Which finding indicates a tear or sprain of the ulnar collateral ligament at the thumb MCP joint?

Which finding indicates a tear or sprain of the ulnar collateral ligament at the thumb MCP joint?

• A. Pain, gapping, and laxity with valgus stress
• B. Pain with radial deviation
• C. Lack of grip strength only
• D. Swelling at the thumb MCP without laxity

Answer: (A)

The ulnar collateral ligament on the thumb MCP joint normally resists valgus (abduction) force to keep the first metacarpophalangeal joint stable. When this ligament is torn or sprained, a valgus stress applied to the thumb MCP causes pain plus gapping and increased laxity compared with the uninjured side. This combination—pain with the stress, visible or palpable joint opening, and looseness under valgus loading—is the telltale sign of an UCL injury at the thumb MCP, often called skier’s or gamekeeper’s thumb. The other findings don’t specifically indicate an UCL tear: pain with radial deviation points more toward injury of structures on the radial side or different mechanics; lacking grip strength alone is nonspecific; swelling at the thumb MCP without laxity suggests a non-ligamentous issue or a less unstable injury.

The ulnar collateral ligament on the thumb MCP joint normally resists valgus (abduction) force to keep the first metacarpophalangeal joint stable. When this ligament is torn or sprained, a valgus stress applied to the thumb MCP causes pain plus gapping and increased laxity compared with the uninjured side. This combination—pain with the stress, visible or palpable joint opening, and looseness under valgus loading—is the telltale sign of an UCL injury at the thumb MCP, often called skier’s or gamekeeper’s thumb.

The other findings don’t specifically indicate an UCL tear: pain with radial deviation points more toward injury of structures on the radial side or different mechanics; lacking grip strength alone is nonspecific; swelling at the thumb MCP without laxity suggests a non-ligamentous issue or a less unstable injury.