Anterior Cruciate Ligament (ACL) Injury and Treatment

Medically Reviewed by Jabeen Begum, MD on January 16, 2024
7 min read

One of the most common ways people hurt their knees is by injuring their ACL (anterior cruciate ligament). This is one of the bands of tissue that holds the bones together within your knee. It also helps to keep your knee stable. You can stretch or tear your ACL if you make a sudden movement or quick, sharp turn when you're running or jumping. It's often painful, and can make it hard to walk or put pressure on the injured leg.

Your doctor will usually classify your ACL injury as grade 1, 2, or 3. Here's what the different grades mean:

  • Grade 1. Mild damage to the ACL. Your ligament may be slightly stretched, but it still keeps your knee joint stable.
  • Grade 2. A rare injury where your ACL is stretched and partially torn.
  • Grade 3. The ACL is torn in half and doesn't keep your knee joint stable.

Your doctor will base your treatment on the grade of your ACL injury and other factors.

You might hear your doctor use "tear" or "rupture" when describing your ACL injury. These terms mean the same thing. An ACL tear happens when you partly or completely rupture the anterior cruciate ligament.

Athletes often get ACL injuries when they stop and quickly change directions while they're running. People who play soccer, football, tennis, basketball, or volleyball, or who do gymnastics, are more likely to twist their knees by mistake when they compete than, say, cross-country runners, who simply move forward at a steady pace. Your speed--combined with the way that you twist or turn your knee--makes it likely that you'll stretch or tear your ACL.

ACL injuries are more common among women than men.

Many people hear a popping noise in their knee when they get hurt. But it doesn't happen to everyone. More common symptoms include:

Pain. If you have a minor injury, you may not feel pain. You may feel sore along your knee's joint line. Some people have trouble standing or putting pressure on the hurt leg.

Swelling. This is most likely to happen during the first 24 hours. You can reduce swelling by putting ice on your knee and elevating (raising) your leg by propping it up on a pillow.

Trouble walking. If you're able to put pressure on your hurt leg, you may notice that it's harder than normal to walk. Some people find that the knee joint feels looser than it should.

Less range of motion. After you damage your ACL, it's very likely that you won't be able to bend and flex your knee like you normally would.

If you have an ACL injury you're more likely to get osteoarthritis in your knee. The condition can happen even after surgery to reconstruct the ligament. Several things can affect your chances of getting arthritis, such as:

  • How bad the initial injury was
  • If you have other injuries to the knee joint
  • How active you are after treatment

Your doctor will want to hear exactly how you injured your knee. They'll look at both knees to see if the sore one looks different. They may also order any of the following:

Tests. Your doctor may ask you to lie on your back and bend your hips and/or your knees at certain angles. They'll then place their hands on different parts of your leg and gently shift you around. If any of your bones move in a way that isn't normal, that could be a sign that your ACL is damaged.

X-ray. Soft tissues like the ACL don't appear on X-rays, but your doctor may want to rule out broken bones.

MRI or ultrasound. These exams can show both soft tissue and bone. If you have a damaged ACL, it should appear on the images.

Arthroscopy. This literally means to "look within the joint." During the exam, an orthopedic surgeon makes a small cut in your skin. They insert a pencil-size tool that contains a lighting system and lens (arthroscope) into the joint. The camera projects an image of the joint onto a TV screen. Your doctor can see what type of injury you have and repair or correct it, if needed.

It depends on how badly you've been hurt. Here are some of the options your doctor may give you:

First aid. If your injury is minor, you may only need to put ice on your knee, elevate your leg, and stay off your feet for a while. You can reduce swelling by wrapping an ace bandage around your knee. Crutches can help to keep weight off your knee.

Medications.Anti-inflammatory drugs can help to reduce swelling and pain. Your doctor may suggest over-the-counter medications or prescribe something stronger. For intense pain, your doctor may inject your knee with steroid medication.

Knee brace. Some people with a damaged ACL can get by with wearing a brace on their knee when they run or play sports. It provides extra support.

Physical therapy. You may need this a few days a week to get your knee back in working order. During your sessions, you'll do exercises to strengthen the muscles around your knee and help you regain a full range of motion. You may be sent home with exercises to do on your own.

Surgery. Your doctor may tell you that you need this if your ACL is torn badly, if your knee gives way when you're walking, or if you're an athlete. With physical therapy, people who have surgery can often play sports again within 12 months.

A surgeon will remove the damaged ACL and replace it with tissue to help a new ligament grow in its place. The tissue comes from another part of your knee or from a donor. You'll continue a physical therapy program after surgery, which can often bring back stability and function to your knee.


Returning to your previous activity level could take a year or more. Throughout rehab, your doctor and physical therapist will test how stable and strong your knee is and how well it functions. Research shows that up to one-third of athletes with an ACL injury will have another tear within 2 years. You may be able to lower your chances of reinjury with a longer recovery time.

You can help avoid an ACL injury with the right training and exercise, including:

  • Core-strengthening exercises 
  • Leg-strengthening exercises, especially those that reinforce the hamstrings
  • Learning the right technique when jumping and landing from jumps
  • Learning the right technique when performing pivoting and cutting movements


The proper footwear and padding for your sport can also help you to avoid an ACL injury. Keep in mind that wearing a knee brace is unlikely to prevent an ACL injury.

Talk to a sports medicine physician, physical therapist, athletic trainer, or other sports medicine expert about ways you can stop an injury from happening.

As part of your recovery from ACL surgery, you'll need to do exercises to strengthen your hip and keep the range of motion in your knee and ankle. Talk to your doctor before starting an exercise program. Here are several stretching exercises you may be able to do at home:

Sitting towel calf stretch

Sit up straight and put a towel on the bottom of your foot, grasping the ends of the towel. Pull the towel, along with your foot, towards you. Hold for 30 seconds and repeat for 2 sets.

Supine hamstring stretch

Sit up straight and put a towel on the bottom of your foot, holding the ends of the towel with both hands. Lie down on your back and lift your leg until you feel a stretch in the back of your leg. Hold the position for 30 seconds, then repeat for 2 sets.

Quad sets

Lie down on your back and place a small, rolled-up towel behind your knee. Tighten your quadriceps (the muscles at the front of your thigh) and hold for 3 to 5 seconds. Repeat for 2 sets of 10.

Ankle pumps

Lie on your back or sit in a chair. Flex your toes and up, then point them down. Repeat for 2 sets of 10.

Heel slides

Sit down with a towel under your foot, grasping the ends of the towel. Pull the ends of the towel, bending your knee as far as you can. Keep your knee bent for 3 to 5 seconds. Bend and straighten your knee for 2 sets of 10.

ACL injuries tend to happen when athletes, particularly in sports like soccer, football, tennis, basketball, or volleyball, abruptly change directions during running. More prevalent among women, symptoms include a popping noise, pain, swelling, trouble walking, and reduced range of motion. 

Diagnosis involves a physical exam, X-rays, MRI or ultrasound scans, and arthroscopy, with treatment ranging from first aid and medications to knee braces, physical therapy, and, in severe cases, surgery for ACL reconstruction.

Can you still walk with a torn ACL?

You may be able to walk with a torn ACL, but if you're in pain don't try to move or use your knee. This can worsen a tear. See a doctor for pain or other symptoms in your knee.

What happens if an ACL injury is not treated?

Left untreated, a torn ACL will continue to give way, raising your chances of further knee injuries. Plus, cartilage damage can lead to osteoarthritis.

Can I live normally with an ACL tear?

Treatment is the only way to heal a torn ACL, but you can live with it, especially if it's a minor tear. Athletes and those who want to go back to their previous activity level will need surgery to reconstruct their ACL.