Common and some not-so-common injuries of this vulnerable joint.
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.
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.
Osgood-Schlatter disease. Usually affecting preteen and young teenage boys, this condition is caused by repetitive stress on the upper area of the tibia, where the bone is growing. In children with this condition, the patellar tendon (which connects the knee cap and tibia) becomes inflamed and may even tear away from the tibia.
Dislocated kneecap. This occurs when an injury causes the patella, or kneecap, to move out of position. The movement of the kneecap is always visible and, often, intensely painful.
Iliotibial band syndrome. This syndrome occurs when a band of tissue rubs against the outer portion of your femur (thigh bone), causing sharp, burning pain on the outer side of the knee. Although this can result from a direct injury to the knee, often the cause is the stress of long-term use, such as long-distance running.
Plica syndrome. This condition occurs when bands of synovial tissue, called plica, are irritated by overuse or injury. Symptoms may include knee pain, swelling, locking and weakness.