Knee pain when bending your leg is a common symptom with ... This buildup may form a Baker cyst, a fluid-filled sac that can cause stiffness, discomfort, or pain behind the knee.

If you experience knee pain after sitting with your legs bent, it may be caused by arthritis, tendonitis, bursitis, or patellofemoral pain. If your knees hurt when sitting, it may be from sitting ...