Anterior drawer test of the knee

Inside the knee, the anterior cruciate ligament helps keep the thighbone and shinbone from shifting out of alignment in the forward-and-backward direction. This ligament prevents the shinbone from moving forward, but an injury can weaken that restraint.

The anterior drawer test uses a hands-on examination to check whether the ligament is supporting the bones properly. The examiner pulls the shinbone forward like a drawer, assessing how far it moves and the resistance felt through the fingertips as the movement stops. Because this physical examination requires only the examiner's hands and no special equipment, it can be performed right in the examination room.

The test usually follows these steps.

1. Getting into position — You lie flat on your back on the examination table, with your hip bent to about 45 degrees, your knee bent to about 90 degrees, and the sole of your foot resting comfortably on the table. 2. Stabilizing the foot — The examiner sits lightly on your foot to hold it in place. The foot needs to stay still so that the shinbone's movement can be felt accurately. 3. Holding the shinbone — The examiner wraps both hands around the upper shinbone just below the knee, placing the thumbs on the joint line at the front of the knee. The muscles at the back of your thigh need to be relaxed. 4. Pulling forward — The examiner gently pulls the shinbone forward, feeling how far it moves and whether it comes to a firm or soft stop. 5. Comparing with the other side — The uninjured knee is tested in the same way to compare movement.

The most important thing for you during the test is to relax without tensing your body. If pain causes your muscles to tighten involuntarily, an accurate examination may be difficult.

The examiner checks both how far the shinbone moves forward and the resistance felt when the movement stops. In a normal knee, the shinbone moves forward a little, then comes to a firm stop as the ligament becomes taut. If the ligament has been stretched or torn, the bone may move farther forward, or the stopping sensation may feel softer.

Comparing the two knees is therefore a basic part of this test. Natural joint flexibility and looseness vary from person to person, so the opposite knee in the same person provides the best reference.

Even with the same test, the findings may feel different depending on when and under what circumstances it is performed.

• Immediately after an injury — Pain and swelling, along with involuntary tightening of the muscles at the back of the thigh that hold the shinbone in place, may make it seem to move less than it actually would. For this reason, in the acute phase, the Lachman test, which serves the same purpose, is performed first or alongside this test.
• After some time has passed — Once swelling and pain subside and the muscles relax, ligament laxity becomes easier to feel. A 2006 meta-analysis of chronic ACL injuries reported a sensitivity of 92% and a specificity of 91% for the anterior drawer test.
• Under anesthesia — Accuracy increases under anesthesia, when the muscles are fully relaxed. In a meta-analysis of acute complete ACL tears, examination in the clinic had a sensitivity of 38% and a specificity of 81%, compared with a sensitivity of 63% and a specificity of 91% under anesthesia.

In clinical practice, conclusions are therefore not drawn hastily from this test alone. The circumstances of the injury are reviewed in detail, and other tests are performed as well. If needed, imaging such as MRI is used to examine the internal structures of the knee and check for an accompanying meniscus injury.

• Wear comfortable clothing. Shorts or loose-fitting trousers that allow the knee to be exposed easily make the examination easier.
• Try to relax. Tensing your leg because you are worried about pain can affect the test results. If you tell the examiner beforehand that you are concerned about pain, they can adjust the force used and examine you more carefully.
• Describe the injury in detail. When it happened, what movement you were making, whether you heard or felt a “pop,” and whether swelling developed immediately are important clues for interpreting the test results.
• Both sides will be tested. Checking the uninjured side as well is a normal part of the process, so there is no need to worry about this.