Bennett's Fractures

What it is. Bennett's fracture is an intra-articular fracture-subluxation of the first carpometacarpal (CMC) joint, first described by Edward Hallaran Bennett in 1882. It is the most common fracture of the thumb metacarpal base, approximately 80% of them, and it is an unstable injury because of the powerful deforming forces acting on the thumb.

The pattern. A small triangular volar-ulnar fragment remains in anatomic position, held by the intact anterior oblique ligament, while the metacarpal shaft subluxates dorsally and radially under the pull of abductor pollicis longus (APL).

Its relatives. The comminuted intra-articular counterpart, a T- or Y-shaped fracture of the same base, is Rolando's fracture; it carries a worse prognosis because the articular surface cannot simply be reduced onto an intact beak fragment. The long-term consequence both share, and the reason anatomical reduction is pursued so hard here, is thumb CMC arthritis. The ligamentous injury of the same thumb is thumb UCL injury.

The joint. The thumb CMC is a saddle-shaped joint, biconcave and biconvex. It allows circumduction and opposition and is the most mobile CMC joint in the hand. It is critical for grip strength and accounts for 40% of hand function.

The ligaments. The classic description of the stabilisers:

The AOL, the beak ligament. It runs from the volar tubercle of the trapezium to the volar-ulnar base of the first metacarpal and is classically described as the strongest stabiliser of the CMC joint. In a Bennett's fracture it remains attached to the volar (beak) fragment, which is why the small fragment stays reduced.

The deforming forces. APL is the main deformer: it pulls the shaft dorsally and radially. Adductor pollicis pulls the shaft ulnarly, and EPL and EPB contribute to extension. The result is a shaft that subluxates dorsal, radial and proximal while the volar-ulnar fragment stays anatomic on its intact AOL, leaving a step-off and an incongruent joint. These forces make a closed reduction unstable.

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Mechanism. An axial load on a partially flexed thumb, transmitted along the thumb ray to the CMC joint: typically a punch or a fall onto the outstretched thumb, and also seen in sport (skiing, football, rugby) and motor vehicle accidents. The fracture it produces is two-part, a triangular volar-ulnar fragment that is typically small and a larger metacarpal shaft fragment that subluxates.

History. Pain at the thumb base is immediate, with swelling over the thenar eminence and an inability to grip or pinch. The thumb appears deformed, shortened and pronated.

Examination. Inspect for swelling at the thenar eminence, ecchymosis at the thumb base, a shortened thumb and any angulation or deformity. On palpation there is point tenderness over the CMC joint and crepitus with gentle motion; assess the stability of the metacarpal. Document the neurovascular status, check for associated injuries, and test thumb opposition if the patient can tolerate it.

The grind test. Axial load with rotation at the CMC joint produces pain and crepitus, and indicates CMC pathology.

Instability. Assess dorsal-volar translation, compare it with the contralateral thumb and document the baseline laxity.

Radiographs. The standard views, and what each is for:

1. PA (posteroanterior) - oblique view of the CMC best
2. True lateral - shows dorsal subluxation
3. Roberts view - thumb fully pronated, beam perpendicular
4. Stress views - if ligamentous injury is suspected

The Roberts view. Place the thumb flat on the cassette, hyperpronated, and direct the beam perpendicular to the thumb metacarpal. This shows the CMC joint in true AP.

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What the films show. The signs of a Bennett's:

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

What to measure. The articular step-off (greater than 1mm is significant), the fragment size as a percentage of the articular surface, and the degree of subluxation.

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CT. For complex fracture patterns and surgical planning. It gives better delineation of fragment size, an assessment of comminution and articular congruity, and 3D reconstructions for planning the operation.

MRI. Rarely needed. Its place is suspected ligamentous injury without a fracture, evaluation of an occult fracture, and instability after reduction.

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.

The 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

Reduction quality versus fixation method. Comparative cohorts and a meta-analysis show that 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.

The ORIF trade-off. ORIF offers modestly higher grip and 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]

Non-OperativeOperativeSpecial Cases

Who. Rarely indicated. The indications are a non-displaced fracture with less than 1mm of step, a perfect reduction that is maintained in the cast, and the elderly or low-demand patient.

The reduction, TAP.

1. Longitudinal Traction on the thumb
2. Abduction of the thumb ray
3. Direct Pressure over the metacarpal base, pushing it volar-ulnar
4. Pronation of the thumb
5. Hold the position and apply the thumb spica

The cast and the follow-up. Reduce under fluoroscopy and hold in a thumb spica in slight extension and abduction, with close radiographic follow-up, weekly for three weeks, to monitor for displacement. Total immobilisation is 4-6 weeks.

Why it usually fails. Redisplacement is frequent and the reduction is difficult to maintain, so most fractures go on to need surgical stabilisation. Non-operative treatment is rarely successful for a true Bennett's fracture because of the powerful deforming forces.

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Indications

• Articular step greater than 1mm
• Subluxation or dislocation that cannot be reduced
• Instability after closed reduction
• Fragment greater than 15-20% of the articular surface

Options

CRPP

Indication

Most cases

Technique

K-wire MC1-trapezium +/- MC1-MC2

ORIF

Indication

Large fragment, failed CR

Technique

Wagner approach, lag screw

Arthroscopy

Indication

Direct visualisation

Technique

1.9mm scope, radial portal

Method	Indication	Technique
CRPP	Most cases	K-wire MC1-trapezium +/- MC1-MC2
ORIF	Large fragment, failed CR	Wagner approach, lag screw
Arthroscopy	Direct visualisation	1.9mm scope, radial portal

Workers' compensation. Document the mechanism clearly, take pre-operative photographs, use objective outcome measures, and arrange a functional capacity evaluation if needed.

High-performance athletes. Early surgical fixation is preferred, followed by aggressive supervised rehabilitation, protective splinting for the return to sport, and monitoring for chronic instability.

Elderly patients. Consider comorbidities and the lower functional demands; some displacement may be accepted, balancing the risks of surgery against its benefits.

Malreduction. The most common complication. A residual step greater than 1mm leads to arthritis and may require revision surgery.

Pin site infection. Occurs in 2-5% of K-wire cases, is usually superficial and is treated with oral antibiotics; a deep infection calls for early wire removal.

Loss of reduction. More common with conservative treatment, and it may also occur after wire removal, which is why close radiographic follow-up is essential.

Post-traumatic arthritis. The most significant long-term complication, with an incidence of 20-30% at long-term follow-up. The risk increases with articular incongruity, and it may require CMC arthrodesis or arthroplasty.

Stiffness. Common, especially after prolonged immobilisation. Start motion early once the fracture is stable; hand therapy is essential.

Weakness. Grip and pinch strength are affected and usually recover over 6-12 months, though a subtle weakness may persist.

CMC instability. Ligamentous incompetence after healing, rare if the fracture was anatomically reduced; it may require ligament reconstruction.

Malunion. Results from inadequate reduction, alters the mechanics of the CMC joint and may accelerate arthritic change. Corrective osteotomy is rarely indicated.

What predicts a good result

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

What predicts a poor one

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

Long-term results. With an anatomic reduction, 80-90% have good or excellent results, with a low rate of symptomatic arthritis and near-normal grip and pinch strength. With a non-anatomic reduction, 50-60% have good results, the rate of arthritis is higher, and a salvage procedure may be required.

Against Rolando.

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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