Patellar tendon rupture
The patellar tendon joins your shinbone’s top end to the top of your kneecap. It may tear or become inflamed, which is known as patellar tendinitis.
If it tears, you could hear tearing or popping noises. It’s possible that you won’t be able to straighten your leg, and your kneecap may feel as though it’s advancing toward your thigh. The bottom of your kneecap may also become indented, and you may experience discomfort, cramps, bruising, and other symptoms.
Arthritis in the knees
Osteoarthritis [5], another name for knee arthritis, occurs when the cartilage that divides the bones in your knee joint wears away. Your knee can pop when you move it because you can feel the bones scraping or grinding against one another.