Patient-induced stress test of the first metacarpophalangeal joint: a radiographic assessment of collateral ligament injuries.

The metacarpophalangeal (MCP) joint of the thumb is frequently injured, and the extent of soft-tissue injury is sometimes difficult to determine clinically. Routine radiographs are often normal, without evidence of a fracture. Radiographs obtained during patient-induced stress of the first MCP joint can show significant collateral ligament injury. It is important to make an early diagnosis of collateral ligament rupture.