An anterior cruciate ligament (ACL) tear is a knee injury that can cause symptoms like pain, swelling, and a popping sound. The tear can be partial or complete, and symptoms are generally more severe with more extensive injuries. Trouble standing is just one sign that you need immediate medical attention.
With partial tears, it's also possible to experience little to no ACL tear symptoms at first. This sounds like a good thing, but it can result in you continuing your activity, further compromising your ligament and potentially worsening the tear.
This article explains the signs and symptoms of an ACL tear. It will also discuss when you need emergency attention and what medical tests your healthcare provider may use to diagnose this condition.
What Is the ACL?
The ACL is the band of tissues that connects the bottom of the thighbone to the top of the shinbone. It helps stabilize the knee.
Signs and Symptoms of an ACL Tear
The signs and symptoms of an ACL injury can vary.
Hearing a "Pop"
Individuals who have an ACL tear may hear a loud "pop" at the time of the injury. Even if you don't hear the pop, you may feel a sudden shift in the joint.
Knee Swelling and Pain
Swelling of the knee joint occurs in almost all individuals with an ACL tear. Swelling may show up within hours after the injury.
This may be due to the injury to the ligament itself or a condition known as hemarthrosis, which is bleeding in a joint. Symptoms of hemarthrosisinclude swelling, pain, warmth, and difficulty with movement.
Pain associated with an ACL tear is common. Keep in mind, the level of pain may vary depending on the severity of the injury.
Because the ACL is critical to the stability of the knee joint, the joint may give out if the ligament tears.
This may happen during cutting or pivoting movements common in many sports. However, in some individuals with this injury, instability can occur while walking or getting into a car.
When to Seek Emergency Care
See a healthcare provider right away if you have:
Knee pain or swelling that lasts more than 48 hours
Trouble standing or walking on the affected knee
An odd appearance on one side of the knee compared to the pain-free side
Diagnosing an ACL Tear
Your healthcare provider will check for a torn ACL by examining your knee and ordering imaging tests, which help them see the severity of your injury.
To check for an ACL tear, your healthcare provider may use specific tests including:
Lachman test:Your healthcare provider will hold the knee slightly bent and stabilize the thigh in one hand. They will then pull the shin forward with their other hand to feel for an ACL tear.
Pivot shift maneuver:This is done while you are lying down with your body fully relaxed. Your healthcare provider will stand on the outside of the injured knee and lift your leg while it is stretched out. They will then manipulate your shinbone and flex your knee to see if you have a torn ACL.
Drawer test:The drawer test is performed with the knee held at a 90-degree bend. The shin is shifted forward and back to check for an ACL injury and other ligament damage.
In addition to performing these specific tests, your healthcare provider will check your knee for swelling and overall strength. The other major knee ligaments may also be assessed.
Your healthcare provider may order imaging tests to check the severity of the injury. Imaging tests may include:
X-rays, which show broken bones and joint changes in the knee
Magnetic resonance imaging (MRI), which shows knee tissue damage
An ACL tear is a knee injury that may cause symptoms like pain, swelling, and a popping sound. Your knee may also give out or generally feel unstable. This is most often caused by athletic activity.
To check for a torn ACL your healthcare provider may perform certain tests and/or order imaging tests like an X-ray or MRI.