Epibasal fracture of the thumb

Epibasal fractures of the thumb (also called pseudo-Bennett fracture) are two-piece fractures of the proximal first metacarpal bone. They are usually stable, depending on the degree of displacement, and often do not require surgery. It is important to distinguish them from intra-articular fractures (e.g. Bennett fracture-dislocation or Rolando fracture), which are usually unstable and require surgery. 

Epidemiology

Epibasal fracture of the thumb account for approximately 3% of all hand fractures and 16% of metacarpal fractures and are mostly (>80%) seen in young men ⁴. 

Mechanism

These fractures usually result from longitudinal axial loading ⁵. 

Radiographic features

Plain films are usually sufficient to diagnose and assess epibasal fractures; however, if adequate views cannot be obtained or there is suspicion of intra-articular involvement, further assessment with CT is prudent ³. 

Plain radiograph

Epibasal fractures are divided according to the direction of fracture into transverse and oblique and can be variably angulated and displaced. 

Treatment and prognosis

The vast majority of epibasal fractures are considered stable and can be treated conservatively with thumb spica immobilization for 4-6 weeks ^2,3. Both oblique fractures and transverse fractures with >30° of angulation usually require closed reduction and Kirschner wire fixation (CRIF) ^2,3.

Practical points

In addition to stating that a fracture is present, one should assess and comment on:

• angulation: >30° usually requires internal fixation
• displacement
• intra-articular extension (Bennett or Rolando fractures)