Patellofemoral Pain Syndrome

Patellofemoral pain syndrome (PFPS) is pain at the front of your knee, around or behind the kneecap, that comes on without an injury. This page explains what causes it, the symptoms, how it is diagnosed and treated, and what to expect.

What is patellofemoral pain syndrome?

Your kneecap (patella) sits in a groove at the end of your thigh bone (femur). The joint between them is called the patellofemoral joint. Each time you bend and straighten your knee, the kneecap glides up and down this groove, and the pressure on it rises when you climb stairs, squat or land from a jump.

In PFPS this joint becomes painful, usually because it has been loaded more than it can cope with. There is no tear, break or dislocation, and scans usually look normal. Doctors use the name once other causes of pain at the front of the knee have been ruled out.

You may also hear it called runner’s knee or anterior knee pain. It overlaps with chondromalacia patella, where the cartilage behind the kneecap has softened or worn. Many people with PFPS have healthy cartilage, and some people with cartilage changes on a scan have no pain at all. The treatment for both is much the same.

What causes patellofemoral pain syndrome?

There is usually no single cause. PFPS often starts when the load on the kneecap goes up faster than the knee can adapt, for example after:

• A sudden increase in running, jumping or training
• Starting a new sport, or a walking holiday with lots of hills and stairs
• A growth spurt in a teenager who plays a lot of sport.

Other things can add to the load or change the way the kneecap moves:

• Weak buttock (gluteal) and thigh (quadriceps) muscles. When these muscles tire, the knee can drift inwards as you squat, step down or land.
• Feet that roll inwards (pronated feet)
• The shape and alignment of the thigh and shin bones, which can make the kneecap run towards the outer side of its groove
• Extra body weight, which adds to the load on stairs and slopes.

PFPS is more common in girls and women, and in teenagers who play sport.^[1]

What are the symptoms of patellofemoral pain syndrome?

The main symptom is a dull ache at the front of the knee, around or behind the kneecap. It is often hard to point to one spot, and some people feel it most along the inner (medial) edge of the kneecap. The pain tends to come on with:

• Going up or down stairs or slopes
• Squatting, lunging, kneeling or jumping
• Running, especially downhill
• Sitting for a long time with your knees bent, such as at the cinema or on a long drive.

You may notice clicking or grinding under the kneecap. This is common, and on its own it is not a sign of damage. Both knees are often affected. The knee does not usually swell much or give way.

When should you see a doctor?

See your GP or physiotherapist if the pain has not eased after a few weeks of cutting back on the activities that bring it on. Seek medical advice sooner if:

• Your knee swells, locks or gives way
• Your kneecap slips out of place (see patellofemoral instability)
• The pain started with an injury, or it wakes you at night
• A child has knee pain with a limp or pain when moving the hip, as hip problems can cause pain that is felt in the knee
• Your knee is hot, red and swollen, or you have a fever. Seek urgent care.

How is patellofemoral pain syndrome diagnosed?

PFPS is diagnosed from your symptoms and an examination. Your doctor or physiotherapist will press around the kneecap, watch you squat or step down from a stair, and test the strength of your hip and thigh muscles. They will also look for other causes of pain at the front of the knee, such as pain in the tendon below the kneecap (patellar tendinopathy) or a kneecap that slips out of place.

Most people do not need a scan. An X-ray or MRI scan may be arranged if the pain started with an injury, if the knee swells, or if it is not improving with treatment. In PFPS, scans are usually normal.

How is patellofemoral pain syndrome treated without surgery?

PFPS is treated without surgery. International guidance recommends exercise therapy as the main treatment, together with advice about how much load your knee can take.^[2][3] Other measures can ease the pain in the short term while the exercises take effect.

Exercise and physiotherapy

A physiotherapist can set a program to strengthen your hip and thigh muscles. Strengthening the hip and knee muscles together reduces pain and improves function more than knee exercises alone.^[4] The program starts at a level your knee can tolerate and builds up gradually. Most people need to keep going for several weeks before they notice a change, and some need a few months.

Understanding the pain and adjusting your activity

Pain in PFPS does not mean your knee is being damaged. For a while, cut back on whatever brings the pain on, such as deep squats, running downhill or sitting for long periods, and then build back up step by step. Most people can keep exercising in a modified way, for example swapping some runs for cycling or swimming.

Taping and braces

Taping the kneecap, or wearing a brace that supports it, can ease pain in the short term and make the exercises more comfortable. There is less certainty about whether they help in the long run.^[2][3]

Foot orthotics

Shoe inserts (orthotics) can reduce pain in the short term for some people, especially if your feet roll inwards.^[2]

Weight loss

If you are carrying extra weight, losing some reduces the load on your kneecap when you climb stairs, squat or walk on slopes.

When is surgery considered?

Surgery is not a treatment for PFPS, even when the pain has lasted a long time. In a randomised trial of people with long-standing kneecap pain, adding keyhole surgery (arthroscopy) to a home exercise program gave no better results than the exercise program alone, at 9 months and again at 5 years.^[5][6] Exercise remains the treatment. If your pain has not settled after a thorough program, your GP or physiotherapist can look again at the diagnosis and adjust your exercises.

What is the outlook for patellofemoral pain syndrome?

Many people improve with exercise, but recovery is often slow and the pain can come and go. In a study of 310 people with PFPS, about 4 in 10 had not recovered well 12 months after starting treatment.^[7] In a smaller follow-up of the same group, more than half still had some symptoms 5 to 8 years later.^[8] Teenagers do not always grow out of it either. In a study of 15 to 19 year olds, more than half of those with knee pain still had it 2 years later, and those with PFPS were more likely to cut back on or stop sport.^[9]

People whose pain had lasted longer before treatment tended to recover more slowly,^[7][8] so it is worth starting an exercise program early and keeping up a home program once physiotherapy ends. In the long-term study, 48 of the 50 people who had X-rays showed no arthritis 5 to 8 years later.^[8]

References