What is the difference between lunate and perilunate dislocation in an adult with a recent history of wrist trauma?

Lunate vs Perilunate Dislocation: Key Differences

The critical distinction is anatomical position: in a perilunate dislocation, the lunate maintains its normal relationship with the radius while the capitate and remaining carpus dislocate dorsally around it; in a lunate dislocation (the end-stage injury), the lunate itself dislocates volarly from both the radius and capitate, representing complete ligamentous disruption.

Anatomical Differences

Perilunate Dislocation

• The lunate remains aligned with the radius while the capitate and rest of the carpus dislocate dorsally 1
• Represents disruption of the relationship between the lunate and capitate specifically 2
• This is an earlier stage in the progressive injury pattern described by Mayfield 1

Lunate Dislocation

• The lunate bone itself dislocates from both the radius and the capitate, typically in a volar direction 1, 2
• Represents complete disruption of all stabilizing ligaments around the lunate 1
• This is the end-stage of the perilunate injury spectrum, with complete ligamentous failure 3

Radiographic Diagnosis

Lateral View (Most Critical)

• Perilunate dislocation: The lunate maintains normal alignment with the radius, but the capitate is displaced dorsally relative to the lunate 2
• Lunate dislocation: The lunate is displaced volarly and appears "spilled" or tilted, losing contact with both the radius and capitate 2
• The lateral radiograph is the primary diagnostic view for distinguishing these injuries 2

PA View Findings

• Look for scapholunate diastasis >4 mm and assess for associated fractures 4
• Evaluate carpal alignment and spacing abnormalities 4

Clinical Presentation

Common Features (Both Injuries)

• High-energy mechanism: fall on outstretched hand (FOOSH), falls from height, or motor vehicle crashes 2
• Pain and swelling over both dorsal and volar wrist surfaces 2
• Severely limited wrist range of motion 2
• Median nerve dysfunction is common, including acute carpal tunnel syndrome requiring urgent assessment 1

Important Caveat

• These injuries are frequently missed on initial presentation 1, 2
• Maintain high clinical suspicion even with relatively trivial trauma, as dorsal lunate dislocations can occur with low-energy mechanisms 3

Classification and Associated Injuries

Greater Arc vs Lesser Arc

• Greater arc injuries: Associated fractures of bones around the lunate (e.g., trans-scaphoid perilunate dislocation) 5
• Lesser arc injuries: Pure ligamentous disruption without fractures 5
• Trans-scaphoid perilunate dislocations may have more favorable outcomes than pure ligamentous injuries 6

Mayfield Classification

• Grades injury severity and guides surgical planning 1
• Progressive stages from scapholunate ligament disruption to complete lunate dislocation 1

Management Principles

Emergency Department

• Immediate closed reduction is mandatory to decompress neurovascular structures 1, 2
• This is temporizing; definitive treatment requires surgery 1

Definitive Treatment

• Open reduction with direct ligamentous stabilization is the treatment of choice 5, 1
• Goals: restore anatomical carpal alignment and maintain stability for ligament healing 1
• Percutaneous pinning alone or closed reduction without ligamentous repair leads to inferior outcomes and persistent carpal instability 6
• Scapholunate ligament repair should be performed routinely to reduce risk of chronic instability 6

Critical Timing

• Delayed management is associated with unfavorable prognosis including radiocarpal arthritis 5
• Emergency reduction and prompt surgical stabilization are paramount 5

Long-Term Outcomes

Expected Functional Results

• Most patients return to work within 6 months 1
• Permanent deficits are common: 20% reduction in grip strength, loss of range of motion (often 60-degree flexion-extension arc in poor outcomes), and chronic pain 6, 1
• Progressive midcarpal arthrosis develops frequently despite optimal treatment 1

Prognostic Factors

• Carpal instability (early or late) is the most bothersome complication and correlates with poor functional outcomes 6
• Trans-scaphoid variants may evolve more favorably than pure ligamentous injuries 6
• Inadequate ligamentous repair leads to persistent instability regardless of initial reduction quality 6