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Updated: Mar 24 2022

Wrist Ligaments & Biomechanics

Images of poirier.jpg Illustration - volar wrist ligaments_moved.jpg radial collat.jpg diagram.jpg of rsc and volar rl lig.jpg
  • Wrist Planes of Motion
    • Joints involved
      • radiocarpal
      • intercarpal
    • Three axes of motion
      • flexion-extension
      • radial-ulnar deviation
      • prono-supination
    • Normal and function motion
      • flexion (65 normal, 10 functional)
        • 40% radiocarpal, 60% midcarpal
      • extension (55 normal, 35 functional)
        • 66% radiocarpal, 33% midcarpal
      • radial deviation (15 normal, 10 functional)
        • 90% midcarpal
      • ulnar deviation (35 normal, 15 functional)
        • 50% radiocarpal, 50% midcarpal
  • Wrist Biomechanics
    • Three biomechanic concepts have been proposed:
    • Link concept
      • three links in a chain composed of radius, lunate and capitate
        • head of capitate acts as center of rotation
        • proximal row (lunate) acts as a unit and is an intercalated segment with no direct tendon attachments
        • distal row functions as unit
      • advantage
        • efficient motion (less motion at each link)
        • strong volar ligaments enhance stability
      • disadvantage
        • more links increases instability of the chain
        • scaphoid bridges both carpal rows
          • resting forces/radial deviation push the scaphoid into flexion and push the triquetrum into extension
          • ulnar deviation pushes the scaphoid into extension
    • Column concept
      • lateral (mobile) column
        • comprises scaphoid, trapezoid and trapezium
        • scaphoid is center of motion and function is mobile
      • central (flexion-extension) column
        • comprises lunate, capitate and hamate
        • luno-capitate articulation is center of motion
        • motion is flexion/extension
      • medial (rotation) column
        • comprises triquetrum and distal carpal row
        • motion is rotation
    • Rows concept
      • comprises proximal and distal rows
        • scaphoid is a bridge between rows
      • motion occurs within and between rows
  • Carpal Relationships
    • Carpal collapse
      • normal ratio of carpal height to 3rd metacarpal height is 0.54
    • Ulnar translation
      • normal ratio of ulna-to-capitate length to 3rd metacarpal height is 0.30
    • Load transfer
      • distal radius bears 80% of load
      • distal ulna bears 20% of load
        • ulna load bearing increases with ulnar lengthening
        • ulna load bearing decreases with ulnar shortening
  • Wrist Ligaments
    • The ligaments of the wrist include
      • extrinsic ligaments
        • bridge carpal bones to the radius or metacarpals
        • include volar and dorsal ligaments
      • intrinsic ligaments
        • originate and insert on carpal bones
        • the most important intrinsic ligaments are the scapholunate interosseous ligament and lunotriquetral interosseous ligament
    • Characteristics
      • volar ligaments are secondary stabilizers of the scaphoid
      • volar ligaments are stronger than dorsal ligaments
      • dorsal ligaments converge on the triquetrum
    • Space of Poirier
      • center of a double "V" shape convergence of ligaments
      • central weak area of the wrist in the floor of the carpal tunnel at the level of the proximal capitate
      • between the volar radioscaphocapitate ligament and volar long radiolunate ligament (radiolunotriquetral ligament)
        • wrist palmar flexion
          • area of weakness disappears
        • wrist dorsiflexion
          • area of weakness increases
      • in perilunate dislocations, this space allows the distal carpal row to separate from the lunate
      • in lunate dislocations, the lunate escapes into this space
  • Extrinsic Ligaments
    • Volar radiocarpal ligaments
      • radial collateral
      • radioscaphocapitate
        • at risk for injury with excessively large radial styloid
        • from radial styloid to capitate, creating a sling to support the waist of the scaphoid
        • preserve when doing proximal row carpectomy
          • acts as primary stabilizer of the wrist after PRC and prevents ulnar drift
      • long radiolunate
        • also called radiolunotriquetral or volar radiolunate ligament
        • counteracts ulnar-distal translocation of the lunate
        • abnormal in Madelung's deformity
          • referred to as Vickers ligament
      • radioscapholunate
        • Ligament of Testut and Kuentz
        • only functions as neurovascular conduit
          • not a true ligament
          • does not add mechanical strength
      • short radiolunate
        • stabilizes lunate
    • Volar ulnocarpal ligaments
      • ulnotriquetral
      • ulnolunate
      • ulnocapitate
    • Dorsal ligaments
      • radiotriquetral
        • also referred to as dorsal radiocarpal ligament (DRC) 
        • must also be disrupted for VISI deformity to form (in combination with rupture of lunotriquetral interosseous ligament rupture)
      • dorsal intercarpal (DIC)
      • radiolunate
      • radioscaphoid
  • Intrinsic (Interosseous) ligaments
    • Proximal row
      • scapholunate ligament
        • primary stabilizer of scapholunate joint
        • composed of 3 components
          • dorsal portion
            • thickest and strongest
            • prevents translation
          • volar portion
            • prevents rotation
          • proximal portion
            • no significant strength
        • disruption leads to lunate extension when the scaphoid flexes
          • creating DISI deformity
      • lunotriquetral ligament
        • composed of 3 components
          • dorsal
          • volar
            • strongest
          • proximal
        • disruption leads to lunate flexion when the scaphoid is normally aligned
          • creating VISI deformity (in combination with rupture of dorsal radiotriquetral rupture)
    • Distal row
      • trapeziotrapezoid ligament
      • trapeziocapitate ligament
      • capitohamate ligament
    • Palmar midcarpal
      • scaphotrapeziotrapezoid
      • scaphocapitate
      • triquetralcapitate
      • triquetralhamate
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