Wrist and Hand Anatomy

Wrist and Hand Anatomy

 

 

• Osteology ( Fig. 2.8)

  • Carpal bones

Ossification begins at the capitate (usually present at 1 year of age) and proceeds in a counterclockwise direction, according to posteroanterior radiographs of the right hand.

 

• Several key features are important to recognize in the individual carpal bones (Table 2.7).

• Metacarpals

  • Several characteristics allow identification of individual metacarpals (Table 2.8).

• Phalanges

Arthrology

 

• Distal radioulnar joint (DRUJ) articulation (most stable in supination)

• Radiocarpal (wrist) joint

  • Ellipsoid shape involving distal radius and the scaphoid, lunate, and triquetrum

  • Located at the level of the crease of proximal wrist flexion

  • Ligaments (Table 2.9; see Fig. 2.8)

    • Extrinsic ligaments bridge carpal bones to radius or metacarpals (e.g., radio-scapho-capitate); intrinsic ligaments attach carpal bones together (e.g., scapholunate).

    • Palmar/volar radiocarpal ligaments are the strongest supporting structures.

Space of Poirier: central weak area in floor of carpal tunnel; implicated in volar dislocation of lunate in perilunate dislocation

 

• Ligament of Testut (radioscapholunate ligament) functions as a neurovascular conduit.

• Triangular fibrocartilage complex (TFCC) (Fig. 2.9, Table 2.10): vascular supply from periphery (central portion avascular)

• Intercarpal joints

  • Proximal row

    • Scaphoid linked to the lunate (via the scapholunate ligament), which is linked to the triquetrum (via the lunotriquetral ligament)

    • Flexes with radial deviation and extends with ulnar deviation

      • SL ligament injury: dorsal intercalated segmental instability (DISI)

      • LT ligament injury: volar intercalated segmental instability (VISI)

    • Dorsal intercarpal ligaments are stronger.

  • Distal row

    • Dorsal and palmar intercarpal ligaments connect trapezium with trapezoid, trapezoid with capitate, and capitate with hamate.

    • Interosseous ligaments are much thicker in the distal row, connecting capitate and hamate (strongest), capitate and trapezoid, and trapezium and trapezoid (weakest).

• Midcarpal joint

  • Transverse articulations between proximal and distal rows are reinforced by palmar and dorsal intercarpal ligaments and carpal collateral ligaments.

  • Radial ligament is stronger.

     

     

     

     

     

    FIG. 2.6 Muscle attachments of the forearm (anterior and posterior views). From Drake RL et al, editors: Gray’s atlas of anatomy, ed 2, Philadelphia, 2015, Churchill Livingstone.

     

     

    Table 2.6

     

    Muscles of Forearm

     

     

    Muscle	Origin	Insertion	Action	Innervation
    Superficial Flexors
    Pronator teres	Medial epicondyle and coronoid	Midlateral radius	Pronating, flexing forearm	Median nerve
    Flexor carpi radialis	Medial epicondyle	Second and third metacarpal bases	Flexing wrist	Median nerve
    Palmaris longus	Medial epicondyle	Palmar aponeurosis	Flexing wrist	Median nerve
    Flexor carpi ulnaris	Medial epicondyle and posterior ulna	Pisiform	Flexing wrist	Ulnar nerve
    Flexor digitorum superficialis	Medial epicondyle, proximal anterior ulna,	Base of middle phalanges	Flexing PIP joint	Median nerve

    	and anterior radius
    Deep Flexors
    Flexor digitorum profundus	Anterior and medial ulna	Base of distal phalanges	Flexing DIP joint	Median–anterior interosseous/ulnar nerves
    Flexor pollicis longus	Anterior and lateral radius	Base of distal phalanges	Flexing IP joint, thumb	Median–anterior interosseous nerve
    Pronator quadratus	Distal ulna	Volar radius	Pronating hand	Median–anterior interosseous nerve
    Superficial Extensors
    Brachioradialis	Lateral supracondylar humerus	Lateral distal radius	Flexing forearm	Radial nerve
    Extensor carpi radialis longus	Lateral supracondylar humerus	Second metacarpal base	Extending wrist	Radial nerve
    Extensor carpi radialis brevis	Lateral epicondyle of humerus	Third metacarpal base	Extending wrist	Radial nerve
    Anconeus	Lateral epicondyle of humerus	Proximal dorsal ulna	Extending forearm	Radial nerve
    Extensor digitorum	Lateral epicondyle of humerus	Extensor aponeurosis	Extending digits	Radial–posterior interosseous nerve
    Extensor digiti minimi	Common extensor tendon	Small finger extensor expansion over proximal phalanx	Extending small finger	Radial–posterior interosseous nerve
    Extensor carpi ulnaris	Lateral epicondyle of humerus	Fifth metacarpal base	Extending/adducting hand	Radial–posterior interosseous nerve
    Deep Extensors
    Supinator	Lateral epicondyle of humerus, ulna	Dorsolateral radius	Supinating forearm	Radial–posterior interosseous nerve
    Abductor	Dorsal	First	Abducting/extending	Radial–posterior

    pollicis longus	ulna/radius	metacarpal base	thumb	interosseous nerve
    Extensor pollicis brevis	Dorsal radius	Thumb proximal phalanx base	Extending thumb MCP joint	Radial–posterior interosseous nerve
    Extensor pollicis longus	Dorsolateral ulna	Thumb dorsal phalanx base	Extending thumb IP joint	Radial–posterior interosseous nerve
    Extensor indicis proprius	Dorsolateral ulna	Index finger extensor apparatus (ulnarly)	Extending index finger	Radial–posterior interosseous nerve

    

• Carpometacarpal (CMC) joints

  • Thumb CMC joint

    • Highly mobile saddle-shaped joint

    • Supported by a capsule and radial, palmar, and dorsal CMC ligaments

  • Finger CMC joints

    • Gliding joints with capsules, dorsal CMC ligaments (strongest), palmar CMC ligaments, and interosseous CMC ligaments

• Metacarpophalangeal (MCP) joints

  • Palmar (volar plate), collateral, and deep transverse metacarpal ligaments

  • Cam mechanism (collateral ligaments tighten with MCP joint flexion)

• Interphalangeal (IP) joints

  • Hinge joints with capsules and obliquely oriented collateral ligaments

• Muscles of the hand ( Fig. 2.10, Table 2.11)

  • Extensor tendon anatomy

    • Extensor compartments of wrist: formed by the extensor retinaculum over dorsal wrist (Fig. 2.11, Table 2.12)

      • Anatomic snuffbox is bordered by tendons of the first and third dorsal wrist compartments. Extensor pollicis brevis (EPB) tendon serves as the radial snuffbox border, extensor pollicis longus (EPL) tendon as the ulnar border.

    • Extensor mechanism anatomy/intrinsic apparatus

      • Complex arrangement of structures that surround digits (Fig. 2.12, Table 2.13)

  • Flexor tendon anatomy

    • Carpal tunnel (Fig. 2.13)

      • Borders of the carpal tunnel listed in Table 2.14

      • Transverse carpal ligament (TCL): attaches radially to the scaphoid tuberosity and trapezial ridge and ulnarly to the hook of the hamate and pisiform

        • Divided in carpal tunnel release

      • Contains the median nerve and nine tendons (one flexor pollicis longus [FPL], four FDS, and four flexor digitorum profundus [FDP])

FDS to the middle and ring fingers are volar to FDS to index and small fingers.

 

• • • Decreases in volume with wrist flexion

 

 

 

 

 

FIG. 2.7 Volar flexors (superficial and deep).

From Drake RL et al, editors: Gray’s atlas of anatomy, ed 2, Philadelphia, 2015, Churchill Livingstone.

 

 

 

FIG. 2.8 Ligaments of the hand and interphalangeal joints.

From Drake RL et al, editors: Gray’s atlas of anatomy, ed 2, Philadelphia, 2015, Churchill Livingstone.

 

Table 2.7

 

Carpal Bone Features

 

 

Carpal Distinctive Features NoteS Bone
Scaphoid	Tubercle (TCL, APB), waist, proximal and distal poles	75% covered by articular cartilage Retrograde blood supply from dorsal carpal branch of radial artery
Lunate	Half moon shaped	Kienböck disease
Triquetrum	Pyramid shaped
Pisiform	Spheroidal (TCL, FCU)	In FCU tendon
Trapezium	FCR groove, tubercle (opponens, APB, FPB, TCL)	May be excised to treat thumb CMC arthritis
Trapezoid	Wedge shaped
Capitate	Largest bone, central location
Hamate	Hook (TCL)	Radial border of Guyon canal Deep motor branch of ulnar nerve under hook

APB, Abductor pollicis brevis; FPB, flexor pollicis brevis.

 

 

Table 2.8

 

Metacarpal Bone Features

 

 

Metacarpal Distinctive Features
I (thumb)	Short, stout; base is saddle shaped
II (index)	Longest, largest base; medial at base
III (middle)	Styloid process
IV (ring)	Small quadrilateral base, narrow shaft
V (small)	Tubercle at base (extensor carpi ulnaris)

 

Table 2.9

 

Extrinsic Ligaments of the Wrist

 

 

Dorsal
Dorsal intercarpal (DIC)	Dorsal support to translation of midcarpal joint
Dorsal radiocarpal (DRC)	aka radiotriquetral Controls ulnar translation
Volar
Radioscaphocapitate (RSC)	Supports scaphoid waist
Long radiolunate (LRL)	Strong tether to lunate displacement
Radioscapholunate (RSL)	Ligament of Testut (neurovascular conduit)
Short radiolunate (SRL)	Prevents dorsal lunate dislocation

 

 

 

Table 2.10

 

Triangular Fibrocartilage Complex

 

 

Component Origin Insertion
Dorsal and volar radioulnar ligament	Ulnar radius	Caput ulnae
Articular disc	Radius/ulna	Triquetrum
Prestyloid recess	Disc	Meniscus homologue
Meniscus homologue	Ulna/disc	Triquetrum/ulnar collateral ligament
Ulnar collateral ligament	Ulna	Fifth metacarpal

 

 

FIG. 2.9 Triangular fibrocartilage complex.

From Miller MD, Thompson SR, editors: DeLee and Drez’s orthopaedic sports medicine: principles and practice, ed 4, Philadelphia, 2014, Saunders.

 

 

 

FIG. 2.10 Muscle attachments (planar and dorsal views).

From Drake RL et al, editors: Gray’s atlas of anatomy, ed 2, Philadelphia, 2015, Churchill Livingstone.

 

Table 2.11

 

Muscles of the Hand

 

 

Muscle	Origin	Insertion	Action	Innervation
Thenar Muscles
Abductor pollicis brevis	Scaphoid, trapezoid	Base of proximal phalanx, radial side	Abducting thumb	Median nerve
Opponens pollicis	Trapezium	Thumb metacarpal	Abducting, flexing, rotating (medially)	Median nerve
Flexor pollicis brevis	Trapezium, capitate	Base of proximal phalanx, radial side	Flexing MCP joint	Median, ulnar nerves
Adductor pollicis	Capitate, second and third metacarpals	Base of proximal phalanx, ulnar side	Adducting thumb	Ulnar nerve
Hypothenar Muscles
Palmaris brevis	TCL, palmar aponeurosis	Ulnar palm	Retracting skin	Ulnar nerve
Abductor digiti minimi	Pisiform	Base of proximal phalanx, ulnar side	Abducting small finger	Ulnar nerve
Flexor digiti minimi brevis	Hamate, TCL	Base of proximal phalanx, ulnar side	Flexing MCP joint	Ulnar nerve
Opponens digiti minimi	Hamate, TCL	Small-finger metacarpal	Abducting, flexing, rotating (laterally)	Ulnar nerve
Intrinsic Muscles
Lumbrical	Flexor digitorum profundus	Lateral bands (radial)	Extending PIP joint	Median, ulnar nerves
Dorsal interosseous	Adjacent metacarpals	Proximal phalanx base/extensor apparatus	Abducting, flexing MCP joint	Ulnar nerve
Volar interosseous	Adjacent metacarpals	Proximal phalanx base/extensor apparatus	Adducting, flexing MCP joint	Ulnar nerve

 

 

FIG. 2.11 Extensor compartments of the wrist (1 to 6) (see Table 2.12). APL, Abductor pollicis longus; ECRB, extensor carpi radialis brevis; ECRL, extensor carpi radialis longus; ECU, extensor carpi ulnaris; EDC, extensor digitorum communis; EDM, extensor digiti minimi; EPB, extensor pollicis brevis; EPL, extensor pollicis longus. Modified from Miller MD et al: Orthopaedic surgical approaches, Philadelphia, 2008, Saunders, Figure HW-6.‌

 

• Guyon canal

• Contains ulnar nerve and artery

  • Borders: flexor retinaculum (deep), volar carpal ligament (superficial), pisiform (ulnar/proximal), hook of hamate (radial/distal)

• Flexor tendon sheath (Fig. 2.14)

  • Covers flexor tendons, protecting and nourishing tendons (vincula)

  • Five anular pulleys (A1–5) with three intervening cruciate attachments (C1–3)

     

     

    Table 2.12

     

    Extensor Compartments of Wrist

     

     

    CompartMent Contents

    NOTES

    I

    Abductor

    pollicis longus

    Pathologic

    CONDITIO

     

    	(APL), extensor pollicis brevis (EPB)	frequently has multiple tendon slips, which should be addressed during release for de Quervain tenosynovitis).
    II	Extensor carpi radialis longus (ECRL), brevis		Extensor ten (intersect syndrom
    III	Extensor pollicis longus (EPL)		Rupture Lister tuber (after fractu Drumme tendi of the
    IV	Extensor digitorum communis (EDC), extensor indicis proprius (EIP)		Extensor tenosyno
    V	Extensor digiti minimi (EDM)		Rupture (rheuma arthritis: Vaughn-Jackson syndrom
    VI	Extensor carpi ulnaris (ECU)	subsheath part of TFCC	Snapping at styloid

     

     

    FIG. 2.12 Extensor apparatus.

    From Drake RL et al, editors: Gray’s atlas of anatomy, ed 2, Philadelphia, 2015, Churchill Livingstone.

     

     

    Table 2.13

     

    Extensor Mechanism of Hand

     

     

    STRUCTURE	ATTACHMENTS	SIGNIFICANCE
    Sagittal bands	Covers MCP joint	Allows MCP extension
    Transverse (sagittal)	Volar plate fibers	Allows MCP flexion (interossei)
    Lateral bands	Covers PIP joint	Allows PIP extension (lumbrical muscles)
    Oblique retinacular ligament (Landsmeer)	A4 pulley, terminal tendon	Allows DIP extension (passive)

    • EPB tendon De Quervain ulnar to APL tenosyno tendon

    • APL

    • ECRL radial to ECRB

    • EPL tendon ulnar to ECRB tendon at the wrist level.

    • Ulnar to Lister tubercle

    • Tested by placing patient’s palm flat on table and lifting thumb.

    • EIP ulnar to index EDC

    • EIP most distal muscle belly

    • Small EDC present in only 25%

    • Sensory PIN in floor

    • EDM ulnar to small EDC

    • ECU

  • A2 and A4 pulleys originate from bone, whereas A1, A3, and A5 pulleys originate from the palmar plates of the metacarpal, proximal IP (PIP), and distal IP (DIP) joints.

  • A2 pulley, overlying the proximal phalanx, is the most critical to function, followed by A4, which covers the middle phalanx.

A1 pulley is involved in trigger digits.

 

Carpal Tunnel Borders

 

 

​​​​​​​​​​​​​​

BORDER	STRUCTURES
Roof	Transverse carpal ligament
Floor	Carpal bones
Radial	Scaphoid tubercle/trapezium
Ulnar	Hook of hamate

 

 

 

 

FIG. 2.14 Flexor tendon sheath.

From Drake RL et al, editors: Gray’s atlas of anatomy, ed 2, Philadelphia, 2015, Churchill Livingstone.

 

 

FIG. 2.13 Anatomy of the carpal tunnel.

From Drake RL et al, editors: Gray’s atlas of anatomy, ed 2, Philadelphia, 2015, Churchill Livingstone.