Many Conditions Can Cause Knee Pain. The knees take a pounding. With every step, pressure is exerted on these vital joints. Athletes and the elderly are particularly vulnerable to knee injuries and degenerative joint disease. In the 2006 National Health Interview Survey, 18 percent of respondents said they experienced knee pain. For some, the discomfort is a minor irritation that flares up once in a while. Others endure extreme pain, and struggle to carry out everyday activities. Knee conditions sometimes lead to disability. The knee pain may emanate from various parts of the joint, and from surrounding ligaments, tendons and bursa. The three bones that join to form the knee joint are the thigh bone (femur), shin bone (tibia) and kneecap (patella). Four ligaments hold the bones together and maintain stability in the knee. The medial and lateral collateral ligaments permit sideways movements. Two cruciate ligaments (on the inside of the knee), the anterior cruciate ligament (in front) and the posterior cruciate ligament (in back) are enable the joint to move forward and backward.