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Overview

Bennett's fracture is an intra-articular fracture-subluxation of the first carpometacarpal (CMC) joint, first described by Edward Hallaran Bennett in 1882. It represents the most common fracture involving the thumb metacarpal base (approximately 80% of thumb MC base fractures) and is considered an unstable injury due to the powerful deforming forces acting on the thumb. The fracture pattern consists of a small triangular volar-ulnar fragment that remains in anatomic position (held by the intact anterior oblique ligament) while the metacarpal shaft subluxates dorsally and radially, pulled by the abductor pollicis longus (APL). Anatomic reduction is essential to preserve the critical function of the thumb CMC joint and prevent post-traumatic arthritis.

Anatomy and Biomechanics

Thumb CMC Joint Anatomy

Articular Surfaces:

• Saddle-shaped (bi-concave/bi-convex) joint
• Allows circumduction and opposition
• Most mobile CMC joint in the hand
• Critical for grip strength (accounts for 40% of hand function)

Ligamentous Stabilizers:

The AOL (Beak Ligament):

• Origin: Volar tubercle of trapezium
• Insertion: Volar-ulnar base of MC1
• Strongest stabilizer of CMC joint
• Remains attached to volar fracture fragment
• This is why the small fragment stays reduced

Muscle Forces

Deforming Forces on Metacarpal Shaft:

• APL: Pulls shaft dorsally and radially (MAIN DEFORMER)
• Adductor pollicis: Pulls shaft ulnarly
• EPL/EPB: Contribute to extension

Result:

• Shaft subluxates dorsal, radial, and proximal
• Volar-ulnar fragment stays anatomic (AOL intact)
• Creates step-off and joint incongruity

Fracture Mechanics

Mechanism:

• Axial load on partially flexed thumb
• Typically from punching, fall on outstretched thumb
• Impact transmitted along thumb ray to CMC joint

Fracture Pattern:

• Two-part fracture (simple Bennett)
• Triangular volar-ulnar fragment (typically small)
• Larger metacarpal shaft fragment (subluxated)

Classification

Fracture PatternGedda ClassificationFragment Size

Bennett vs Rolando vs Extra-articular

Bennett Fracture (Two-Part):

• Two-part intra-articular fracture
• Volar-ulnar fragment attached to trapezium
• Most common pattern (80%)

Rolando Fracture (Three-Part or Comminuted):

• Comminuted intra-articular fracture
• Y-shaped or T-shaped pattern
• Worse prognosis due to articular damage

Extra-articular Base Fracture:

• Transverse or oblique fracture
• Does not involve CMC joint
• Better prognosis

Bennett's fracture is the most common pattern accounting for approximately 80% of thumb metacarpal base fractures.

Gedda Classification (Historical)

Type	Description
Type I	Large single volar fragment with subluxation
Type II	Impaction fracture without subluxation
Type III	Small volar fragment with dislocation

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Fragment Size Classification

Small Fragment (less than 15%):

• Harder to fix with screws
• K-wire fixation often preferred
• Good prognosis if reduced

Large Fragment (15-30%):

• Amenable to screw fixation
• Better purchase for internal fixation

Very Large Fragment (greater than 30%):

• Consider lag screw fixation
• May need plate if comminuted

Fragment size directly influences fixation choice and surgical approach.

Clinical Presentation

History

Mechanism:

• Axial load on flexed thumb (punching)
• Fall onto extended thumb
• Sports injury (skiing, football, rugby)
• Motor vehicle accident

Symptoms:

• Immediate pain at thumb base
• Swelling over thenar eminence
• Inability to grip or pinch
• Thumb deformity (shortened/pronated)

Physical Examination

Inspection:

• Swelling at thenar eminence
• Ecchymosis at thumb base
• Thumb appears shortened
• Possible angulation/deformity

Palpation:

• Point tenderness over CMC joint
• Crepitus with gentle motion
• Assess metacarpal stability

Assessment:

• Document neurovascular status
• Check for associated injuries
• Test thumb opposition (if tolerable)

Key Examination Findings

Positive Grind Test:

• Axial load + rotation at CMC joint
• Produces pain and crepitus
• Indicates CMC pathology

Instability Assessment:

• Compare to contralateral thumb
• Assess dorsal-volar translation
• Document baseline laxity

Investigations

Radiographic Assessment

Standard Views:

1. PA (Posteroanterior): Oblique view of CMC best
2. True Lateral: Shows dorsal subluxation
3. Roberts View: Thumb fully pronated, beam perpendicular
4. Stress Views: If ligamentous injury suspected

Robert's View Technique:

• Place thumb flat on cassette (hyperpronated)
• Beam perpendicular to thumb MC
• Shows CMC joint in true AP

Radiographic Findings

Key Measurements:

• Articular step-off (greater than 1mm = significant)
• Fragment size (% of articular surface)
• Degree of subluxation

Signs of Bennett's:

• Triangular volar-ulnar fragment at CMC
• Dorsal/radial subluxation of MC shaft
• Widening of CMC joint space
• Overlap of MC1 and trapezium on lateral

CT Imaging

Indications:

• Complex fracture patterns
• Surgical planning
• Assessment of fragment size
• Evaluation of articular congruity

CT Findings:

• Better delineation of fragment size
• Assessment of comminution
• 3D reconstruction for surgical planning

MRI (Rarely Needed)

Indications:

• Suspected ligamentous injury without fracture
• Occult fracture evaluation
• Post-reduction instability

📊 Management Algorithm

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Management

Treatment Goals

1. Anatomic articular reduction (less than 1mm step)
2. Stable fixation allowing early motion
3. Restore CMC joint stability
4. Prevent post-traumatic arthritis

Surgical Technique

CRPPORIFArthroscopic

Closed Reduction and Percutaneous K-Wire Fixation

Most Common Technique

Step-by-Step:

1. Closed reduction under fluoroscopy
2. K-wire (1.1-1.4mm) through MC1 into trapezium
3. May add second K-wire through fragment
4. Or pin MC1 to MC2 (prevents redisplacement)
5. Protect with thumb spica
6. Remove wires at 4-6 weeks

K-Wire Options:

• MC1 to trapezium: Direct joint stabilization
• MC1 to MC2: Indirect stabilization
• Through fragment: Fragment fixation (if large enough)

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K-Wire Placement Tips

Avoid placing wires too close to articular surface. Entry point should be proximal enough to avoid CMC joint penetration. Fluoroscopy in multiple planes is essential.

Open Reduction Internal Fixation

Indications:

• Large articular fragment (greater than 20%)
• Failed closed reduction
• Complex fracture patterns
• Need for direct articular visualization

Wagner Approach (Volar-Radial):

1. Incision at thumb CMC along thenar crease
2. Protect radial artery branches (terminal branches)
3. Reflect thenar muscles ulnarly
4. Visualize joint capsule
5. Open capsule to expose fracture
6. Reduce under direct visualization
7. Fix with screws or K-wires

Fixation Options:

• Mini-fragment screws (1.5-2.0mm)
• Lag screw technique for large fragments
• K-wires for small fragments
• Supplemental K-wire MC1-trapezium

Structures at Risk

• Radial artery (terminal branches)
• Superficial radial nerve branches
• APL tendon

Arthroscopic-Assisted Reduction

Advantages:

• Direct visualization of articular reduction
• Minimal soft tissue trauma
• Can assess cartilage injury
• Theoretically better outcomes

Technique:

• 1.9mm arthroscope via radial portal
• Ulnar portal for instrumentation
• Reduction under direct visualization
• Percutaneous K-wire fixation

Limitations:

• Requires specialized equipment
• Steep learning curve
• Limited availability

Arthroscopy is most useful when reduction quality needs direct confirmation or cartilage assessment is required.

Complications

Early Complications

Malreduction:

• Most common complication
• Greater than 1mm step leads to arthritis
• May require revision surgery

Pin Site Infection:

• Occurs in 2-5% of K-wire cases
• Usually superficial
• Treat with oral antibiotics
• Early wire removal if deep infection

Loss of Reduction:

• More common with conservative treatment
• May occur after wire removal
• Close radiographic follow-up essential

Late Complications

Post-Traumatic Arthritis:

• Most significant long-term complication
• Risk increases with articular incongruity
• May require CMC arthrodesis or arthroplasty
• Incidence: 20-30% at long-term follow-up

Stiffness:

• Common, especially after prolonged immobilization
• Early motion when fracture stable
• Hand therapy essential

Weakness:

• Grip and pinch strength affected
• Usually recovers over 6-12 months
• May have persistent subtle weakness

CMC Instability:

• Ligamentous incompetence after healing
• May require ligament reconstruction
• Rare if fracture anatomically reduced

Malunion:

• Results from inadequate reduction
• Causes altered CMC mechanics
• May accelerate arthritic change
• Corrective osteotomy rarely indicated

Postoperative Care

Timeline

Outcomes and Prognosis

Prognostic Factors

Good Prognosis:

• Anatomic reduction (less than 1mm step)
• Small articular fragment
• Young patient
• Early treatment
• Stable fixation

Poor Prognosis:

• Articular step greater than 2mm
• Large fragment involvement
• Delayed treatment
• Associated soft tissue injury
• Comminuted pattern (Rolando)

Long-Term Results

Anatomic Reduction:

• 80-90% good/excellent results
• Low rate of symptomatic arthritis
• Near-normal grip/pinch strength

Non-Anatomic Reduction:

• 50-60% good results
• Higher rate of arthritis
• May require salvage procedure

Comparison to Rolando Fracture

Evidence Base

Australian Guidelines

Hand Trauma Management:

• Royal Australasian College of Surgeons guidelines
• Emphasis on early fixation and mobilization
• Referral to hand surgeon recommended

PBS Considerations:

• Fixation hardware not PBS listed
• Private health insurance or self-funding

Viva Scenarios

MCQ Practice Points

Australian Context

Epidemiology in Australia:

Bennett's fractures are common in the Australian population, particularly in young males involved in contact sports (rugby, AFL) and manual occupations. The pattern of axial loading injury from punching is frequently seen in Emergency Departments, particularly on weekend nights. Hand trauma represents a significant burden on the Australian healthcare system.

Management Considerations:

Most Bennett's fractures in Australia are managed in the public hospital system, with surgical cases typically performed as day surgery procedures. K-wire fixation remains the most common technique, with ORIF reserved for larger fragments or failed closed reduction. Metropolitan centres with hand surgery units typically manage complex cases, while regional centres may transfer patients requiring ORIF.

Rehabilitation Access:

Hand therapy services are generally accessible through public hospital outpatient departments, though wait times may vary. Private health insurance holders often access faster rehabilitation services. The Medicare system covers surgical consultations and procedures, with rebates available for hand therapy under chronic disease management plans in some cases.

Workers' Compensation:

Bennett's fractures are commonly claimed under workers' compensation schemes (WorkCover, Comcare) when sustained in occupational settings. Documentation of mechanism and functional impact is critical for claim management. Return to work timelines depend heavily on occupation type, with manual workers requiring longer recovery periods.

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