carpal instability

definition

· carpal injury where loss of normal alignment of the carpal bones develops

epidemiology

· 10% of all carpal injuries result in instability

aetiology

· injury may vary

· minor sprain

· major ligamentous disruption

· fracture

· dislocation

· fracture-dislocation

· may be end-stage of

· nonunion or malunion of fracture

· rheumatoid arthritis

pathomechanics

· lunate is in state of dynamic balance

· scaphoid induced to flex under compressive load and induces flexion force on lunate

· triquetral inherently prefers to extend and induces extension force on lunate

· when dynamic balance interrupted, lunate follows unbalanced force

· loss of radial support from scaphoid

· lunate extends

· called dorsal intercalated instability

· loss of ulnar support from triquetral

· lunate flexes

· called volar intercalated instabiity

classification

· complex with no concurrence

· most frequent terms used introduced by Linschield and Dobyns

Terms

DISI (dorsal intercalated segment instability)

· most common

· lunate rotates into dorsiflexion

VISI (volar intercalated segment instability

· less common

· lunate rotates into flexion

Ulnar translocation

· ulnar shift of carpus on radius

· usually seen with rheumatoid arthritis

Dorsal subluxation

· dorsal shift of carpus on radius

· commonly seen with malunion of distal radial fractures

Types

Static

· recognisable on routine x-rays by loss of normal alignment of carpal bones

· end-stage condition

Dynamic

· x-rays normal

· carpal alignment changes from normal to abnormal during movement

Groups

CID (carpal instability dissociative)

· instability due to loss of linkage between individual carpal bones

· includes DISI and VISI

CIND (carpal instability nondissociative)

· no dissociation between carpal bones

· instability at radiocarpal or midcarpal joints

· includes ulnar translocation and dorsal subluxation

CIC (carpal instability complex)

· instabilities not otherwise classifiable

DISI

· most common form

Aetiology

· scaphoid fracture

· isolated trauma

· caused by fall on outstretched extended wrist where thenar eminence strikes ground first

· results from scapholunate dissociation

Pathomechanics

· palmarflexion of scaphoid with dorsiflexion of lunate

Clinical

Symptoms

· history of injury

· pain on radial side of wrist

· weakness of wrist

· certain movements may cause clicking or snapping

Signs

· swelling and tenderness over scapholunate joint is most specific

· Kirk-Watson test

· start with passive wrist ulnar deviation and thumb on scaphoid tuberosity

· painful clunk felt with passive wrist radial deviation

· clunk is dorsal displacement of proximal pole

Radiology

AP

· increased scapholunate interval

· > 3 mm

· called Terry Thomas sign

· palmarflexion of scaphoid

· scaphoid shortened

· ring sign (end-on view of cortex of distal pole of scaphoid)

· dorsiflexion of lunate

· appears quadrilateral

Lateral

· increased scapholunate angle

· > 70^o (usually 45^o)

· palmarflexion of scaphoid

· dorsiflexion of lunate

Stress

· with wrist

· clenched

· in ulnar deviation

· in radial deviation

· may show Terry Thomas sign

Bone scan

· increased uptake

· due to hyperaemia from synovitis

Arthrogram

· may show leak from ligamentous tears

· of limited use unless can compare with other side

CT and MRI

· of limited benefit

Arthroscopy

· best method of diagnosis

Treatment

Early

· within 3-6 weeks

· closed reduction

· anatomical reduction achieved

· may require percutaneous K wires

· cast for 8 weeks

· ligamentous repair

· if closed reduction unsuccessful

· dorsal and volar approach

· direct repair of ligaments

· temporary stabilisation with K wires

Late

· > 6 weeks

· surgery only for significant disability

· options are

· ligament repair and capsulodesis

· limited fusion

· best results from STT fusion

Prognosis

SLAC

· scapholunate advanced collapse

· pattern of osteoarthritis and subluxation seen in untreated chronic scapholunate dissociation

· degenerative changes

· between radial styloid and scaphoid

· in lunocapitate joint

· subluxation

· dorsal subluxation of capitate on lunate

· treatment

· replacement of scaphoid with implant

· midcarpal fusion

VISI

· less common

Aetiology

· isolated trauma

· caused by fall on outstretched extended wrist where hypothenar eminence strikes ground first

· results from triquetrolunate dissociation

Pathomechanics

· palmarflexion of lunate with dorsiflexion of triquetrum

Clinical

Symptoms

· history of injury

· pain on ulnar side of wrist

· weakness of wrist

Signs

· swelling and tenderness over triquetro-lunate joint

· positive ballottement test of Reagan

· triquetro-lunate ballottement

Radiology

AP

· palmarflexion of scaphoid

· scaphoid shortened

· ring sign

· palmarflexion of lunate

· appears triangular

· triquetrum distally displaced

· broken Shenton’s line (of proximal carpal row)

Lateral

· decreased scapholunate angle

· < 30^o (usually 45^o)

· palmarflexion of lunate

· dorsiflexion of scaphoid

Other

· as above

Treatment

Early

· within 3-6 weeks

· closed reduction and casting

· may use percutaneous K wires

Late

· > 6 weeks

· limited fusion

· triquetrohamate