Courtesy: Prof Nabil Ebraheim, University of Toledo, Ohio, USA

 

 

Perilunate and Lunate Dislocation

Carpal Bone Arrangement

Normal proximal-to-distal relationship:

• Scaphoid
• Lunate
• Triquetrum
• Capitate

Carpal bones are stabilized by strong interconnecting ligaments.

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Types of Perilunate Injuries

Lesser Arc Injury

• Purely ligamentous injury

Greater Arc Injury

• Combination of ligamentous and bony injury

Common patterns:

1. Trans-radial styloid perilunate injury
2. Trans-scaphoid perilunate injury
3. Pure ligamentous perilunate injury
4. Combined ligamentous + bony injury
5. Chauffeur fracture (radial styloid fracture)
6. Trans-scaphoid perilunate fracture-dislocation

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Mayfield Stages of Perilunate Instability

Stage 1

Scapholunate Ligament Injury

• Initial disruption occurs at scapholunate ligament

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Stage 2

Capitolunate Injury

• Injury progresses through capitolunate articulation

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Stage 3

Lunotriquetral Injury

• Disruption of lunotriquetral ligament and joint

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Stage 4

Lunate Dislocation

• Failure of dorsal radiocarpal ligament
• Lunate rotates and dislocates volarly
• Produces classic:
  • “Spilled teacup sign”

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Lunate Dislocation

Key Features

• Lunate displaced volarly
• Loses normal articulation with radius
• Remaining carpus remains aligned with radius

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Clinical Importance

May compress median nerve causing:

• Acute carpal tunnel syndrome
• Numbness in radial three-and-a-half digits

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Radiographic Diagnosis

Important Radiological Signs

1. Gilula Lines

• Smooth carpal arcs should remain continuous

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2. Terry Thomas Sign

• Increased scapholunate gap
• Indicates scapholunate dissociation

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3. Piece of Pie Sign

• Triangular appearance of dislocated lunate on AP view

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4. Spilled Teacup Sign

• Volarly tilted lunate on lateral view

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5. Ring Sign

• Indicates volar flexion of scaphoid

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Carpal Alignment

Check collinearity of:

• Radius
• Lunate
• Capitate

Loss of alignment suggests perilunate instability.

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Important Angles

Scapholunate (SL) Angle

Normal:

• Approximately 30–60°
• Average around 47°

Abnormal:

• 60° suggests scapholunate dissociation

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DISI and VISI

DISI

(Dorsal Intercalated Segment Instability)

Mechanism:

• Scapholunate ligament disrupted
• Scaphoid flexes volarly
• Lunate follows triquetrum dorsally

Findings:

• Lunate dorsiflexed
• Increased SL angle

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VISI

(Volar Intercalated Segment Instability)

Mechanism:

• Lunotriquetral ligament disrupted
• Lunate follows scaphoid volarly

Findings:

• Lunate volar flexion

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Pathomechanics

Normal tendencies:

• Scaphoid tends to flex volarly
• Triquetrum tends to dorsiflex

Ligament disruption determines direction of lunate instability.

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Treatment

Acute Injuries (<8 weeks)

Initial Management

• Urgent closed reduction
• Relieves median nerve compression

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Definitive Treatment

• Open ligament repair
• Approaches:
  • Dorsal
  • Combined dorsal + volar

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Additional Procedure

• Carpal tunnel release if median nerve symptoms persist

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Chronic Injuries (>8 weeks)

Usually due to:

• Missed diagnosis
• Untreated instability

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Surgical Option

Proximal Row Carpectomy

Removal of:

• Scaphoid
• Lunate
• Triquetrum

Important:

• Preserve radiocapitate ligament
• Prevents carpal collapse

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Key Clinical Pearls

• Perilunate injuries are commonly missed
• Median nerve compression is an emergency
• “Spilled teacup sign” indicates lunate dislocation
• Terry Thomas sign indicates scapholunate dissociation
• DISI:
  • Scapholunate ligament injury
  • Lunate dorsiflexed
• VISI:
  • Lunotriquetral ligament injury
  • Lunate volar flexed
• Chronic missed injuries may require proximal row carpectomy