Whether from a sports collision or an accidental fall, an ACL injury is very common today. Initial ACL diagnosis will include the individual feeling a sudden pain and a giving way of the knee. Many patients report hearing a pop, followed by swelling, tenderness, and looseness (laxity) in the joint.
A clinical ACL diagnosis will include an assessment of range of motion, limb alignment, muscle strength, neurovascular status, and a thorough comparison with the uninjured knee. During the initial consultation, your physician will evaluate the type of ACL injury, will obtain a full report on how the injury occurred, determine if the injury is new or pre-existing, determine if the injury is combined with other injury, and discuss the details of the treatment options. He will perform a physical examination that will involve several injury specific tests. These tests will help him to accurately diagnose the ligamentous and patellofemoral instabilities that exist within the knee. These tests may include:
The Pivot-shift test checks for anterior instability. With the patient supine the knee will be extended; the ACL-deficient knee will demonstrate anterior tibial subluxation. As the patient’s knee is flexed to 30° to 40°, while valgus force is applied, the anterolateral tibial subluxation will abruptly reduce.
Anterior Drawer Test
The Anterior Drawer Test is used to check for anterior instability. With the patient supine and the knee flexed to 90°, an anterior force is applied to the proximal tibia. Tibial anterior translation and quality of the endpoint are evaluated.
The Lachman Test is also used to check for anterior instability. With the patient supine and the knee flexed to 30°, an anterior force is applied to the proximal tibia. Tibial anterior translation and quality of the endpoint are evaluated.
Magnetic Resonance Imaging (MRI)
During each of these tests, the knee will feel unstable and loose, and the patient may experience muscle guarding in anticipation of movement. While your physician can often diagnose the ACL injury through a series of these tests during the clinical evaluation, he will always order a set of x-rays to make sure that there are no broken bones in the knee or other damage. If your physician suspects that there is damage to the ligaments, menisci, joint surfaces (cartilage), or bone, he will also want to obtain an MRI. Unfortunately, almost half of all ACL knee injuries involve the menisci, and an MRI is the best way to obtain a visual of how much damage has occurred. Based on all of these evaluations, your physician will be able to provide an accurate ACL diagnosis.