X-rays show central and peripheral erosions of these joints and there may be associated small erosions of the first carpometacarpal and trapezioscaphoid joints.
The part of opposition that this muscle is responsible for is the flexion of the thumb's metacarpal at the first carpometacarpal joint.
The movements permitted in the second through fifth carpometacarpal joints is most readily observable in the (distal) heads of the metacarpal bones.
If the thumb or its carpometacarpal joint is absent, centralization can be followed by pollicization.
The configuration of the thumb carpometacarpal joint plays an important role in the mechanism of opposition.
For this "true", pulp-to-pulp opposition to be possible, the thumb must rotate about its long axis (at the carpometacarpal joint).
The bone itself is located between the joints called the metacarpophalangeal joint and the carpometacarpal joint.
The abductor pollicis brevis does this by acting across both the carpometacarpal joint and the metacarpophalangeal joint.
