High-yield overview

Keystone Carpal Bone | Risk of AVN | Kienbock's Disease Precursor

Under 3%Of all carpal fractures

DorsalMost common fragment location

AVN RiskUnique vascular pattern

Kienbock'sAssociated disease progression

TEISEN CLASSIFICATION (5 TYPES)

Type I

PatternVolar pole fracture

TreatmentProtected ROM, surgery if displaced

Type II

PatternChip fracture (dorsal or volar)

TreatmentImmobilization, excision if symptomatic

Type III

PatternDorsal pole fracture

TreatmentScrew fixation or excision

Type IV

PatternSagittal body fracture

TreatmentORIF with screws

Type V

PatternTransverse body fracture

TreatmentORIF, high AVN risk

Critical Must-Knows

Lunate is keystone of proximal carpal row - central to wrist biomechanics
Vulnerable blood supply - I-pattern lunates lack intraosseous redundancy (Gelberman)
Kienbock's disease may follow acute fracture or develop insidiously
Negative ulnar variance increases lunate loading and injury risk
Body fractures (Type IV/V) have highest risk of AVN and nonunion

Clinical Pearls

"
Lunate fractures are rare but frequently missed on plain radiographs
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MRI is essential for diagnosis and assessing vascularity
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Negative ulnar variance is major risk factor for Kienbock's
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Displaced body fractures require ORIF to prevent AVN

High-Yield Lunate Fracture Exam Points

The Keystone Bone

The lunate is the central link in the proximal carpal row, articulating with radius, scaphoid, triquetrum, capitate, and hamate. Its integrity is essential for normal wrist kinematics. Injury disrupts the entire wrist biomechanics.

Vascular Vulnerability

Gelberman described three intraosseous patterns (Y, I and X). The I-pattern lunate has a single dominant intraosseous vessel with minimal anastomosis, making it highly susceptible to avascular necrosis (AVN) when a body fracture crosses the central supply. Micro-CT work (van Alphen 2016) found around 14% of lunates have no dorsal nutrient vessel, creating volar-approach ischaemia risk.

Kienbock's Association

Acute lunate fracture can progress to Kienbock's disease (lunate AVN). However, most Kienbock's cases arise from repetitive microtrauma rather than acute fracture. Both share the common endpoint of lunate collapse and carpal arthritis.

Ulnar Variance Factor

Negative ulnar variance (short ulna) concentrates force on the lunate. This is a risk factor for both acute fracture and Kienbock's disease. Ulnar lengthening may be part of treatment in select cases.

At a Glance: Lunate Fracture Management

Fracture Type	Location	Management	Key Consideration
Type I - Volar pole	Volar lip	Immobilization or screw	Associated with perilunate injury
Type II - Chip	Dorsal or volar	Immobilization, excision if needed	Usually good prognosis
Type III - Dorsal pole	Dorsal lip	Screw fixation or excision	Assess for scapholunate injury
Type IV - Sagittal	Through body	ORIF with headless screws	Moderate AVN risk
Type V - Transverse	Through body	ORIF critical	High AVN risk - needs early fixation

Mnemonic

LUNATE - KLUNATE - Key Fracture Features

L	Location central Keystone of proximal carpal row
U	Ulnar variance matters Negative variance increases lunate load
N	Necrosis risk I-pattern (single dominant vessel) lacks redundancy - high AVN risk
A	Associated injuries Check for perilunate injury, SL damage
T	Teisen classification Types I-V based on fracture pattern
E	Early MRI essential Assess vascularity and occult fractures

L	Location central Keystone of proximal carpal row	N	Necrosis risk I-pattern (single dominant vessel) lacks redundancy - high AVN risk	T	Teisen classification Types I-V based on fracture pattern
U	Ulnar variance matters Negative variance increases lunate load	A	Associated injuries Check for perilunate injury, SL damage	E	Early MRI essential Assess vascularity and occult fractures

Hook:LUNATE - the keystone bone with Necrosis risk requiring early Assessment

Mnemonic

KIEN - KKIEN - Kienbock's Disease Features

K	Keystone collapse Progressive lunate collapse and fragmentation
I	Insidious onset Often no acute injury - repetitive microtrauma
E	Early MRI changes Signal changes precede X-ray findings
N	Negative ulnar variance Major risk factor - increased lunate load

K	Keystone collapse Progressive lunate collapse and fragmentation	E	Early MRI changes Signal changes precede X-ray findings
I	Insidious onset Often no acute injury - repetitive microtrauma	N	Negative ulnar variance Major risk factor - increased lunate load

Hook:KIEN-bock's develops Insidiously with Negative ulnar variance

Mnemonic

BOCK - MBOCK - Management Algorithm

B	Bone vascularity MRI to assess blood supply - critical for prognosis
O	Offload the lunate Radial shortening or ulnar lengthening
C	Core decompression For early disease - preserves bone structure
K	Kinematic fusion For advanced disease - limited intercarpal fusion

B	Bone vascularity MRI to assess blood supply - critical for prognosis	C	Core decompression For early disease - preserves bone structure
O	Offload the lunate Radial shortening or ulnar lengthening	K	Kinematic fusion For advanced disease - limited intercarpal fusion

Hook:BOCK management: assess Bone vascularity, Offload, Core decompression, Kinematic fusion

Overview and Epidemiology

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 one third of radio-ulno-carpal load through the radio-lunate joint (Schuind 1995)
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.

Anatomy/Biomechanics

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

Lunate bone anatomy and vascular supply patterns showing dorsal and volar vessel entry points — Lunate anatomy demonstrating vascular supply patterns - the majority have single vessel (I-pattern) supply making them susceptible to AVNCredit: Wikimedia Commons (CC BY-SA)

Blood Supply Pattern

Gelberman's classic cadaveric study described three intraosseous patterns, with a dorsal-volar anastomosis present in every specimen:

Y-Pattern

Dorsal and volar vessels meet in a robust intraosseous anastomosis
Most redundant supply, more protected from AVN

X-Pattern

Crossed dorsal and volar vessels with intermediate anastomosis
Intermediate AVN risk

I-Pattern

A single dominant intraosseous vessel with minimal anastomosis
Least redundant supply, highest risk of AVN when a fracture crosses it

Vessel Entry Points

Dorsal: 2-3 vessels feeding a dorsal capsular plexus, with 1-2 nutrient vessels entering the dorsal pole
Volar: 3-4 vessels feeding a volar plexus, with 1-2 nutrient vessels entering the volar pole
Micro-CT work (van Alphen 2016) found roughly 14% of lunates have no dorsal nutrient vessel
No intraosseous penetration from radial or ulnar surfaces

Vascular Pattern Determines Prognosis

The I-pattern lunate, with a single dominant intraosseous vessel and minimal anastomosis, explains why body fractures (Type IV/V) carry such high AVN risk - the fracture line can isolate a major portion of the bone from its only supply. Pattern cannot be determined before surgery.

Biomechanics

Load Transmission

The radio-lunate joint transmits approximately one third of radio-ulno-carpal load; the radio-scaphoid joint carries about 55% and the TFCC about 10% (Schuind 1995)
Forces concentrated on the lunate 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.

Classification Systems

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.

Classification Comparison

Teisen Type	Location	AVN Risk	Typical Treatment
Type I	Volar pole	Low	Immobilization or ligament repair
Type II	Chip/avulsion	Very low	Cast, excision if symptomatic
Type III	Dorsal pole	Low-moderate	Screw fixation or excision
Type IV	Sagittal body	Moderate-high	ORIF with screws
Type V	Transverse body	High	Urgent ORIF

Classification guides treatment urgency and prognosis discussion.

Clinical Assessment

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.

Differential Diagnosis

Dorsal central wrist pain after a fall has a wide differential. The lunate fracture must be distinguished from injuries with overlapping tenderness and from chronic lunate pathology.

Differential Diagnosis of Central Dorsal Wrist Pain

Diagnosis	Key Distinguishing Feature	Best Discriminating Investigation
Lunate fracture	Lunate fossa tenderness; subtle or absent fracture line on X-ray	MRI (occult fracture, viability) or CT
Kienbock's disease (lunate AVN)	Insidious onset, no clear acute injury; lunate sclerosis/collapse	MRI - low T1 signal; X-ray for staging
Scaphoid fracture	Anatomical snuffbox and scaphoid tubercle tenderness	Scaphoid-series X-ray; MRI if occult
Perilunate / lunate dislocation	Deranged carpal arcs; 'spilled teacup' or 'piece-of-pie' sign on lateral	PA and lateral X-ray; CT for fractures
Scapholunate ligament injury	Positive Watson scaphoid-shift test; SL gap on clenched-fist view	Stress X-ray; MRI/arthroscopy
Distal radius fracture	Dorsal metaphyseal tenderness and deformity	PA and lateral X-ray
Wrist sprain / occult bone bruise	Diffuse tenderness, normal X-ray, settles with time	MRI if persistent

Investigations

Plain Radiographs

Lateral radiograph showing lunate position and carpal alignment assessment — Radiographic assessment of lunate fracture - lateral view is essential for evaluating lunate position and detecting DISI/VISI patternsCredit: Radiopaedia (CC BY-NC-SA)

Standard Views

PA view: May show fracture line, sclerosis, or collapse
Lateral view: Assess lunate position (DISI/VISI), dorsal fractures
Scaphoid view: Additional perspective on carpal relationships

Radiographic Signs of Acute Fracture

Fracture line (often subtle or absent)
Slight density change
Associated carpal malalignment

Signs of Kienbock's Disease

Increased lunate density (sclerosis)
Loss of carpal height
Lunate collapse and fragmentation
Secondary arthritis (late)

Ulnar Variance Measurement

Measure on neutral rotation PA view
Negative variance (short ulna) is risk factor
Compare to contralateral if available

CT Scanning

Indications

Characterize fracture pattern for surgical planning
Assess for occult fracture not seen on X-ray
Evaluate associated carpal injuries

Key CT Findings

Fracture line orientation (sagittal vs transverse)
Fragment size and displacement
Articular surface involvement
Comminution assessment

MRI

Critical Role in Lunate Pathology

MRI is essential for:

Detecting occult fractures missed on X-ray
Assessing lunate vascularity
Differentiating acute fracture from Kienbock's
Evaluating ligamentous injuries

Signal Changes

Normal lunate: Isointense to other carpal bones
Early ischemia: Decreased T1 signal
Established AVN: Low T1 and T2 signal
Revascularization: Mixed signals

Gadolinium Enhancement

Enhanced signal suggests preserved vascularity
Absence of enhancement indicates AVN
Helps predict prognosis

Bone Scan

Limited Role

Sensitive but not specific
Hot lunate in any pathology
Superseded by MRI for most indications

Investigations are summarized in the table below.

Imaging Modalities for Lunate Fractures

Modality	Primary Role	Advantages	Limitations
Plain X-ray	Initial screening	Available, low cost	Misses early/occult fractures
CT scan	Fracture characterization	Bone detail, 3D planning	No vascularity assessment
MRI	Vascularity, occult injury	Soft tissue, blood supply	Cost, availability
Bone scan	Rarely needed	Sensitive for pathology	Non-specific

MRI is the key investigation for determining treatment and prognosis.

Management Algorithm

Non-Operative Management

Indications

Type I (volar pole) - undisplaced
Type II (chip fractures) - most cases
Type III (dorsal pole) - small, undisplaced fragments
Elderly, low-demand patients with body fractures

Protocol

Immobilization

Short arm cast or splint
Wrist in neutral position
Include thumb if scaphoid concern
Duration: 6-8 weeks minimum

Follow-Up

Week 2: Clinical review, check cast
Week 6: Repeat radiographs
Week 8-12: MRI if symptoms persist
Monitor for AVN development (may take months)

Transition to Rehabilitation

Begin ROM when clinically healed
Progressive strengthening
Monitor for late complications

Expected Outcomes

Type II fractures: Excellent prognosis
Type I/III: Good with proper immobilization
Body fractures: Higher failure rate with non-operative treatment

Non-operative management requires vigilant monitoring for AVN.

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

Surgical Technique

Dorsal Approach for Lunate Fracture ORIF

Patient Positioning

Supine with arm table
Tourniquet on upper arm
Consider traction tower for visualization

Incision and Exposure

Skin Incision

Dorsal longitudinal over wrist
Centered on Lister's tubercle
4-5 cm length

Deep Dissection

Incise retinaculum between 3rd and 4th compartments
Protect EPL tendon (retract radially)
Retract EDC ulnarly
Capsulotomy - ligament-sparing technique preferred

Fracture Reduction

Visualization

Flex wrist to expose lunate dorsum
Identify fracture pattern
Assess vascularity (bleeding from bone)

Reduction Technique

Gentle manipulation of fragments
Provisional K-wire fixation
Confirm reduction with fluoroscopy
Assess articular surface congruity

Fixation

Headless Compression Screw

Select appropriate screw size (2.0-2.4mm)
Start at dorsal cortex
Aim for volar cortex (or far fragment)
Countersink beneath cartilage
Confirm position on multiple fluoroscopy views

Supplemental Fixation

K-wire for rotational control if needed
Second screw for large body fractures

Closure

Repair capsule meticulously
Close retinaculum loosely
Standard skin closure
Splint in neutral position

Gentle handling throughout preserves the tenuous blood supply.

Surgical technique must minimize further vascular compromise.

Complications

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)

High risk after displaced body fractures (Type IV/V) that cross the central supply; small case series rather than large cohorts inform exact rates
May present months after injury
Progressive pain, decreased motion
Treatment depends on stage and viability (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

Complication Management Summary

Complication	Risk Factors	Prevention	Management
AVN	Displaced body fractures, I-pattern supply	Early fixation, gentle technique	Stage/viability-dependent: unloading to salvage
Nonunion	AVN, inadequate fixation	Stable fixation, bone graft	Revision fixation, vascularized graft
Arthritis	Malreduction, AVN	Anatomic reduction	Arthrodesis options
Hardware problems	Prominent implants	Countersink screws	Hardware removal

AVN is the dominant concern in lunate fracture management.

Postoperative Care

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

Timepoint	Assessment	Imaging
Week 2	Wound check	Optional
Week 6	ROM, healing	Radiographs
Week 12	Function	Radiographs
Month 6	AVN surveillance	MRI recommended
Year 1	Long-term outcome	As needed
Year 2	Final review	If symptomatic

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

Outcomes and Prognosis

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
Moderate-to-high AVN risk
May require secondary procedures

Type V (Transverse Body)

Most guarded prognosis
Highest AVN risk of the Teisen types
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.

Evidence Base

Level V (cadaveric)

Gelberman RH, Bauman TD, Menon J, Akeson WH. The vascularity of the lunate bone and Kienbock's disease

Key Findings:

35 cadaver lunates injected and cleared; extraosseous supply via 2-3 dorsal and 3-4 volar vessels
Intraosseous supply formed three consistent patterns (Y, I and X) with a dorsal-volar anastomosis in every specimen
The I-pattern (single dominant intraosseous vessel with minimal anastomosis) is the least redundant and most vulnerable
Findings support a compression-fracture theory for Kienbock's disease

Clinical Implication: The original lunate vascularity study. Although every specimen had some anastomosis, the I-pattern subgroup has the least intraosseous redundancy, explaining why body fractures crossing the central bone carry the highest avascular necrosis risk and why soft-tissue stripping must be minimised.

Source: J Hand Surg Am 1980;5(3):272-8

Verify on PubMed (PMID 7400565)

Level IV

Teisen H, Hjarbaek J. Classification of fresh fractures of the lunate

Key Findings:

Radiographs of 17 patients with acute lunate fractures reviewed with long-term follow-up
Proposed the five-group classification (volar pole, chip, dorsal pole, sagittal body, transverse body)
Fractures classified by radiological appearance and by lunate vascular anatomy
Body fractures crossing the nutrient supply carry the worst prognosis

Clinical Implication: The Teisen classification remains the reference standard for describing acute lunate fractures and links fracture geometry to the vascular territory at risk.

Source: J Hand Surg Br 1988;13(4):458-62

Verify on PubMed (PMID 3249151)

Level V (review)

Lichtman DM, Pientka WF, Bain GI. Kienbock disease: a new algorithm for the 21st century

Key Findings:

Updated algorithm integrating the osseous (Lichtman) stage with perfusion (Schmitt) and cartilage (Bain) classifications
Early intact-lunate disease is protected non-operatively, then unloaded if it fails
Compromised lunate reconstructed with medial femoral condyle graft or proximal row carpectomy
Advanced collapse (KALC) managed by salvage procedures only

Clinical Implication: Modern staging is multi-dimensional (bone plus perfusion plus cartilage); treatment of lunate avascular necrosis after fracture is stage- and viability-dependent, not stage-alone.

Source: J Wrist Surg 2016;6(1):2-10

Verify on PubMed (PMID 28119790)

Level V (biomechanical model)

Horii E, Garcia-Elias M, Bishop AT, Cooney WP, Linscheid RL, Chao EY. Effect on force transmission across the carpus in procedures used to treat Kienbock's disease

Key Findings:

Rigid-body spring model; intact radio-lunate joint carried a mean 32% of total radio-ulno-carpal load
A 4 mm radial shortening or ulnar lengthening reduced radio-lunate load by 45%
Limited intercarpal fusions reduced radio-lunate load by no more than 15%
Capitate shortening unloaded the lunate but dangerously overloaded adjacent joints

Clinical Implication: Provides the biomechanical rationale for joint-levelling osteotomy as a lunate-unloading procedure and explains why radial shortening is preferred over fusion or capitate shortening for unloading.

Source: J Hand Surg Am 1990;15(3):393-400

Verify on PubMed (PMID 2348055)

Level V (biomechanical model)

Schuind F, Cooney WP, Linscheid RL, An KN, Chao EY. Force and pressure transmission through the normal wrist: a theoretical two-dimensional study in the posteroanterior plane

Key Findings:

Force transmission at the radio-ulno-carpal joint was 55% radio-scaphoid, 35% radio-lunate and 10% through the TFCC
Peak pressure was highest at the proximal radio-scaphoid pole
Ligaments resisting ulnar translation were most important for load transfer
Wrist morphology and age had little effect on load distribution

Clinical Implication: Quantifies that roughly one third (not one half) of axial wrist load passes through the lunate fossa, with the TFCC sharing about 10%, underpinning the role of ulnar variance in lunate loading.

Source: J Biomech 1995;28(5):587-601

Verify on PubMed (PMID 7775494)

Level IV

Israel D, Delclaux S, Andre A, Apredoaei C, Rongieres M, Bonnevialle P, Mansat P. Peri-lunate dislocation and fracture-dislocation of the wrist: retrospective evaluation of 65 cases

Key Findings:

65 surgically treated perilunate injuries; 62 of 65 displaced dorsally
Lunate osteonecrosis occurred in 7.7% and wrist arthritis in 58.5% at a mean 8-year follow-up
Secondary surgery was required in 26% of cases
Osteochondral lesions and a changed scapholunate angle predicted later osteoarthritis

Clinical Implication: Acute lunate injuries frequently occur within a high-energy perilunate pattern; early anatomic reduction with ligament repair and fracture fixation is needed, and long-term arthritis and osteonecrosis surveillance is essential.

Source: Orthop Traumatol Surg Res 2016;102(3):351-5

Verify on PubMed (PMID 26897257)

The evidence supports joint-levelling for lunate unloading, anatomic fixation of body and perilunate injuries, and long-term avascular necrosis surveillance.

Viva Scenarios

Clinical Decision Scenarios

Use these scenarios to practise clinical reasoning and management decisions

CLINICAL SCENARIOStandard

Acute Lunate Fracture Evaluation

CLINICAL PROMPT

"A 28-year-old manual laborer presents 2 days after a fall from scaffolding. He has wrist pain, and X-rays show a possible lunate abnormality. How do you evaluate this injury?"

PRACTICAL APPROACH

This is a young patient with high-energy wrist trauma requiring thorough evaluation. **Initial Assessment:** I would first confirm the mechanism - a fall from scaffolding suggests significant axial loading which can cause occult carpal injuries. I would examine the entire upper limb for associated injuries and document neurovascular status, particularly median nerve function. **Plain Radiograph Analysis:** On the PA view, I would assess lunate contour and density, looking for fracture lines or sclerosis. On the lateral, I would check lunate position (DISI or VISI pattern would suggest associated ligamentous injury). I would also measure ulnar variance, as negative variance increases lunate loading. **Advanced Imaging:** Given the clinical suspicion and high-energy mechanism, I would obtain a CT scan to characterize any fracture pattern. More importantly, I would obtain an MRI to assess for occult fracture not visible on CT and to evaluate lunate vascularity with T1-weighted sequences. Decreased T1 signal would indicate early vascular compromise. **Classification:** Using the Teisen classification, I would categorize the fracture as: - Type I-III (pole or chip): Generally good prognosis - Type IV (sagittal body): Moderate AVN risk - Type V (transverse body): High AVN risk requiring surgical fixation **Treatment Decision:** If this is a body fracture (Type IV or V), I would recommend surgical fixation with headless compression screws to optimize reduction and potentially reduce AVN risk. Pole or chip fractures can often be managed non-operatively with cast immobilization.

KEY CLINICAL POINTS

High-energy mechanism warrants thorough evaluation

MRI is essential for vascularity assessment

Teisen classification guides prognosis and treatment

Body fractures require surgical consideration

COMMON PITFALLS

Missing occult fracture by relying only on X-ray

Not assessing ulnar variance as risk factor

Failing to evaluate for associated perilunate injury

FURTHER QUESTIONS

"What would you do if the MRI shows decreased T1 signal in the lunate?"

"How does ulnar variance affect your treatment recommendation?"

"What associated injuries would you specifically look for?"

CLINICAL SCENARIOChallenging

Lunate Fracture with AVN Risk

CLINICAL PROMPT

"CT and MRI confirm a Type V transverse lunate body fracture in a 35-year-old office worker. MRI shows intact signal on T1 sequences. How do you counsel this patient and plan treatment?"

PRACTICAL APPROACH

This is a high-risk lunate fracture pattern that requires careful management and counseling. **Patient Counseling:** I would explain that a transverse body fracture carries a significant risk of avascular necrosis (AVN), because the fracture line crosses the lunate's central blood supply. The good news is that current MRI shows intact blood supply, suggesting we have a window to optimize outcomes with treatment. **Treatment Recommendation:** I would strongly recommend surgical fixation for this Type V fracture. My goals are to achieve anatomic reduction, provide stable fixation with a headless compression screw, and minimize further vascular compromise through gentle surgical technique. **Surgical Approach:** I would use a dorsal approach through the 3rd and 4th extensor compartments. I would perform a ligament-sparing capsulotomy to preserve as much soft tissue blood supply as possible. Using fluoroscopic guidance, I would reduce the fracture and fix it with a 2.0-2.4mm headless compression screw, ensuring it is countersunk beneath the cartilage. **Postoperative Protocol:** Splinting for 2 weeks, then protected ROM in a removable splint. I would obtain repeat MRI at 3-6 months to monitor for AVN development, even if clinical progress seems satisfactory. **Prognosis Discussion:** Despite optimal treatment, there remains a significant AVN risk. If AVN develops, treatment would be stage-dependent - from core decompression for early disease to partial wrist fusion for advanced collapse. I would ensure the patient understands the need for long-term surveillance.

KEY CLINICAL POINTS

Type V transverse body fractures carry the highest AVN risk

Preserved MRI signal is favorable but not protective

ORIF with gentle technique to preserve blood supply

Long-term MRI surveillance is essential

COMMON PITFALLS

Underestimating AVN risk with reassuring MRI

Aggressive soft tissue dissection during surgery

Not planning for MRI surveillance postoperatively

FURTHER QUESTIONS

"What is your surgical approach and fixation technique?"

"How would you manage if AVN develops despite optimal treatment?"

"What is your postoperative surveillance protocol?"

CLINICAL SCENARIOChallenging

Kienbock's Disease Management

CLINICAL PROMPT

"A patient you treated for a lunate fracture 18 months ago returns with progressive wrist pain. MRI shows Stage IIIA Kienbock's disease. How do you manage this complication?"

PRACTICAL APPROACH

This patient has developed avascular necrosis progressing to Kienbock's disease, which is the most significant complication of lunate fractures. **Stage IIIA Assessment:** Stage IIIA Kienbock's indicates lunate collapse has begun, but carpal height is maintained and the scaphoid has not developed fixed rotation. This is an important stage because motion-preserving procedures may still be possible. **Imaging Review:** I would obtain current radiographs to confirm staging and assess for any progression. CT can help evaluate the degree of lunate fragmentation. MRI would show the extent of necrosis and any revascularization attempts. **Treatment Options:** For Stage IIIA, I would discuss several options: **1. Ulnar Lengthening or Radial Shortening:** If the patient has negative ulnar variance (which is common in Kienbock's), unloading the lunate by correcting variance may halt progression. I would favor radial shortening osteotomy as it is technically more reliable. **2. Core Decompression:** If there is any residual vascularity on MRI, core decompression with or without bone grafting may promote revascularization. However, in established Stage III disease, success rates are lower. **3. Partial Carpal Fusion:** If the lunate is severely fragmented, a limited intercarpal fusion (scaphocapitate fusion or scaphotrapeziotrapezoid fusion) can offload the lunate while preserving some motion. **4. Proximal Row Carpectomy:** If the capitate head cartilage is intact, PRC can provide reasonable motion and pain relief, but I would reserve this for more advanced disease or failed treatments. **My Recommendation:** For this Stage IIIA with negative ulnar variance, I would recommend radial shortening osteotomy as the first-line treatment, combined with core decompression of the lunate. This addresses the mechanical overload while attempting to preserve the bone.

KEY CLINICAL POINTS

Stage IIIA allows motion-preserving procedures

Correct ulnar variance to unload the lunate

Radial shortening preferred over ulnar lengthening

Multiple options exist based on patient factors

COMMON PITFALLS

Proceeding directly to fusion without considering unloading

Not assessing ulnar variance as treatment target

Missing the window for motion-preserving surgery

FURTHER QUESTIONS

"What if this patient has neutral ulnar variance?"

"When would you consider proximal row carpectomy?"

"What is the expected outcome with radial shortening osteotomy?"

MCQ Practice Points

Vascular Anatomy

Q: What are the three intraosseous vascular patterns of the lunate, and which carries the highest AVN risk? A: Gelberman described the Y, X and I patterns. The I-pattern has a single dominant intraosseous vessel with minimal anastomosis and the least redundancy, so it carries the highest avascular necrosis risk when a body fracture crosses the central supply.

AVN Risk by Fracture Type

Q: Which Teisen classification type has the highest risk of avascular necrosis? A: Type V (transverse body) fractures carry the highest AVN risk because the transverse fracture line crosses and can isolate the dominant intraosseous vessel from a large part of the bone. Type IV (sagittal body) is the next highest; pole and chip fractures rarely develop AVN.

Ulnar Variance Association

Q: What ulnar variance pattern is associated with increased lunate fracture and Kienbock's disease risk? A: Negative ulnar variance (short ulna relative to radius) concentrates axial load on the lunate. This is a major risk factor for both acute fracture and progressive AVN.

Keystone Position

Q: How is axial wrist load shared at the radio-ulno-carpal joint? A: Schuind's biomechanical model found roughly 55% passes through the radio-scaphoid joint, about 35% (around one third) through the radio-lunate joint, and about 10% through the TFCC. The lunate is still the central "keystone" of the proximal carpal row, and negative ulnar variance shifts more load onto it.

MRI Findings

Q: What MRI finding indicates early avascular necrosis of the lunate? A: Decreased T1 signal relative to other carpal bones indicates early AVN, as fat in the bone marrow is replaced by edema or necrotic tissue. T2 signal may be variable depending on the stage.

Kienbock's Staging

Q: What distinguishes Stage IIIA from Stage IIIB Kienbock's disease? A: Stage IIIA has lunate collapse but maintained carpal height and no fixed scaphoid rotation. Stage IIIB shows scaphoid rotation (ring sign on X-ray) and proximal capitate migration, indicating more advanced carpal collapse.

Understanding these key concepts will help with exam success.

Guidelines, Registries & Global Practice

Global Epidemiology

Isolated lunate fractures are rare, reported as under 3% of carpal fractures, and acute lunate injury most often occurs within a high-energy perilunate pattern. In a 65-case European perilunate series, 62 of 65 injuries displaced dorsally, lunate osteonecrosis occurred in 7.7% and post-traumatic arthritis in 58.5% at a mean 8-year follow-up (Israel 2016). Kienbock's disease, the related lunate avascular necrosis, classically affects manual workers aged 20-40 and is associated with negative ulnar variance.

Guidance & Consensus on Lunate Injury and Kienbock's Disease

Body / Source	Position	Evidence Level
AO Foundation (Surgery Reference)	Acute displaced body fractures and perilunate injuries treated by anatomic reduction and stable fixation; preserve dorsal/volar blood supply	Expert consensus / Level V
BSSH / EFORT hand consensus	MRI is the key investigation for occult fracture and lunate viability; isolated chip/pole fractures usually non-operative	Level IV-V
Lichtman algorithm (AAOS/JWS)	Stage- and viability-based pathway: protect intact lunate, unload, reconstruct, then salvage	Level V review
Biomechanical evidence (Horii 1990)	Radial shortening / ulnar lengthening preferred for unloading - 45% radio-lunate load reduction	Level V model

Practice Variation

Diagnosis: high-resource settings use early MRI and CT routinely; in limited-resource settings diagnosis relies on radiographs and clinical follow-up, raising the rate of missed occult fractures.
Kienbock's unloading: radial shortening osteotomy is the most widely adopted joint-levelling procedure internationally because it is technically reliable and avoids a separate graft site; ulnar lengthening is used less often.
Reconstruction: vascularised bone grafting (including medial femoral condyle flaps) for the compromised but reconstructable lunate is concentrated in specialist hand-surgery and microsurgery centres.
Registries: there is no dedicated carpal-fracture joint registry (the major arthroplasty registries such as the NJR, AJRR and AOANJRR do not capture lunate fracture or Kienbock's outcomes), so evidence rests on case series and biomechanical studies rather than registry data.

Rehabilitation through specialist hand therapy and long-term avascular-necrosis surveillance with delayed MRI are recommended internationally after body fractures and perilunate injuries.