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