Distal radioulnar joint
The distal radioulnar joint is a synovial joint between the distal ends of the radius and ulna.
This is a uniaxial pivot joint that allows the movements in one degree of freedom; pronation-supination. In simple words, these are the rotatory movements by which the forearm and hand rotate around the long axis of the forearm.
In pronation, the palm of the hand faces downwards, while in supination, it faces upwards. Within the whole human body, these movements are unique to the forearm of the upper limb.
|Type||Synovial pivot joint; uniaxial|
|Articular surfaces||Distal head of ulna, ulnar notch of radius|
|Ligaments||Triangular fibrocartilage complex: Articular disc of distal radioulnar joint, ulnar collateral ligament, dorsal and palmar radioulnar ligaments, base of extensor carpi ulnaris sheath, ulnolunate and ulnotriquetral ligaments|
|Innervation||Anterior and posterior interosseous nerves|
|Blood supply||Anterior interosseous, posterior interosseous and ulnar arteries|
|Movements||Pronation - supination|
This article will discuss the anatomy and function of the distal radioulnar joint.
- Articular surfaces
- Ligaments and joint capsule
- Blood supply
- Muscles acting on the distal radioulnar joint
The distal radioulnar joint is the articulation between the crescent-shaped convex distal head of ulna and the concave ulnar notch of radius. Both surfaces are lined by the hyaline cartilage.
The joint contains a triangular fibrocartilaginous articular disc. The apex of the disc is attached to the lateral surface of the styloid process of ulna, while the base is anchored to the inferior margin of the ulnar notch of radius.
Besides taking part in the distal radioulnar joint, the disc participates in the radiocarpal joint with its inferior surface. The disc is thinner centrally than peripherally, meaning that a potential perforation of its central part would open the communication between the distal radioulnar and radiocarpal joints.
Ligaments and joint capsule
The joint is enclosed by a fibrous capsule that attaches to the margins of the articular surfaces. The internal surface of the capsule is lined by a synovial membrane. The synovial membrane projects superiorly to the interosseous space between the radius and ulna, extending beyond the joint capsule. This projection of the synovial cavity is called the recessus sacciformis (saccular recess).
The stability of the distal radioulnar joint is provided by the extrinsic and intrinsic stabilizers. The extrinsic stabilizers are the tendons of extensor carpi ulnaris, pronator quadratus and the interosseous membrane of forearm. The former two cross the joint and hold it tight, while the latter holds the facing surfaces of the shafts of the radius and ulna firmly connected. The intrinsic stabilizers are the joint capsule, triangular fibrocartilage complex (TFCC) and distal radioulnar ligaments.
Triangular fibrocartilage complex (TFCC)
The triangular fibrocartilage complex (TFCC) is a biconcave ligamentous complex that stabilizes and cushions the joints of the wrist region; distal radioulnar, ulnocarpal and radiocarpal joints. It consists of the articular disc of the distal radioulnar joint, ulnar collateral ligament, dorsal and palmar radioulnar ligaments, the base of the extensor carpi ulnaris sheath, and the ulnolunate and ulnotriquetral ligaments.
The core of the TFCC is the articular disc of the distal radioulnar joint. The dorsal and palmar parts of the TFCC are thickened and known as the dorsal and palmar radioulnar ligaments, respectively. Each of these ligaments consists of the superficial and deep components which differ by their ulnar attachments. The superficial components insert onto the styloid process of ulna, while the deep ones insert slightly more laterally. The ulnar collateral, ulnolunate and ulnotriquetral ligaments join the TFCC on its ulnar attachment. The dorsal margin of the TFCC is fused with the floor of the base of the extensor carpi ulnaris sheath.
The function of the TFCC is to stabilize the joints within the wrist region by transmitting and distributing the load from the hand to the ulna.
The innervation for the distal radioulnar joint comes from the branches of the anterior and posterior interosseous nerves. The former is a branch of the median nerve, while the latter stems from the radial nerve.
The distal radioulnar joint is supplied by the palmar and dorsal branches of the anterior interosseous artery. The posterior interosseous and ulnar arteries contribute to the joint vascularization to a smaller extent.
Working together with the proximal radioulnar joint, the distal radioulnar joint enables the rotatory movements of the forearm around a sagittal axis. The distal radioulnar joint is a uniaxial joint that has one degree of freedom;
- Pronation (61-66°) - supination (70-77°)
During these movements, the distal end of radius rotates around the head of ulna. The axis for rotation is not static and changes depending on the forearm position. In supination, the axis passes through the center of the head of radius proximally and through the ulnar attachment of the articular disc in the distal radioulnar joint. In pronation, the distal point of the axis moves medially, passing through the head of ulna.
The distal radioulnar joint takes a closed packed position at the 5° of supination. The open packed (resting) position occurs when the forearm is at 10° of supination. The capsular pattern of the distal radioulnar joint is full range of motion, with pain at extreme rotation. The distal radioulnar joint permits the accessory movements of anteroposterior gliding of the head of ulna against the radius.
Muscles acting on the distal radioulnar joint
The muscles that pronate the forearm at the distal radioulnar joint are the pronator quadratus and pronator teres. The pronator quadratus can carry out the movement when it’s not resisted, but the pronator teres is necessary for the quick movements and movements against resistance.
Supination is produced by the supinator muscle when the forearm is extended and not loaded. For the movements against resistance and/or when the forearm is flexed, the biceps brachii muscle acts as an accessory supinator.
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