRUJ (against the anular ligament + radial notch of ulna)
- The distal radius sweeping over the head of the ulna at the DRUJ
- The interosseous membrane linking both movements
Axis of rotation
Runs obliquely from the center of the humeral capitulum (at PRUJ) down to the styloid process of the ulna (at DRUJ). The ulna effectively stays stationary while the radius revolves around it.
Muscles (4 total)
| Movement | Muscles |
|---|---|
| Supination | Biceps brachii (most powerful, especially in flexion) + Supinator |
| Pronation | Pronator teres (proximal forearm) + Pronator quadratus (distal forearm, acts even in extension) |
Key Connections Between the Two Joints
| Structure | Role |
|---|---|
| Anular ligament | Holds radial head at PRUJ |
| Interosseous membrane | Links both joints; fibers run obliquely from radius to ulna (inferiorly); transfers forces from radius to ulna; does NOT restrict rotation |
| Articular disc (TFCC) | Stabilizes DRUJ; separates it from wrist |
| Oblique cord | Additional ligamentous band above the interosseous membrane |
Classic Injury Patterns (Exam Favorite)
| Injury | What Breaks | What Dislocates |
|---|---|---|
| Monteggia | Proximal 1/3 ulna fracture | Radial head dislocates (PRUJ) |
| Galeazzi | Distal 1/3 radius fracture | Distal radio-ulnar joint (DRUJ) disruption |
"Whenever a fracture of the radius or ulna is demonstrated radiographically, further images of the elbow and wrist should be obtained to exclude dislocations." - Gray's Anatomy for Students
Range of motion: ~80° pronation + ~90° supination (total ~170°)
- Gray's Anatomy for Students, pp. 895-896
- THIEME Atlas: General Anatomy and Musculoskeletal System, pp. 297-301
- Imaging Anatomy: Bones, Joints, Vessels and Nerves, p. 541
Detail about Ligaments of Radio ulnar joint
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Here is a detailed, textbook-level breakdown of all the ligaments of both radio-ulnar joints:
Ligaments of the Radio-Ulnar Joints
PROXIMAL RADIO-ULNAR JOINT (PRUJ) Ligaments
1. Anular Ligament of the Radius (Primary stabilizer)
| Feature | Detail |
|---|---|
| Origin | Anterior border of the radial notch (lesser sigmoid notch) of the ulna |
| Insertion | Posterior border of the radial notch of the ulna |
| Shape | Ring/cuff - wraps around the head and neck of the radius |
| Inner surface | Lined with fibrocartilage (gliding surface) - withstands compressive loads during rotation |
| Function | Holds the radial head firmly against the radial notch of the ulna; allows the head to spin freely without dislocating |
Key structural features:
- The anular ligament blends with the radial collateral ligament of the elbow anterolaterally
- It blends with the elbow joint capsule but is separate posteriorly
- The inner surface has the fibrocartilaginous structure of a gliding tendon, enabling it to withstand compressive loads during rotation
- Below the free lower margin of the anular ligament, the synovial membrane forms a sacciform recess - a pocket that expands during pronation/supination to accommodate radial head rotation
- Its attachment on the crista supinatoris blends with fibers from the lateral collateral ligament
"The anular ligament is of key importance in stabilizing the proximal radioulnar joint. It runs from the anterior to the posterior border of the radial notch of the ulna, wrapping around the radial head and pressing it into the ulnar articular surface." - THIEME Atlas of Anatomy
2. Oblique Cord (accessory ligament)
| Feature | Detail |
|---|---|
| Origin | Tubercle at the lateral side of the ulnar tuberosity |
| Insertion | Proximal end of the radius (just below the radial tuberosity) |
| Direction | Runs obliquely, proximal to distal from ulna to radius (opposite to interosseous membrane fibers) |
| Function | Reinforces the PRUJ area; its fibers run in the opposite direction to the central band of the interosseous membrane |
Note: The oblique cord is sometimes described as the uppermost part of the interosseous membrane; it resists downward (distal) pull on the radius.
DISTAL RADIO-ULNAR JOINT (DRUJ) Ligaments
The DRUJ has no simple capsular ligaments like the elbow. Instead, it is stabilized almost entirely by the Triangular Fibrocartilage Complex (TFCC) - a complex of 5-6 distinct structures.
The Triangular Fibrocartilage Complex (TFCC)
The TFCC is the primary stabilizer of the DRUJ. It is also called the ulnocarpal complex because it stabilizes both the DRUJ and the ulnocarpal articulation.
Components of the TFCC:
| Component | Description |
|---|---|
| Articular disc (TFC proper) | Fibrocartilaginous disc; extends from the distal rim of the sigmoid notch to the ulnar fovea and styloid via proximal and distal laminae |
| Palmar radioulnar ligament (PRUL) | Primary DRUJ stabilizer |
| Dorsal radioulnar ligament (DRUL) | Primary DRUJ stabilizer |
| Meniscus homologue (ulnomeniscal homologue) | Dense irregular connective tissue; distal continuation of the disc |
| Ulnar collateral ligament | Runs to the ulnar carpus |
| ECU subsheath | Sheath of the extensor carpi ulnaris tendon |
3. Palmar Radioulnar Ligament (PRUL)
| Feature | Detail |
|---|---|
| Origin | Palmar (volar) aspect of the sigmoid notch of the radius |
| Insertion | Converges toward the base of the ulnar styloid and ulnar fovea |
| Course | Runs in a triangular/convergent fashion toward the ulna |
| Function | Primary static stabilizer of the DRUJ; resists dorsal displacement of the ulna (or ventral displacement of radius) during pronation |
4. Dorsal Radioulnar Ligament (DRUL)
| Feature | Detail |
|---|---|
| Origin | Dorsal aspect of the sigmoid notch of the radius |
| Insertion | Converges toward the base of the ulnar styloid and ulnar fovea |
| Course | Triangular convergent course toward the ulna |
| Function | Primary static stabilizer of the DRUJ; resists palmar displacement of the ulna (or dorsal displacement of radius) during supination |
"The PRUL and DRUL are the primary stabilizers of the DRUJ. They originate from the dorsal and palmar aspect of the sigmoid notch and converge in a triangular fashion toward the base of the ulnar styloid." - Rockwood & Green's Fractures in Adults, 10th ed.
MRI appearance: The volar and dorsal radioulnar ligaments are best seen on axial MRI through the ulnar styloid and fovea, where they converge toward the fovea in a "V" shape.
MRI: Sigmoid notch (left), ulnar fovea and meniscus homologue (MH), ulnar collateral ligament (UCL) visible on right. The ligamentum subcruentum (LS) lies between the two laminae.
5. Articular Disc (TFC Proper)
| Feature | Detail |
|---|---|
| Shape | Triangular/biconcave fibrocartilaginous disc |
| Radial attachment | Distal rim of the sigmoid notch of the radius (cartilage margin) |
| Ulnar attachment | Ulnar fovea (via proximal lamina) and ulnar styloid (via distal lamina) |
| Function | Separates DRUJ cavity from the wrist joint; transmits load from carpus to ulna; contributes to DRUJ stability |
"The articular disc extends from the distal rim of the sigmoid notch to the ulnar edge of the lunate facet, blending in the periphery with the PRUL and DRUL." - Rockwood & Green's
Connecting Ligament: The Interosseous Membrane (IOM)
Though not a specific joint ligament, the IOM is the structural link between both radio-ulnar joints and critically important:
| Feature | Detail |
|---|---|
| Direction of fibers | Obliquely from radius (proximal) to ulna (distal) - approximately 20° to the forearm axis |
| Central band | Thickened central portion = "interosseous ligament"; 3.5 cm wide; responsible for 71% of longitudinal stiffness after radial head resection |
| Function | Links the two radio-ulnar joints; transfers loads from radius to ulna; does NOT restrict pronation/supination |
| Clinical relevance | In Essex-Lopresti injury (radial head fracture + IOM tear), proximal migration of the radius occurs because the central band is torn |
Summary Table: All Ligaments at a Glance
| Ligament | Joint | Primary Function |
|---|---|---|
| Anular ligament | PRUJ | Keeps radial head in radial notch; allows spin |
| Oblique cord | PRUJ (accessory) | Resists distal pull on radius |
| Palmar radioulnar ligament (PRUL) | DRUJ | Resists dorsal ulnar displacement; key stabilizer in pronation |
| Dorsal radioulnar ligament (DRUL) | DRUJ | Resists palmar ulnar displacement; key stabilizer in supination |
| Articular disc (TFC proper) | DRUJ | Separates DRUJ from wrist; load transmission |
| Meniscus homologue | DRUJ/ulnocarpal | Distal TFCC extension; ulnocarpal stability |
| Ulnar collateral ligament | DRUJ/ulnocarpal | Ulnar side wrist stability |
| Interosseous membrane (central band) | Both joints | Longitudinal force transfer; links both joints |
Clinical pearl - Pulled elbow (Nursemaid's elbow): In children, the radial head is not yet fully developed and the anular ligament is lax. A sudden longitudinal pull on the child's arm causes the radial head to slip under the anular ligament (radial head subluxation), catching it between the radial head and the capitulum.
- THIEME Atlas of Anatomy: General Anatomy and Musculoskeletal System, pp. 299-301
- Rockwood & Green's Fractures in Adults, 10th ed., pp. 1774-1775
- Gray's Anatomy for Students, pp. 885, 895
- Imaging Anatomy: Bones, Joints, Vessels and Nerves, p. 590
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