Wrist Ligaments

a. Interosseous: Extend deeply, directly between two bones

  • Radioscapholunate (RSL) aka Ligament of Testut (neurovascular conduit to SL ligament)
  • Scapholunate (SL) and Lunotriquetral (UL) – volar, dorsal and proximal fibrocartilaginous membrane components
  • Capitohamate (CH)

b. Palmar-proximal V: Converge as an “upside-down V” from the radius/ulna to lunate

  • Radio-luno-triquetral (RLT) – forms the radial part of proximal V (strongest ligament of wrist)
  • Ulnotriquetral (UT) and Ulnolunate (UL) – forms the ulnar part of proximal V
  • Triangular fibrocartilage (TFC)

c. Palmar-distal V: Converge as an “upside-down V” from radius/triquetrum to capitate

  • Radioscaphocapitate (RSC)
  • Scaphocapitate (SC)
  • Triquetrocapitoscaphoid (TCS)
  • Scaphotrapeziotrapezoid (STT)

d. Dorsal V: Converge as “horizontal V” from radius/scaphoid to triquetrum

  • Dorsal radiotriquetral (DRT)
  • Dorsal intercarpal ligament

e. Collateral:

  • Radial collateral
  • Ulnar collateral

Space of Poirier: an anatomical defect or weak spot in the floor of the carpal tunnel; it lies at the volar aspect of the proximal capitate, lying between the volar radiocapitate and volar radiotriquetral ligaments (see ligaments); area expands when wrist is dorsiflexed & disappears in palmar flexion; rent develops during dorsal dislocations, & it is through this defect that lunate displaces into the carpal canal.

Scapholunate instability:

  • >3 mm gap of scapholunate interval on AP view X-ray
  • Cortical ring sign on scaphoid (scaphoid flexes and beam catches tubercle on end)
  • Scapholunate angle >60 degrees in lateral X-ray (dorsiflexion instability), i.e. lunate is tilted dorsally

Lunotriquetral instability:

  • Cortical ring sign of scaphoid on AP view X-ray and triangular lunate
  • Scaphoid and Lunate are palmar flexed (Scapholunate angle <30 degrees)
  • Often no clear widening of lunotriquetral interval

Ulnar translocation:

  • Ratio of distance between the distance of center of capitate to longitudinal axis of ulna to the length of 3rd metacarpal <0.3

Mayfield classification of carpal instability: 4 stages of progressive perilunate dislocation

  • I – Scapholunate
  • II – Capitolunate
  • III – Perilunate
  • IV – Lunate

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