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Runner's Knee, The Patellofemoral Pain Syndrome (PFPS)

Cause, Treatment, Moving Ahead

by Stephen M. Pribut, D.P.M.

Introduction:

Runner's Knee has been the long used term for pain in the area around the patella or knee cap. It is a general term and is too broad to detail all of the possible causes of anterior knee pain in runners. Other general terms that refer to this condition are the patellofemoral pain syndrome and peripatellar pain syndrome. Pain in this region may be related to cartilage injury below the patella, quadriceps tendinopathy, or patellar tendon tendinopathy. The actual cause of the pain is still controversial. This condition is seen less often now than 20 years ago. While peripatellar pain has declined, iliotibial band syndrome (ITB Syndrome) has increased. Core muscle weakness may play a role as an ancillary risk factor. Clinically, gluteus medius weakness is nearly always seen with ITB syndrome and some degree of gluteus maximus weakness may be seen with patellofemoral pain syndrome.

Symptoms and Causes:

The symptoms of runner's knee include pain near the knee cap usually at the medial (inner) portion and below it. Pain is usually also felt after sitting for a long period of time with the knees bent. Running downhill and sometimes even walking down stairs can be followed by pain. This has been called the "movie theatre sign". The symptoms are aggravated when the knee is bent since (with increased vectors of force) increased pressure exists between the joint surface of the knee cap and the articular surface of the femur (thigh bone). This increase in force over-stresses the injured area and leads to pain.

simplified patellofemoral anatomyAnatomy

The knee is a complex joint. It includes the articulation between the tibia and femur (leg and thigh) and the patella (knee cap) and femur. The most common knee problems in running relate to what is called the "patellofemoral complex". This consists of the quadriceps, knee cap and patellar tendon. What is now called patellofemoral pain syndrome (PFPS) has also been called runner's knee, anterior knee pain, or chondromalacia of the patella. For many years runner's knee was considered to be a direct result of chondromalacia of the patella. This essentially means a softening of the cartilage of the knee cap. The anatomical sources of pain in this area is now considered to be from the richly innervated subchondral bone (bone below the articular cartilage), infrapatellar fat pad, or the medial and lateral retinaculum of the joint.

“...certain mechanical conditions may predispose you to a mistracking knee cap.”

Cartilage does not have the same blood supply that bone does. It relies on intermittent compression to squeeze out waste products and then allow nutrients to enter the cartilage from the synovial fluid of the joint. During running certain mechanical conditions may predispose you to a mistracking knee cap. Portions of the cartilage may then be under either too much or too little pressure and the appropriate intermittent compression that is needed for waste removal and nutrition supply may not be present. This may result in cartilage deterioration, which at the knee usually occurs on the medial aspect or inner part of the knee cap. All patello-femoral pain though may not be caused by this mechanism, although uneven stresses across the joint are believed to play an important role in the development of pain in this area.

Contributing Causes

The stability or lack of stability of the knee cap and adjacent structures come into play in adding to peripatellar mechanical stresses. The concept of impairment of the stabilizers has been refined to include:

Stabilizers of the patellofemoral complex (Senavongse and Amis, 2005):

  1. Active stabilizers: the quadriceps muscles
  2. Passive stabilizers: the retinaculum and ligamentous structures
  3. Static stabilizers: the joint surfaces

Medial stability is provided mainly by the vastus medialis oblique, the medial patellofemoral ligament and to some degree the medial patellar retinaculum. The patella (knee cap) has been found, in studies, to have the least medial stability at about 20 degrees of flexion. Often the concept of strengthening the vastus medialis is mentioned. But, the VMO can only be specifically exercised using biofeedback. Another mechanism must be coming into play, since quadriceps strengthening often works well. I've proposed the mechanism of neurofacilitative training of the quadriceps. The repeated, regular, rhythmic contractions with the body in a position with the hip and knee in a relationship similar to that of running or walking seems to improve the overall function and strength of the quadriceps allowing improved synergy of the 4 muscles. The pain in peri-patellar pain syndrome seems to be caused by an overload of the well innervated subchondral bone, the extensor retinaculum and the infrapatellar fat pad.

Factors that increase what is known as the "Q" (Quadriceps) angle increases the chance of having runners knee. The Q angle is an estimate of the effective angle at which the quadriceps averages its pull. It is determined by drawing a line from the Anterior Superior Iliac Spine (bump above and in front of your hip joint) to the center of your knee cap and a second line from the center of your knee cap to the insertion of the patellar tendon (where the tendon below your knee cap inserts). Normal is below 12 degrees, abnormal is usually considered to be above 15 degrees. Many times adding to the strong lateral pull of the bulk of the quadriceps is a weak vastus medialis (VMO). This is the portion of the quadriceps that helps medially stabilize the patella. It runs along the inside portion of the thigh bone to join at the knee cap with the other three muscles making up the quadriceps. Some of the mechanical conditions that may contribute to this are listed below. And of course watch out for the "terrible too's" of overtraining: too much, too soon, too fast, too often, with too little rest!

“ ...watch out for the "terrible too's" of overtraining: too much, too soon, too fast, too often, with too little rest!”

Risk Factors

 

Q Angle of Knee Q Angle

Treatment of Runners Knee

At an early stage running should be decreased to lessen stress to this area and allow healing to begin. It is important to avoid downhill running which stresses the patello-femoral complex.

Exercises performed with the knee bent should be avoided. When the knee is bent the forces under the knee cap are increased. Many people feel that the vastus medialis (VM) muscle works only during the final thirty degrees of extension of the knee but research does not fully support this. This muscle helps to dynamically stabilize the knee cap medially and prevents it from shifting laterally and tracking improperly at the patello-femoral joint. The Vastus Medialis Oblique (VMO) and Vastus Medialis Longus (VML) have been shown to be considerably weaker than the Vastus Lateralis (VL) in patients with Patellofemoral Pain Syndrome compared to normals (Makhsous et. al. 2004). Delayed firing of the VMO has also been hypothesized (Cowan et. al. 2001). Straight leg lifts strengthen the vastus medialis muscles and do not significantly stress the undersurface of the knee cap. They should be done in sets of 10 times on each side. Start with 5 sets of 10 and work your way up to 10 sets of 10. Straight leg lifts are best performed lying on a cushioned but firm surface, with the exercising leg held straight and the non-exercising leg somewhat bent to take pressure off of the back. Lying on a carpet or mat on the floor is a perfect place to perform this exercise. The repetitive nature of this exercise in addition to strengthening the quadriceps muscles, may also enhance the earlier "firing" of the VMO and train the quadriceps to work together with improved synergy. Repeated straight leg lifts act as a neurofacilitative exercise and may assist in training the quadriceps to act synergistically. In summary the benefits of straight leg lifts are that this exercise strengthens the quadriceps, improves the synergy and timing of the quadriceps and the vastus medialis and does not significantly stress the undersurface of the knee cap.

Tight posterior muscles should be stretched. In many cases tight calf muscles or hamstrings lead to a "functional equinous" and make the foot pronate while running or walking. This pronation is accompanied by an internal rotation of the leg which increases the Q angle and contributes to the lateral subluxation of the knee cap. On occasion a tight iliotibial band may contribute to PFPS.

“...Straight leg lifts strengthen the quadriceps, improves the synergy and timing of the quadriceps and of the vastus medialis and does not significantly stress the undersurface of the knee cap.”

If you over-pronate make sure you use shoes that offer more anti-pronation features. Move up a ranking in the amount of stability and pronation control that your shoes offer. If further control of pronation is needed orthotics should be considered. The late George Sheehan, M.D., sports medicine physician and philosopher, was the first to coin the term "runner's knee" and to popularize the notion that it was important to look at the foot when runner's knee occurs. It is also important to rule out other knee problems when knee pain occurs in runners and not just lump every pain as "runner's knee".

Core muscle strength and weak hip muscles may also play a role in this problem. Core work should be a part of every runners routine. This includes most definitely the gluteal muscles, particularly the gluteus maximus. Be sure to perform the above exercises first, since they are more specific to the problem being addressed. I often recommend gluteal strengthening to assist the quadriceps in its "braking" action during gait. Immediately after foot contact many of the muscle groups act as brakes to prevent the limb from collapsing. The Quadriceps contracts to slow up the rate of knee flexion. The calf muscles contract to slow the tibia's forward movement and the hip extensors (gluteal muscles and hamstrings) slow the forward progresson of the femur (leg bone). The hip extensors may make their greatest contribution during acceleration, speed work, faster running and hill running. If they are weak, the quadriceps will have more than it's share of work to do at this point in the running gait cycle.

Patellar Tendinopathy and Jumper's Knee

Supine bridges are useful. Repeat the bridge 10 - 15 times. After this becomes easy, one legged bridges may be performed also with 8 - 12 repetitions. The core and hip strengthening is especially important for individuals with patellar tendinopathy (pain in the patellar tendon). Bridges can be especially helpful to basketball players with pain in this area. Patellar tendinopathy has been called "jumpers" knee.

Orthotics:

Orthotics can be a great assist in the therapy of patellofemoral pain syndrome and patellofemoral dysfunction. A variety of studies over the years have shown their effectiveness in treating this in runners. A recent study (Saxena 2003) claimed 76% improved, 2% asymptomatic after previous failed treatment. Orthotics limit the maximum amount of excessive pronation. They also have been demonstrated to reduce the speed (acceleration) of internal tibial rotation. Reducing the speed of internal tibial rotation will reduce the amount of sudden stresses applied to the undersurface of the patella and the need for the VMO ( vastus medialis ) to work so hard in maintaining proper tracking and positioning of the patella. As per Newton's Laws slower motions will require less force to counterbalance them.

Treatment Summary:

See: Dr. Pribut's Tips Dr. Pribut's Runner's Knee Tips

 

Differential Diagnosis of Peri-patellar Knee Pain

REFERENCES

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About Dr. Pribut: Dr. Pribut is a member of the Advisory Board of Runner's World magazine. He is a past president of the American Academy of Podiatric Sports Medicine (AAPSM). He served as chair of the AAPSM Athletic Shoe Committee for 5 years and has served on the Education Committee, the Research Committee, the Public Relations Committee and the Annual Meeting Committee. He is a co-Editor of the current AAPSM Student's Manual. Dr. Pribut is a past president of the District of Columbia Podiatric Medical Association, serving in that post for 4 years. Dr. Pribut currently is a member of the American Podiatric Medical Association's Clinical Practice Advisory Committee. Dr. Pribut is a Clinical Assistant Professor of Surgery at the George Washington University Medical Center.

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