Drop leg Lachman test. A new test of anterior knee laxity.

We describe a new method of evaluating anterior cruciate stability that we call the drop leg Lachman test. This test is performed with the patient supine and the leg to be examined abducted off the side of the table and flexed 25 degrees. The thigh is stabilized to the examining table with one of the examiner's hands, and the patient's foot is held between the examiner's legs. The examiner's free hand provides the anteriorly directed force as done in the Lachman test. A prospective study of 52 patients who were identified as unilaterally anterior cruciate ligament deficient was conducted. Forty-two subjects were tested while conscious, and 40 subjects were tested under anesthesia. Each subject was examined with a KT-1000 arthrometer. In the conscious group, the drop leg Lachman test resulted in 1.8 mm greater average excursion than the Lachman test. In the anesthetized group, the drop leg Lachman test resulted in 2.4 mm more average translation than the Lachman test. In both groups, the difference between tests was statistically significant. The drop leg Lachman test is physically easier to perform than the Lachman test, and it is a sensitive method of demonstrating anterior laxity in an anterior cruciate ligament-deficient knee.