Causes / typical injury mechanism:

• First carpometacarpal (CMC) dislocations usually occur due to axial loading while the thumb is in flexion.
• The overwhelming majority of first CMC dislocations occur dorsally.
• This is a rare dislocation (less than 1% of hand fractures / dislocations) due to the anatomy of the joint and abundance of ligament stability.

Classic history and presentation:

• High-speed trauma to the CMC, usually resulting in a dorsal dislocation.
• Often missed due to distracting associated high-energy injuries.
• Axial loading of the thumb can also occur after punching injuries or participation in sports.

Prevalence:

• Age – Usually occurs in second to fifth decade.
• Sex / gender – More common in male patients.

Risk factors: Trauma and degenerative disease.

Pathophysiology: There are a total of 16 ligaments that stabilize the first CMC joint. Four of these are thought to be the most important in stabilizing the joint: the volar, intermetacarpal, dorsoradial, and dorsal oblique ligaments. The dorsoradial and volar ligaments are most commonly torn / sheared off during dislocations.