Evaluating acutely injured patients for internal derangement of the knee.

Although historical findings have some value in diagnosing internal derangement of the knee, a thorough physical examination can often rule out fracture and ligamentous and meniscal injuries. The Ottawa Knee Rule can help physicians determine which patients require radiography. Positive physical examination tests and findings of acute effusion suggest internal derangement. An abnormal McMurray or Thessaly test strongly suggests meniscal injury, whereas a normal Thessaly test may rule out meniscal injury. Absence of evidence of joint effusion significantly decreases the probability of internal derangement. Magnetic resonance imaging should be reserved for ruling out internal derangement in patients with suggestive historical and physical examination findings.