The Anterior Drawer Test (ADT) is a physical examination technique utilized by healthcare professionals, such as orthopedists and physical therapists, to evaluate the stability of a patient’s knee joint. This manual maneuver assesses the integrity of the ligaments connecting the thigh bone (femur) to the shin bone (tibia). Performed in a clinical setting without specialized equipment, the ADT is a common initial step in diagnosing knee injuries. By applying a specific force, the examiner observes and quantifies any abnormal movement, or laxity, within the joint.
What the Test Assesses
The Anterior Drawer Test primarily checks for injury to the Anterior Cruciate Ligament (ACL) in the knee. The ACL is a band of connective tissue positioned deep within the knee joint, crossing diagonally from the femur to the tibia. Its main function is to prevent the tibia from sliding too far forward relative to the femur and to resist excessive rotational movement. When an injury, such as a sprain or tear, compromises the ACL, the knee loses this natural restraint, leading to instability. The test specifically evaluates the ligament’s ability to restrict this forward motion of the shin bone.
Performing the Anterior Drawer Test
The procedure begins with the patient lying flat on their back (supine position). The hip of the injured leg is flexed to about 45 degrees, and the knee is bent to a 90-degree angle. This positioning relaxes the hamstring muscles, which otherwise might resist the forward movement of the tibia and produce a false negative result. The examiner then sits lightly on the patient’s foot to keep it firmly planted on the examination table, stabilizing the lower leg.
The examiner places both hands around the upper tibia, just below the knee joint line. The thumbs are positioned on the prominent ridge of the tibia, and the fingers wrap around the calf muscle. This hand placement allows the examiner to grasp the bone segment that will be moved. A sudden, gentle pulling force is then applied, drawing the tibia straight forward (anteriorly) toward the examiner.
The action mimics the motion the ACL is designed to prevent, and the examiner looks for any excessive forward translation of the tibia from underneath the femur. The force must be applied parallel to the line of the tibia to isolate the movement being tested. The goal is to provoke movement in the joint that would not occur if the ACL were fully intact, assessing both the degree of movement and the quality of the sensation felt at the end of the motion.
Interpreting the Findings
Interpretation relies on two main factors: the amount of forward movement (translation) of the tibia and the resistance encountered at the end of that movement, known as the end-point. A “negative” result occurs if the tibia moves minimally (usually less than 5 millimeters) and the examiner feels a distinct, sudden stop, described as a firm end-point. This finding suggests the ACL is intact and stable.
A “positive” test is indicated by excessive anterior translation compared to the uninjured, contralateral knee. If the tibia slides forward too far, and the resistance felt at the end of the motion is soft or mushy, it suggests the ligament is no longer providing stabilization. This lack of a firm end-point is a strong clinical sign of a significant ACL tear.
The degree of laxity observed is graded to estimate injury severity.
Grading Laxity
- Grade 1: Indicates a mild sprain or translation of 0 to 5 millimeters beyond the normal side.
- Grade 2: Suggests moderate laxity, corresponding to a displacement between 5 and 10 millimeters.
- Grade 3: Means the tibia translates forward by more than 10 millimeters, often correlating with a complete rupture of the ligament.
Even with a positive ADT result, a definitive diagnosis of an ACL tear usually requires confirmation through advanced imaging techniques, such as a Magnetic Resonance Imaging (MRI) scan, to assess the extent of the damage to the soft tissues.