WRIST INSTABILITY
There is a long list of wrist ligaments, which can be divided anatomically - see list below
Be aware that there is some variation in nomenclature
Instability patterns and classification continue to evolve
Whatever the classification used (see below), careful x-ray interpretation is paramount

On all frontal and lateral x-rays, look for

      • Abnormal intercarpal distances
      • Scapholunate gap > 4mm
      • Scaphoid rotation (can be mimicked with radial deviation)
      • Shows as cortical ring sign
      • Scapholunate angle on lateral 40 - 60
      • Radiolunate angle on lateral 15 degrees

Stress views may demonstrate more subtle injury
Include PA in radial, ulnar deviation and grip and lateral grip
Used when there is clinical concern but normal baseline images

Clinical test include for scaphoid rotation and
Lunate ballotment test


PATTERNS OF ACUTE CARPAL INSTABILITY

      • Perilunate Trans-scaphoid
                  Scapholunate dissociation (VISI)
                  Scaphoid fracture
                  Lunocapitate ligament / Capitate fracture / Scaphocapitate syndrome
                  Lunotriquetral ligament dissociation (VISI)
                  Perilunate dislocation
                  Lunate dislocation
      • Radiocarpal
      • Midcarpal
      • Peritrapezium
      • Peritrapezium Peritrapezoid
      • Transtrapezium
      • Transhamate Peripisiform
      • Perihamate Peripisiform
      • Perihamate Transtriquetrum



VISI is abnormal volar angulation of the lunate
DISI is dorsal angulation
The normal scapholunate angle is 40-60 degrees
Look especially as the above when the scaphoid or distal radius is fractured
If wrist instabiity is missed and progresses SLAC wrist may develop

There are other classifications proposed, for example CIND (Carpal instability nondissociative) which group VISI and DISI in a slightly different way