Anterior cruciate ligament injury

Medical quality assurance by Dr. Albrecht Nonnenmacher, MD at April 21, 2016
StartDiseasesAnterior cruciate ligament injury

A ligament that connects the upper and lower leg bone, which stabilizes the knee, is called the anterior cruciate ligament (ACL). An anterior cruciate ligament injury or ACL injury can be in the form of a minor tear to the ligament or a complete separation from ligament and bone. While the ACL can be injured in many different ways, it is most often damaged playing a sport that requires a constant stop-and-go movement or change of direction such as football or soccer.


Definition & Facts

The ACL is one of four ligaments that work together to prevent the knee from overextending. In many cases, the anterior cruciate ligament will suffer a fractional or complete tear when the ligament has been critically overstretched.

When the ACL is damaged, movement to the knee is less controlled. Left untreated and without the ligaments in their proper place, the bones are more likely to rub against each other. Known as chronic ACL deficiency, this can lead to further impairment, such as tears in the cartilage or broken bones.

Symptoms & Complaints

Depending on the severity of the ACL injury, symptoms may vary. While the person may be able to walk, it is imperative that they stop what they are doing and seek medical attention. Some complaints patients have expressed that would indicate an ACL injury include:

  • Swelling or pain that limits the movement to the knee or is felt when trying to put weight on the knee.
  • A “popping” sound when the injury occurred.
  • Directly after the injury the knee may become unstable or give out.
  • Pain that is centralized to the back of the knee or outside of the knee.
  • Increased swelling in the first six hours after the injury. This could indicate blood inside the joint.


There are many ways to tear the anterior cruciate ligament. Hyperextending the knee, bending it from side to side or twisting the knee are the most typical ways to tear the ACL. This can happen during normal day-to-day activities, such as stepping down from a curb. Accidentally falling from a ladder or stepping into a ditch or hole are also common causes of ACL injury.

Most often playing a sport that puts an increased amount of pressure on the ACL, like basketball, skiing or gymnastics will see the highest number of injuries. Football players are at an increased risk when being tackled or having another player fall on the knee.

After the age of 40 the leg muscles begin to weaken. An already inactive adult runs a higher risk of an ACL tear just performing everyday activities. Women tend to damage their ACL much more than men.

Diagnosis & Tests

An orthopedic surgeon or a doctor who specializes in sports medicine will be able to diagnose an ACL injury. There are several steps a doctor will take to insure a proper diagnosis. They include:

  • Taking a detailed medical history that is comprised of general health questions, an explanation of how the knee was injured, any symptoms that were noted at the time of injury and if the knee had any prior damage before the incident.
  • A doctor will then examine the knee with a Lachman test which indicates the degree of flexibility in the knee. The doctor will also note how stable the knee is, what range of movement is present and if the knee is tender and swollen.
  • An X-ray is often performed if the level of pain the patient experiences is very high or if there is extreme swelling. While this test may not be able to show a definitive ACL tear, it can show broken bones or bone fragments, if there is bleeding in the knee or if there is a complete tear of the ACL.
  • A doctor may also recommend an imaging scan, such as an MRIs, which can tell if tearing to the ligaments has occurred. A CT scan can determine any minute bone breaks.

Treatment & Therapy

Initial at-home first aid treatment will be needed to decrease the swelling and reduce pain. Bed rest while elevating the knee and applying ice compresses will be recommended. Over-the-counter pain relievers such as acetaminophen or ibuprofen can help with pain.

For a few days after the injury a doctor may require the use of crutches or a splint when moving around. The extent of the tear, the overall health of the patient and whether the ACL injury is due to a chronic condition will determine the next course of treatment.

A physical therapy program may be all that is needed to heal and strengthen the knee. The overall treatment plan is designed to help the knee become stabilized. Therefore, every patient will have an individual time-frame as to when the knee is healthy enough for normal activity.

In more severe cases, ACL surgery may be performed to repair the tear, followed by an extensive rehab program. The arthroscopic surgery consists of inserting small surgical tools into tiny incisions to repair the tear. Many patients who have had ACL surgery report very good results in that they have the ability to return to normal activity with good function and little pain.

Prevention & Prophylaxis

There are some things that can be done to decrease the chances of an ACL injury.

  • Limit or avoid contact sports that require a quick stop-and-go movement or severe twisting.
  • Wear low-heeled shoes. High heels can cause instability, increasing the chances for injury.
  • Contact sports that require cleats should also be avoided.

If the patient has experienced a past ACL injury, these things should be done to not further damage the ligament.

  • Stop participating in sports that hyperextend or twist the knee.
  • Wear a knee brace during activities when the knee might be compromised will offer support.
  • Continue with a physical therapy program designed to teach proper stretching and jumping techniques to add strength and stability to the knee and ligaments.