At first glance, your knee may resemble a simple hinge, like the one that allows a door to swing open and closed. But your knee is far more complex than that. The joint can make twisting and turning motions, and it allows your leg to hold up the weight of your body.

Your knee also contains more moving, interacting parts than you may have realized. And because of all these factors, a lot can go wrong with different areas of the joint to cause knee pain. Let's take a closer look at the anatomy of the knee.

Anatomy of Knee Pain: An Overview of a Knee

Two large bones and a small bone meet in your knee. Within the joint, the bottom end of your thigh bone (the femur) encounters the top end of your shin bone (the tibia). The smaller bone is your kneecap (the patella). The kneecap rests against a groove at the end of the femur, in which it can move around.

Each of these bones has a protective coating of tissue called cartilage. The bones are constantly moving around each other in a small area, but the smooth cartilage provides cushioning and allows them to glide around easily. Disks of tissue called menisci found between the femur and tibia also help absorb the pounding the knee takes when you walk and run.

Problems that can affect these tissues include:

  • Osteoarthritis. This causes the protective cartilage to grow thin and rough, leaving the bones in the joint with less protection. The bones can become damaged, and walking can cause knee pain.
  • Meniscal tears. You can tear a meniscus if you turn your knee the wrong way while you're putting weight on it, as while suddenly twisting in an athletic sport. It can cause mild or major knee pain and may cause your knee to get "stuck" while you're moving it.

Several soft tissues are also attached around the knee. These include a tendon that attaches your quadriceps muscles to your kneecap and four ligaments. These ligaments attach the femur and tibia to each other. The medial and lateral collateral ligaments are found at the sides of your knee, and the anterior and posterior cruciate ligaments criss-cross each other inside the knee.

Problems that can affect these structures include:

  • Tendon issues. A tendon can become painfully inflamed if you repeat a leg motion too many times. A tendon can also be torn. Either of these injuries, not surprisingly, can result in knee pain. A full tendon tear can also make it difficult to move your leg.
  • Iliotibial band syndrome. Another source of knee pain can be the iliotibial band. This is a thick band of tissue that runs down the side of the thigh to where it attaches near the knee. As it slides back and forth over the outside of the knee during an activity like running, it can become irritated. You will typically feel pain just on the outside of the knee during or after the physical activity.
  • Ligament issues. Direct trauma to the knee, such as from contact sports, can tear a ligament. So can shifting directions quickly during a sport. Depending on which ligament is injured, you may have pain as well as a sense of instability in your knee.

No matter what type of knee pain you have or which specific parts of the knee are affected, be sure to see your doctor to get the right diagnosis and treatment to prevent further damage.