The “Unhappy Triad”

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What is the Unhappy Triad?

The unhappy triad, also referred to as the O’Donoghue Triad, was originally cited in 1950 by O’Donoghue and stated this extensive damage and rupture should bring upon early surgical intervention. The unhappy triad is a severe acute injury to the knee, classically involving three major components that provide important stability to the structure. These components are the anterior cruciate ligament, medial collateral ligament and medial meniscus.

How does the Unhappy Triad occur?

The unhappy triad occurs most often from a large lateral force or blow that is applied to the knee. This generally occurs in a sporting event, like soccer, rugby or football where tackling or pivoting on a twisted knee occurs. This is frequently from a situation where the foot is strongly plated and strong torsion is applied.

What are the symptoms?

Many of the symptoms in the unhappy triad are similar to other knee conditions. These often include swelling, bruising, popping sensation at time of injury, difficult bending/straightening the knee, pain and feeling unsteady on the injured extremity.

How often does this injury occur?

In a study by Shelbourne and Nitz, 52 injuries with a second-degree tear of the ACL and MCL that were confirmed under arthroscopy were analyzed for medial meniscus injury. Interestingly, 80% of knees that had both, third-degree tears of the ACL and MCL had lateral meniscus tears and only 29% had medial meniscus injuries. There were no isolated medial meniscus injuries without lateral meniscus tears. This was later confirmed in multiple larger retrospective studies, specifically by Shelbourne and Hagino, which confirmed lateral meniscus tears are more common in ACL injury than medial meniscus as O’Donoghue originally proposed.

How do we treat the Unhappy Triad?

The unhappy triad most often will require arthroscopic surgery. Since the high-grade injury to the ACL is almost always present, this requires grafting and repair. Many larger meniscus injuries do not have enough blood flow to heal without repair. These surgeries can be performed at the same time and the MCL can often repair without fixation and only immobilization/rest. Recovery will require extensive rehabilitation and return to play can be expected around 6-9 months.

How can knee injuries be prevented?

There appears to be a higher incidence of reported isolated ACL injuries in young female athletes than compared to other populations. It may be of benefit for this population to seek out personal trainers or physical therapists to improve body mechanics and provide neuromuscular training techniques to help strengthen and balance surrounding structures. These therapists can target weakened areas, often hip muscles, that cause athletes to land from a jump in a knock-kneed position that put strain on the ACL. The Unhappy Triad injury is harder to prevent than an isolated ACL tear as this is more often from a larger impact than an unusual landing. Avoiding blind tackles in your sport if possible could be of benefit.

By Kailey Osbaugh and Mo Mortazavi, MD


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