The radiocarpal joint is a synovial joint formed between the radius, its articular disc and three proximal carpal bones; the scaphoid, lunate and triquetral bones. Technically, the radiocarpal joint is considered to be the only articular component of the wrist joint; many references, however, may also include adjacent joints, such as the carpal joints, in this definition.
In the radiocarpal joint, the large concave facet located on the distal end of radius directly articulates with the scaphoid and lunate bones. The articulation between the distal radius and triquetral bone is indirect and it is facilitated via a biconcave articular disk.
|Synovial ellipsoid joint;
|Proximal component - distal end of radius, articular disc
Distal component - scaphoid, lunate and triquetral of the proximal row of carpal bones (also includes triangular fibrocartilage complex)
|Palmar radiocarpal joint, dorsal radiocarpal ligament, ulnar collateral ligament, radial collateral ligament
|Anterior interosseous nerve arising from median nerve (C5-T1)
Posterior interosseous nerve arising from radial nerve (C7-C8)
Deep and dorsal branches of the ulnar nerve (C8-T1)
|Branches of the dorsal and palmar carpal arches
|Flexion, extension, adduction and abduction
- Articular surfaces
- Ligaments and joint capsule
- Blood supply
- Muscles acting on the radiocarpal joint
The radiocarpal joint is an articulation between the distal portion of the radius and three of the four proximal carpal bones; the scaphoid, lunate and triquetrum. The articular surface of the distal radius is roughly triangular and concave in appearance, presenting two articular facets separated by a slight anteroposterior ridge. These are the scaphoid and lunate fossae, which are in direct articulation with the corresponding carpal bones. The articulation between the distal radius and triquetrum bone is indirect, mediated by a biconcave structure known as the triangular fibrocartilage complex.
The distal component of radiocarpal joint is formed by articular surfaces on the scaphoid, lunate and triquetrum bones, which are held in place by interosseous ligaments. The scaphoid and lunate bones collectively form a convex articular surface which articulates with the concavity formed by the radius, and the radial portion of the triangular fibrocartilage complex . The triquetrum has a small articular surface on its proximal surface, which may or may not articulate with the triangular fibrocartilage complex.
Fortify your knowledge about the bones of the wrist and hand with the following quiz.
Ligaments and joint capsule
The radiocarpal joint is enclosed by a two-layered joint capsule which covers the articulation of the osseous components, in addition to some soft tissue structures. The outer portion of the capsule is composed of fibrous connective tissue which provides structural support to the joint, while the inner layer is composed of a synovial membrane responsible for the secretion of synovial fluid, keeping the joint lubricated.
Proximally, the capsule is usually independent of that of distal radioulnar joint, and it attaches to the distal aspects of radius and ulna. Distally, the joint capsule attaches on the margins of the proximal articular surfaces of the involved carpal bones.
The ligaments of the wrist joint are quite variably described in the literature, which can lead to a degree of confusion in regards to their anatomy. A notable feature of the ligaments of the wrist is that none of them are truly extracapsular; most of them are rather defined as thickenings of the joint capsule, providing it with additional support. The palmar ligaments are notably more numerous than those of the dorsal wrist joint, with almost the entire palmar portion of the joint capsule being composed of individual ligaments. The palmar ligaments tend to converge distally, presenting as an apex-distal ‘V’ when viewed collectively.
Palmar radiocarpal ligaments
The palmar radiocarpal ligament arises from anterior/palmar distal border of the radius and extends distally to the scaphoid, lunate and capitate bones. It functions to limit overextension of the wrist joint and is often described as having four distinct parts:
- Radioscaphocapitate ligament: forms the lateral portion of the joint capsule and extends from the styloid process of radius to the distal aspect of scaphoid bone, with a small number of fibres continuing and proximal aspect of the capitate bone. The lateralmost borders of this ligament also extend fibres to the trapezium bone, forming the radial collateral (carpal) ligament.
- Long radiolunate ligament: runs in parallel along the ulnar border of the radioscaphocapitate ligament, from the distal radius to the lunate bone. This ligament was formerly known as the radiolunotriquetral ligament, however the amount of fibres continuing to the triquetrum is negligible.
- Radioscapholunate ligament (ligament of Testut): arises ulnar to the long radiolunate ligament and merges with the scapholunate interosseous ligament. It is composed of branches of the radial artery and anterior interosseous neurovascular bundle, with small amounts of collagen fibres interspersed between. Therefore it is not always considered as a ‘true’ ligament.
- Short radiolunate ligament: arises as a flat band of fibres from the margin of the lunate fossa of the distal radius, extending to the palmar margin of lunate bone.
Dorsal radiocarpal ligament
The dorsal radiocarpal ligament (a.k.a. radiotriquetral, or radiolunotriquetral ligament) is less thick and less strong than its palmar counterpart. It arises from either side of the dorsal radial tubercle, forming two parts. The wider superficial part is lateral to the dorsal tubercle and extends in an oblique manner between the distal radius with the dorsal surface of the triquetrum bone. The narrower deep part arises medial to dorsal tubercle attaches to the lunotriquetral interosseous ligament. The function of the dorsal radiocarpal ligament is to limit full flexion of the wrist joint.
Palmar ulnocarpal ligament
The palmar ulnocarpal ligament arises from the anterior margin of the triangular fibrocartilage complex, the palmar radioulnar ligament and ulnar styloid process. It divides into three parts and courses distally obliquely towards the capitate, lunate and triquetrum bones, forming the unlocapitate, ulnolunate and ulnotriquetral divisions, respectively.
The ulnotriquetral division is sometimes also referred to as the ulnar collateral (carpal) ligament. Working together, these ligaments serve to prevent palmar translocation of the ulnar carpal bones and allow the hand to follow the radius in its movements. It also limits the adduction/ulnar deviation of the wrist joint.
Triangular fibrocartilage complex
The triangular fibrocartilage complex (TFCC) is a load-bearing structure located on the medial aspect of the wrist region. As its name suggests, it consists of a triangular fibrocartilage articular disc, in addition to the ulnomeniscal homologue, ulnar collateral ligament, dorsal and palmar radioulnar ligaments, the base of the extensor carpi ulnaris sheath, and the ulnolunate and ulnotriquetral parts of the palmar ulnocarpal ligament.
Proximally, the triangular fibrocartilage attaches to the ulnar aspect of the lunate fossa of the radius, ulnar head and ulnar styloid process. On its ulnar attachment, it is joined and thickened by the ulnar collateral ligament. Distally, it attaches to the lunotriquetral interosseous ligament, triquetrum, hamate and base of the fifth metacarpal. 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 TFCC functions as a major stabilizer of both radiocarpal and ulnocarpal joints. It prevents ulnocarpal abutment by transmitting and distributing the axial load from the carpus to the ulna. It also facilitates the complex movements at the wrist joint.
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The radiocarpal joint receives its innervation from articular branches of the following nerves;
The radiocarpal joint receives its blood supply from the branches of the dorsal and palmar carpal arches.
The dorsal carpal arch arises from dorsal carpal branches of the radial ulnar, anterior interosseous and posterior interosseous arteries.
When all of the components are functioning, this ellipsoid joint allows movements along two axes (transverse and sagittal). These movements are: flexion and extension, as well as abduction and adduction (also sometimes referred to as radial/ulnar deviation, respectively). They are associated with movements at the midcarpal joint, as the same group of muscles act on both of these joints.
Flexion ( or palmar flexion) at the radioulnar joint is described as the movement in which the palmar aspect of the hand moves towards the forearm in the sagittal plane. During flexion, the scaphoid and lunate bones glide over the concave articular surface of the distal radius in a posterosuperior direction. Extension (or dorsal flexion) conversely allows the palmar aspect of the hand to move away from the front of the forearm. Extension happens as the same bones move in the opposite direction with the additional rotation of the scaphoid about its long axis. The range of motion for flexion in the radiocarpal joint is about 50°, while for extension it is somewhere around 35°.
Adduction (ulnar deviation) and abduction (radial deviation) also occur in this joint with ranges of motion of 30° and 7° respectively. In adduction the rotation of the scaphoid bone enables the lunate to move laterally and situate completely distal to the inferior surface of radius. Following the lunate, the triquetral also moves laterally positioning itself immediately distal to the triangular fibrocartilage complex. The movement is limited by the ulnar styloid process.
Abduction is a more limited movement of this joint. In abduction, the lunate and triquetral move medially. The lunate ends in the same plane with the inferior radioulnar joint, while the triquetral moves farther away from the radius. The movement is limited by contact between the tubercle of scaphoid bone against the radial styloid process.
In the close-packed position, the radiocarpal joint is extended with a slight degree of abduction/radial deviation, while the loose-packed (or resting) position is neutral with a small degree of adduction/ulnar deviation. The capsular pattern (or loss of passive range of motion during inflammation) of these joints is flexion and extension equally limited.
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Muscles acting on the radiocarpal joint
All the movements of the wrist joint are performed by the muscles of the forearm.
- Flexion is mainly produced by the flexor carpi ulnaris and flexor carpi radialis, with the support from the flexor digitorum superficialis.
- Extension is mainly produced by the extensor carpi radialis longus, extensor carpi radialis brevis, and extensor carpi ulnaris muscles, with assistance from extensor digitorum.
- Adduction is produced by the extensor carpi ulnaris and flexor carpi ulnaris.
- Abduction is produced by the abductor pollicis longus, flexor carpi radialis, extensor carpi radialis longus and extensor carpi radialis brevis.
For more information about the anatomy and movements of the wrist joint, take a look below:
Among the most common injuries in clinical practice are the injuries of the wrist joint. They include sprains, fractures and dislocations of bony and ligamentous structures that comprise the wrist. These injuries usually occur among the elderly population due to the fall onto an outstretched hand (FOOSH injury).
These types of falls not only cause damage to the bony structures of the radiocarpal joint, but also to its related ligamentous structures, vessels and nerves. One of the most commonly fractured bones in this region is the distal radius and scaphoid, while the most commonly injured ligament/sprain is the scapholunate ligament that plays an important role in wrist stability.
The typical symptoms of wrist injuries are pain and swelling of the wrist region, and wrist popping or clicking with wrist extension and grip. These injuries are typically diagnosed by x-ray and require physical therapy or surgical approach in treatment.
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