Causes / typical injury mechanism: Thumb fractures are caused by a downward / axial force occurring while the thumb is in a hyperflexed or hyperextended position. This is usually caused by direct trauma such as falling on an outstretched hand or facing a direct blow to the hand. Indirect causes include excessive twisting motions and strong muscle contractions.

Classic history and presentation: Injury due to twisting or flexing the thumb during –

• Carpentry
• Skiing
• Contact sports
• Martial arts
• Basketball
• Wrestling

Prevalence:

• Thumb fractures are common because the thumb is highly mobile. Thumb fractures account for 25% of all metacarpal fractures, with 80% involving the base of the thumb.
• This is most common in children younger than 16 years (often from crush mechanisms) and adults older than 65 years.
• Thumb metacarpal fractures usually occur in younger males between ages 10 and 30 years.

Risk factors:

• Calcium deficiency
• History of bone disease
• Previous thumb injury

Grade / classification system: Green and O'Brien classification –

• Type I (Bennett fracture)
  • Most common thumb fracture.
  • Intra-articular fracture involving the carpometacarpal (CMC) joint with a clean break, resulting in a palmar ulnar fragment.
• Type II (Rolando fracture)
  • Intra-articular fracture involving the CMC joint with a Y-shaped or T-shaped break, resulting in 2 or more fragments.
• Type III
  • Extra-articular oblique or transverse fracture.
  • Extra-articular epibasal thumb fracture (pseudo-Bennett).
• Type IV
  • Extra-articular pediatric fracture involving the proximal physis.
• Intra-articular comminuted
  • Severely shattered intra-articular fracture.