Unhappy Triad of the Knee

Unhappy triad knee injury

The unhappy triad is a severe injury which involves damage to three of the four major ligaments in the knee. This is a major knee injury that often occurs after a severe impact.

What is the Unhappy triad injury?

The unhappy triad, also known as the terrible triad, or O’Donoghue triad is a severe knee injury. It involves full or partial tears of the:

What are the Symptoms?

  • Extreme pain in the knee after a traumatic injury.
  • Rapid, extreme swelling.
  • A popping or tearing sound at the time of injury.
  • Difficulty and pain on trying to move the knee.
  • Bruising usually appears within 2-3 days.
  • An unstable feeling knee.

What Causes an Unhappy Triad?

This kind of injury will only occur after a considerable force has been applied to the knee. In sports, it tends to be a result of a tackle (such as football, rugby or soccer), or occasionally where the foot is planted and the knee is twisted. They may also happen after car accidents.

acl sprain
  • The anterior cruciate ligament crosses the middle of the knee and prevents forward movement of the tibia (shin bone).
  • The medial ligament is on the inside of the knee and prevents sideways movement of the knee joint.
  • Part of the medial meniscus on the inside of the knee attaches to the medial ligament. Therefore it is often torn with a bad medial ligament sprain.


Immediate Treatment

  • Apply ice or cold therapy.
  • Rest and support the knee in an elevated position.
  • If possible use a compression bandage.
  • Seek medical help as soon as possible.

Further Treatment

  • An X-ray or MRI will usually be taken to confirm the diagnosis.
  • Depending on the severity of the ACL and meniscus tears, surgery will usually be advised.
  • ACL reconstruction from a graft is performed. The graft is usually taken from the hamstrings or patella tendon.
  • A meniscus tear repair or removal is performed at the same time.
  • The MCL is usually left to heal naturally.
  • The leg will be immobilized to allow healing.
  • A lengthy rehabilitation programme is then required to regain full strength and mobility at the knee
This article has been written with reference to the bibliography.
Scroll to Top