The hinge-like movement of your knee is supported by a network of bones, muscles, ligaments, and tendons.
But these tissues can cause knee pain if they are overused, become inflamed, or are subject to a blow or other injury. Each element of the knee is susceptible to some common sports injuries.
Many of the symptoms for knee injuries are similar, which is why the diagnosis of a doctor or sports specialist is important to say definitely what's causing your knee pain.
But if you know the main causes of knee pain—and the occasional distinctive symptoms—you're closer to the diagnosis and treatment you need.
Bone or kneecap injuries
Bone dislocation can occur if the femur (thigh bone) or tibia (shin bone) get out of alignment, or if the patella (kneecap) slips out of place. The patella can also be fractured. These are almost always as a result of severe trauma, such as a fall or car accident.
Both patellar fractures and dislocations cause knee pain, but the pattern is slightly different: For a dislocation, the pain will be sharp but fade with rest. Patellar fractures, on the other hand, tend to cause sharp pain immediately after injury, then remain consistently aching throughout healing.
The anterior cruciate ligament (ACL) crisscrosses with one other ligament in the knee. It keeps the knee aligned and prevents it from slipping forward or backward. However, it's prone to rips or tears, particularly when the knee twists sideways. An ACL tear is a common sports injury, and women are more prone to it.
ACL injuries almost always occur after a sudden blow or pivot. They can also occur when the knee is hyperextended. People hear a "pop," then experience pain and a feeling of the knee "giving out" from under them.
The ACL is the most common ligament injured, but three other knee ligaments can also cause problems when injured, usually as a result of a blow to the front or side of the knee.
Two tendons in the knee can also cause knee pain if injured. The patellar tendon attaches your kneecap to your tibia. It can become inflamed and cause pain when it's jarred from below repeatedly; this is why it's also known as "jumper's knee."
Pain can also originate from the tendon between the kneecap and femur. This is patellofemoral pain syndrome (PPS) or "runner's knee."
As these nicknames imply, tendons are often injured through overuse. Pain may be minor and felt only when exercising, but more severe cases can affect daily activities. Tendon injuries may also cause swelling, redness, or warmth.
The C-shaped pad of cartilage between the femur and tibia is known as the meniscus. The meniscus can be torn either through a single traumatic injury or a series of smaller traumas over time. A torn meniscus causes knee pain, swelling, stiffness, and sometimes locking or instability of the knee.
Knee pain from arthritis
Knee pain can also be the result of damage to the knee joint from arthritis. Knee osteoarthritis risk factors include age, being overweight, family history, or a history of knee trauma, such as one of the injuries listed above.
If you're experiencing knee pain or stiffness that comes and goes, or pain that gets worse after inactivity (such as when you get up in the morning), this may be the result of arthritis.
To learn more about the ways arthritis can affect the knees, visit Arthritis-health's article: What Is Knee Osteoarthritis?
Both knee injuries and knee arthritis have treatment options that can decrease pain and help you maintain mobility and strength, so see your doctor if you're having trouble with knee pain.