Causes
Patellar maltracking – A common cause of discomfort in the knee is when the kneecap tracks laterally (sideways) to where it is supposed to go. This causes increased friction on the back of the patella and the gradual wearing of the cartilage on the back of the knee cap. This condition is more common in women and in people with an increased angle from the kneecap to the foot.(Q angle)

Tendonitis – This condition arises from repetitive tasks which cause stress on the tendons surrounding the knee. The most commonly affected is the patellar tendon which is used to straighten the knee and is called on in such activities as squatting, jumping, and running.

Poor exercise and weight-lifting technique. Poor body mechanics and form while exercising and lifting weights can predispose you to some conditions of the knee and other joints. You should correct form before lifting heavier weights and progress in a gradual fashion instead of big jumps in resistance.

Improper hamstring training. The hamstrings should be trained not only as knee flexors but also as hip extensors. Failing to train in this manner can lead to hamstring injuries, especially in sprinting and sports that require sprinting.

Treatment
Ice – Ice is always the first line of defense in knee conditions. This will help eliminate inflammation and swelling associated with most knee conditions. Ice should be applied for not more than 20-30 minutes at a time to avoid other complications.

Stretching – Many times stretching the hamstrings and quadriceps will make a difference with tendonitis episodes when combined with ice; however, this condition often requires more involved care. Stretching these muscle groups, however, is good for general wellness and flexibility.
Seek medical care if knee pain lingers more than two weeks, or if there is a significant increase in swelling and a worsening of signs and symptoms.

Be wary…
Knee pain usually has a mechanical cause, so passive therapies will have limited effectiveness. It is always important to look at the joints above and below the involved joint to determine their possible involvement in the condition.