What is Patello-Femoral Pain?
Patello-femoral pain describes a wide range of conditions beginning with the common mild pain arising from under the knee cap (patella) and extending up to frank arthritis of the patello-femoral joint. Previously the term chondromalacia was used to describe all of these conditions, however, it is now felt that this term should be reserved for those few people with patello-femoral pain who have a demonstrable change to the lining of the patella (articular cartilage).
The word chondromalacia literally means cartilage (chondro) softening (malacia) and whilst this condition can occur in any joint it is most often used to describe the process that occurs under the patella (kneecap). The term chondromalacia patellae refers specifically to a pathological condition resulting in structural changes in the cartilage surface of the patella. The cartilage referred to is the shiny white lining cartilage that forms the bearing surface of all joints and is distinctly different from the meniscal cartilages which are the shock absorbing wedges that are found in the knee and commonly torn.
The changes found in the cartilage lining range from a softening of the normally firm white glistening surface through a stage of fraying, weakening/cracking of the cartilage surface and up to the worse scenario of full thickness cartilage loss with exposure of the underlying bone. This process may be localised to one area or may involve the whole of the patella. Sometimes these changes may affect the underlying groove in the femur (thigh bone) in which the patella tracks.
The whole process can be likened to the development of a pothole in the road. Initially the changes are deep below the surface and cannot be seen. Later on with increased stress the deep layers start to separate from the surface and a blister may develop. After this it is only a matter of time before the blister starts to crack and fissures are seen. Eventually craters may develop exposing the underlying bedrock (or bone in the kneecap). Therefore, as can be appreciated in the majority of instances these changes have been going on for some time before they become apparent. Only rarely is the injury so great as to cause major visible damage immediately.
What are the symptoms?
Just as there is large range in the changes that may be seen in the cartilage lining so the symptoms experienced by patients with this condition may vary tremendously. Unfortunately however, the degree of symptoms experienced may correlate poorly with the underlying pathology and hence some patients who have minimal (if any) changes may in fact be very symptomatic and vice versa. However, once the changes become pronounced the term osteo-arthritis becomes applicable indicating irreversible wear and tear .
The signs and symptoms of patello-femoral pain are variable and different from one individual to another. Generally, there is a dull aching pain across the front of the knee, but it may not be as specific as this and may be felt on the sides of the knee or even at the back of the knee.
The pain may occur during, or more commonly after an aggravating activity. There may be a mild puffiness or feeling of fullness about the knee. There is often a notable popping or grating with knee motion. Prolonged periods of sitting, e.g. long journey or watching a film at the cinema, often results in an aching stiffness. Squatting, climbing stairs, and in particular going down stairs and slopes provoke knee pain. The pain experienced in this condition is felt to result from increased pressure on the bone under the area of stressed lining cartilage.
The pain caused by this may inhibit quadriceps muscle function and this may cause the knee to give way or collapse. In addition the joint may become swollen due to a build up of fluids.
What is the anatomy of the area where this pain occurs?
The patella, a small round bone, lies embedded within the tendon of the quadriceps muscle (see diagram above) whose main function is to extend (straighten) the knee and this occurs when the muscle contracts. The patella aids the quadriceps muscle in extending the knee joint by improving its mechanical advantage. It does this by lifting the tendon out of the groove in the femur. During motion of the knee (flexion and extension), the patella glides (downwards and upwards respectively) in this groove present at the end of the femur.
The patella and femoral groove are each covered by the smooth cartilaginous surfaces discussed above and these allow the patella to glide during knee motion. The cartilage surface of the patella is the thickest such surface in any joint of the body and is about 4-6mms in depth. This cartilage helps to absorb and disperse the large forces placed on the knee during the various activities as well as to provide a low friction gliding surface for the joint. Walking on level ground exerts a force equivalent to half of the body weight on the patello-femoral joint. Climbing on stairs may increase that force up to nearly 3 times body weight and arising from a full squat may generate forces as large as 8-10 times body weight.
What causes this condition?
Patello-femoral pain may develop following an acute injury to the knee such as a direct blow to the patella or a fracture or dislocation of the patella. However, more often it has an insidious onset not specifically related to any one injury. In these cases there may be an underlying anatomical variation of the patella or femoral groove shape, or there may be excessively tight supporting tissues around the patella which increases the pressure under the patella. Malalignment of the lower extremity secondary to excessive rotation of the femur or tibia (shin bone), abnormal angles between these bones at the knee (knock knee or bow leg), or altered foot alignment may be present. In general, any variation which results in maltracking of the patella in the femoral groove during knee motion may expose the cartilage lining to abnormally high loads resulting in abnormal wear of that cartilage.
Who is likely to suffer from Patello-Femoral Pain?
It appears that patello-femoral pain is more common in women than in men. It is seen most frequently during the adolescent and early adult years but may occur at any age. In a number of cases a specific activity can be identified that makes the condition symptomatic. It may be recreational, job related or due to an activity of daily living. It is seen more often in those individuals involved in activities that require a significant amount of kneeling, squatting or even walking (particularly when steps or hills are involved). It is also aggravated in some individuals by running and jumping and, in runners, increased mileage or hilly terrain may bring on the symptoms. Because bent knee activities are mostly to blame even swimmers can develop the problem if they chose to swim breaststroke.
How is the condition diagnosed?
There is no one test that is effective. Generally it is diagnosed on the symptoms of the condition and this is supported by examination findings. However, examination like x-rays may be normal. X-rays can be helpful in more advanced cases or in those cases with definite maltracking of the patella. Similarly arthroscopy may be helpful, though often no abnormality will be seen.
How is the condition treated?
Rarely does patello-femoral pain result in any serious or permanent damage to the knee. This is particularly so in the growing adolescent where, with growth, the anatomy of the patella and its relationship with the femoral groove keep changing. The problem may not stop until a child is fully grown. Typically, the patient with patello-femoral pain will experience ups and downs in their symptoms, usually related to their activities. Part of the treatment therefore is aimed at reducing the frequency and severity of the painful episodes by avoiding or decreasing aggravating activities.
This in turn then allows the lining articular cartilage to stabilise and possibly heal. As this tissue metabolises very slowly it only has the capacity to heal very slowly, and therefore if the condition has persisted for some time it may take longer than expected get better.
A patient with patello-femoral pain needs to identify those activities which cause symptoms and these need to be excluded or modified (where possible) so that they cause less pain. This may involve modification or elimination of several sporting activities, usually those that involve running, jumping or squatting.
A specific exercise programme designed to strengthen the quadriceps muscles and to stretch the hamstring muscles often helps. This may need to be done in association with a taping programme which is designed to help pull the patella across medially. The object of these special exercises is to build up the inside part of the quadriceps muscle (the VMO or vastus medialis obliquus) which is the muscle normally responsible for ensuring the patella tracks correctly in its groove. With a correct exercise programme to build up the muscle, enough strength can be gained to take over from the tape, thus making the tape unnecessary. Once this happens, normal activities including sport, are generally possible.
Where there is an underlying biomechanical abnormality such as squinting patella (kneecaps that turn in to face each other) often caused by pronated or flat feet, a muscle strengthening programme may not in itself be adequate in which case some alteration in the biomechanics may be necessary. The simplest form of this is an orthotic which is placed inside the shoe to alter the position of the feet, which may improve the tracking of the patellae. This technique may be effective particularly where tape is helpful but cannot be dispensed with despite adequate VMO exercises.
Where maltracking continues to be a problem, a stabilising patella brace may be helpful. Though results are often disappointing and rarely totally successful.
Icing down the knee after painful activities or therapy is often helpful and anti-inflammatory medication is sometimes helpful particularly when there is an effusion (swelling) in the knee.
Surgery is very rarely necessary. However, in cases where the problem keeps recurring, an arthroscopy (in which a telescope is placed into the knee joint) may be considered to try and identify and tidy up any damage to the cartilage surfaces. At the same time other causes of this sort of pain can be looked for and treated e.g. rubbing plica (a curtain like membrane that is present in some knees) and fat pad impingement (where the tip of the fat pad gets caught between the patella and the underlying femoral groove). In cases where there are possible maltracking problems, it can help confirm the degree of maltracking and direct treatment appropriately. Whilst arthroscopy can be helpful for a few cases, for the majority it is not an alternative to a good exercise programme which, in the hands of an experienced sports physiotherapist, is approximately 90% successful.
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