Functional Anatomy of the Wrist

This article or area is currently under construction and may only be partially complete. Please come back soon to see the finished work! (30/08/2023)

Original Editor - User Name

Top Contributors - Ewa Jaraczewska, Jess Bell and Kim Jackson  

Introduction

The wrist joint has two degrees of freedom including flexion and extension and radial and ulnar deviation. Both flexion and extension takes place in proximal and distal raws of the carpal bones. The radial and ulnar deviation occurs when wrist alignment alters: during the radial deviation, the proximal row flexes and the distal row extends. In ulnar deviation, the proximal row extends and the distal row flexes. This two-dimensional wrist motion is controlled by the ligamentous stabilisers and by the proximal forearm muscles.

The functional range of the wrist required to perform basic activities of daily living is 30 degrees of extension, 5 degrees of flexion, 10 degrees of radial deviation, and 15 degrees of ulnar deviation. However, the actual motion required to complete each individual task is much higher, according to Nelson et al.Optimal wrist and function allows for the performance of activities of daily living which leads to independent living and improves quality of life.

This article discusses the key anatomical structures of the wrist complex, including the bony structures, articulations, ligaments, muscles, nerves and the vascular supply.

Key Terms

Axes: lines around which an object rotates. The rotation axis is a line that passes through the centre of mass. There are three axes of rotation: sagittal passing from posterior to anterior, frontal passing from left to right and  vertical passing from inferior to superior. The rotation axes of the foot joints are perpendicular to the cardinal planes. Therefore, motion at these joints results in rotations within three planes. Example: supination involves inversion, internal rotation, and plantarflexion.

Bursae: reduces friction between the moving parts of the body joints. It is a fluid-filled sac. There are four types of bursae: adventitious, subcutaneous, synovial, and sub-muscular.

Capsule: one of the characteristics of the synovial joints. It is a fibrous connective tissue which forms a band that seals the joint space, provides passive and active stability and may even form articular surfaces for the joint. The capsular pattern is "the proportional motion restriction in range of motion during passive exercises due to tightness of the joint capsule."

Closed pack position: the position with the most congruency of the joint surfaces. In this position, joint stability increases. The closed pack position for interphalangeal joints is a full extension.

Degrees of freedom: the direction of joint movement or rotation; there is a maximum of six degrees of freedom, including three translations and three rotations.

Ligament: fibrous connective tissue that holds the bones together.

Open (loose) pack position: position with the least joint congruency where joint stability is reduced.

Planes of movement: describe how the body moves. Up and down movements (flexion/extension) occur in the sagittal plane.Sideway movements (abduction/adduction) occur in the frontal plane. The transverse plane movements are rotational (internal and external rotation).

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

Carpal Bones

Proximal raw:

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.

Distal raw:

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	A major synovial joint of the wrist. It contains the concaved surface of the distal end of the radius, the articular disc of the distal radioulnar joint, and the convexed surface of the proximal carpal row. The combined motion of midcarpal and radiocarpal joints makes up the total range of wrist motion.
Proximal articulation: Scaphoid Lunate Triquetrum Distal articulation: Trapezium Trapezoid Capitate Hamate	Midcarpal	Articulation of proximal and distal carpal rows. In particular, the midcarpal motion includes the combined motion of three types of joint systems: between the scapoid and the distal raw, between the lunate and triquetrum and the distal row; and the intercarpal joints of the proximal row.

Wrist Kinematics

The wrist kinematics is essential in completing the activities of daily living. The following are the examples of wrist involvement in a specific task:

• Pouring a water from a jug into a cup: requires stable wrist in the sagittal and coronal planes and ability to complete pronation/supination motion.

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	Synovial joint-multiaxial ellipsoid joint	Saggital Frontal	Flexion (40%) Extension (66%) Ulnar deviation (50%) Radial deviation (10%) Circumduction (circular hand motions about the wrist)	Flexion: 65-80 degrees 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	Synovial joint-gliding joint	Saggital Frontal	Flexion (60%) Extension (33%) Radial deviation (90%) Ulnar deviation (50%)	Ulnar deviation:30-35 degrees Radial deviation:15-25 degrees	Extension with ulnar deviation	Neutral or slight flexion with ulnar deviation

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 list 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: It is 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	Palmar surface of the carpal bones	Adjacent carpal bones	Define the structure of the ligamentous palmar arch.

Wrist Retinacula

A band of thickened deep fascia around tendons is called a retinaculum. Its role is to hold the tendon in place. The wrist has two retinacula: flexor and extensor.

• Wrist flexor retinaculum is a fibrous band on the palmar side of the hand near the wrist. It arches over the carpal bones of the wrist and forms the carpal tunnel.
  • Medial attachment: pisiform bone and the hook of the hamate.
  • Lateral attachment: the tubercle of the scaphoid, and the crest of the trapezium.
  • Role: It serves as a pulley system for the carpal flexor muscles and provides stabilisation to the carpal system by supporting the transverse carpal arch.

• Extensor retinaculum is a fibrous, thickened band that holds the extensor tendons at the dorsum of the wrist. It is an oblique band runs downwards and medially.
  • Lateral attachment: the lower part of the anterior border of the radius
  • Medial attachment: the styloid process of the ulna, triquetral and pisiform bones.
  • The extensor retinaculum is located superficial to the extensor tendons and is continuous with the volar carpal ligament.
  • Role: prevents bowstringing (failure of the finger to fully flex accompanied by pain and discomfort)

Muscles of the Wrist

The muscles of the wrist can be grouped into compartments or based on the wrist action they perform.

The anterior compartment of the forearm has three layers: superficial, intermediate and deep. The superficial layer houses flexor carpi ulnaris, palmaris longus, flexor carpi radialis, pronator teres. Flexor digitorum superficialis is located in intermediate layer. Deep layer contains flexor pollicis longus, flexor digitorum profundus and pronator quadratus.

The posterior compartment of the forearm is divided into a superficial and deep layer. The superficial layer includes the extensor digitorum communis, extensor digiti minimi, extensor carpi ulnaris, and anconeus. The supinator is the muscle from the deep compartment of the posterior forearm.

The tables below present the wrist muscles according to their function:

Forearm Pronators

Muscle	Origin	Insertion	Innervation	Action
Pronator teres	Medial epicondyle of the humerus via the common flexor tendon The coronoid process of the ulna	The lateral surface of the radial shaft	Median nerve (C6-C7)	Elbow flexion Forearm pronation
Pronator quadratus	The oblique ridge of the ulnar shaft	The anterior surface of the radial shaft.	The anterior interosseous nerve	Pulls the distal end of the radius over the ulna, which results in the pronation of the radioulnar joint.
Brachioradialis	The lateral supracondylar ridge	The styloid process of the radius	Radial nerve (C5-C6)	Elbow flexor when the forearm is neutral Involved in pronation to neutralwhen the forearm is in supination

Forearm Supinators

Muscle	Origin	Insertion	Innervation	Action
Supinator	Supinator crest of the ulna The radial collateral ligament The annular ligament The lateral epicondyle of the humerus	Lateral surface of the radial shaft	Radial nerve (C5-C6)	Prime supinator of the forearm
Biceps brachii: Short head(SH) Long head(LH)	SH: the coracoid process of the scapula LH: the supraglenoid tubercle of the scapula	SH/LH: radial tuberosity	Musculocutaneous nerve	Flexes the elbow joint, particularly when the forearm is supinated. Assists with forearm supination
Brachioradialis	The lateral supracondylar ridge	The styloid process of the radius	Radial nerve (C5-C6)	Elbow flexor when the forearm is neutral Assist in supinating the forearm to neutral when the forearm is in pronation

Wrist Flexors

Muscle	Origin	Insertion	Innervation	Action
Flexor digitorum profundus	Ulnar shaft and the interosseous membrane	Distal phalanges of fingers two to five through four tendons	Median nerve (C7,8, T1) Ulnar nerve (C8, T1)	Fingers and wrist flexion
Flexor pollicis longus	The anterior surface of the shaft of the radius and the interosseous membrane	The distal phalanx of the thumb	Median nerve (C8, T1)	Weak wrist flexor in addition to flexing the thumb
Flexor digitorum superficialis humeroulnar head (HUH) radial head (RH)	HUH: medial epicondyle via the common flexor tendon and the coronoid process RH: radial tuberosity	The middle phalanges of fingers two to five via four tendons	Median nerve (C7-8, T1)	Wrist and fingers flexor
Flexor carpi radialis	The medial epicondyle of the humerus via the common flexor tendon	The bases of the second and third metacarpals	Median nerve (C6, C7)	Wrist flexion and radial deviation
Flexor carpi ulnaris	The medial epicondyle via the common flexor tendon The head of the ulna	The hamate and the base of the fifth metacarpal	Ulnar nerve (C7, C8)	Wrist flexion and ulnar deviation
Palmaris longus	The medial epicondyle via the common flexor tendon	The flexor retinaculum and palmar fascia	Median nerve (C8)	Weak wrist flexor Note: may be absent is some population

Wrist Extensors

Muscle	Origin	Insertion	Innervation	Action
Extensor carpi ulnaris	Lateral epicondyle of humerus via the common extensor tendon Posterior border of ulna	The base of the fifth metacarpal	Radial nerve (C7,8)	Wrist extension Wrist ulnar deviation
Extensor carpi radialis longus
Extensor carpi radialis brevis
Extensor digitorum

Ulnar Deviation

Muscle	Origin	Insertion	Innervation	Action

Radial Deviation

Muscle	Origin	Insertion	Innervation	Action

Innervation of the Wrist

Nerve	Origin	Branches	Motor fibres	Sensory fibres
Median nerve	Brachial plexus lateral and medial cords	Anterior interosseous	Pronator teres, flexor carpii radialis, palmares longus, flexor digitorum superficialis	The skin over thenar eminence, palmar aspect of the thumb, index, middle finger and radial half of the ring finger
Ulnar nerve	Brachial plexus medial cord	Articular branches Muscular branches The palmar and dorsal cutaneous branches Terminal branches in the hand: superficial branch of ulnar nerve deep branch of ulnar nerve.	Flexor carpi ulnaris, ulnar half of flexor digitorum profundus	Cutaneous innervation to the medial forearm and medial wrist
Radial nerve	Brachial plexus posterior cord	Superficial branch: lateral branch medial branch Deep branch: posterior interosseous nerve Posterior brachial cutaneous nerve Inferior lateral brachial cutaneous nerve Posterior antebrachial cutaneous nerve Muscular branches	Extensor carpii radialis brevis, supinator, extensor digitorum, extensor digiti minimi , extensor carpii ulnaris, extensor pollicis longus, abductor pollicis longus, extensor indicis	Touch, pain and temperature sensations to portions of the back of the upper arm, forearm, the back of the hand and fingers

Vascular Supply of the Wrist

Artery	Origin	Branches	Supply
Radial artery	Terminal branch of brachial artery
Ulnar artery	Terminal branch of brachial artery	Anterior and posterior ulnar recurrent arteries Common interosseous artery, palmar carpal arch, superficial palmar arch, and dorsal carpal branch
Common interosseous artery	Branch of ulnar artery	anterior and posterior interosseous arteries

Resources

• bulleted list
• x

or

1. numbered list
2. x

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
3. Carpal instability can be classified into (1) proximal or distal carpal rows instability, or carpal instability dissociative (CID), (2) instability related to disturbed midcarpal joint kinematics, or carpal instability nondissociative (CIND) characterized by clicking or snapping.
4. Midcarpal instability can occur as a result of the injury to the ulnar arm of the arcuate ligament. Palmar midcarpal instability is a painful condition characterised by a snap during the ulnar deviation motion, known as the catchup clunk.