During the physical exam, your doctor will check your knee for swelling and tenderness — comparing your injured knee to your uninjured knee. He or she may also move your knee into a variety of positions to assess range of motion and overall function of the joint.
Often the diagnosis can be made on the basis of the physical exam alone, but you may need tests to rule out other causes and to determine the severity of the injury. These tests may include:
- X-rays. X-rays may be needed to rule out a bone fracture. However, X-rays don't show soft tissues, such as ligaments and tendons.
- Magnetic resonance imaging (MRI). An MRI uses radio waves and a strong magnetic field to create images of both hard and soft tissues in your body. An MRI can show the extent of an ACL injury and signs of damage to other tissues in the knee, including the cartilage.
- Ultrasound. Using sound waves to visualize internal structures, ultrasound may be used to check for injuries in the ligaments, tendons and muscles of the knee.
Prompt first-aid care can reduce pain and swelling immediately after an injury to your knee. Follow the R.I.C.E. model of self-care at home:
- Rest. General rest is necessary for healing and limits weight bearing on your knee.
- Ice. When you're awake, try to ice your knee at least every two hours for 20 minutes at a time.
- Compression. Wrap an elastic bandage or compression wrap around your knee.
- Elevation. Lie down with your knee propped up on pillows.
Medical treatment for an ACL injury begins with several weeks of rehabilitative therapy. A physical therapist will teach you exercises that you will perform either with continued supervision or at home. You may also wear a brace to stabilize your knee and use crutches for a while to avoid putting weight on your knee.
The goal of rehabilitation is to reduce pain and swelling, restore your knee's full range of motion, and strengthen muscles. This course of physical therapy may successfully treat an ACL injury for individuals who are relatively inactive, engage in moderate exercise and recreational activities, or play sports that put less stress on the knees.
Your doctor may recommend surgery if:
- You're an athlete and want to continue in your sport, especially if the sport involves jumping, cutting or pivoting
- More than one ligament or the fibrous cartilage in your knee also is injured
- The injury is causing your knee to buckle during everyday activities
During ACL reconstruction, the surgeon removes the damaged ligament and replaces it with a segment of tendon — tissue similar to a ligament that connects muscle to bone. This replacement tissue is called a graft.
Your surgeon will use a piece of tendon from another part of your knee or a tendon from a deceased donor.
After surgery you'll resume another course of rehabilitative therapy. Successful ACL reconstruction paired with rigorous rehabilitation can usually restore stability and function to your knee.
There's no set time frame for athletes to return to play. Recent research indicates that up to one-third of athletes sustain another tear in the same or opposite knee within two years. A longer recovery period may reduce the risk of re-injury.
In general, it takes as long as a year or more before athletes can safely return to play. Doctors and physical therapists will perform tests to gauge your knee's stability, strength, function and readiness to return to sports activities at various intervals during your rehabilitation. It's important to ensure that strength, stability and movement patterns are optimized before you return to an activity with a risk of ACL injury.
Explore Mayo Clinic studies testing new treatments, interventions and tests as a means to prevent, detect, treat or manage this condition.
Preparing for your appointment
The pain and disability associated with an ACL injury prompt many people to seek immediate medical attention. Others may make an appointment with their family doctors. Depending on the severity of your injury, you may be referred to a doctor specializing in sports medicine or a specialist in bone and joint surgery (orthopedic surgeon).
What you can do
Before an appointment, be prepared to answer the following questions:
- When did the injury occur?
- What were you doing at the time?
- Did you hear a loud pop or feel a "popping" sensation?
- Was there much swelling afterward?
- Have you injured your knee before?
- Have your symptoms been continuous or occasional?
- Do any specific movements seem to improve or worsen your symptoms?
- Does your knee ever "lock" or feel blocked when you're trying to move it?
- Do you ever feel that your knee is unstable or unable to support your weight?