Anterior cruciate ligament tear occurs most often during sports. Approximately 80% of ACL tears occur without contact with another athlete. The most typical story is that of an athlete who suddenly changes direction (cutting or twisting) and feels his knee come out from under his body .
You hear the beep “pop”
People with a torn ACL generally report hearing a “popping” sound during an injury. Most people are surprised at how loud it can be, and many passersby have heard it on the fields of a soccer game. Even if you don’t hear applause, people often feel a sudden change in the joint .
The ACL is critical to the stability of the knee, and when an ACL tear occurs, the joint is often unstable . This means that the knee joint tends to fail. Giving up or instability often occurs with jerky movements or turns, which are common in many sports . However, in some patients with an ACL tear, instability can occur even with simple movements while walking or getting into a car .
Swelling and pain in the knees.
Knee swelling occurs in almost all patients with an ACL tear. This swelling is usually quite large and occurs quickly, within a few minutes of the injury.
When the ACL tears, the vessels supplying the ligaments can fill the joint space with blood, a condition known as hemarthrosis . Symptoms of hemarthrosis include swelling, redness, warmth, bruising, and a blistering sensation in the joint.
Pain associated with ACL tear is common, although it can vary depending on the associated injury in and around the knee joint . Most of the pain with a torn ACL is due to inflammation of the joints .
Abnormal physical examination
Your healthcare provider can evaluate your knee ligaments using special tests. The most commonly used tests to determine the presence of an ACL tear include:
- Lachman test: The Lachman test is performed to assess abnormal forward movement of the tibia. By pulling the tibia forward, the surgeon can palpate the torn anterior cruciate ligament (ACL). The knee is slightly bent (about 20-30 degrees), the thigh is stabilized in one hand and the tibia in the other.
- Pivot change maneuver: The pivot change is difficult to perform in the office and is often most useful in the operating room when the patient is under anesthesia. The hinge shift maneuver detects abnormal knee motion in the presence of an ACL tear.
- Drawer test: The drawer test is performed with the knee bent 90 degrees. The tibia is moved back and forth to assess the intact ACL (forward pull) and the intact PCL (push back).
In addition to performing these specific tests, your surgeon will also check your knee for swelling, mobility, and strength. Other important knee ligaments can also be evaluated.
Your healthcare provider will also evaluate knee X-rays to assess possible fractures, and an MRI may be ordered to assess damage to the ligaments or cartilage . However, an MRI may not be required to diagnose an ACL tear. In fact, a physical exam and medical history are as good as an MRI at diagnosing an ACL tear . MRI can be especially helpful in diagnosing concomitant injuries, such as torn meniscus and cartilage damage.
When to contact a healthcare provider
The signs and symptoms of an ACL injury are not always the same, so it is important to see your doctor if you experience any of the following:
- Knee pain or swelling that lasts more than 48 hours.
- Problems standing or walking on the affected knee.
- Inability to bear weight on the affected knee
- A misshapen or odd appearance on one side of the knee compared to the painless side.