The knee is one of the joints most prone to injury. Its structure and many components put it at risk of many types of injuries, which can result in knee pain or loss of function.

Sometimes a knee injury happens suddenly as a result of the knee being hit, fallen on, twisted or moved beyond its intended range of motion.  Sudden knee injuries are common among athletes and may result in tears to one of three major ligaments of the knee –  the anterior cruciate ligament (ACL), medial collateral ligament (MCL) or posterior cruciate ligament (PCL) – or the menisci, crescent-shaped wedges of cartilage within the knee designed to distribute your body weight across the joint.

At other times, knee injuries happen slowly. For example, a problem such as a leg-length discrepancy or arthritis in the hip that causes you to walk awkwardly can throw off the alignment of the knee, leading to damage. Constant stress to the knee – from sports or jobs that require bending and lifting, for example – can cause joint cartilage to wear down over time.

The following are some of the more common knee injuries:

Meniscal Injuries. Menisci can be torn when the knee is bent and then twisted, such as turning to hit a tennis ball. If the outside of the knee is hit, during contact sports, for example, the ligaments can be torn as well. Meniscal injuries that are not repaired increase the risk of developing osteoarthritis years later.

Read about research into meniscal and ligament tears and the later development of osteoarthritis.  

Anterior Cruciate Ligament and Posterior Cruciate Ligament Injuries.  A sudden twisting motion or change in direction can lead to injury of the anterior cruciate ligament, whereas the posterior cruciate ligament is more likely to be damaged from direct impact, such as being tackled in football. Medial cruciate ligament injuries are often the result of a direct blow to the outside of the knee. The anterior cruciate ligament is the ligament most commonly injured.

Tendon Injuries. Ranging from inflammation (tendinitis) to ruptures, tendon injuries can result if you overwork or over-stretch your tendon. Activities that can injure tendons include running, jumping, dancing and squatting, especially to lift heavy items.

Bursitis. Some injuries to the knee can lead to inflammation of the bursae, small fluid-filled sacs that normally cushion the knee and reduce friction between the joint and surrounding ligaments and tendons. Injury to bursa can lead to swelling, warmth, pain and stiffness.

Loose bodies. Sometimes an injury to the knee can cause a piece or pieces of bone or joint cartilage to break off into the joint space. These loose bodies may interfere with joint movement and cause pain.