How to Perform a Lachman's Test on the Knee

The ACL, or anterior cruciate ligament, is a strong band of connective tissue that keeps the knee from hyperextending during activity. The Lachman's Test of the Knee is a reliable and sensitive test doctors use for diagnosing injuries to the ACL. It's similar to the Anterior Drawer Test, but provides more accurate results.

Instructions

• 1

  Ask the patient to lay down with his back on the examination table.

• 2

  Extend both of the patient's legs fully.

• 3

  Place the patient's injured knee in about 20 degrees of flexion.

• 4

  Grasp the patient's femur with one of your hands. Your thumb should be on top of his thigh.

• 5

  Grasp the patient's tibia with your other hand. Be sure to position your thumb on top of the bony bulge at the top of the shinbone, known as the tibial tuberosity.

• 6

  Alternate pulling the patient's tibia forward and backward. If the ACL is healthy, the endpoint of its forward motion will feel firm. If the ACL is ruptured, this endpoint will feel soft or mushy.

• 7

  Perform Steps 2 through 5 on the patient's other leg. This allows you to compare the results from the injured knee and the healthy knee to make a diagnosis.