Differential Diagnosis for Thumb Pain and Laxity
- Single most likely diagnosis
- Ulnar collateral ligament (UCL) injury: This is the most likely diagnosis given the mechanism of injury (falling during skiing) and the physical examination findings (gross laxity in the first metacarpophalangeal joint with thumb abduction). The UCL is commonly injured in such scenarios, leading to instability and pain in the thumb.
- Other Likely diagnoses
- Radial collateral ligament (RCL) injury: Although less common than UCL injuries, RCL injuries can also occur from a fall onto an outstretched hand, leading to pain and laxity in the thumb.
- Volar plate injury: The volar plate is a fibrocartilaginous structure that provides stability to the metacarpophalangeal joint. An injury to this structure could lead to joint laxity and pain, especially with certain movements.
- Do Not Miss diagnoses
- Scaphoid fracture: Although the radiograph revealed no fracture, it's crucial to consider the possibility of a scaphoid fracture, which might not be immediately visible on initial X-rays. A missed scaphoid fracture can lead to serious complications, including avascular necrosis and chronic wrist pain.
- Metacarpal neck fracture: Similar to a scaphoid fracture, a metacarpal neck fracture might not be immediately apparent on radiographs, especially if it's a non-displaced or hairline fracture. This type of fracture requires prompt diagnosis and treatment to avoid complications.
- Rare diagnoses
- Sesamoid bone fracture: The sesamoid bones are small bones embedded within the flexor pollicis brevis tendon. A fracture of one of these bones could potentially cause thumb pain and laxity, although this would be a less common injury.
- Gamekeeper's thumb (chronic UCL instability): While more commonly associated with chronic instability rather than an acute injury, gamekeeper's thumb could be considered if the patient has a history of repetitive thumb injuries or instability.