A Bennett fracture is a fracture of the base of the thumb resulting from forced abduction of the first metacarpal. It is defined as an intra-articular two-part fracture of the base of the first metacarpal bone.

Radiographic features

Plain radiograph

• two piece fracture of the base of the thumb metacarpal 

• intra-articular extension 

• dorsolateral displacement

• small fragment of 1^st metacarpal, attached to anterior oblique ligament, continues to articulate with trapezium, 

• lateral retraction of the first metacarpal shaft by abductor pollicis longus

When an intra-articular fracture of the 1^st metacarpal is comminuted, producing at least three parts, it is referred to as a Rolando fracture which has a worse prognosis.

Treatment and prognosis

Non-operative treatment in a thumb spica cast for 3-4 weeks can be considered in stable, non-displaced fractures. 

Operative treatment is recommended for unstable fracture patterns and intra-articular displacement of >1 mm. While open reduction and internal fixation with a screw or K-wire are both common practice, screws are often preferred as K-wires must be removed after union. 

The treatment algorithm is also influenced by the age and profession/hobbies of the patient.

Complications

Untreated or malreduced fractures can lead to post-traumatic osteoarthritis, which can cause significant pain and functional decline.  

History and etymology

It is named after Edward Hallaran Bennett (1837-1907), a surgeon from Dublin, Ireland.

Differential diagnosis

• epibasal (pseudo-Bennett) fracture: extra-articular fractures through the first metacarpal base 

• Rolando fracture: comminuted intra-articular fracture through the first metacarpal base