ABIM IM Practice Test 13

A 24-year-old woman is evaluated 3 days after twisting her right knee when landing from a jump during a basketball game; she felt a pop, and the knee swelled within hours. She can bear weight with a limp. She has no other medical problems. Vital signs are normal. Examination shows a moderate effusion, full extension and pain-limited flexion. Based on the history and initial examination, her physician estimates the probability of an anterior cruciate ligament tear at 40%. The Lachman test then shows increased anterior tibial translation with a soft end point. Assume that the Lachman test has a sensitivity of 90% and a specificity of 85% for an anterior cruciate ligament tear. Which of the following is the best estimate of the probability of a tear after this positive test?