Epibasal fracture of the thumb

Last revised by Leonardo Lustosa on 04 Apr 2022

Epibasal fractures of the thumb (also called pseudo-Bennett fracture) are extra-articular 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. 

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

These fractures usually result from longitudinal axial loading 5

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

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

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 (CRIF2,3.

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) 

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