Opponens minimi digiti serves to flex and laterally rotate the 5th metacarpal about the 5th carpometacarpal joint, as when bringing little finger and thumb into opposition.
The joint space between trapezium and trapezoid, or that between trapezoid and capitate, may communicate with cavities of the carpometacarpal joints, most commonly the second and third.
This complete extension at the interphalangeal joint is not possible, or considerably more difficult, with the carpal, carpometacarpal, and metacarpophalangeal joints simultaneously extended.
The abductor pollicis brevis does this by acting across both the carpometacarpal joint and the metacarpophalangeal joint.
The bone itself is located between the joints called the metacarpophalangeal joint and the carpometacarpal joint.
For this "true", pulp-to-pulp opposition to be possible, the thumb must rotate about its long axis (at the carpometacarpal joint).
The configuration of the thumb carpometacarpal joint plays an important role in the mechanism of opposition.
If the thumb or its carpometacarpal joint is absent, centralization can be followed by pollicization.
