Which describes common signs and symptoms of an ACL tear?

• A. MOI of planting foot with thigh rotation; hearing a POP sound, pain, swelling
• B. MOI of direct blow to knee with no swelling
• C. MOI of twisting with no popping
• D. Sudden numbness in foot

Answer: (A)

An ACL tear typically happens during a sudden twisting or pivoting of the knee when the foot is planted. The classic signs are a loud pop at the moment of injury, followed by rapid swelling inside the joint, plus pain and a sense of the knee giving way or instability that makes it hard to continue activity. The described mechanism—planting the foot with thigh rotation—together with a popping sound, pain, and swelling fits this pattern most closely, because these features commonly occur with an ACL tear. A direct blow to the knee with no swelling is less consistent, as a tear usually causes swelling from joint bleeding. Twisting with no popping can occur but is less typical, since a pop is a common clue. Sudden numbness in the foot points to nerve or vascular injury, not an ACL tear.