What is the most likely diagnosis for a subluxation of the metacarpophalangeal joint of the thumb with abduction?

The most likely diagnosis for a subluxation of the metacarpophalangeal joint of the thumb with abduction is Gamekeeper's thumb. This condition is characterized by an injury to the ulnar collateral ligament at the base of the thumb, often resulting from repetitive stress or trauma, such as when the thumb is forcibly abducted.

In cases of Gamekeeper's thumb, the mechanism of injury typically involves a significant force applied to the lateral aspect of the extended thumb, causing the ulnar collateral ligament to be stretched or torn. This leads to instability at the metacarpophalangeal joint, making it prone to subluxation, particularly when the thumb is abducted.

Understanding the other conditions provides context:

A Bennett fracture is an intra-articular fracture of the base of the first metacarpal associated with joint instability, but it doesn't specifically relate to the subluxation of the joint with abduction as described.

Skier's thumb shares a similar mechanism of injury to Gamekeeper's thumb, where the ulnar collateral ligament is injured, but the term is more commonly used in acute cases, particularly when occurring during skiing or similar activities.

Mallet finger involves the extensor tendon rather