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Knee injuries

Meniscus tears

The meniscus is a firm, rubbery piece of cartilage in the knee. It lies between your thigh bone and your shin bone. The meniscus acts as a shock absorber to protect the articular cartilage. Articular cartilage is the tough but smooth tissue that covers the ends of the bones in your knee. This allows the joint to glide smoothly.

Your meniscus also helps keep the knee joint stable.

A tear in the meniscus may happen suddenly during activity. Other times, a small tear may be present without any symptoms at first. Pain and other symptoms can get worse as the tear in the meniscus gets larger.

Some symptoms of a meniscus tear are:

  • Knee pain when walking, twisting, bending, and straightening the knee
  • Locking or "catching" of the knee joint
  • Difficulty squatting down
  • A "pop" or crunching sound when the injury occurs
  • Swelling or warmth in the knee joint

Most of the time, a meniscus tear that is causing symptoms will need to be addressed with surgery. This is done using knee arthroscopy.

Ligament injuries

Ligaments are thick bands of tissue that help hold the knee joint together and keep it stable. Their job is to make sure the bones in your knee joint move only in certain directions.

There are two important pairs of ligaments in the knee:

  • The collateral ligaments (medial and lateral collateral ligaments) run along the inside and outside of the knee joint. Of these, the medial collateral ligament (MCL) is the one that is injured most often. It runs along the inside of knee.
  • The cruciate ligaments (anterior and posterior cruciate ligaments) are in the middle of the knee. They prevent the lower leg shin bone from sliding away from the upper leg thigh bone. The anterior cruciate ligament (ACL) is the ligament that is injured most often in sports such as soccer or basketball.

These ligaments may be sprained, partially torn, or completely torn and separated. Ligament injuries may be caused by:

  • A blow to the front or side of the knee, which can occur during a football tackle or other sports.
  • Coming to a quick stop to change direction (pivot) while running.
  • Landing from a jump.

Most of the time, you will notice symptoms right away after an injury to these ligaments. Most of the time, you won't be able to continue with sports after the injury.

You may have:

  • A "popping" sound at the time of injury.
  • Knee swelling and warmth that happen quickly within 6 hours of an ACL injury.
  • Pain, especially when you try to put weight on the injured leg.
  • Locking or catching of the knee when you move it.
  • A sensation of your knee giving out, so you don't feel secure putting weight on the leg.

People who have only a mild injury may not notice symptoms at first. Over time, the knee may feel unstable or seem to give way when using it.

Unstable kneecap

Your kneecap (patella) sits in the front of your knee joint. As you bend or straighten your knee, the underside of the patella glides in a groove in the thigh bone that makes up the knee. When the groove in the bone is not deep enough or when the ligaments holding the kneecap are torn, the kneecap can slide out of place.

If you have an "unstable" kneecap, the kneecap may move too much from side to side. Symptoms you may notice are:

  • Your knee cap slides when you turn or pivot
  • Knee pain behind the kneecap when you are sitting that gets worse when you are active
  • Your knee locks, or catches, when you move it
  • You feel grating or grinding when you move your knee
  • You have knee pain when you go up and down stairs

Your kneecap may also become completely pushed to the outside of the knee. This is called a dislocated patella. Symptoms of this are:

  • You cannot straighten your knee joint
  • Your kneecap is pushed to the outside of your knee
  • Your knee is swollen

If your kneecap dislocates, your doctor will help put the kneecap back in place. Then your knee will be placed into a knee immobilizer to prevent you from moving it for several weeks (usually about 3 weeks).

After that, physical therapy can help you build back your muscle strength and improve your knee's range of motion and stability.

If your knee remains unstable, you may need surgery to stabilize your kneecap. This may be done using arthroscopic or open surgery.

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Review Date: 8/9/2018

Reviewed By: C. Benjamin Ma, MD, Professor, Chief, Sports Medicine and Shoulder Service, UCSF Department of Orthopaedic Surgery, San Francisco, CA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.

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