The Lachman test, which may also be referred to as the Ritchie, Trillat, or Lachman-Trillat test, is the best indicator of injury to the anterior cruciate ligament, especially the posterolateral band. It is a test for one plane anterior instability.
The patient lies supine with the involved leg beside the examiner. The examiner holds the patient’s knee between full extension and 30° of flexion. This position is close to the functional position of the knee, in which the anterior cruciate ligament plays a major role. The patient’s femur is stabilized with one of the examiner’s hands (the “outside” hand) while the proximal aspect of the tibia is moved forward with the other (“inside”) hand.
The tibia should be slightly laterally rotated and the anterior tibial translation force should be applied from the posteromedial aspect.Therefore the hand on the tibia should apply the translation force.
An intact ACL should prevent forward translational movement ("firm endpoint") while an ACL-deficient knee will demonstrate increased forward translation without a decisive 'end-point' - a soft or mushy endpoint indicative of 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.
In the hands of the experienced clinician, accuracy of this test has been found to be very sensitive.
A number of factors can influence the results of the Lachman test.
An inability of the patient to relax.
The degree of knee flexion.
The size of the clinician's hand.
The stabilization (and thus relaxation) of the patient's thigh.
The grading of knee instability is as follows:
1+ (mild): 5 mm or less.
2+ (moderate): 5 to 10 mm.
3+ (serious): more than 10 mm.
False-negatives with this test can occur. False-negatives may be caused by a significant hemarthrosis, protective hamstring spasm, or tear of the posterior horn of the medial meniscus.
The test is named after orthopaedic surgeon, John Lachman, late Chairman of the Department of Orthopaedic Surgery and Sports Medicine at Temple University School of Medicine in Philadelphia, PA.