Summary

Injuries of ACL and anterolateral compartment seems to occur in the very early phase of the injury when the knee is forced into internal rotation. The “unhappy triad” of injuries to the knee is actually a tetrad, involving not just the ACL, medial collateral ligament and medial meniscus, but also routinely involves the anterolateral complex.

Abstract

Purpose

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) tear were selected for this study. Only cases with a grade II or III lesion at Hughston classification of the medial collateral ligament (MCL) were included in the study (11 patients). All patients underwent ACL reconstruction and exploration of the anterolateral complex that was then assessed, photographed, classified and eventually repaired. Open MCL surgical repair was performed with a valgus stress test more than 10 mm as revealed by fluoroscopy.

Results

The anterolateral complex was involved in all cases. 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 antero-lateral complex lesion repaired by direct suture and re-tensioning.

Discussion

On the basis of a recent analysis performed by Koga et al. 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.