Which type of injury pattern is commonly associated with a rapid effusion in the knee after trauma?

• A. Fracture of the femur
• B. Meniscus tear
• C. ACL injury
• D. Distal fibular fracture

Answer: (C)

A rapid effusion in the knee after trauma is most commonly associated with an ACL (anterior cruciate ligament) injury due to the body's response to injury and inflammation. When the ACL is torn, it often results in bleeding into the joint (hemarthrosis), leading to swelling. This swelling can occur soon after the injury, typically within a few hours, and presents as a rapid accumulation of fluid in the knee.

Injuries such as a meniscus tear, while they can cause swelling, often present with symptoms that develop more gradually. Meniscal injuries may not cause immediate significant effusion, as they are less likely to result in bleeding into the joint at the time of injury compared to an ACL tear.

A fracture of the femur can also lead to knee swelling but would generally involve significant trauma and more complicated injury patterns, and the effusion may not be limited to the knee joint as it can encompass soft tissue and other structures.

A distal fibular fracture typically would not lead to a rapid effusion in the knee joint itself, as it mainly involves the ankle area and is not directly associated with knee joint structures.

The mechanics and physiological responses to an ACL injury specifically make it the most likely candidate for a rapid effusion in