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