Possible causes of knee pain when squatting or kneeling include bursitis, illiotibial band syndrome, Osgood-Schlatter Disease, osteoarthritis and patellar tendonitis, according to WebMD. These issues can result from an injury or overuse, which is typically seen with athletes.
Bursitis of the knee (prepatellar bursitis) can arise from overuse (repeated bending or kneeling) or a fall that has irritated the bursa, which is a sac of fluid over the kneecap joint, notes WebMD. It can result in discomfort as well as swelling in the knee, and since it is often caused by repeated kneeling, it can also be referred to as "preacher's knee."
If the knee pain is more concentrated to the outside of the knee, it is possible that the cause is illiotibial band syndrome. The illiotibial band is located on the outside of the leg, from the hip to the knee, and can become inflamed or painful with overuse.
Osgood-Schlatter Disease is evidenced by a painful or sensitive bump just below the knee. The tendon that runs from the knee to the shin becomes painful, and this particular issue is very popular with young male and female athletes around 13 to 14 years of age.
Osteoarthritis is very common in patients over the age of 50, whether or not they are athletic. Osteoarthritis can cause knee pain and make it difficult to move freely.
Tendons around the knee can become inflamed and sore, resulting in "runner's knee" or patellar tendonitis.