What is a bipartite patella?

Your patella is a triangular-shaped bone in the front of your knee that’s also known as your kneecap. About 1 to 2 percent of people have a bipartite patella, which means their patella is made up of two bones instead of one. You may have a bipartite patella in one or both of your knees.

A bipartite patella usually doesn’t cause any symptoms. Most people don’t even know they have one until they get an X-ray or MRI scan due to another condition. You’re more likely to notice symptoms if you injure your kneecap or play sports that require lots of knee-related movement. This can cause the synchondrosis, the tissue that connects the two bones, to become inflamed, irritated, or torn.

Symptoms of an injured synchondrosis include:

  • tenderness around your kneecap
  • pain, especially when you extend you knee
  • swelling
  • a bony ridge near the outer edge of your kneecap
  • the feeling that your knee is unsteady

When you’re born, your kneecap is made up of mostly cartilage and blood vessels. As you grow, the cartilage expands. By the time you’re 3 to 5 years old, the cartilage starts to turn into bone. This process continues until you’re about 10. At this point, a single kneecap is formed.

Doctors aren’t sure why, but sometimes the bones don’t completely fuse, creating a bipartite patella. This extra bone is usually near the upper outer edge or lower bottom edge of your knee.

Most people with a bipartite patella are never diagnosed because it doesn’t cause any symptoms. However, if you have an MRI scan or X-ray done in the area for an unrelated condition, it will likely show up. At first, it may look like a broken kneecap, but on closer look, a bipartite patella doesn’t have the jagged edges and sharp angles of a broken bone.

A bipartite patella usually doesn’t need treatment. If it’s causing you pain, your doctor may suggest:

If you don’t notice any improvement after about six months, you might need surgery. There are several options for treating a bipartite patella, including:

  • removing the smaller of the two bones
  • replacing the connective tissue that binds the bones together with a screw
  • adjusting the tissue that keeps your kneecap centered

In a 2015 study on the surgical treatment of a bipartite patella, 84.1 percent of participants had reduced pain, and 98.3 percent were able to return to their presurgery activity levels once they healed. Recovery time depends medical history, age, and type of surgery. However, most people recover within a few months.

Having a bipartite patella is rare, and most people with them don’t even know they have one. If it does cause you pain, there are several effective treatment options available. While you may need to rest for a few months after treatment, you should be able to return to your normal level of activity after you recover.