Unhappy Triad of the Knee

Unhappy triad of the knee

The unhappy triad is a severe injury involving damage to three of the four major ligaments in the knee.

Medically reviewed by Dr. Chaminda Goonetilleke, 31st Dec. 2021

Hinged knee braces

What is the Unhappy triad injury?

The unhappy triad is also called the terrible triad, or the O’Donoghue triad. It is a particularly severe knee injury involving full or partial tears of the following:

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 in trying to move the knee.
  • Bruising usually appears within 2-3 days.
  • An unstable feeling knee.


An X-ray or MRI usually confirms the diagnosis.

What Causes an Unhappy Triad?

This kind of injury only occurs after a considerable force to the knee. In sports, it tends to result from a tackle, for instance in football, rugby, or soccer. Or occasionally twisting the knee with a planted foot.

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 often occurs in conjunction with a bad medial ligament sprain.


Immediate first aid is to apply the PRICE principles of protection, rest, ice, compression, and elevation.

Cold therapy

Cold knee wrap

Apply ice or cold therapy. Do not apply ice directly to the skin because it may cause ice burns. Instead, wrap in a wet tea towel, or use a commercially available hot and cold wrap.


Rest and support the knee in an elevated position. If possible use a compression bandage.

Seek medical help as soon as possible.


Surgery is usually indicated. This depends on the severity of your ligament tears. Your surgeon may perform reconstruction using a graft of tissue taken from your hamstrings or patella tendon.

Hinged knee braces

They may also perform a meniscus tear repair or removal at the same time.

The MCL is usually left to heal naturally.

The leg is immobilized to allow it to heal.

A full knee rehabilitation program regains full knee strength and mobility.

Related articles

  • Dislocated knee

    A dislocated knee occurs when the femur (thigh bone) and the tibia (shin bone) move apart. This is different from a patella dislocation where the…

  • Torn cartilage meniscus

    Medically reviewed by Dr. Chaminda Goonetilleke, 14th Dec. 2021 A torn meniscus is a tear of one of the semi-circular cartilage discs in the knee…

  • Medial knee pain

    Medically reviewed by Dr. Chaminda Goonetilleke, 30th Nov. 2021 Pain on the inside of the knee is known as medial knee pain. Injuries which occur…

  • MCL sprain

    Medically reviewed by Dr. Chaminda Goonetilleke, 5th Dec. 2021 A medial collateral knee ligament sprain or MCL sprain is a tear of the ligament on…

  • Tibial plateau fracture

    A tibial plateau fracture is a break to the upper surface of the tibia (shin bone). The tibial plateau is prone to becoming fractured in…

  • Knee joint injuries

    An acute knee injury is a sudden onset sprain, strain, dislocation or fracture, usually caused either by direct trauma or twisting. Here we explain the…

  • Isometric quads knee rehabilitation

    Medically reviewed by Dr. Chaminda Goonetilleke, 13th Dec. 2021 MCL sprain exercises should form part of a full rehabilitation program. Mobility, stretching, strengthening, proprioception, functional…

  • American football injuries

    American Football is an intensive contact sport where serious injuries are not uncommon. However, it is also one of the best protected, due to the…

  • ACL sprain

    An ACL sprain (torn ACL) is a tear of the anterior cruciate ligament in the knee joint. Medically reviewed by Dr. Chaminda Goonetilleke, 21st Dec.…

  • Hamstring strain exercises

    Torn knee meniscus exercises include mobility, stretching, strengthening, and sports-specific exercises. Here we outline some rehabilitation exercises which may form part of a meniscus injury…

Scroll to Top