Lunate Fractures

Definition

Lunate fractures are fractures of the lunate carpal bone, the central "keystone" of the proximal carpal row. These fractures range from minor avulsion injuries to complete body fractures with significant implications for wrist function.

Epidemiology

• Incidence: Under 3% of all carpal fractures (very rare)
• Age distribution: Typically young to middle-aged adults
• Gender: Male predominance in acute trauma
• Mechanism: High-energy axial loading or hyperextension

Relationship to Kienbock's Disease

Kienbock's disease (lunate avascular necrosis) may develop:

• Following acute lunate fracture
• From repetitive microtrauma without acute fracture
• Due to inherent vascular compromise

The relationship between acute fracture and Kienbock's is complex, with both potentially representing points on a spectrum of lunate injury.

Clinical Significance

The lunate occupies a critical position in the wrist:

• Transmits approximately 50% of carpal load
• Central to proximal row kinematics
• Articulates with multiple carpal and forearm bones
• Injury affects entire wrist function

Understanding the lunate's central role is essential for appreciating the significance of these fractures.

Osseous Anatomy

Shape and Configuration

• Crescent-shaped when viewed laterally (lunate = moon-shaped)
• Volar horn: Projects palmarly, attachment for radiocarpal ligaments
• Dorsal horn: Smaller, attachment for dorsal intercarpal ligament
• Proximal surface: Convex, articulates with lunate facet of radius

Articular Surfaces

• Proximal: Articulates with radius (70%) and TFCC (30%)
• Radial: Articulates with scaphoid
• Ulnar: Articulates with triquetrum
• Distal: Articulates with capitate and often hamate (Type II lunate)

Type I vs Type II Lunates

• Type I (35%): Single distal facet for capitate only
• Type II (65%): Two distal facets - capitate and hamate
• Type II may have altered biomechanics affecting injury patterns

Vascular Anatomy

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Blood Supply Pattern

The lunate receives blood supply through two main patterns:

Y-Pattern (20%)

• Dorsal and volar vessels anastomose within bone
• More protected from AVN

I-Pattern (80%)

• Single dominant vessel (usually dorsal)
• No significant intraosseous anastomosis
• High risk of AVN with any fracture disrupting this vessel

Vessel Entry Points

• Dorsal: 1-3 vessels entering dorsal pole
• Volar: 1-2 vessels entering volar pole
• No intraosseous penetration from radial or ulnar surfaces

Biomechanics

Load Transmission

• Lunate transmits approximately 50% of axial wrist load
• Forces concentrated when ulnar variance is negative
• Normal lunate tilts volarly 10-15 degrees

Carpal Kinematics

• Part of proximal row "intercalated segment"
• Moves with scaphoid and triquetrum as functional unit
• Disruption leads to carpal instability patterns (DISI/VISI)

Ulnar Variance Impact

• Negative variance: Increased lunate loading
• Positive variance: Load shared with TFCC
• Average: Neutral (0 +/- 1mm)

Understanding the anatomy explains why certain fracture patterns carry higher risks.

TeisenLichtmanVascular

Teisen Classification

The Teisen classification is the most widely used system for acute lunate fractures:

Type I - Volar Pole Fracture

• Avulsion of volar horn by short radiolunate ligament
• Often associated with perilunate injury pattern
• Usually small fragment - may not require fixation
• Treatment: Immobilization if undisplaced, surgery if part of perilunate

Type II - Chip Fracture

• Small dorsal or volar avulsion fragment
• Usually minimal clinical significance
• Most common acute lunate fracture pattern
• Treatment: Cast immobilization, excision if persistently symptomatic

Type III - Dorsal Pole Fracture

• Larger dorsal horn fragment
• May involve scapholunate ligament attachment
• Risk of dorsal intercalated segment instability
• Treatment: Screw fixation if large, excision if small

Type IV - Sagittal Body Fracture

• Sagittal split through lunate body
• Moderate risk of AVN
• Disrupts articular surfaces
• Treatment: ORIF with headless compression screws

Type V - Transverse Body Fracture

• Coronal/transverse split through body
• Highest AVN risk (disrupts dominant vessel)
• Poor prognosis without treatment
• Treatment: Urgent ORIF, close monitoring for AVN

This classification guides prognosis and treatment selection.

Lichtman Classification (Kienbock's Disease)

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While not specific to acute fractures, this staging is essential for managing lunate pathology:

Stage I

• Normal radiographs
• MRI shows decreased T1 signal
• Bone intact structurally

Stage II

• Sclerosis visible on radiographs
• No collapse
• Bone scan positive

Stage IIIA

• Lunate collapse begins
• Carpal height maintained
• No fixed scaphoid rotation

Stage IIIB

• Lunate collapse with carpal changes
• Scaphoid rotation (ring sign)
• Proximal capitate migration

Stage IV

• Secondary degenerative arthritis
• Radiocarpal and intercarpal involvement
• End-stage disease

Understanding Kienbock's staging helps predict progression after acute lunate injury.

Gelberman Vascular Classification

This anatomical classification describes blood supply pattern:

Y-Pattern (20%)

• Multiple entering vessels
• Intraosseous anastomoses
• Lower AVN risk

X-Pattern

• Variant with crossed vessels
• Moderate anastomosis
• Intermediate risk

I-Pattern (80%)

• Single dominant vessel
• No significant anastomosis
• Highest AVN risk

Vascular pattern cannot be determined preoperatively but explains the high overall AVN rate after body fractures.

Classification guides treatment urgency and prognosis discussion.

History

Mechanism of Injury

• High-energy fall: FOOSH with axial loading
• Direct trauma: Rare due to protected position
• Sports injury: Gymnastics, contact sports
• Insidious onset: May indicate developing Kienbock's rather than acute fracture

Key History Points

• Exact mechanism and energy of injury
• Prior wrist symptoms (may indicate pre-existing Kienbock's)
• Occupational demands (manual labor, vibration exposure)
• Hand dominance
• Duration of symptoms

Physical Examination

Inspection

• Swelling may be subtle due to deep location
• No obvious deformity unless associated carpal injury
• Compare to contralateral wrist

Palpation

• Lunate fossa tenderness: Palpate with wrist slightly flexed
• Dorsal lunate: Tender with wrist extended
• May be difficult to localize with surrounding swelling

Range of Motion

• Limited wrist flexion and extension
• Pain with forearm rotation
• Grip weakness

Neurovascular Assessment

• Usually preserved
• Check median nerve (carpal tunnel with swelling)
• Document baseline for comparison

Special Tests

Watson Test (Scaphoid Shift)

• Assess for associated scapholunate injury
• Often positive with perilunate pattern injuries

Ballottement Test

• Lunotriquetral stability
• Assess for associated LT injury

Grind Test

• Axial load with rotation
• Positive if pain reproduced

Carpal Tunnel Assessment

• Phalen's and Tinel's tests
• May be positive with acute swelling

Clinical examination is often non-specific; imaging is essential for diagnosis.

📊 Management Algorithm

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Management decisions must consider the high risk of AVN with body fractures.

Surgical technique must minimize further vascular compromise.

Intraoperative Complications

Iatrogenic Fracture

• Lunate is small and fragile
• Risk during screw insertion
• Prevention: Careful technique, appropriate implant size
• Management: Additional fixation if occurs

Screw Malposition

• Joint penetration causes arthritis
• Prevention: Multiple fluoroscopy views
• Management: Revise if intra-articular

Vascular Injury

• Further compromise to tenuous blood supply
• Prevention: Minimize soft tissue stripping
• Cannot be assessed intraoperatively

Early Complications

Wound Complications

• Infection: Unusual but problematic for this small bone
• Dehiscence: May expose hardware
• Management: IV antibiotics, debridement if deep

Hardware Problems

• Screw prominence: May irritate extensor tendons
• K-wire migration: Remove early
• Management: Hardware removal once healed

Carpal Tunnel Syndrome

• May develop with swelling
• Treatment: Splinting, elevation, decompression if persistent

Late Complications

Avascular Necrosis (Most Critical)

• Occurs in up to 50% of body fractures
• May present months after injury
• Progressive pain, decreased motion
• Treatment depends on stage (see Kienbock's management)

Nonunion

• More common with body fractures
• Related to AVN in many cases
• Treatment: Bone grafting, revision fixation

Post-Traumatic Arthritis

• Consequence of AVN or articular malreduction
• Progressive wrist pain and stiffness
• Treatment: Activity modification to fusion

Carpal Instability

• DISI or VISI pattern may develop
• Related to associated ligament injury
• May require carpal fusion

AVN is the dominant concern in lunate fracture management.

Immediate Postoperative Care (0-2 Weeks)

Immobilization

• Splint in neutral wrist position
• Allow immediate finger motion
• Maintain elevation

Pain Management

• Multimodal analgesia
• Ice application
• Elevate extremity

Monitoring

• Watch for signs of infection
• Neurovascular checks
• Swelling assessment

Wound Care

Dressing Changes

• First change at 48-72 hours
• Assess wound healing
• K-wire site cleaning if applicable

Suture Removal

• 10-14 days postoperatively
• Apply steri-strips for support

Rehabilitation Phases

Phase 1: Protection (Weeks 0-2)

• Active finger motion
• Shoulder and elbow ROM
• Edema control with elevation and compression

Phase 2: Early Motion (Weeks 2-6)

• Begin gentle wrist ROM
• Removable splint between exercises
• Continue edema management
• Hand therapy referral

Phase 3: Progressive Loading (Weeks 6-12)

• Progress to functional activities
• Light grip strengthening
• Discontinue splint (usually at week 6)
• Normal ADLs

Phase 4: Return to Function (Weeks 12+)

• Progressive strengthening
• Sport-specific activities
• Work conditioning
• Full recovery may take 6-12 months

Follow-Up Schedule

MRI surveillance for AVN is critical, especially for body fractures.

Functional Outcomes by Fracture Type

Type I-III (Pole/Chip Fractures)

• Generally good to excellent outcomes
• Full ROM recovery expected
• Return to previous activities typical
• Low AVN risk

Type IV (Sagittal Body)

• Moderate outcomes
• Some motion loss common
• AVN in 30-40%
• May require secondary procedures

Type V (Transverse Body)

• Most guarded prognosis
• AVN in up to 50%
• Significant motion loss common
• Often progresses to Kienbock's

Prognostic Factors

Favorable Factors

• Pole or chip fractures
• Undisplaced pattern
• Early diagnosis and treatment
• MRI showing preserved vascularity
• Neutral or positive ulnar variance

Unfavorable Factors

• Body fractures (Type IV/V)
• Delayed diagnosis
• Associated carpal injuries
• MRI showing avascularity
• Negative ulnar variance

Natural History of Untreated Fractures

Chip Fractures

• May remain asymptomatic
• Occasional persistent pain
• Rarely progress to AVN

Body Fractures

• High rate of nonunion
• Progressive AVN development
• Eventual carpal collapse
• Secondary arthritis

Long-Term Outcomes

Without AVN

• Good grip strength recovery (80-90% of contralateral)
• Near-normal ROM
• Return to previous occupation and sport

With AVN (Kienbock's Development)

• Progressive deterioration
• May require salvage procedures
• Outcomes depend on stage at intervention:
  • Stage I-II: Core decompression or revascularization may preserve function
  • Stage IIIA: Motion-preserving procedures possible
  • Stage IIIB-IV: Limited wrist fusion or arthroplasty

Prognosis is largely determined by development or avoidance of AVN.

The evidence supports early fixation for body fractures and long-term AVN surveillance.

Understanding these key concepts will help with exam success.

Lunate fractures are uncommon injuries managed across Australian trauma centers. High-energy mechanisms including workplace falls in construction and mining industries, as well as motor vehicle and motorcycle accidents, account for most acute presentations.

The Australian orthopaedic community follows international consensus regarding the importance of MRI for diagnosis and vascularity assessment. Most major centers have ready access to MRI, though regional patients may experience delays that could impact early intervention.

Kienbock's disease management in Australia aligns with international practice, with radial shortening osteotomy being the preferred unloading procedure when indicated. Access to hand surgery subspecialists with experience in wrist reconstruction is available in capital cities, with telehealth consultation supporting regional practitioners.

Rehabilitation services through hand therapy are widely available in metropolitan areas. Workers compensation pathways support appropriate treatment and rehabilitation for occupationally-acquired injuries.

The Australian healthcare system provides comprehensive coverage for lunate fracture treatment through both public and private pathways, ensuring access to appropriate surgical care and long-term surveillance for AVN development.