The Unhappy Triad of the Knee Re-Revisited

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International Orthopaedics


Aim of the study: To describe the surgical findings of the anterolateral complex in patients with the "unhappy triad" lesion of the knee.

Method: One hundred and twenty-five consecutive patients presenting with acute anterior cruciate ligament (ACL) tears were selected for this study. Only cases, evaluated with a valgus stress test under fluoroscopy, with a medial opening more than 5 mm of the medial collateral ligament (MCL) were included in the study (11 patients). For the included cases, open MCL surgical repair was performed only in cases with a valgus stress test more than 10 mm as revealed by fluoroscopy (3 patients). All included cases (11 patients) underwent ACL reconstruction and exploration of the anterolateral complex that was then assessed, photographed, classified, and eventually repaired.

Results: At clinical evaluation under anaesthesia, all patients presented a positive Lachman test and a pivot shift test graded as ++ in four cases and +++ in five cases, not valuable in two cases. At surgical exploration, the anterolateral complex was involved in all cases (11 patients): one case demonstrated a type I injury, eight cases a type II injury, two cases a type III injury, and no patient with a type IV injury (Segond's fracture). All anterolateral complex lesions were repaired by direct suture and re-tensioning.

Discussion: On the basis of a recent analysis performed by other authors, we could speculate that injuries of ACL and anterolateral compartment occur in the very early phase of the injury when the knee is forced into internal rotation. The MRI evidence of bone bruising in the lateral compartment in most cases of the present series support the hypothesis of an internal rotation torque.

Conclusions: The unhappy triad of injuries to the knee is actually a tetrad involving not just the ACL, MCL, and medial/lateral meniscus but also involved the anterolateral complex.



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ACL, Anterolateral complex, Knee, Multiple ligament injuries