Do your knees hurt when you walk up and down stairs? Do you hate going to the movies because when you sit for too long your knee becomes so stiff that you think that it will break when you get up? Are you afraid to squat because you heard that it aggravates knee problems? If you can identify with these situations, then you may be one of the many people who have a patellofemoral (PF) dysfunction that leads to pain. Learn about the most common knee disorder, theories on the cause, and some solutions in this article.

A Little Anatomy
The knee joint consists of the femur (thigh bone), the tibia (shin bone), and the patella (kneecap). Patellofemoral means the union between the patella and the femur. The primary muscles surrounding the knee joint are the quadriceps muscles (vastus lateralis, vastus intermedius, vastus medialis, and rectus femoris) on the front of the thigh, the adductor muscles on the inside of the thigh, the hamstring muscles on the back of the thigh, and the tensor fascia latae and iliotibial band on the outside of the thigh. The patella is located inside the tendon of the rectus femoris muscle, which connects the femur to the tibia. The femur has a concavity or groove where the patella rides up during extension (knee straightening) and down during flexion (knee bending). The underside of the patella has many ridges that are covered with protective cartilage. The patella’s function is to give the quadriceps muscles increased efficiency and protect the front of the femur.

What Causes Patellofemoral Dysfunction?
Many theories have been proposed to describe why and how people experience PF pain. The most commonly accepted theory on how PF pain is caused is that abnormal patellar tracking (laterally) in the femoral groove increases the stress between the patella and the femur and wears out the cartilage on the underside of the patella [1]. When the cartilage is healthy and the ridges fit into the femur well, the knee is pain-free. However, if the patella and femur do not mesh well together, the cartilage can wear down and it could predispose a person to PF pain. Although the cartilage itself has no pain receptors, the bone underneath does [2]. But the “why” question of PF dysfunction is really an individualized issue and based on a patient to patient case. In some cases, a congenital malalignment of the lower body may be the culprit. Tight and/or weak musculature, lax ligaments, overuse, or trauma may be to blame. Whatever the “hows” and “whys” may be, the signs and symptoms are generally consistent. They run the gamut from swelling, loss of range of motion, a sense of instability where the knee might “give-away,” to pain with prolonged sitting, squatting, and walking up and down stairs.

A Little Biomechanics
Before considering what treatments may be effective for PF dysfunction, it helps to understand how the joint works and what kinds of forces it may be susceptible to during daily activities and exercises. The patellofemoral joint reaction (PFJR) force is the result of the amount of knee flexion and the force of the quadriceps muscles creating pressure on the patella against the femur [3]. As the knee flexes, the patella is mostly in contact with the femoral groove [4]. This large amount of contact area can help dissipate compressive forces. However, as the knee extends, the patella has minimal contact with the groove. This small contact area cannot disperse compressive forces as well. When applying this concept to exercise, large compressive forces can be seen when performing a seated knee extension as the quadriceps have to generate great force to overcome gravity and lift weight. The compressive forces are great as the knee extends and the patella cannot dissipate the forces. As the knee flexes while squatting, the PFJR force increases, but the load is more evenly distributed across the patella that comes into contact with the femur.

Treatment
Previously treatments were based on the hypothesis that the vastus medialis muscle could be individually activated and this could “pull” the patella medially (toward the inside of the thigh) and more into the femoral groove [5]. Many studies have now shown that this is impossible [6]. When trying to selectively strengthen the VMO, the entire quadriceps muscle group is activated, which is the desired outcome. When the entire quadriceps group is strengthened, it may help change the contact areas between the patella and femur and redistribute the pressures [7]. This in turn can relieve painful areas of worn cartilage.
The first course of action with any inflammatory condition is to treat the symptoms with rest and ice. Anti-inflammatory medicines may also be prescribed by a medical doctor. Once the painful symptoms are reduced, treating the cause of the problem can be tackled. Strengthening and flexibility of the entire lower extremity from the hip to the foot is important. Exercises that are safe and effective include: backward walking/running, backward stair climbing, lateral step ups/downs, and bicycling with the seat high and resistance low. In addition, leg presses and squats should be kept in the range of 0o to 30o and knee extensions only from 90o to 60o to decrease the PFJR forces [8]. However, the rule of thumb should be that all exercises be performed pain-free. If more range-of-motion can be obtained in the leg press or squat pain-free, the best quadriceps strengthening can be found from 88o to 102o [9]. Bracing and taping can be effective in decreasing pain so the joint can be strengthened. They may improve patellar tracking by positioning the patella better in the femoral groove. Orthotics for the feet may be indicated to correct malalignments. Surgery in the form of an arthroscopic debridement or drilling of the patella and femur, a lateral retinaculum release, realignment of the extensor mechanism, patellectomy (removal of the patella), or total knee replacement are all last resort options [10].