American Board of Internal Medicine (ABIM) Certification Practice Exam

What symptom is associated with a complete medial or lateral collateral ligament tear?

1. Palpable fluid collection

2. Knee joint instability and tenderness

3. Popping sound during movement

4. Localized heat and redness

The correct answer is: Knee joint instability and tenderness

A complete tear of the medial or lateral collateral ligament (MCL or LCL) results in knee joint instability and tenderness primarily because these ligaments are crucial for maintaining the stability of the knee structure during movement. The collateral ligaments provide support and prevent excessive side-to-side motion of the knee, so when one of these ligaments is completely torn, the knee loses its ability to stabilize properly. This instability often leads to the sensation of the knee giving way, which is a common report from patients with these types of injuries. Additionally, tenderness in the area of the ligament is typical due to the injury's impact on surrounding tissues. While palpable fluid collection, popping sounds, and localized heat and redness can occur in various knee injuries, they do not specifically characterize a complete collateral ligament tear. Fluid collection can suggest other knee injuries or effusions, popping sounds are often associated with meniscal tears or ligament sprains, and localized heat may indicate inflammation or infection rather than the specific symptoms of a collateral ligament tear.