The Kneecap (Patella) and Knee Joint

Front view of knee joint.

The kneecap (patella) is a small triangular bone. It is just one of the many parts that make up the knee joint. Some of the other parts are muscles, ligaments, and leg bones. The kneecap provides leverage for your muscles as they bend and straighten the leg. It also protects the knee joint.

  • Quadriceps muscles. These are at the front of the thigh. They help the kneecap slide against the thighbone. They also help to straighten the leg.

  • Kneecap. This allows the quadriceps muscles to work better as they tighten. The kneecap also protects the bones and tissues under it.

  • Retinacula. These are fibrous bands on the sides of the knee. They help hold the kneecap in place. 

  • Patellar tendon. This is a fibrous cord that connects the kneecap to the shinbone.

The kneecap up close

Take a closer look at this small bone to see how it works.

Front view of patella.

From the front, you can see the kneecap’s slightly rounded, shield-like shape.

Back view of patella.

From the back, you can see cartilage. This is tough, cushiony tissue that covers the bone. It helps the kneecap slide easily against the thighbone.

From the top, you can see that the kneecap sits in a groove or “track” in the thighbone.

Front view of bent knee showing normal cartilage.


A closer view of the kneecap shows the difference between the smooth cartilage and the rougher bone beneath.