Doctors at NYU Langone diagnose and manage all types of knee sprains, strains, and tears.
The knee is the largest joint in the body. It consists of ligaments, bones, cartilage, and tendons. Four ligaments, which are tough cords of tissue, connect the thigh bone, or femur, to the lower leg bones, called the tibia and fibula. These ligaments keep the knee stable when a person walks, jumps, bends, or pivots.
In between the femur and tibia is a thick layer of smooth cartilage called the meniscus. This tissue, which is molded to the shape of your bones, helps the knee absorb and distribute body weight during movement. Tendons anchor muscle to bone.
Many knee injuries occur during athletic activities—particularly contact sports, such as soccer and football. But everyday mishaps, such as twisting your knee as you step off a curb, may also cause an injury.
If you have a knee sprain, the fibers in one of the ligaments have stretched or torn. This can be caused by a sudden impact, such as a collision during sports, or from putting too much weight or pressure on a muscle, tendon, or ligament, such as during weightlifting. A sudden twist or another movement that stretches a muscle, tendon, or ligament too far can also cause a knee sprain.
A strain is a tear that occurs in muscle fibers or in the tendons. A strain may occur after a dramatic increase in activity. For example, many visitors to New York City develop muscle strains in their knees from walking more than they might at home.
A knee tear is an injury to one of the ligaments or layers of cartilage that supports and stabilizes the knee. A knee tear may be partial, in which some of the structure is damaged, or complete, in which a ligament or meniscus is torn in two or separates from the bone.
Knee tears are common injuries among athletes, especially those who participate in contact sports that involve sudden changes in direction or tackling. Skiing may also increase the risk of a knee tear because a fall can cause the knee to twist sideways, damaging internal structures. A knee tear can also occur as a result of a fall, a misstep, or a car accident.
Doctors categorize the severity of a knee tear on a scale of one to three. Grade one indicates a mild injury, grade two indicates a partial tear, and grade three indicates a complete tear.
Some mild knee tears may not limit your ability to walk or cause serious discomfort. Others may cause significant pain and prevent you from putting weight on the knee.
There are three different types of knee tears.
The cruciate ligaments are two strong, short ligaments located in the center of the knee joint. These ligaments, which cross each other to form an “x” shape, connect the femur to the tibia.
The anterior cruciate ligament, or ACL, is located slightly in front of the posterior cruciate ligament, or PCL. Together, these ligaments help stabilize the knee.
An injury to the ACL is the most common type of knee tear and frequently occurs as the result of athletic activity. Sports that require sudden changes in direction, such as the pivoting movements common in soccer and basketball, can lead to too much force being placed on the ACL, causing it to tear.
The PCL is stronger and less likely to tear than the other ligaments in the knee. The most common injury to this area is the “dashboard” injury, in which the front of the knee and shin hit the dashboard during a car accident.
The collateral ligaments are long, ropy cords of soft tissue located on each side of the knee. The medial collateral ligament is located on the inner side of the knee—the side closest to your other leg—and the lateral collateral ligament is located on the outer side. These ligaments hold the thigh and lower leg bones together and form an internal “brace” that keeps the tibia, which is one of the lower leg bones, in position and prevents it from moving sideways.
If the ligament tear is severe, you may feel a sudden weakness on one side of the knee. It may be accompanied by a popping sound.
Injuries to these ligaments typically occur during contact sports, such as soccer and football. They can also happen during a sideways fall while skiing, which can force the knee to bend at an awkward angle.
Injuries in which only the lateral collateral ligament tears occur less frequently than other types of knee tears.
Within the knee joint is a firm, smooth layer of cartilage composed of two menisci: the lateral meniscus and the medial meniscus. Each meniscus is shaped like a horseshoe and rests between the femur and the tibia. The open ends of the menisci face each other to form an almost complete ring that circles the anterior cruciate and posterior cruciate ligaments.
Meniscal tears are most common in people who play contact sports. However, the cartilage that comprises the menisci may degenerate over time. If the meniscus wears thin, even a minor injury or fall may cause a tear.
Damage to the meniscus increases the risk of damage to another type of cartilage in the knee joint, called articular cartilage. It lines the ends of the bones and prevents them from rubbing together during movement. If articular cartilage erodes and bones become damaged, a condition called osteoarthritis of the knee may be developing.
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