Patellofemoral Syndrome Causes and Risk Factors

The term patellofemoral pain syndrome refers to pain that occurs in the front of the knee. Sometimes called “runner’s knee,” this disorder affects the area of the lower femur (thighbone) where the kneecap slides through a groove. Patellofemoral pain syndrome ranks among the most common knee complaints and affects athletes and non-athletes alike.

Patellofemoral pain is the medical term used when pain occurs at the front of the knee, around the kneecap (patella), without signs of any damage or other problems in the knee joint.

It is also called patellofemoral pain syndrome, patellofemoral syndrome or anterior knee pain.

What is the patella?

Cross-section of the knee showing the patella

The patella is the kneecap bone. It lies within the quadriceps tendon. This large tendon from the powerful thigh muscles (quadriceps) wraps round the patella and inserts into the top of the lower leg bone (tibia).

The quadriceps muscles straighten the leg.

The back of the patella is covered with smooth cartilage. This helps the patella to glide over the lower part of the thigh bone (femur) when you straighten your leg.

What causes patellofemoral pain?

It is probably due to a combination of different factors which increase the pressure between the kneecap (patella) and the lower part of the thigh bone (femur).

This may happen during running, cycling, squatting and going up and down stairs. It is likely that the cause is not the same in everyone affected.

Situations where this can occur include:

Overuse of the knee, such as in certain sports – particularly at times of increased training. Cycling when the saddle is too low or too far forward.

Some people may have a slight problem in the alignment of the patella where it moves over the lower femur. This may cause the patella to rub on, rather than glide over, the lower femur.

It may be due to the way the knee has developed.

Or, it may be due to an imbalance in the muscles around the knee and hip – for example, the large quadriceps muscle above the knee and the muscles that stop the hips from tilting when standing on one leg.

A combination of an alignment problem (as above) and overuse with sports may be the most common reason for getting patellofemoral pain.

Weak hip muscles may cause patellofemoral pain by causing the thigh bone to be slightly turned inwards, leading to the patella being pulled slightly to one side.

Foot problems may also play a part – for example, where the feet do not have strong arches (flat feet). This makes the foot roll inwards (pronate), which means the knee has to compensate for the inward movement.

However, it is unclear whether this causes the knee problems or may be an effect.

Injury to the knee – including repeated small injuries or stresses due to sports, or due to slack ligaments (hypermobile joints).

Signs and Symptoms

The most common symptom of patellofemoral pain syndrome is a dull ache underneath the kneecap while walking down stairs, squatting or getting up after sitting for long periods of time.

In addition, your knee may catch when bending, and you may experience a painful grating or creaking sensation.

Although many active people notice symptoms when starting new activities or increasing their level of intensity, especially with respect to high-impact sports, non-active people can suffer patellofemoral pain during routine daily activities as well.


Your doctor will likely ask when you noticed your knee pain, how it has been feeling since the pain began and if you’ve injured your knee before.

He or she also may ask about any other conditions you have, such as diabetes and allergies, and if you are currently taking any medications.

Your doctor will assess the injury by feeling the knee area.

Because the kneecap is easily accessible, he or she can quickly test for pain and tenderness by moving your kneecap and check how well it tracks as you flex and extend your leg.

After this brief exam, your doctor most likely will be able to tell whether your discomfort is due to patellofemoral pain syndrome or another knee problem.


Eighty to 90 percent of people suffering from patellofemoral pain recover fully and are able to resume their previous activities. Most active people respond to non-surgical treatments.

Surgery is prescribed only in rare cases when patellofemoral pain cannot be eased with braces, rest or physical therapy.

Depending on the amount of malalignment, you typically will be asked to try a well-supervised rehabilitation program for six weeks to six months.

In most cases, you will need to continue the exercises you learn in physical therapy for life, which include specific movements for strengthening the knee, hamstring and calf muscles.

If your patellofemoral pain continues, surgery may be recommended, although this is relatively uncommon.

What is the outlook (prognosis)?

The outlook is good. Most people get better with simple treatments such as physiotherapy. However, it may take 4-6 months for full recovery and, meanwhile, you may need to reduce activities such as sports training.

Unfortunately symptoms may persist in 25% of people for up to 20 years but patellofemoral pain is an area of active research interest.

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