Wrist joint
In its structure, the wrist joint (articulatio radiocarpalis) is ellipsoid and biaxial. It serves as the main connecting link between the forearm and the hand.
The articular surfaces are represented by:
- On the forearm side — by the distal end of the radius and a special intra-articular disc.
- On the hand side — by the proximal row of carpal bones, which includes the scaphoid, lunate, and triquetrum bones.
The joint capsule here is thin, attaching strictly along the margins of the contacting articular surfaces. The articulation is reinforced by several groups of ligaments:
- Collateral ligaments: ligg. collateralia ulnare et radiale.
- Palmar and dorsal ligaments: ligg. radiocarpalia dorsalia et palmaria.
The biaxial structure allows for flexion and extension, as well as abduction and adduction. A combination of these movements permits circumduction.
Wrist joints
The anatomy of the wrist includes several groups of articulations that ensure the structural integrity and flexibility of this region.
Midcarpal joint (articulatio mediocarpalis) is located directly between the proximal and distal rows of carpal bones. It is a complex and combined articulation characterized by an S-shaped joint space. Its capsule is shared with the intercarpal joints. Notably, this joint is biomechanically linked to the radiocarpal joint — their movements occur in conjunction.
Intercarpal joints (articulationes intercarpales) are situated between the bones of each individual carpal row. In shape, they are plane joints and belong to amphiarthroses (slightly movable joints). Additional stability is provided by strong interosseous ligaments.
Metacarpal joints and thumb articulation
Carpometacarpal joints (articulationes carpometacarpales) connect the bases of the II–V metacarpal bones to the distal carpal row. They are also plane and slightly movable joints.
However, there is a striking exception among them — the first carpometacarpal joint (thumb articulation). In shape, it is a saddle joint, which determines its high mobility. It is precisely thanks to this joint that the thumb can perform flexion and extension, abduction and adduction, and most importantly, opposition (oppositio) to the other fingers and reposition (repositio) back to the starting position.
Between the bases of metacarpal bones II–V, there are also intermetacarpal joints (articulationes intermetacarpales). They are plane in shape and reinforced by corresponding ligaments.
Finger joints
Movements of the fingers themselves are provided by two groups of joints.
Metacarpophalangeal joints (articulationes metacarpophalangeae) are formed by the spherical heads of the metacarpal bones and the concave bases of the proximal phalanges. Their ligamentous apparatus includes ligg. collateralia, ligg. palmaria, and the deep transverse metacarpal ligament — ligg. metacarpea transversa profunda. Flexion, extension, abduction, adduction, and circumduction are possible in these joints.
Interphalangeal joints (articulationes interphalangeae manus) are located between the phalanges themselves. In shape, they are typical ginglymus (hinge) joints. They are reinforced by ligg. collateralia and ligg. palmaria ligaments. Unlike the metacarpophalangeal articulations, the biomechanics here are strictly limited: only flexion and extension are possible.
Briefly: answers to topical questions
Which specific bones form the articular surfaces of the midcarpal joint?
The articular surfaces of the midcarpal joint are formed by the bones of the first (proximal) and second (distal) rows of the carpus, with the exception of the pisiform bone.
- Proximal row (articular socket) — scaphoid (os scaphoideum), lunate (os lunatum), and triquetrum (os triquetrum) bones.
- Distal row (articular head) — trapezium (os trapezium), trapezoid (os trapezoideum), capitate (os capitatum), and hamate (os hamatum) bones.
Which bones make up the distal carpal row?
The distal (second) row of the carpus consists of four short spongy bones.
- Trapezium bone (os trapezium).
- Trapezoid bone (os trapezoideum).
- Capitate bone (os capitatum).
- Hamate bone (os hamatum).
On the surfaces of these bones, there are articular facets for articulation with neighboring bones, and on the palmar surface of some of them, there are tubercles for the attachment of muscles and ligaments.
With which bone does the pisiform bone articulate?
The pisiform bone (os pisiforme) articulates exclusively with the triquetrum bone (os triquetrum). This connection forms a separate, independent pisiform joint (art. ossis pisiformis). The pisiform bone itself is a sesamoid bone, which developed and is located within the tendon of the flexor carpi ulnaris muscle (m. flexor carpi ulnaris).
Which muscles provide flexion in the radiocarpal joint?
Flexion of the hand in the radiocarpal joint is provided by the following forearm muscles:
- Flexor carpi radialis (m. flexor carpi radialis) — performs flexion and abduction of the hand.
- Flexor carpi ulnaris (m. flexor carpi ulnaris) — provides flexion and adduction of the hand.
- Palmaris longus — participates in hand flexion.
These muscles are innervated by branches of the median and ulnar nerves.
To remember the most important movements of the thumb in the saddle joint, keep the Latin pair in mind: oppositio (opposition) and repositio (reposition).
Class and exam questions
Which bones form the articular surfaces of the radiocarpal joint?
The joint is formed by the distal end of the radius, the articular disc, and three bones of the proximal carpal row: the scaphoid, lunate, and triquetrum.
Which hand joint has an S-shaped joint space?
An S-shaped joint space is characteristic of the midcarpal joint (articulatio mediocarpalis), located between the proximal and distal rows of carpal bones.
What is the specific feature of the carpometacarpal joint of the thumb?
Unlike the other plane carpometacarpal joints, the thumb joint is a saddle joint. This enables the opposition (oppositio) of the thumb to the other fingers.
What movements are possible in the interphalangeal joints of the hand?
Since the interphalangeal joints are hinge joints, movements along only one axis are possible in them: flexion and extension of the phalanges.
What else to study on this topic
- Topography and functions of the collateral ligaments of the radiocarpal joint
- Biomechanics of the S-shaped space of the midcarpal joint
- Features of the deep transverse metacarpal ligament
- Anatomy of the interosseous carpal ligaments
- Saddle joint: detailed analysis of opposito biomechanics
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