The knee is a very stable type of joint called a “hinge joint”, because it moves only in one direction, flexing to approximately 140 degrees.
One of the most common causes of knee pain is a misalignment, or twist of the upper leg relative to the lower leg causing tendons, ligaments, cartilage and bone to move and rub against structures that they are not supposed to, eventually wearing them down and leading to tendonitis and/or arthritis. This cause of knee pain is most often due to improper foot alignment (most commonly ‘pronation’, or a fallen arch in one foot more than the other). This misalignment or twist transfers most of the weight-bearing to the medial side (or side closest to the other leg) of the joint, and is responsible for the majority of knee replacement surgeries.
Improper knee alignment and pain may also be due to injury or muscle imbalance or an improper firing pattern of the muscles.