Review Question - QID 109202

This patient is presenting with trauma to his knee, instability of the knee joint, and erythema and effusion on physical exam suggesting a most likely diagnosis of an anterior cruciate ligament (ACL) tear. In an ACL tear, anterior translation of the tibia relative to the femur is found on physical exam.

An ACL tear typically occurs when there is a posterior impact to a planted leg. The typical event will be an audible popping sound, followed by acute pain, erythema, and edema of the knee with a feeling of instability when bearing weight. Though other injuries can present in this manner, the most likely injury epidemiologically is an ACL tear. On physical exam there will be anterior translation of the tibia relative to the femur when traction is applied to the leg.

Incorrect Answers:
Answer 1: Laxity to valgus stress suggests a diagnosis of a medial collateral ligament tear. A medial collateral ligament tear typically occurs with lateral impact to a planted leg. Such an acute presentation is more suggestive of an ACL tear.

Answer 2: Laxity to varus stress suggests a diagnosis of a lateral collateral ligament tear. This injury is common when there is medial impact to a planted leg.

Answer 3: Clicking and locking of the joint with motion is suggestive of a meniscal tear. Though it could present similarly to an ACL tear (or could co-occur), it is a less likely injury than an ACL tear epidemiologically and would not have such a severe/acute presentation.

Answer 5: Posterior translation of the tibia relative to the femur suggests a diagnosis of a posterior cruciate ligament (PCL) tear. A PCL tear occurs more commonly with anterior impact to a planted leg. It is a less common injury than an ACL tear.

Bullet Summary:
An ACL tear is the most common ligament injury of the knee and is associated with anterior translation of the tibia relative to the femur.