Carpal instability is loss of normal alignment and motion between the carpal bones, most often from scapholunate ligament injury causing dorsal intercalated segment instability (DISI). Untreated instability can progress to scapholunate advanced collapse (SLAC) arthritis.

Definition

Situation where normal alignment of carpal bones is lost

Aetiology

DISI
- due to disruption of scapho-lunate articulation
VISI
- secondary to disruption of lunate & triquetral
Ulnar translocation
- rarely results from injury but is commonly seen in wrists affected by rheumatoid arthritis

Epidemiology

Scapholunate dissociation is the most common carpal instability
Lunotriquetral instability is less common
Young adults after falls and sporting injuries
Scapholunate injury is often associated with distal radius fractures
Frequently missed at initial presentation

Anatomy

Eight carpal bones arranged in proximal and distal rows
Proximal row is an intercalated segment with no tendon insertions
Scaphoid links proximal and distal rows
Under load the scaphoid tends to flex and the triquetrum to extend
SL and LT ligaments balance these opposing forces through the lunate

Two major groups of ligaments
- extrinsic ligaments course between carpal bones & radius or metacarpals
- intrinsic ligaments originate & insert in carpus
extrinsic ligaments are stiffer while intrinsic ligaments are capable of greater elongation before permanent deformation occurs

Extrinsic

Palmar

palmar extrinsic ligaments consist of 2 V-shaped ligamentous bands
- one is proximal & connects forearm to proximal carpal row
  - proximal limb consists of
    - radiolunotriquetral & radioscaphoid ligs laterally
    - ulnolunate & ulnotriquetral ligs medially
- one is distal & connects forearm to distal carpal row
  - distal limb of palmar extrinsic ligs consists of
    - radioscaphocapitate ligament laterally
    - ulnocapitate ligament medially

Dorsal

dorsal extrinsic ligaments
- radiotriquetral
- scaphotriquetral

Intrinsic

intrinsic ligs connect adjacent carpal bones
Proximal row
- intraarticular
  - connecting scaphoid to lunate & lunate to triquetrum
  - strong
  - critical for carpal stability

TFCC

separates ulna from carpus
- Made up of
  - TFC
  - dorsal & volar radio-ulna ligaments
  - ulnar collateral ligament
  - meniscus homologue
  - articular disc
  - sheath of ECU
- Variable thickness of TFC from 1 – 5mm depending on station of ulna (ulna variance)
- No tendons are directly attached to carpus

Rows/Columns

Traditional view
- proximal & distal row of carpal bones- scaphoid joining them
Taliesnik
- three columns
  - scaphoid being radial column
  - triquetral ulnar column
  - lunate & capitate with remaining carpal bones making up middle column
Navarro
- Three column modification
  - scaphoid, trapezium & trapezoid making up radial column
  - triquetral ulnar column
  - capitate & lunate along with hamate middle column

Pathology

Ligament disruption causes loss of normal carpal kinematics
SL disruption lets the scaphoid flex and the lunate extend, producing DISI
LT disruption lets the lunate flex with the scaphoid, producing VISI
Untreated SL dissociation progresses to SLAC arthritis
SLAC begins at the radial styloid, then radioscaphoid, then capitolunate, sparing radiolunate
Perilunate injuries progress from radial to ulnar (Mayfield stages)

Classification

4 Major Types of Carpal Instability

Type	Description
DISI	Dorsi-flexion (Dorsal Intercalated Segment Instability). Most common, where lunate is rotated into dorsi-flexion (zig zag alignment of radiolunatocapitate alignment)
VISI	Palmar flexion (Volar Intercalated Segment Instability)
Ulnar translocation	Abnormal translocation of lunate ulnarward Type 1 entire carpus is translocated ulnarward Type 2 relationship between radius & scaphoid is normal but scapholunate gap is wide Rheumatoid
Dorsal subluxation	Malunion fracture distal radius with reversal of normal palmar tilt

Original publication Linscheid RL, Dobyns JH, Beabout JW, Bryan RS. Traumatic instability of the wrist. Diagnosis, classification, and pathomechanics. J Bone Joint Surg Am. 1972;54(8):1612-32.

Instabilities May Be

Type	Description
Static	Loss of normal alignment can be seen on XR
Dynamic	Routine XR within normal limits. Instability can be produced by either voluntary movement or manipulation, eg between scaphoid + lunate, between lunate + triquetrum, or at midcarpal joint

Instabilities May Also Be Termed

Type	Description
Dissociative	S-L dissociation DISI L-T dissociation VISI
Nondissociative	May also result in VISI or DISI but 3 bones (S, L, T) act as unit, eg dorsal carpal subluxation, mid-carpal instability, Type 1 ulnar translocations

History

Fall on outstretched hand with wrist extension and ulnar deviation
Dorsal wrist pain and weak grip
Painful clicking or clunking with loading
Previous wrist injury and duration of symptoms
Hand dominance and occupation

Examination

painful wrist
clicking or clunking
Ballottement test
Watson test for scaphoid 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 dissociation
  - 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

Differential Diagnosis

Scaphoid fracture or non union
TFCC tear
Dorsal wrist ganglion
Kienböck disease
Midcarpal instability
Radiocarpal or STT arthritis
ECU subluxation

Treatment

of chronic instability depends on patients symptoms
Nonsurgical
- little disability
- > 80% of ROM
- > 80% grip strength

Scapholunate dissociation

Acute
- either closed manipulation or open reduction with pinning
Chronic: if no associated Osteoarthritis
- reattachment of scapholunate ligament
- dorsal capsuloligamentodesis (Blatt)
  - dorsal capsular flap used to prevent scaphoid from subluxing in palmar direction
  - ref: Blatt & Nathan ” Dorsal Capsulodesis for rotatory subluxation of scaphoid: review of long term results” Proc Am Soc of Surgery of Hand 1992
- STT fusion
  - problem is with radial impingement
- S-L or S-C fusion
  - if associated Osteoarthritis (ie SLAC)
- Excise (?replace) scaphoid & perform mid carpal fusion that is fusion of capitate, hamate, triquetral & lunate
  - (= 4 – corner fusion)
- total wrist fusion

Lunatotriquetral instability

Acute
- either immobilisation in BEPOP or direct repair of ligament
chronic
- Lunatotriquetral arthrodesis

Ulnar Translocation

Acute
- Repair of disrupted volar & dorsal radiocarpal ligs
Chronic
- ligament repair unreliable
- relocation of carpus & maintenance of reduction by radiolunate arthrodesis more reliable

Dynamic VISI & DISI

trial of nonoperative management with AEPOP/ NSAIDS/ local injection of steroids
Stabilisation of midcarpal joint limited fusion
Capsuloligamentodesis
tenodesis

Complications

SLAC wrist
Persistent pain and stiffness after reconstruction
Failure of repair with recurrent instability
Loss of wrist flexion after capsulodesis
Superficial radial nerve injury and pin site infection

Prognosis

Acute repair within about six weeks gives better results than late reconstruction
Static instability has a worse prognosis than dynamic instability
Untreated SL dissociation progresses to SLAC wrist
Salvage procedures relieve pain at the cost of motion

Reviewed by Professor Phong Tran, Head of Orthopaedic Surgery, Western Health. Last updated 10 October 2026.