Wrist and Hand Anatomy – Review Flashcards

Wrist & Hand Skeleton

• TWO SEGMENTED SYSTEMS
  • Forearm terminates at the distal radius/ulna
  • Hand begins at the carpals
• Carpal bones (8) ➜ two rows, mnemonic “Some Lovers Try Positions / That They Can’t Handle”
  • Proximal Row (radial ➜ ulnar)
  • Scaphoid
    • Tubercle
    • Aka “navicular”; most-fractured carpal (FOOSH)
    • Waist fractures interrupt distal→proximal blood flow → risk of mal-/non-union, AVN
    • Sx: pain over anatomic snuff-box
    • Immobilize in neutral; may need ORIF
  • Lunate
  • Triquetrum
  • Pisiform (sesamoid) – forms floor of Tunnel of Guyon w/ hamate hook
  • Distal Row
  • Trapezium (tubercle; saddle surface for 1st metacarpal)
  • Trapezoid
  • Capitate (large “keystone”)
  • Hamate (hook = Guyon roof)
• Metacarpals (5)
  • Base, shaft, head; numbered 1\rightarrow5 radial→ulnar
  • 1st MC saddle base → wide thumb ROM at CMC
  • Heads = knuckles (MCP joints)
• Phalanges
  • Medial four fingers: proximal, middle, distal
  • Thumb: proximal & distal only
  • Each ↔ concave base, shaft, convex head
• Sesamoids
  • Typical pair at 1st MCP within FPB & adductor pollicis; FPL runs between
  • Up to five sesamoids common → increase moment arm & protect tendons

Major Joints

Distal Radioulnar Joint (DRUJ)

• Synovial pivot between ulnar notch (radius) & ulnar head
• Pronation / supination
• Separated from carpals by TFCC

Radiocarpal Joint (RCJ)

• Distal radius + TFCC articulating with scaphoid, lunate (+triquetrum in ulnar deviation)
• Motions: flex/extend, radial (abd)/ulnar (add) deviation
• Issue: ulna does NOT articulate directly → TFCC provides seat & shock absorption

Intercarpal & Midcarpal Joints

• Plane synovials; cumulative gliding augments wrist range

Carpometacarpal (CMC)

• 2–5 = plane, minimal motion
• 1st = saddle; motions: flex, ext, abd, add, opposition, retroposition, axial rotation

Metacarpophalangeal (MCP)

• Condyloid: flex/extend (incl. hyper-ext), abd/add
• Reinforced by deep transverse MC lig & palmar plate; radial & ulnar collaterals (oblique dorsal→palmar)

Interphalangeal (PIP, DIP, IP-thumb)

• Hinge: flex/extend only; collateral ligs & palmar plate

Triangular Fibrocartilage Complex (TFCC)

• Components
  1. Dorsal & palmar radio-ulnar ligs
  2. Articular (ulnocarpal) disc
  3. Ulnolunate & ulnotriquetral ligs
  4. Meniscus homolog
  5. Ulnar collateral lig
• Functions
  • Completes RC articulation for ulna, transmits load \approx20\% axial force
  • Stabilizes DRUJ; cushions; smooth pronation/supination
• Pathology: degeneration / tear → ulnar-sided wrist pain, instability, early OA
• Ulnar variance
  • Positive variance (ulna longer) ↑TFCC compression; negative variance ↑Kienböck risk
  • Can change after radius fracture; monitor 16.9 mm example in slide

Extrinsic Ligamentous Support

• Flexor retinaculum (transverse carpal lig)
• Radial (lateral) collateral
  • Styloid → scaphoid & trapezium; resists ulnar deviation
• Ulnar (medial) collateral
  • Styloid → triquetrum & pisiform; resists radial deviation
• Palmar radiocarpal (strong)
  • Distal radius → proximal row; oblique ulnar course pulls hand into supination w/ forearm supination
• Dorsal radiocarpal (thin)
  • Oriented to carry hand with radius during pronation

Thumb Motion Vocabulary

• Extension, flexion
• Abduction, adduction
• Opposition (thumb pad to any finger), retroposition (return from opposition)
• Rotation (medial/internal during opposition; lateral external return)

Soft-Tissue Architecture

Palmar Aponeurosis

• Superficial & deep layers; skin anchor (grip) + protection; deep layer helps form carpal tunnel
• Clinical: Dupuytren’s Contracture → fibrosis, flexion of digits 4–5 (middle-aged males)

Digital Pulleys / Retinacula

• Flexor sheaths: Annular (A1–A5) & Cruciform (C) ligs create constant moment arm
• Rupture → bowstringing → ↑moment arm but tendon needs more excursion (active insufficiency)
• Extensor mechanism also has sagittal bands

Synovial Sheaths

• Surround all long flexor/extensor tendons; inflammation = tenosynovitis (vs. tendinitis)

Carpal Tunnel

• Roof: flexor retinaculum (scaphoid tub. & trapezium ↔ pisiform & hook of hamate)
• Contents (10): 4 FDS + 4 FDP + 1 FPL + median n.
• FCR in separate groove lateral
• Variants: thick synovium, cysts, lumbrical hypertrophy, FDS muscle belly, etc.
• Compression → CTS; evaluate for double-crush (proximal lesions)

Tunnel of Guyon

• Pisohamate canal for ulnar nerve/artery; susceptible to handlebar neuropathy

Intrinsic Hand Muscles

Thenar (median n. via recurrent br.–except Adductor)

1. Abductor pollicis brevis – abducts, assists opposition
2. Flexor pollicis brevis – flexes 1st MCP (superficial head median, deep head ulnar)
3. Opponens pollicis – opposition at 1st CMC
4. Adductor pollicis (oblique & transverse heads; deep ulnar n.) – thumb adduction

Hypothenar (deep ulnar n.)

• Abductor digiti minimi – abducts 5th
• Flexor digiti minimi – flexes 5th MCP
• Opponens digiti minimi – opposition of 5th to thumb

Lumbricals (4)

• Origins: FDP tendons; lateral 2 unipennate (median n.), medial 2 bipennate (deep ulnar)
• Actions: MCP flex + IP extend (via DDE)

Interossei

• Palmar (3) – “PAD” adduct digits 2,4,5; also MCP flex/IP extend (deep ulnar)
• Dorsal (4) – “DAB” abduct digits 2-4; assist lumbricals (deep ulnar)

Dorsal Digital / Extensor Expansion

• Triangular aponeurosis where ED splits: central slip → middle phalanx; lateral bands → distal
• Interossei & lumbricals join lateral bands for coordinated motion

Extensor Tendon Pathologies

• Mallet Finger: rupture/avulsion of ED at distal phalanx ⇒ DIP flexion lag; splint 6–8 wks or surgery
• Boutonnière Deformity: central slip rupture ⇒ PIP flexion + DIP hyper-ext; treat with PIP ext splint
• Swan-Neck Deformity: volar plate rupture or RA ⇒ PIP hyper-ext, DIP flexion; dorsal migration of bands

Neurovascular Supply

Arterial

• Ulnar a. → superficial palmar arch (gives 4 common palmar digital aa.)
• Radial a.
  • In snuff-box gives dorsal carpal branch → dorsal carpal arch (with ulnar dcb) → dorsal metacarpal/digital aa.
  • Princeps pollicis & radialis indicis, then continues as deep palmar arch (anastomoses w/ deep branch ulnar a.)
• Deep arch → palmar metacarpal aa. → join superficials

Venous: paired vv. follow aa. (not detailed in slides)

Nerves (terminal branches of brachial plexus)

• Musculocutaneous (C5–7): anterior arm; ➜ lateral antebrachial cutaneous
• Radial (C5–T1*): all posterior arm/forearm extensors; deep branch → PIN; sensation dorsum hand lat. 3½ digits
• Median ((C5)6–T1): most forearm flexors, thenar, lateral lumbricals; travels with brachial a.; AIN branch
• Ulnar (C8–T1): FCU, ulnar FDP half, hypothenar, interossei, adductor pollicis, medial lumbricals; passes cubital tunnel & Guyon canal

Nerve Entrapment “Blue Boxes”

• Median
  • Ligament of Struthers (supracondylar process) compression
  • Pronator syndrome (between pronator teres heads)
  • Carpal tunnel syndrome (CTS)
• Ulnar
  • Arcade of Struthers (medial arm fascial canal)
  • Cubital tunnel syndrome (posterior to medial epicondyle)
  • Guyon canal syndrome / handlebar neuropathy
• Radial
  • Mid-humerus fractures or Saturday-night palsy; PIN entrapment at supinator

Other Clinical Considerations

• Fractures: scaphoid, hamate, metacarpals (Boxer), phalanges
• Wrist dislocations & instabilities (e.g., perilunate)
• Capsulo-ligamentous injuries: Bull-Rider’s Thumb (UCL of thumb MCP), Skier’s thumb (gamekeeper’s)
• Hand infections: fascial spaces allow spread; tenosynovitis → urgent due to sheath continuity
• Ischemia: laceration of palmar arches can threaten digits; Allen test prior to arterial sticks
• Dermatoglyphics: palmar skin creases relate to aponeurosis; changes in Down syndrome

Cross-Sections & Imaging Pointers

• Carpal tunnel = volar; extensor compartments dorsally (6 fibro-osseous tunnels)
• MRI: look for TFCC tears, scaphoid waist fracture line, dorsal band disruptions

Summary of Functional Themes

• Hand relies on bony arcs (carpal rows, metacarpal arch) + ligamentous checks (palmar/dorsal RC, pulleys)
• Thumb mobility (saddle CMC + sesamoids) underpins precision grip & opposition
• Intrinsics balance extrinsic flexors/extensors allowing fine MCP/IP posture control via extensor expansion
• Neurovascular layout spirals from forearm into palm → compression sites often occur at fibro-osseous tunnels
• Clinical rehab: preserve glide after tendon repair (“no-man’s-land” zone II), maintain pulley integrity, protect vascular & neural structures after trauma