Lunotriquetral Instability

Lunotriquetral instability results from injury to the lunotriquetral interosseous ligament (LTIL), causing ulnar wrist pain and VISI (Volar Intercalated Segment Instability) deformity. Treatment depends on acuity and severity, with LT arthrodesis being the gold standard for chronic instability.

Definition

Lunotriquetral instability: Loss of stability between lunate and triquetrum due to LTIL injury, causing:

• Ulnar wrist pain: Pain on ulnar side of wrist
• VISI deformity: Lunate flexes volarly, triquetrum extends dorsally
• Functional impairment: Weakness, clicking, instability

LTIL (Lunotriquetral Interosseous Ligament):

• Connects lunate and triquetrum
• Stabilises ulnar carpus
• Injury causes VISI deformity

Epidemiology

• Incidence: 5-10% of carpal ligament injuries
• Age: Peak 20-40 years (trauma population)
• Gender: No clear predominance
• Mechanism: Fall on outstretched hand with ulnar deviation, or direct trauma
• Associated injuries: Perilunate dislocations, other carpal injuries

LTIL Anatomy

Lunotriquetral Interosseous Ligament (LTIL):

• Location: Between lunate and triquetrum
• Structure: Dorsal, volar, and interosseous components
• Function: Stabilises ulnar carpus, prevents VISI deformity
• Blood supply: Dorsal and volar carpal arches

Carpal kinematics:

• Proximal row: Scaphoid, lunate, triquetrum move together
• LT joint: Contributes less than 5% to wrist motion
• VISI: Lunate flexes volarly when LTIL disrupted

Pathophysiology

Injury mechanism:

• Fall on outstretched hand: With ulnar deviation
• Direct trauma: To ulnar side of wrist
• Perilunate dislocation: Often associated with LTIL injury

VISI deformity:

• Lunate: Flexes volarly (opposite of DISI)
• Triquetrum: Extends dorsally
• Capitolunate angle: Less than 0 degrees (normal 0-15 degrees)
• Scapholunate angle: Normal (SL intact)

Why VISI occurs:

• LTIL disruption: Loss of stabilisation between lunate and triquetrum
• Lunate unopposed: Flexes volarly (volar ligaments intact)
• Triquetrum: Extends dorsally (dorsal ligaments intact)

History

Symptoms:

• Ulnar wrist pain: Pain on ulnar side of wrist
• Clicking or clunking: With wrist movement
• Weakness: Grip strength reduced
• Instability: Feeling of wrist giving way

Mechanism:

• Fall on outstretched hand with ulnar deviation
• Direct trauma to ulnar side of wrist
• High-energy trauma (perilunate dislocation)

Physical Examination

Inspection:

• Swelling on ulnar side of wrist
• VISI deformity (if static)
• Prominence of ulnar head (if VISI)

Palpation:

• LT interval tenderness (ulnar to lunate)
• Ulnar wrist pain
• Crepitus at LT joint

Range of Motion:

• Wrist ROM may be limited
• Pain with ulnar deviation
• Clicking with motion

Special Tests

LT Ballottement Test (Reagan's Test):

1. Stabilise lunate with one hand
2. Translate triquetrum dorsally and palmarly with other hand
3. Positive: Pain, crepitus, or increased motion
4. Compare to contralateral side

LT Compression Test:

1. Ulnar deviation of wrist
2. Apply axial load through ring/small finger metacarpals
3. Positive: Pain at LT interval

Ulnar Snuffbox Test:

• Palpate ulnar snuffbox (between triquetrum and ulnar styloid)
• Positive: Tenderness indicates LT injury

Nonunion

10-15% incidence:

• Cause: Inadequate graft, poor fixation, smoking
• Prevention: Rigid fixation, bone graft, smoking cessation
• Management: Revision fusion with bone graft

Persistent Pain

10-15% incidence:

• Cause: Incomplete fusion, arthritis, other pathology
• Prevention: Complete cartilage removal, adequate graft
• Management: Assess for other causes, consider revision

Immediate Postoperative

• Immobilisation: Short arm cast (6-8 weeks)
• Weight bearing: Non-weight bearing on hand
• ROM: Finger ROM immediately
• PT: Wrist ROM after cast removal

Rehabilitation Protocol

Weeks 0-6:

• Short arm cast
• Finger ROM exercises
• Elevation to reduce swelling

Weeks 6-8:

• Cast removal
• Begin wrist ROM exercises
• Progressive strengthening

Weeks 8-12:

• Full ROM
• Progressive activity
• Return to sport/activity

Union and Hardware Removal

Union timeline: Typically 8-12 weeks postoperatively.

Hardware removal: Consider if prominent or symptomatic, usually after union confirmed (3-6 months).

Overall Outcomes

LT arthrodesis:

• Success rate: 85-90% (union, pain relief)
• Functional outcomes: 80-85% return to pre-injury level
• Motion loss: Minimal (LT contributes less than 5% to wrist motion)

Direct repair (acute):

• Success rate: 70-80% (if acute, less than 6 weeks)
• Functional outcomes: 70-75% return to pre-injury level
• Motion: Full motion preserved

Functional Outcomes

Return to activity:

• Timeline: 3-6 months postoperatively
• Rate: 80-85% return to pre-injury level
• Factors: Treatment method, timing, rehabilitation compliance

Pain relief:

• LT arthrodesis: 85-90% pain relief
• Direct repair: 70-80% pain relief (if acute)

Long-Term Prognosis

Arthritis progression:

• With arthrodesis: 5-10% develop adjacent joint arthritis
• Without treatment: 20-30% develop arthritis
• Risk factors: Chronic instability, associated injuries

Ulnar-sided wrist pain has many causes - LT instability is one of the harder diagnoses because radiographs are often normal. The following are the key mimics to exclude.

LT instability is a relatively uncommon, often under-diagnosed cause of ulnar-sided wrist pain worldwide. There are no large dedicated registries or formal society guideline statements specific to LT instability - management is guided by hand-surgery consensus and case-series evidence. The cross-cutting controversy globally is whether chronic LT instability is best treated by LT arthrodesis, soft-tissue/tendon-graft reconstruction, or by addressing an underlying positive ulnar variance with ulnar-shortening osteotomy.

Global Epidemiology

• Relative frequency: Far less common than scapholunate injury; estimated at a minority of intrinsic carpal-ligament injuries presenting with ulnar wrist pain.
• Two distinct populations: (1) younger patients with a traumatic hyperextension/twisting mechanism or perilunate-spectrum injury; (2) older patients with degenerative tears related to ulnar-positive variance and ulnocarpal impaction (Shin AY et al, JAAOS 2000).
• Frequent comorbidity: TFCC tears and positive ulnar variance commonly coexist and must be assessed - they change the operation.

Side-by-Side Practice (no single society guideline)

Registry and Evidence Notes

• No implant registry captures LT-specific procedures (these are bone-and-soft-tissue, not arthroplasty), so evidence rests on small retrospective series and systematic reviews (Athlani L et al, Hand Surg Rehabil 2023).
• Arthrodesis outcomes are not uniform: union/failure rates vary widely between centres - from union in all patients with rigid Herbert-screw + K-wire fixation (Nelson DL et al, 1993) to ~45% nonunion in another series (Vandesande W et al, 2001). This heterogeneity is itself an exam discussion point.

High- vs Limited-Resource Settings

• High-resource: Wrist arthroscopy for diagnosis and staging, MRI, intra-operative fluoroscopy, and CT to confirm union are routine.
• Limited-resource: Diagnosis relies on clinical ballottement testing, plain radiographs (including stress/clenched-fist views) and, where available, arthrography. Immobilisation and ulnar-shortening or fusion with simpler fixation are pragmatic; advanced arthroscopic reconstruction may be unavailable.