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Carpal Instability

Investigations

  • AP
    • AP wrist under axial load (clenched fist)
    • hand in radial & ulnar deviation
    • Findings
      • May demonstrate ­ distance between scaphoid & lunate or lunate & triquetral
    • DISI pattern
      • ­scapholunate gap
      • ring sign
        • with flexed scaphoid seen end on
      • scaphoid foreshortened
        • distance between ring & proximal pole less than 7mm
      • flexed scaphoid is seen with dorsiflexed lunate
      • (quadrilateral) & with triquetrum in distal (dorsiflexed) position
    • VISI pattern
      • ring sign
      • scaphoid foreshortened
      • lunate volar flexed (triangular)
      • triquetrum distal in relation to hamate ( dorsiflexed)
      • distance between ulnar head & triquetrum is reduced ( Mayersbach sign)
      • convex outline of proximal carpal row (= Shentons line of wrist) is interrupted by step off between lunate & triquetrum
    • Ulnar Translocn
      • Carpal-Ulnar distance
        • is distance from centre of head of capitate ( ie centre of rotation of carpus) & line produced along line of centre of ulna
        • Normally ratio of C-U distance/ length of 3rd metacarpal = .30 ± .03
        • ¯ in ulnar translocation
          • Lat: to assess opposite rotations of scaphoid & lunate
    • DISI pattern
      • when scapholunate joint is dissociated
        • scaphoid is palmar flexed
        • lunate is dorsiflexed
      • Scapho-lunate angle
        • Normal 30- 60° (av 46o)
        • DISI > 70°
    • VISI pattern
      • lunate palmar flexed
      • lunotriquetral angle
        • Normal -16 deg
        • Abn neutral or +ve
    • Ulnar Translocation
      • often associated with VISI
  • SLAC wrist (scapho-lunate advanced collapse)
    • With S-L dissocation
      • All load going through Radioscaphoid joint
      • degenerative process
      • radial styloid & scaphoid
      • luno-capitate joint (commonest pattern of degeneration 55%)
      • triscaphoid degeneration
        • between scaphoid, trapezium + trapezoid
        • 2nd most common pattern
  • Other Ixs
    • Bone scan
      • is useful to identify pathology
      • When bone scan is negative it suggests either that there is no injury or more frequently that problem is minor & can be treated non operatively
    • Arthrography
      • is helpful in finding ligament tears but ? significance as these may not necessarily be result of trauma but may indicate age related degenerative change
      • NB: need to compare with normal side
    • Arthroscopy
      • can directly visualise pathology