To do this, lay the patient supine on a bed. Put the patient's knee in about 20-30 degrees flexion. The examiner should place one hand behind the tibia and the other on the patient's thigh. It is important that the examiner's thumb be on the tibial tuberosity. On pulling anteriorly on the tibia, an intact ACL should prevent forward translational movement of the tibia on the femur ("firm endpoint").
Anterior translation of the tibia associated with a soft or a mushy endpoint indicates a positive test. More than about 2 mm of anterior translation compared to the uninvolved knee suggests a torn ACL ("soft endpoint"), as does 10 mm of total anterior translation. An instrument called a "KT-1000" can be used to determine the magnitude of movement in mm.
The Lachman test is recognized by most authorities as the most reliable and sensitive clinical test for the determination of anterior cruciate ligament integrity, superior to the Anterior Drawer test commonly used in the past.
This test is named after orthopaedic surgeon, John Lachman, M.D.. A graduate of both Temple University and Temple University School of Medicine , Dr. Lachman also completed his orthopaedic residency at Temple under John Royal Moore, M.D., the first professor and chairman of the Department of Orthopaedic Surgery. Remaining on the faculty at Temple following his residency, in 1956 he succeeded Dr. Moore as professor and chairman.