Patella Fracture (Broken Knee Cap)

Because your kneecap (patella) acts like a shield for your knee joint, it can easily be broken. Falling directly onto your knee, for example, is a common cause of patellar fractures.

These fractures are serious injuries and often require surgery to heal. Over the long term, they may cause arthritis in the knee.

Cause
Patellar fractures are most commonly caused by a direct blow, such as from a fall or motor vehicle collision. The patella can also be fractured indirectly. For example, your thigh muscles can contract so violently that it pulls the patella apart.

Osteonecrosis of the knee is also associated with certain conditions and treatments, such as obesity, sickle cell anemia, lupus, kidney transplants, and steroid therapy. Steroid-induced osteonecrosis frequently affects multiple joints and is usually seen in young patients.

Regardless of the cause, if the disease is not identified and treated early, it can develop into severe osteoarthritis.

Symptoms
The major symptoms of a patellar fracture include pain and swelling in the front of the knee.

Additional symptoms include:

Bruising

Inability to straighten the knee

Inability to walk