Most people assume if they have knee pain the problem is due to a problem with the knee joint. This is not always the case! While the discomfort can be due to a knee condition, often it is the result of a disc protrusion in the back.
The nerves that send the sensation of pain to the legs and feet are located in the lower back region. Occasionally with age or injury, the discs between the vertebrae can buldge out and press on these nerves. When this occurs the nerve becomes irritated and sends out pain signals. The location of the pain depends on which disc is protruded. How bad the pain is depends on how much of the disc is pressing on the nerve.
The nerves that send fibers to the knee are located at the second, third, and fourth lumbar vertebral levels. If a disc is compressing on the nerves at these locations, the pain very may be felt in the knee region. This condition can be diagnosed by your physician with a thorough history and physical exam.
I agree with the above article. A lot of people assume right away that having knee pain is caused by local irritation on the knee area (esp arthitis). Our leg innervation came from the spine. Any problem from the spine like nerve impingement may cause referred pain to the distal part of the nerve ending, on the above topic, to the knee. Poor body posture and poor quality shoes sole are another reasons. It is very important to discuss to the doctor the past medical history and to have a thorough physical examination before assuming a cause of knee pain.
-Risty PT , Theramax Houston