WebMD explains that pain that occurs when bending the knees is a common symptom of bursitis, a condition in which the sac of fluid that protects the knee joints becomes inflamed and irritated due to repeated bending, injury or overuse. Bursitis that is caused by kneeling is often referred to as "housemaid's knee" or "preacher's knee."
The National Health Service UK explains that torn ligaments and tendons can cause pain when bending or putting weight on the knee. If the tendons on the side of the knee are injured, pain can occur even when the knee is at rest. If the knee feels out of balance and tends to give way when bending or standing, it is important to consult with a physician to determine if the ligament is torn.
The American Academy of Orthopaedic Surgeons explains that patellofemoral pain, also referred to as runner's knee, is a common condition that affects athletes. Patellofemoral pain is caused by overuse of the muscles, improper stretching and muscle imbalance. Patellofemoral pain occurs when using stairs, kneeling, sitting with bent knees and squatting. Treatment of patellofemoral pain is typically non-surgical in nature and includes rest, ice, compression and elevation of the knee. This treatment plan is often referred to as "RICE." Additional treatments include taping up the kneecap, knee braces and orthopedic shoe inserts.