The ulnar collateral ligament (UCL) of the thumb is an important stabilizing ligament located at the metacarpophalangeal (MCP) joint, which is the base joint where the thumb connects to the hand.

What it is

The UCL is a tough band of tissue found on the inner side of the thumb’s base joint, positioned toward the index finger. It helps maintain proper alignment and stability of the thumb during gripping and pinching activities.

Function of the UCL

This ligament plays several key roles, including:

  • Preventing the thumb from moving too far away from the hand
  • Providing stability during pinching and gripping movements
  • Working with surrounding muscles and ligaments to control thumb motion

Without a healthy UCL, the thumb becomes weak and unstable, making everyday tasks more difficult.

Common injuries

UCL injuries usually occur when the thumb is forced outward or bent backward. This often happens during:

  • Falls onto an outstretched hand
  • Skiing accidents (commonly known as “skier’s thumb”)
  • Contact or ball sports such as basketball or football

Symptoms may include:

  • Pain at the base of the thumb on the inner side
  • Swelling and bruising
  • Reduced grip strength or difficulty pinching
  • A feeling that the thumb is unstable or loose
  • Pain during grasping or lifting objects

Levels of injury

  • Mild sprain: The ligament is stretched but still intact
  • Partial tear: Some fibers are torn, causing weakness
  • Complete tear: The ligament is fully torn, leading to significant instability

In some complete tears, a Stener lesion may occur, where the torn ligament shifts out of position and cannot heal properly without surgical treatment.

Diagnosis

Doctors typically assess UCL injuries by:

  • Examining thumb stability and movement
  • Checking for pain and weakness during grip tests
  • Using imaging such as X-rays to rule out fractures or MRI scans to evaluate soft tissue damage

Treatment options

Treatment depends on how severe the injury is:

  • Mild cases: Rest, ice, splinting, and anti-inflammatory care
  • Moderate injuries: Immobilization with a thumb spica cast or brace
  • Severe tears: Surgical repair or reconstruction of the ligament

Recovery time

  • Mild injuries: a few weeks
  • Moderate injuries: around 4–6 weeks or longer
  • Surgical cases: several months, including rehabilitation

Conclusion

The ulnar collateral ligament of the thumb is essential for maintaining strength and stability during gripping and pinching. Injuries to this ligament, especially from sports or falls, can significantly affect hand function. However, with proper diagnosis and treatment, most cases recover well and restore normal thumb use over time.