Lunate and Perilunate Dislocations

Perilunate and lunate dislocations represent a spectrum of high-energy carpal injuries following the Mayfield progression of ligamentous disruption. Perilunate dislocation (Mayfield Stage III) maintains the lunate in the lunate fossa while the carpus dislocates dorsally. Lunate dislocation (Mayfield Stage IV) shows volar lunate displacement into the carpal tunnel ("spilled teacup" sign). Trans-scaphoid perilunate is the most common greater arc injury. These injuries are commonly missed on initial X-rays (25%). Treatment is urgent open reduction with ligament repair to prevent median nerve damage and progressive carpal instability.

Perilunate and lunate dislocations represent a spectrum of high-energy carpal injuries characterized by progressive failure of the perilunate ligamentous structures. These injuries are frequently missed on initial presentation (up to 25% of cases), leading to delayed diagnosis and poorer outcomes.

The mechanism involves forced hyperextension, ulnar deviation, and intercarpal supination, typically from a fall on an outstretched hand with the wrist in dorsiflexion. The injury progresses through predictable stages (Mayfield classification) as sequential ligaments fail.

Key Concepts:

• Perilunate dislocation: Lunate remains articulated with radius; carpus dislocates dorsally around it
• Lunate dislocation: Lunate dislocates volarly while proximal carpal row reduces
• Both are part of a continuous spectrum of progressive perilunar instability
• Associated fractures (greater arc) are common, especially scaphoid

Perilunate Ligamentous Anatomy

The lunate is the keystone of the proximal carpal row, with critical ligamentous attachments:

Intrinsic Ligaments (Interosseous):

• Scapholunate ligament: Strongest dorsally, key stabilizer
• Lunotriquetral ligament: Strongest volarly
• Both critical for carpal stability

Extrinsic Ligaments:

• Volar radiocarpal ligaments: RSC (radioscaphocapitate), LRL (long radiolunate), SRL (short radiolunate)
• Dorsal radiocarpal ligaments: DRC (dorsal radiocarpal)
• Space of Poirier: Weak zone between RSC and LRL - path of lunate dislocation

Greater Arc vs Lesser Arc

Lesser Arc (Pure Ligamentous):

• Injury passes through ligaments only
• Arc around the lunate through SL, capitolunate space, LT ligament
• Pure soft tissue injury
• More challenging reconstruction

Greater Arc (Fracture-Dislocation):

• Injury passes through bones
• Common fracture patterns:
  • Trans-scaphoid (most common)
  • Trans-radial styloid
  • Trans-capitate
  • Trans-triquetral
• Bone healing potentially easier than ligament healing

Mechanism of Injury

Typical mechanism:

• Fall on outstretched hand (FOOSH)
• Wrist in dorsiflexion
• Combined hyperextension + ulnar deviation + intercarpal supination
• High-energy trauma (MVA, fall from height, sports)

Force transmission:

1. Axial load through palm
2. Ground reaction force applied to thenar eminence
3. Wrist forced into hyperextension
4. Sequential ligament failure from radial to ulnar side

History

Mechanism:

• High-energy trauma typically
• Fall on outstretched hand
• Motor vehicle accident
• Sports injury (contact sports, cycling)

Symptoms:

• Severe wrist pain
• Rapid swelling
• Inability to move wrist
• Numbness in median nerve distribution (especially Stage IV)
• History may include feeling of "pop" or "shift"

Physical Examination

Inspection:

• Marked swelling of wrist
• Loss of normal wrist contour
• May see dorsal prominence (perilunate) or volar fullness (lunate)
• Skin tension assessment critical

Palpation:

• Diffuse tenderness
• Possible palpable lunate volarly (Stage IV)
• Assess for open injury or skin compromise

Neurovascular Examination:

• Critical: Median nerve function assessment
• Sensation in thumb, index, middle finger
• Thenar muscle strength (opponens pollicis)
• Two-point discrimination
• Compare with contralateral side

Range of Motion:

• Severely limited due to pain
• Do not force examination
• Document baseline for postoperative comparison

Red Flags Requiring Emergent Intervention

1. Acute carpal tunnel symptoms (numbness, tingling, weakness)
2. Open injury
3. Skin blanching or tension
4. Vascular compromise
5. Compartment syndrome signs

Differential Diagnosis

The painful, swollen, deformed wrist after a fall on the outstretched hand has several mimics. The single most important discriminator is the lateral radiograph: in a perilunate/lunate dislocation the normal radius-lunate-capitate colinearity is lost. Failure to make this distinction underlies the 25% missed-diagnosis rate (Herzberg 1993).

Plain Radiographs

Standard Views:

• PA (posteroanterior)
• True lateral
• Oblique views

PA View Findings:

Normal landmarks (Gilula's arcs):

• Arc I: Proximal articular surfaces of proximal row
• Arc II: Distal articular surfaces of proximal row
• Arc III: Proximal articular surfaces of capitate/hamate

Abnormal findings:

• Disruption of Gilula's arcs
• Widened SL interval (greater than 3mm = "Terry Thomas sign")
• Overlap or crowding of carpal bones
• Triangular or pie-shaped lunate = rotated lunate

Lateral View Findings:

Normal alignment:

• Radius, lunate, and capitate should be collinear
• Lunate "cup" should hold capitate "ball"

Perilunate dislocation (Stage III):

• Lunate remains in lunate fossa
• Capitate dislocated dorsally
• Lunate no longer articulates with capitate

Lunate dislocation (Stage IV):

• Lunate tilted volarly out of fossa
• "Spilled teacup" appearance
• Capitate may partially reduce into lunate fossa

CT Scan

Indications:

• Confirm diagnosis
• Identify associated fractures (greater arc injuries)
• Pre-operative planning
• Assess reduction quality post-operatively

Key Findings:

• Fracture lines in scaphoid, capitate, triquetrum, or styloid
• Extent of articular involvement
• Fragment size and displacement

MRI

Indications:

• Usually not needed acutely
• May help assess ligament integrity subacutely
• Useful for planning staged reconstruction

Findings:

• Ligament tears (SL, LT)
• Bone bruising pattern
• TFCC injury assessment

Early Complications

Median Nerve Injury:

• Acute compression from displaced lunate (Stage IV)
• Iatrogenic during reduction
• Carpal tunnel syndrome post-operatively
• Usually improves with reduction and CTR

Infection:

• Higher risk with open injuries
• Standard surgical infection risk

Failure of Reduction:

• Interposed tissue (capsule, tendons)
• Inadequate surgical technique
• May require repeat surgery

Late Complications

Post-traumatic Arthritis:

• Most common long-term complication
• Occurs in 50-70% at long-term follow-up
• May be asymptomatic
• Radiocarpal and midcarpal joints affected

Carpal Instability:

• Recurrent SL or LT dissociation
• Progressive collapse patterns (SLAC, SNAC equivalent)
• May require salvage procedures

Scaphoid Nonunion:

• In trans-scaphoid perilunate injuries
• Risk factors: Delay, inadequate fixation, smoking
• Requires revision surgery with bone grafting

AVN of Lunate:

• Rare but devastating
• Blood supply vulnerable during injury
• May lead to Kienböck's pattern
• Limited salvage options

Stiffness:

• Expected to some degree
• ROM typically 50-70% of normal
• Grip strength 60-80% of normal
• Therapy critical for optimization

Complex Regional Pain Syndrome

• Rare but serious complication
• Early recognition and treatment essential
• Multidisciplinary approach required

Immediate Postoperative (Day 0-2):

• Strict elevation to reduce swelling
• Neurovascular checks every 2 hours initially
• Watch for compartment syndrome (rare but catastrophic)
• Pain control with multimodal analgesia
• Finger range of motion exercises started immediately

Week 0-2:

• Volar splint or short arm cast
• Strict wrist immobilization
• Continue finger ROM
• First dressing change at 2 weeks
• Wound check and suture removal

Week 2-6:

• Continue immobilization
• May transition to removable splint for hygiene
• No active wrist motion yet
• K-wires remain in situ
• Serial X-rays every 2 weeks to assess alignment

Week 6-8 (K-wire Removal):

• X-rays to confirm maintained reduction
• K-wire removal in clinic (local anesthesia)
• Begin gentle active ROM exercises
• Avoid forceful grip or loading
• Hand therapy initiated

Week 8-12:

• Progressive ROM exercises
• Begin gentle strengthening
• Therapist-supervised program
• May use heat before exercises
• Continue to protect from forceful loading

Week 12-16:

• Unrestricted ROM exercises
• Progressive strengthening with weights
• Putty and grip exercises
• Functional activities

Month 4-6:

• Return to work (light duty may be earlier)
• Sports return based on individual progress
• Heavy labor typically 6 months minimum
• Expect ROM 50-70% of normal long-term
• Expect grip strength 60-80% of normal

Long-Term Follow-Up:

• X-rays at 6 months and 1 year
• Monitor for post-traumatic arthritis development
• Counsel regarding arthritis risk (50-70%)
• Salvage options if symptomatic arthritis develops

Functional Outcomes

Range of Motion:

• Expect 50-70% of normal wrist ROM long-term
• Extension typically most affected (loss of 30-40 degrees)
• Flexion loss of 20-30 degrees
• Radial/ulnar deviation relatively preserved
• Forearm rotation usually normal

Strength:

• Grip strength typically 60-80% of contralateral side
• Improves with therapy and time
• Plateaus around 12-18 months

Pain:

• Most patients have some residual pain
• Usually activity-related
• May worsen with arthritis development
• Pain scores improve with time if no arthritis

Return to Activities:

• Light work: 3-4 months
• Heavy labor: 6 months minimum
• Contact sports: 6-9 months
• Full recovery plateau: 12-18 months

Prognostic Factors

Good Prognosis Factors:

• Early treatment (within 7-14 days)
• Anatomic reduction achieved
• Secure ligament repair
• Greater arc injury (paradoxically - better bone healing)
• Young patient with good bone quality
• Compliant with therapy

Poor Prognosis Factors:

• Delayed diagnosis (over 4 weeks)
• Incomplete or malreduced carpus
• Failed ligament repair
• Lesser arc injury (poorer ligament healing)
• Associated nerve injury
• Multiple carpal fractures
• High-energy mechanism

Long-Term Arthritis Risk

Post-Traumatic Arthritis:

• Develops in 50-70% of patients by 5-10 years
• Radiographic arthritis often asymptomatic initially
• Risk factors:
  • Residual carpal malalignment
  • Articular cartilage damage at injury
  • Chronic instability
  • Delayed treatment

Arthritis Patterns:

• Radiocarpal joint most commonly affected
• Midcarpal joint (capitolunate) also common
• May progress to scaphoid nonunion advanced collapse (SNAC) or scapholunate advanced collapse (SLAC) equivalent pattern

Management of Symptomatic Arthritis:

• Conservative: NSAIDs, activity modification, splinting
• Injections: Corticosteroid for temporary relief
• Salvage surgery options:
  • Proximal row carpectomy (if capitate articular surface intact)
  • Four-corner fusion
  • Total wrist fusion (last resort for severe symptoms)
  • Wrist denervation for pain relief

Global Epidemiology

Perilunate injuries are rare but consistently under-recognised. They constitute roughly 7% of all carpal traumas in a pooled systematic review (van der Oest 2021), and pure carpal-bone dislocations are far less common than the much more frequent scaphoid fracture in population series (in a Singapore carpal-fracture cohort the scaphoid accounted for 99 of 162 carpal fractures, with only a small minority being perilunate fracture-dislocations; Hey 2011). Across the literature the demographic is strikingly uniform worldwide: young men injured by high-energy mechanisms (falls from height, road trauma, sport), reflecting the force required to fail the perilunate ligamentous ring.

Guideline & Consensus Landscape

No major society publishes a disease-specific clinical practice guideline dedicated to perilunate/lunate dislocations; management rests on body-of-evidence consensus rather than formal AAOS/NICE guidance. The points of broad international agreement are summarised below.

Registries

There is no dedicated international perilunate-injury registry, and arthroplasty registries (AOANJRR, the UK NJR, the American AJRR) do not capture these soft-tissue/carpal injuries because they are not arthroplasty procedures. The best population-level data therefore come from trauma databases and pooled systematic reviews (Liechti 2023; van der Oest 2021) rather than from a formal registry.

Practice Variation & Service Delivery

Internationally, the dominant modifiable factor is timely recognition and referral rather than choice of implant. Practice variation centres on approach (combined dorsal-volar versus dorsal-only versus arthroscopic-assisted reduction and fixation) and on routine versus selective carpal tunnel release; pooled data favour less invasive techniques where the injury pattern allows (Liechti 2023). High-income trauma systems with 24/7 hand-surgery cover and ready CT access achieve earlier definitive fixation, whereas in many settings inter-hospital transfer from regional centres is the rate-limiting step to surgery within the optimal window.

Australian Context

In Australia these high-energy injuries are triaged through major trauma networks to centres with hand-surgery support; inter-hospital transfer from regional centres is often required to achieve timely definitive fixation. CT is readily available at major trauma centres and is essential to distinguish trans-scaphoid (greater-arc) fracture-dislocations from pure ligamentous injuries and to plan fixation. Hand-therapy rehabilitation is accessible through public and private sectors, with return to heavy manual work typically around 4-6 months, though access can be limited in rural and remote regions. Workplace injuries are covered by state-based workers' compensation (WorkCover) schemes and road-trauma cases by state compulsory third-party (CTP) insurance; careful documentation of mechanism, initial neurovascular status and functional impairment is important for medico-legal and permanent-impairment assessment.