The knee is a complicated joint. It moves like a door hinge, allowing a person to bend and straighten their legs so they can sit, squat, jump, and run.
The knee is made up of four components:
The femur, commonly known as the thighbone, is at the top of the knee joint. The shinbone, or tibia, makes up the bottom of the knee joint. The patella or kneecap covers the meeting point between the femur and tibia.
The cartilage is the tissue that cushions the bones of the knee joint, helping ligaments slide easily over the bones and protecting the bones from impact.
There are four ligaments in the knee that act similarly to ropes, holding the bones together and stabilizing them. Tendons connect the muscles that support the knee joint to bones in the upper and lower leg.
There are many different types of knee injuries. Below are 10 of the most common injuries of the knee.
Any of the bones in or around the knee can be fractured. The most commonly broken bone in the joint is the patella or kneecap.
2. Anterior cruciate ligament injuries
The anterior cruciate ligament (ACL) runs diagonally down the front of the knee, providing critical stability to the joint. Injuries to the ACL can be serious and require surgery.
ACL injuries are graded on a scale from one to three. A grade 1 sprain is a mild injury to the ACL, while a grade 3 refers to a complete tear.
Athletes who participate in contact sports such as football or soccer often injure their ACLs. However, contact sports are not the only cause of this injury.
Improperly landing from a jump or quickly changing the direction of motion can lead to a tear in the ACL.
Dislocating the knee happens when the bones of the knee are out of their proper placement and alignment.
In a knee dislocation, one or more of the bones may slip out of place. Structural abnormalities or traumas, including car accidents, falls, and contact sports, can cause a knee dislocation.
4. Meniscal tears
When people refer to torn cartilage in the knee, they are probably talking about a meniscal tear.
The menisci are two rubbery wedges of cartilage between the thighbone and shinbone. These pieces of cartilage can tear suddenly during sporting activities. They may also tear slowly due to aging.
When the meniscus tears due to the natural aging process, it is referred to as a degenerative meniscus tear.
With a sudden meniscus tear, a pop may be heard or felt in the knee. After the initial injury, pain, swelling, and tightness may increase over the next few days.
Bursae are small fluid-filled sacs that cushion the knee joints and allow the tendons and ligaments to slide easily over the joint.
These sacs can swell and become inflamed with overuse or repeated pressure from kneeling. This is known as bursitis.
Most cases of bursitis are not serious and can be treated by self-care. However, some instances may require antibiotic treatment or aspiration, which is a procedure that uses a needle to withdraw excess fluid.
Tendonitis can affect physically active people.
The patellar tendon works with the front of the thigh to extend the knee so a person can run, jump, and perform other physical activities.
Often referred to as jumper’s knee, tendonitis is common among athletes who frequently jump. However, any physically active person can be at risk of developing tendonitis.
7. Tendon tears
Tendons are soft tissues that connect the muscles to the bones. In the knee, a common tendon to be injured is the patellar.
It is not uncommon for an athlete or middle-aged person involved in physical activities to tear or overstretch the tendons. Direct impact from a fall or hit may also cause a tear in the tendon.
8. Collateral ligament injuries
Collateral ligaments connect the thighbone to the shinbone. Injury to these ligaments is a common problem for athletes, particularly those involved in contact sports.
Collateral ligament tears often occur due to a direct impact or collision with another person or object.
9. Iliotibial band syndrome
Iliotibial band syndrome is common among long-distance runners. It is caused when the iliotibial band, which is located on the outside of the knee, rubs against the outside of the knee joint.
Typically, the pain starts off as a minor irritation. It can gradually build to the point where a runner must stop running for a period to let the iliotibial band heal.
10. Posterior cruciate ligament injuries
The posterior cruciate ligament is located at the back of the knee. It is one of the many ligaments that connect the thighbone to the shinbone. This ligament keeps the shinbone from moving too far backward.
An injury to the posterior cruciate requires powerful force while the knee is in a bent position. This level of force typically happens when someone falls hard onto a bent knee or is in an accident that impacts the knee while it is bent.
When to see a doctor
If knee pain becomes chronic, is severe, or lasts for more than a week, a person should consult a doctor. It is important to see a doctor if there is a reduced range of motion in the joint or if bending the knee becomes difficult.
In cases of blunt force or trauma, a doctor should be seen immediately after an injury has occurred.
Treatment will vary based on the cause of the knee pain and the specifics of the injury. In cases of strain or overuse injuries, rest and ice will typically allow the knee to heal over time.
Treatment may also involve managing pain and inflammation with medication. In most cases, a person will need to rest for a period of time.
Tears or other trauma-induced injuries may require bracing, popping the knee back into place, or surgery. In the case of surgery, a person will likely not be able to use the knee after the procedure and may need either crutches or a wheelchair while recovering.
In some cases, physical therapy may be needed to help a person regain movement and strength in their knee and leg.
Preventing knee injuries is not always possible, but a person can take precautions to reduce the risk. For instance, people who run or play sports should wear the appropriate shoes and protective gear.
In cases of iliotibial band syndrome and overuse injuries, a person may want to consider reducing the number of miles they run.
Certain exercises also help strengthen the smaller leg muscles, which may help prevent injury. Finally, stretching before and after exercise can help prevent injury to the knees.