Unhappy triad

Medical quality assurance by Dr. Albrecht Nonnenmacher, MD at August 1, 2016
StartDiseasesUnhappy triad

An unhappy triad of the knee or simply unhappy triad is a severe injury in which important ligaments and cartilage of the knee – the ACL (anterior cruciate ligament), the MCL (medial collateral ligament), and the meniscus - are injured at the same time. For a knee injury to be considered an unhappy triad, it must include a complete or partial tear to each one. This injury is also referred to as a terrible triad and an O'Donaghue's triad.


Definition & Facts

Athletes, while working to reach great heights in their sport and their health, can be at risk for knee injuries - a type of sports injury. Many common exercises and athletic movements put strain on the knees and cause injuries that can range from soreness to severe conditions like the unhappy triad.

The anterior cruciate ligament, or ACL, runs behind the knee and helps keep the tibia, which is the shin bone, and femur, which is the thigh bone, in place and stable. The medial collateral ligament, or MCL, connects these two bones on the inner side of the joint. The meniscus is a cartilage pad in the joint between the tibia and the femur that prevents the bones from painfully rubbing into each other.

The most severe injury in an unhappy triad is a torn ACL. The ACL cannot heal on its own so it must be repaired surgically. The recovery process can take four to seven months. A torn meniscus is also very severe and needs to be repaired surgically. These two procedures can be performed during the same surgery. The tears in the MCL can heal on their own but are usually set in place during the surgery for the ACL and meniscus so that they heal along with the other injuries.

Symptoms & Complaints

When a person experiences an unhappy triad, a number of painful and severe symptoms ensue. A popping, tearing, or clicking sound is usually heard, and there will be extreme knee pain and pain in the surrounding area. 

The knee area will have rapid and extreme swelling, and in two to three days bruising will appear on the knee and on the bones. The leg will feel wobbly and unstable and it will be difficult to have full range of motion or straighten and bend it.


The causes of an unhappy triad are varied. It is usually a result of an accident or fall. One way this can happen is when the knee is forcefully twisted. A lateral hit to the knee can also cause this injury. The unhappy triad can occur when the knee is pushed while the foot is planted on the ground.

Basically, any major force hitting the knee can cause the unhappy triad. These incidents can occur anywhere, but mostly athletes sustain such injuries during contact sports. Football, rugby, hockey, and soccer are the sports most commonly being played when athletes get unhappy triad injuries.

Also, skiing, snowboarding and other snow sports are the source of many of these injuries. Skateboarding and motocross are becoming more popular and athletes participating in these sports are becoming increasingly prone to this painful injury.

Extra weight such as from being overweight or obese can increase the chances of osteoarthritis, add stress to the knee, and increase the chance for injury.

Diagnosis & Tests

When such an injury occurs, it is essential to see a doctor. The injury needs to be tested and diagnosed. It will become worse if left untreated as it cannot heal on its own. Patients should immediately apply the RICE (medicine) method by staying off of the knee (rest) and icing the knee (ice). They should also put a bandage to compress the knee (compression) and keep it elevated (elevation) until they can get medical attention.

In order to detect whether a knee injury is an unhappy triad, a doctor will perform some tests. He or she will need to touch the knee to see if it feels normal, take note of the swelling and the pain levels, and check out the range of motion and stability of the knee. The doctor will usually have a magnetic resonance imaging (MRI) test done and maybe an X-ray taken to help him or her diagnose the injury.

Treatment & Therapy

Once the injury is confirmed as an unhappy triad, treatment must happen immediately. Surgery should be performed to repair the multiple tears.  The ACL will be reconstructed from a graft which may be taken from a patellar ligament or a hamstring. The meniscus will be repaired at the same time.

Months of physical therapy and rest are required to allow the knee and the tendons to fully recover and gain back a full range of motion. It can take six to nine months for the athlete to recover from an unhappy triad and regain a full range of motion in order to participate again in physical activity and sports. The long recovery time is mostly due to the ACL reconstruction that is often necessary for complete recovery.

Prevention & Prophylaxis

There are some preventative approaches people can take to try to prevent the unhappy triad. Athletes can help prevent knee injuries by maintaining a healthy weight. Well-fitting shoes with good support help keep the leg aligned and balanced, and also lessens the chance for injury.

Another preventative measure athletes can take to keep their knees healthy is to warm up before exercising or playing a sport. Doing light exercises to break a sweat, and then stretching the front and back thigh muscles will decrease the pressure on the tendons and relieve pressure on knees.

Another option for people with painful knees is to do low-impact exercises like elliptical machines, rowing machines or cross-country skiing machines. When exercising outside of the gym, swimming and walking are also easy on the knees. These low-impact exercises do not pound on the knees. Strengthening leg muscles through weight training with an expert trainer is also a good way to help support the knees and avoid injuries.

Athletes should also try to maintain a consistent level of training. Sudden decreases in exercise can weaken the leg and knee, and sudden increases can add strain to the knees. A physical therapist can help athletes with existing knee problems put together a regimen that is safe for them.

While various methods can decrease the chances of knee injuries such as the unhappy triad, athletes should seek medical attention as soon as possible if they suspect they have a severe knee injury.