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

Differential Diagnosis

The painful, swollen thumb base after axial loading has several mimics. The Roberts (true AP) and true lateral views, plus CT where needed, distinguish them.

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

Decision-Making and Controversies

• Reduction quality versus fixation method: comparative cohorts and a meta-analysis show CRPP and ORIF give similar arthritis rates and functional scores when an acceptable reduction is achieved; the reduction itself matters more than the construct. [PMID 12631486] [PMID 37929064]
• The under-1 mm dogma is debated: older series tie residual displacement to arthritis [PMID 2307882] [PMID 7714650], yet a 7-year ORIF series found no correlation between reduction accuracy (gap/step under 2 mm) and arthritis [PMID 22438128]. Anatomic reduction remains the sensible goal, but the linear relationship is not absolute.
• ORIF trade-off: ORIF offers modestly higher grip/pinch strength and less adduction deformity, but at a higher complication rate. [PMID 37929064]
• No RCT exists: every recommendation rests on retrospective evidence; individualise by fragment size, reducibility, displacement and patient demand. [PMID 36514567]

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

The contemporary evidence base for Bennett's fracture is built almost entirely on retrospective cohorts and two systematic reviews — there is no randomised controlled trial. The recurring themes are that (1) the quality of articular reduction historically correlated with long-term arthrosis, (2) open and closed techniques give broadly similar functional outcomes when an acceptable reduction is achieved, and (3) cast-only management gives poor long-term results.

Viva Scenarios

MCQ Practice Points

Guidelines, Registries & Global Practice

Bennett's fracture is a worldwide injury with a remarkably consistent demographic profile. The discussion below frames the global standard of care plus the regional nuances a candidate may be examined on, irrespective of board.

Global Epidemiology

Hand fractures are among the most common skeletal injuries. In a population-based study of approximately 4 million people, the annual incidence of hand fracture was around 36 per 10,000, of which roughly 42% involved the metacarpals, with a male-to-female relative risk of about 2:1 and a peak in young men aged 15–40 years. [PMID 16945705]

Registry & Practice-Trend Evidence

Bennett's fractures are not tracked by joint-replacement registries (which cover arthroplasty), so evidence derives from national fracture cohorts and administrative datasets rather than implant registries. Population-level analyses report a clear secular trend away from closed reduction toward open reduction and internal fixation of metacarpal and phalangeal fractures over the past two decades, reflecting wider availability of fine fragment fixation and hand-surgery expertise. [PMID 35785509]

Global Practice Variation

• High-resource settings: ready access to fluoroscopy, fine K-wires/screws and arthroscopy; increasing use of ORIF and arthroscopic-assisted reduction.
• Limited-resource settings: closed reduction and percutaneous K-wiring predominate — low cost, widely available, and supported by evidence that technique matters less than reduction quality (Thurston). [PMID 8297298]
• Athletes / manual workers: lower threshold for stable internal fixation to allow earlier protected mobilisation and predictable return to work or sport.
• Elderly / low-demand patients: a degree of residual displacement may be accepted, balancing arthritis risk against surgical morbidity.

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