Valgus maneuver producing ligament laxity indicates injury to which ligament?

• A. Medial collateral ligament
• B. Lateral collateral ligament
• C. Anterior cruciate ligament
• D. Posterior cruciate ligament

Answer: (A)

Valgus stress on the knee opens the medial joint space, so a laxity observed with a valgus maneuver points to injury of the medial collateral ligament. The MCL is the primary restraint against valgus forces at the knee, helping prevent the knee from gapping on the medial side. In contrast, the lateral collateral ligament resists varus stress, while the ACL and PCL control anterior-posterior translation and rotational stability rather than medial opening. So when valgus stress produces laxity, the ligament torn is the medial collateral ligament; it runs from the medial femoral epicondyle to the medial tibial condyle (and is closely related to the medial meniscus), which is why medial-sided laxity is a hallmark of MCL injury.