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http://stagingupload.orthobullets.com/topic/6005/images/link joint.jpg
http://stagingupload.orthobullets.com/topic/6005/images/space of poirier.jpg
http://stagingupload.orthobullets.com/topic/6005/images/TTC Illustration - volar wrist ligaments_moved.jpg
http://stagingupload.orthobullets.com/topic/6005/images/mra radial collat.jpg
http://stagingupload.orthobullets.com/topic/6005/images/rsc diagram.jpg
http://stagingupload.orthobullets.com/topic/6005/images/mra 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  
    • 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   
      • 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
        • 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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