The unhappy triad is the name of a severe injury involving three crucial parts of your knee joint.

Other names for it include:

  • terrible triad
  • O’Donoghue’s triad
  • blown knee

Your knee joint runs from the bottom of your femur, which is your thigh bone, to the top of your tibia, your shin bone. Ligaments connect these two bones and provide stability for your knee joint.

Ligaments are strong, but they aren’t very elastic. If they stretch out, they tend to stay that way. And when stretched too far, they can tear.

The unhappy triad involves damage to your:

  • Anterior cruciate ligament (ACL). The ACL crosses your inner knee joint diagonally. It helps to prevent your tibia from moving too far forward and stabilize your leg when you twist at the waist.
  • Medial collateral ligament (MCL). The MCL prevents your knee from bending too far in the direction of your other knee.
  • Medial meniscus. This is a wedge of cartilage on the tibia in your inner knee. It acts like a shock absorber when you walk or run while also stabilizing your knee.

Read on to learn more about the unhappy triad, including how it’s treated and how long it takes to recover from surgery.

The symptoms of the unhappy triad come on suddenly immediately after your knee is injured.

They can include:

  • severe pain on the inside of your knee
  • significant swelling that begins within minutes of the injury
  • difficulty moving or putting weight on your knee
  • feeling like your knee will give out
  • knee stiffness
  • sensation that your knee is locking or catching on something
  • bruising that appears a few days after the injury

The unhappy triad usually results from a hard blow to your lower leg while your foot is planted on the ground. This pushes your knee inward, which it isn’t used to doing.

It also causes your femur and tibia to twist in opposite directions. This causes your medial meniscus and ligaments to stretch too far, making them prone to tearing.

This might happen when a football player has their cleats planted in the ground while being hit with great force on their outer knee.

It can also happen to a skier if their ski doesn’t release from the bindings during a fall. The ankle can’t turn in a ski boot, so the knee ends up twisting, which can stretch or rupture ligaments.

Treatment depends on how severe the injury is.

If the tears in your ligaments and meniscus are mild, you might be able to avoid surgery by:

  • resting your knee so it can heal without getting worse
  • applying ice packs to reduce inflammation and swelling
  • wearing compression bandages to reduce swelling
  • elevating your knee while keeping it supported whenever possible
  • doing physical therapy to increase strength and mobility

A Cochrane Review found that active adults with ACL injuries didn’t have any reduced knee function two and five years after injury. This was the same for those who underwent nonsurgical treatment and those who opted for surgery.

However, 51 percent of those treated without surgery ended up having the surgery within 5 years due to knee instability. This is something to keep in mind when considering your treatment options.

Another potential problem is that by delaying surgery, the potential for developing arthritis exists because of the instability that could affect the knee as the patient gets older.

If you do need surgery, there are several options based on what needs to be repaired and how severe the injury is.

Most surgeries are done using a minimally invasive approach called arthroscopy. This allows a surgeon to insert miniature surgical tools through a through a small incision in your knee.

The unhappy triad includes three injuries, but only two tend to require surgery:

  • The ACL can be reconstructed using a tendon graft from a muscle in your leg.
  • The meniscus can be repaired by removing the damaged tissue with a procedure called a meniscectomy. A surgeon may instead decide to repair or transplant the meniscus.

The MCL usually doesn’t need to be repaired because it heals on its own.

Physical therapy

Physical therapy is an important part of your recovery regardless of whether you have surgery. Your doctor will likely recommend doing six to nine months of physical therapy and rehabilitation to help regain strength and range of motion in your knee.

If you have surgery, you can expect a recovery time of at least six months. Initially, you’ll need to wear a knee brace for a while to keep your leg from moving.

For two to four weeks following surgery, you’ll likely focus on strengthening all the joints in your leg and doing exercises to improve your range of motion.

Gradually, you can start putting weight on your knee. Over the next five months, you’ll focus on doing exercises to both strengthen your your leg and continue improving your range of motion.

Most people can return to their previous level of activity after about six to nine months of recovery. But if your injury was severe, your doctor might recommend low-impact activities, such as swimming or biking, to reduce the amount of force placed on your knee.

An unhappy triad injury is one of the most severe sports injuries. Most cases require surgery and a recovery period of six to nine months. But if you keep up with physical therapy and give your knee ample time to heal, you’ll likely be able to get back to your usual activities in under a year.