Functional Anatomy of the Wrist

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Wrist Structure

The wrist structure include three joints, distal ends of the two forearm bones, seven carpal bones and proximal bases of the metacarpal bones:

• Distal ulna and distal radius make up the distal radioulnar joint
• The scaphoid, the lunate, and the triquetrum, which are proximal carpal bones and the radius are part of the radiocarpal joint
• The trapezium, trapezoid, capitate, and hamate bones are the distal carpal bones. Together with the proximal carpal bones they make up the midcarpal joint.
• The pisiform is the fourth bone located in the proximal row. It does not however articulate as part of the radiocarpal joint, as it sits on top of the triquetrum.

Distal ulna: includes the ulnar head and the styloid process.

• Ulnar head has two articular surfaces: lateral and inferior
  • The lateral surface which is convex articulates with the ulnar notch of the distal radius.
  • The inferior surface articulates with an articular disc (the triangular fibrocartilage).
  • Due to its articulation with the disc, the head of distal ulna is separated from the carpal bones therefore does not have a direct contribution to the wrist joint
• Styloid process: short and rounded. Can be palpated at the dorsomedial aspect of the wrist.

Distal radius: contains four articular surfaces and dorsal tubercle, known as Lister’s tubercle

• Articular surfaces
  • Concaved anterior surface
  • The medial surface with its concaved ulnar notch for holding the head of the ulna
  • The lateral surface with its radial styloid process
  • The inferior surface with two facets articulating with two carpal bones: the scaphoid and lunate
• Dorsal tubercle located on the posterior surface

The scaphoid (navicular): belongs to the proximal raw of the carpal bones. Located the most laterally. Its palmar surface contains the tubercle which is the attachment point for the muscles and the floor for the anatomical snuffbox.

The lunate: part of the proximal raw of the carpal bones. It articulates with the scaphoid on the lateral, and with the triquetrum on the medial side.

The triquetrum: other names include triquetral bone, triangular bone or cuneiform bone. It is triangular and pyramidal shaped bone located in the proximal raw, on the medial side of the wrist. It contains multiple articulation surfaces: lateral for the lunate, anterior for the pisiform, and the distal for the hamate.

The trapezium: located in the distal raw of the carpal bones, on its radial side. It has fours articulations for the first metacarpal, second metacarpal, scaphoid and trapezoid bones. This bone is part of the mechanism responsible for a wide mobility of human hand where the articulation between the first metacarpal and the trapezium allows for the opposable thumbs function.

The trapezoid: the lesser multangular bone is another name for this bone. This is the smallest bone of the distal raw of the carpal bones. It gives structure to the palm of the hand.

The capitate: the largest and most central carpal bone belonging to the distal raw. It articulates with the bases of the 2nd and 3rd metacarpal bones forming part of the common carpometacarpal joint in the hand. In addition it articulates with the following: scaphoid and lunate on the proximal, trapezoid on the lateral, and the hamate on the medial surfaces.

The hamate: sits on the medial side of the distal row of carpal bones. The hook of hamate is the bony process extending from the palmar surface. This carpal bone forms the medial border of the carpal tunnel.

Bones, Articulations and Kinematics of the Wrist

Wrist mobility depends on the interaction between seven carpal bones and the radius. The ulna and the pisiform are excluded from this motion as the pisiform is a sesamoid bone and the ulna is separated from the carpal bones by the disc. Each of the carpal bones has a separate motion axis, however their movement depends on the carpal alignment with the distal radius.

The greatest degree of motion occurs between the radius and the proximal raw of the carpal bones and less motion between the proximal and distal raw of the carpal bones. There is no motion between the distal raw of the carpal bones and the metacarpals. The wrist' proximal raw is responsible for maintaining wrist stability while the distal row functions to support the bases of the metacarpals.

The wrist biomechanics can be described by the following theories:

• The row-theory when the carpal bones are grouped into proximal and distal raws
• The column-theory when the central column include the lunate, the capitate, and the hamate; the lateral column (described as the mobile column) includes the scaphoid, the trapezium, and the trapezoid; and the medial column ( rotation column), contains the triquetrum and the pisiform.
• The row-column-theory which is the modified column-theory. The trapezium and trapezoid are added to the central column and the pisiform was eliminated from the medial column.
• The ring-model where the wrist has two mobile links: the mobile trapezioscaphoid articulation and the rotatory triquetrohamate joint.
• The link joint-theory with the radius, the proximal raw and the distal raw comprising the individual links.
• The clamp-theory where bones are "clamped" together into masses: the scaphoid bone as one mass, the lunate and triquetrum as the second mass, and the hamate, capitate, and trapezoid as a distal mass.

Bones and Articulations

Bones	Articulations	Characteristics	Key palpation points
Distal ulna Distal radius	Distal radioulnar joint	Essential joint for forearm rotation When forearm supination and pronation are lost, it significantly affects the function of the upper limb
Proximal articulation: Distal radius Articular disc Distal articulation: Scaphoid Lunate Triquetrum	Radiocarpal
Proximal articulation: Scaphoid Lunate Triquetrum Distal articulation: Trapezium Trapezoid Capitate Hamate	Midcarpal

Wrist Kinematics

Joint	Type of joint	Plane of movement	Motion	Kinematics	Closed pack position	Open pack position
Distal radioulnar	Synovial joint-uniaxial pivot joint	Transverse	Pronation Supination	Pronation:80 degrees Supination: 85 degrees	5 degrees of supination	10 degrees of supination
Radiocarpal		Saggital Frontal	Flexion (40%) Extension (66%) Ulnar deviation (50%)	Flexion: 65-80degrees Extension:55-65 degrees	Extension with a slight degree of abduction and radial deviation	Neutral with a small degree of adduction and ulnar deviation.
Midcarpal		Saggital Frontal	Flexion (60%) Extension (33%) Radial deviation (90%) Ulnar deviation (50%)	Ulnar deviation:30-35 degrees Radial deviation:15-25 degrees

Ligaments of the Wrist

The ligaments of the wrist can be divided into extrinsic and intrinsic ligaments. The extrinsic ligament connect the carpal bones to the radius or metacarpals. They can be further separated into volar and dorsal ligaments. The intrinsic ligament originate and insert onto the different carpal bones (except there is no ligamentous connections between the lunate and capitate).

Wrist ligaments can also be grouped into the ligaments supporting each of the wrist joints:

• The distal radioulnar joint is supported by the volar and dorsal radioulnar ligaments.
• The radiocarpal joint is stabilised by the dorsal and the palmar radiocarpal ligaments, the palmar ulnocarpal ligaments, ulnar collateral carpal ligament, and the radial collateral carpal ligament.
• The midcarpal joint is reinforced by the dorsal and palmar intercarpal ligaments and the deltoid ligament.

The tables below describe the wrist ligaments supporting each joint.

Ligaments Supporting Distal Radioulnar Joint

Key ligaments	Origin	Insertion	Action/role	Key palpation points
Volar radioulnar ligament	Anterior margin of the ulnar notch at the distal radius	Anterior portion of the head of the ulna	Reinforces distal radioulnar joint Belongs to the triangular fibrocartilage complex (TFCC) and helps to support the triangular fibrocartilage disc Provides load-bearing Helps to stabilise the ulnar side of the wrist
Dorsal radioulnar ligament	Posterior margin of the ulnar notch at the distal radius	Posterior portion of the head of the ulna

Ligaments Supporting Radiocarpal Joint

Key Ligaments	Origin	Insertion	Action/role	Key palpation points
Dorsal radiocarpal ligament (radiolunotriquetral ligament)	Dorsal radial tubercle at distal end of radius	Triquetrum	Stabilises the radiocarpal joint Restricts full wrist flexion
Palmar (Volar) radiocarpal ligaments: Radioscaphocapitate (RSC) ligament Long radiolunate (LRL) ligament Short radiolunate (SRL) ligament Radioscapholunate (RSL) ligament (ligament of Testut)	RSC: radial styloid process LRL: ulnar to the radioscaphocapitate ligament SRL: palmar to the lunate facet of the distal radius articular surface RSL: ulnar to the long radiolunate ligament	RSC: the radial aspect of the waist of the scaphoid LRL: radial half of the palmar surface of the lunate SRL: proximal margin of the palmar surface of the lunate RSL: merges with the scapholunate interosseous ligament. Note: not always considered a ‘true’ ligament as it includes branches of the radial artery and the neurovascular bundle	Connect the radius to the carpal bones RSC: Primary stabilizer of the wrist Prevents ulnar drift
Palmar (volar) ulnocarpal ligaments: Ulnolunate ligament Ulnocapitate ligament	Anterior margin of the triangular fibrocartilage complex The palmar radioulnar ligament	Capitate and lunate bones	Prevent palmar translocation of the ulnar carpal bones Allow radial deviation of the wrist Limit the adduction and ulnar deviation of the wrist joint.
Ulnar collateral carpal ligament (Ulnotriquetral division of the palmar ulnocarpal ligament)	The end of the ulnar styloid process	Triquetrum
Radial collateral carpal ligament (radioscaphoid ligament )	The radial styloid process	Distally at the radial surface of the scaphoid bone	Radial stabiliser of the wrist Limits abduction

Ligaments Supporting Midcarpal Joint

Key ligaments	Origin	Insertion	Action/role	Key palpation points
Dorsal intercarpal ligaments	Dorsal tubercle of the triquetrum	The dorsal groove of the scaphoid bone The lunate bone The trapezium bone (in 50% of individuals)	Provides stability to the carpal bones, especially the stability of the scapholunate complex Prevents scapholunate dissociation during upper limb weight-bearing activities
Deltoid (arcuate) ligament: scaphocapitate ligament (SCL) triquetrohamocapitate ligament (THL)	Proximal carpal raw: scaphoid and triquetrum bones	Distal carpal raw: capitate and hamate bones	Midcarpal stabilising ligament
Palmar (volar) intercarpal ligaments

Resources

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Clinical Relevance

1. The distal radius fracture
2. scaphoid fractures pain in the anatomical snuff box after a hyperextension trauma. Common scaphoid fracture complications include avascular necrosis and nonunion