Ligamentous Knee Injury

Abstract

The four ligaments of the knee are the anterior and posterior cruciates, and the medial and lateral collaterals. Physical examination is key to the diagnosis of ligamentous knee injuries, which can be confirmed with MRI. In particular, anterior cruciate ligament injury (ACL) commonly occurs via a pivoting or cutting motion, most often seen in young athletes. Multi-ligamentous knee injuries often result from higher energy trauma and may represent knee dislocation, prompting more urgent evaluation.

Classically, what injuries compose the “unhappy triad ” or “terrible triad ” injury to the knee?	Anterior cruciate ligament (ACL), medial collateral ligament (MCL), medial meniscus injury
Which meniscus (medial or lateral) is commonly injured in an acute ACL rupture ?	Lateral meniscus
What is the reason for the limited healing potential of the cruciate ligaments relative to the collateral ligaments?	Intra-articular structures have poor blood supply relative to the rich extra-articular supply
What motion does the ACL primarily prevent?	Anterior tibial translation
What knee injury is commonly seen in a dashboard-type injury where a patient sustains a posterior acetabular wall fracture?	Posterior cruciate ligament (PCL) tear
When performing ACL reconstruction, what technical error is associated with early ACL failure?	Vertically oriented ACL graft, often resulting from a femoral tunnel placed too anteriorly
A patient has a multi-ligamentous knee injury after a motorcycle accident, suspicious for a knee dislocation that was reduced in the field. What studies would you want to obtain urgently?	Pulse exam, ankle-brachial index (ABI), CT angiogram if ABI <0.9 (due to the risk of popliteal artery injury)