Understanding Knee Pain and Common Knee Injuries
From the American Academy of Orthopaedic Surgeons, we are summarizing common knee injuries, including:
- Anterior Cruciate Ligament (ACL) Injuries
- Posterior Cruciate Ligament (PCL) Injuries
- Collateral Ligament Injuries
- Meniscal Tears
- Tendon Tears
- Fractures
- Dislocation
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Knee Joint Anatomy
The knee is the body’s largest joint and easily injured, comprising four main structures: bones, cartilage, ligaments, and tendons.
- Bones: The femur, tibia, and patella form the knee joint, with the patella providing protection.
- Articular Cartilage: Covers the ends of the femur, tibia, and patella, allowing smooth movement.
- Meniscus: Two tough, rubbery cartilage pieces act as shock absorbers and stabilize the joint.
- Ligaments: Connect bones and stabilize the knee, including collateral ligaments (side-to-side motion) and cruciate ligaments (front-to-back motion).
- Tendons: Connect muscles to bones, with the quadriceps tendon linking thigh muscles to the patella and the patellar tendon connecting the patella to the tibia.
Understanding Common Knee Injuries and Their Symptoms
The most common knee injuries include sprains and tears of soft tissues (e.g., ligaments, meniscus), fractures, and dislocation. In many cases, injuries involve more than one structure in the knee.
Pain and swelling are the most common signs of knee injury. In addition, the knee may catch or lock. Some knee injuries (e.g., ACL tear) cause instability — the feeling that your knee is giving way.
Anterior Cruciate Ligament (ACL) Injuries
The anterior cruciate ligament is often injured during sports activities. ACL injuries are more likely to occur in athletes who participate in cutting and pivoting sports like soccer, football, and basketball. Changing direction rapidly or landing from a jump incorrectly can tear the ACL.
About half of all injuries to the anterior cruciate ligament occur along with damage to other structures in the knee, such as articular cartilage, meniscus, or other ligaments.
Comparison of Normal and Torn ACL in the Knee
Tears or ruptures of the ACL, a major ligament in the knee, are often due to sports injuries that involve sudden stops, jumps, or changes in direction such as soccer, basketball, football, skiing, tennis, or gymnastics.
Posterior Cruciate Ligament (PCL) Injuries
The posterior cruciate ligament is often injured from a blow to the front of the knee, while the knee is bent. This often occurs in motor vehicle crashes and sports-related contact. Posterior cruciate ligament tears tend to be partial tears with the potential to heal on their own.
Collateral Ligament Injuries
Injuries to the collateral ligaments are usually caused by a force that pushes the knee sideways. These are often contact injuries.
- Injuries to the MCL are usually caused by a direct blow to the outside of the knee and are often sports-related.
- Blows to the inside of the knee that push the knee outwards may injure the lateral collateral ligament (LCL). Lateral collateral ligament tears occur less frequently than other knee injuries.
Meniscal Tears
- Acute meniscal tears often happen during sports. Tears in the meniscus can occur when twisting, cutting, pivoting, or being tackled.
- Meniscal tears may also occur as a result of arthritis or aging. Even an awkward twist when getting up from a chair may be enough to cause a tear if the menisci have weakened with age.
Illustration of Knee Meniscus Tear Anatomy
Injury to the cartilage between the femur and tibia, which can occur from twisting or turning quickly, often with the foot planted while he knee is bent.
Tendon Tears
The quadriceps and patellar tendons can be stretched and torn. Although anyone can injure these tendons, tears are more common among middle-aged people who play running or jumping sports. Falls, direct force to the front of the knee, and landing awkwardly from a jump are common causes of knee tendon injuries.
Fractures
The most common bone broken around the knee is the patella. The ends of the femur and tibia where they meet to form the knee joint can also be fractured. Many fractures around the knee are caused by high energy trauma, such as falls from significant heights and motor vehicle collisions.
Dislocation
A dislocation occurs when the bones of the knee are out of place, either completely or partially. For example, the femur and tibia can be forced out of alignment, and the patella can also slip out of place.
- Dislocations can be caused by an abnormality in the structure of a person’s knee.
- In people who have normal knee structure, dislocations are most often caused by high energy trauma, such as falls, motor vehicle crashes, and sports-related contact.