Unhappy triad
| Unhappy triad | |
|---|---|
 |
|
| Knee | |
| Classification and external resources | |
| Specialty | emergency medicine |
| ICD-10 | S83.7 |
| MedlinePlus | 001074 |
An unhappy triad (or terrible triad, "horrible triangle", O'Donoghue's triad or a "blown knee") is an injury to the anterior cruciate ligament, medial collateral ligament, and the medial meniscus. Originally the "unhappy triad" included the medial meniscus and not the lateral meniscus. However, during the 1990s, analysis indicated that the 'classic' O'Donoghue triad is actually an unusual clinical entity among athletes with knee injuries. Some authors mistakenly believe that in this type of injury, acute tears of the medial meniscus always present with a concomitant lateral meniscus injury. However, the lateral meniscus tears are more common than medial meniscus tears in conjunction with sprains of the ACL according to the 1990s study.
In 1936, Cambell stated that an "impairment of the anterior crucial and medial ligaments is associated with injuries of the internal cartilage". In 1950, O'Donoghue described the unhappy triad as: (1) rupture of the medial collateral ligament, (2) damage to the medial meniscus and (3) rupture of the anterior cruciate ligament. O'Donoghue estimated the incidence rate in the traumatic sports knee to be 25%.
In 1991, Shelbourne and Nitz questioned the validity of O'Donoghue's terrible triad study. A review of all arthroscopically confirmed acute injuries of second degree or worse to the ACL and MCL was performed. Of the 52 knees reviewed, 80% of group 1 had lateral meniscus tears and 29% had associated medial meniscus tears. None of the medial meniscus tears were isolated; medial meniscus tears were not present in the absence of a lateral meniscus tear. From this study, it was concluded that the structures more typically involved in a triad were the anterior cruciate ligament, medial collateral ligament, and the lateral (not medial) meniscus.
Skeletal components involved in the unhappy triad include:
No muscles are directly involved in this injury, only ligaments; However, strengthening the hip flexor and hip extensor muscles may help alleviate the injury.
The medial collateral ligament, posterior cruciate ligament, anterior cruciate ligament, and lateral collateral ligament are the four primary ligaments of the knee. The medial and lateral collateral ligaments primarily provide support to varus and valgus forces whereas the anterior and posterior cruciate ligaments prevent anterior and posterior translation of the tibia on the femur.
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