The Unhappy Triad Revisited

The term “unhappy triad” was first used in 1964 by one of the fathers of orthopaedic sports medicine, O’Donoghue, and identifies a very serious knee injury affecting the anterior cruciate ligament (ACL), the medial collateral ligament (MCL) and the medial meniscus, occurring in an estimated 25% of acute athletic knee injuries. Later, Werner Mueller and Shelbourne and Nitz reported possible involvement of the lateral compartment, including the lateral meniscus and the anterolateral femorotibial ligament. Based on our surgical findings with a consecutive series of eleven patients with acute unhappy triad collected over a period of three years among 125 patients with acute ACL tears, we can reasonably state that the unhappy triad is actually a tetrad, with the fourth component being a tear of the anterolateral ligament (ALL), whose involvement was found in all patients. The unhappy “tetrad”, which includes injuries of the ACL, medial or lateral meniscus, MCL and ALL, results from a “two steps” severe knee sprain that, starting from valgus internal rotation (pivot shift-like mechanism), suddenly turns towards true valgus external rotation. Surgical repair of the medial collateral ligament should be advisable in cases of more severe valgus instability with a medial opening exceeding 10 mm.