ACL Injuries

The human knee is held together by four ligaments.

Ligaments are strong bands of tissue that connect bones to bones. Without them, the parts of the knee would be unstable and move out of place.

The anterior cruciate ligament, or ACL, is located in the center of the knee. It holds together your thighbone and your shinbone. It prevents your shinbone from moving in front of your thighbone.

Twisting your ACL too far can damage it. It may rupture, or tear, when your shinbone moves too far forward or your knee bends backward.

An ACL injury happens most often during sports activities. For instance, a sudden pivot and twist while playing basketball can tear your ACL. You may also suffer an ACL injury if your knee is hit, such as during a car accident. An ACL tear often makes the knee feel unstable or wobbly. The ACL won’t heal without medical care.


A diagnosis often includes a physical exam and questions about your medical history. You may also need an X-ray and magnetic resonance imaging, or MRI.

Results from an MRI, tests that show the knee is unstable, and a history of frequent falls or the knee giving way will help determine if you have completely torn your ACL.

Arthroscopy is sometimes used, too. The scope contains a light and a camera. Pictures from the scope appear on a video screen. They can show damage inside the knee.

Complete and partial tears of the ACL may cause swelling and pain. To ease swelling, a syringe may be used to drain any fluid in the knee. If blood appears in the syringe, you likely have a torn ACL.


An ACL injury doesn’t always require surgery.  In fact, people who don’t play sports that involve cutting or pivoting usually don’t need surgery.

Non-surgical treatment for an ACL injury often includes physical therapy and a special brace to protect the knee. You may also need to avoid activities that may further hurt the knee.

If you need surgery, it’s best if you recover as much as possible before the procedure. That’s because rehabilitation after surgery typically involves six months of intense therapy.

A number of methods are available to repair a torn ACL. The surgeon will decide on the best method for you based on your individual situation.

Arthroscopy is commonly used to repair a torn ACL. In this procedure, the surgeon inserts tiny surgical tools into the knee, along with the scope, through small incisions. Pictures sent to a video screen let the surgeon see and work inside the knee.

In most cases, the ACL is rebuilt using another tendon from around the knee. The material used to rebuild it is called a graft. Often, a graft comes from the patellar tendon or the hamstring.

In a typical operation, a surgeon first removes the torn ends of the ACL. A tunnel is then drilled into both the shinbone and the thighbone. The graft is threaded across the knee. Screws, staples, sutures, or another small anchoring device secure the graft into place.


After the procedure, recovery includes easing pain, reducing swelling, and regaining knee motion and strength. Physical therapy helps many people return to full activity within a year after surgery.

What We Have Learned

  1. The ACL is located in the center of the knee and holds together your thighbone and your shinbone. True or False?
    The answer is True. It prevents your shinbone from moving in front of your thighbone.

  2. A torn ACL can heal without medical attention. True or False?
    The answer is False. Your knee will likely remain unstable without, physical therapy, a special brace, or surgery.

  3. Every torn ACL needs surgical treatment. True or False?
    The answer is False. People who don’t play sports or take part in activities that involve cutting or pivoting rarely need surgery.