Carpal Instability

Carpal instability is a complex condition characterized by abnormal biomechanics in the carpus mainly by ligamentous disruption within or around carpus.

Lunate is normally under flexion force by scaphoid and extension force by triquetrum so lunate is stable.

Fall on an outstretched hand (FOOSH), Extension and Ulnar deviation

This will cause the axial load on the wrist. So there will be a tension site and compression site around the wrist

After the injury to scapholunate ligaments, the intercalated segment is pulled towards the triquetrum so a gap occurs between the scaphoid and lunate which is seen as a Terry -Thomas sign

Terry-Thomas Sign (AP view)

In lateral view:- Lunate will go with triquetrum in extension which is called Dorsal (Extension) intercalated segment instability (DISI) and scaphoid flexed.

Scaphoid gives Signet Ring appearances

X-ray findings

Terry Thomas sign, Signet ring sign

Clinical Test

Watson Test

FOOSH in extension and Radial deviation

This will also cause the axial load on the wrist. So there will be a tension site and compression site around the wrist

Scaphoid fracture/ Radial styloid fracture occurs in compression site

Lunate goes with scaphoid in flexion Volar (Flexion) intercalated segment instability(VISI)

Clinical Test

Reagen Ballotment Test

FOOSH in extension over the thenar eminence

The variable degree of axial load will cause perilunate dislocation

Mayfield stages of perilunate dislocation

Stage I: Scapho-lunate disruption

Stage II: Stage I + Luno-capitate disruption

Stage III: Stage II +Luno-triquetral disruption (Perilunate)

Stage IV: Ulno-triquetral( Lunate dislocated from lunate fossa; usually volar)

X-rays findings

The anteroposterior and lateral views will show

Spilled cup sign, Wedge shape sign

Classifications of Carpal Instability