What causes knee pain?
There is no single cause for painful knee joints. Of course, the most obvious factor is a traumatic injury, such as falling hard on the knee joint, or being struck on or near the knee. Traumatic injuries usually happen suddenly and with great force. Chronic injuries develop over a longer period of time, and are often the result of repeated stress to the knee. This stress can cause the knee joints to move out of normal alignment; in some cases, your kneecaps may either be closer to each other ("knock kneed") or farther apart than they should be. Other possible reasons for chronic injuries may include obesity, ligament weakness, not having enough protection from heel-strike shock, foot/ankle problems, improper exercise or lifting techniques, etc. Organic conditions would include infections and tumors.
Your doctor will give you a thorough examination - which may include range of motion (ROM) and orthopedic testing, looking for possible alignment/tracking problems, and testing for signs of muscle or ligament weakness - to help determine the cause of your knee pain.
What are some of the causes of knee alignment problems?
The knee is actually two joints involving three bones: the larger weight-bearing ginglymus ("hinge") joint between the femur and tibia bones, and a smaller joint between the femur and patella ("kneecap"). As a hinge joint, the healthy knee bends in one plane of motion much more than it rotates, although some rotation is involved during the gait (walking) cycle. In a normal posture, the kneecaps point straight ahead over the feet. This is the knee posture which gives the most support to the hips and spine.
Problems occur when a knee becomes misaligned, and one cause for this can originate in the foot/ankle. If one or both feet has a structural problem ("flat feet", high arch, weak ankles, for example), this condition can cause the leg to rotate improperly, which in turn produces stress on the knee. As knee muscles and ligaments weaken, the joint may begin to move out of its proper position. These imbalances have a potential "ripple effect" which can affect the hips, low back, and neck. That's why you'll often encounter someone whose back started hurting after he/she began having knee problems.