Patellofemoral pain syndrome, sometimes called runner’s knee or anterior knee pain syndrome, is a common cause of pain at the front of the knee, especially in active adolescents and adults. This condition often develops from overuse or repeated stress on the knee joint. Most people with patellofemoral pain syndrome can manage their symptoms with rest, exercise, and other nonsurgical treatments. With the right approach, many return to their usual activities, though some may have ongoing symptoms.

Patellofemoral pain syndrome is a condition marked by pain around or behind the kneecap. This pain usually gets worse with activities that put weight on a bent knee, such as squatting, running, climbing stairs, or sitting for long periods.

The term “patellofemoral” refers to the area where the kneecap (patella) meets the thigh bone (femur). The kneecap sits in a groove at the end of the thigh bone and helps the leg straighten by acting as a lever for the thigh muscles. In patellofemoral pain syndrome, the pain is not caused by a clear injury or damage seen on scans, but rather by irritation or stress in the tissues around the kneecap.

Doctors diagnose patellofemoral pain syndrome when other causes of knee pain, such as ligament injuries, meniscus tears, or arthritis, have been ruled out. The condition is especially common in teenagers, young adults, and people who are physically active. It affects women more often than men.

The causes of patellofemoral pain syndrome are complex and often involve several factors working together. The most common cause is overuse, which means the knee is exposed to more stress or activity than it can handle or adapt to quickly enough.

Overuse can lead to small injuries in the tissues around the kneecap, such as the bands of tissue that hold it in place, the bones, or the small nerves. This often happens during periods of increased physical activity, such as starting a new sport, running longer distances, or training more intensely.

Other factors that can contribute to patellofemoral pain syndrome include:

• Malalignment, meaning the kneecap does not move smoothly in its groove, which can be due to differences in leg length, abnormal foot shape, or the way the hip and thigh muscles work
• Muscle weakness or imbalance, especially in the thigh (quadriceps) and hip muscles, can affect how the kneecap tracks during movement
• Trauma, such as a direct blow to the knee or a fall, can sometimes trigger symptoms
• Tight muscles, tendons, or soft tissues, especially the hamstrings or the band on the outside of the thigh (iliotibial band), can increase pressure on the kneecap
• Foot problems, such as flat feet or high arches, may change the way forces are distributed through the knee

The main risk factors for patellofemoral pain syndrome are activities and body features that increase stress on the front of the knee. Risk factors include:

• High levels of physical activity, such as running, jumping, cycling, or sports that involve frequent knee bending, which increase the load on the kneecap
• Sudden increases in training intensity, duration, or frequency, which can overload the knee
• Weak thigh or hip muscles, which may lead to poor kneecap tracking and increased joint stress
• Muscle tightness, especially in the hamstrings or iliotibial band, which can affect knee movement
• Abnormal foot structure, such as flat feet or high arches, which can change the way the knee moves
• Leg length differences, which may alter the forces on the knee
• Female sex, as studies show women are affected about twice as often as men
• Adolescence and young adulthood, since the condition is more common in these age groups
• Higher body weight, which increases the load on the knee joint
• Previous knee injuries or surgeries, which may change how the knee moves

The symptoms of patellofemoral pain syndrome usually involve pain at the front of the knee, but the pattern and severity can vary. Common symptoms include:

• Aching or sharp pain around or behind the kneecap, often described as “under” or “around” the patella
• Pain that gets worse with activities that load the knee while it is bent, such as squatting, running, climbing or descending stairs, or sitting for a long time with the knee bent
• Stiffness or discomfort after sitting for a long period, sometimes called the “theater sign”
• A feeling of the knee “giving way” or buckling, usually due to pain rather than true instability
• A sensation of catching, popping, or creaking in the knee, especially when standing up after sitting or going up or down stairs
• Mild swelling or a feeling of fullness around the kneecap, though severe swelling is uncommon

Diagnosis of patellofemoral pain syndrome is based mainly on a person’s symptoms and a physical examination. The doctor will ask about the location, timing, and triggers of knee pain, as well as any recent changes in activity, previous injuries, or surgeries.

During the physical exam, the doctor will:

• Examine the knee and leg for muscle loss, swelling, or changes in alignment
• Feel the kneecap and surrounding tissues for tenderness or warmth
• Test muscle strength, especially in the thigh and hip, and compare the affected leg with the other leg
• Check the range of motion of the knee and whether there is creaking or grinding with movement
• Assess flexibility of the hamstrings and other muscles
• Examine the feet and hips to check for alignment issues or signs that knee pain may be coming from another area

Special tests may be used to help confirm the diagnosis or rule out other causes. These include:

• Squatting test, which checks for pain when squatting, a common symptom of this condition
• Step-down test, which involves stepping off a low step to see if pain increases
• Patellar glide and tilt tests, which involve gently moving the kneecap to assess its mobility and alignment
• Popliteal angle measurement, which checks hamstring flexibility, as tightness can contribute to symptoms
• Observation of gait and single-leg squat, which can show abnormal movement patterns or weakness

Imaging tests are usually not needed for initial diagnosis. However, they may be used if symptoms do not improve with treatment or if another cause is suspected:

• X-rays, which are used to rule out fractures, arthritis, or other bone problems
• Magnetic resonance imaging (MRI), which is used to look for cartilage injuries or other soft tissue problems if symptoms persist
• Ultrasound, which is sometimes used to check for tendon or soft tissue issues

Treatment for patellofemoral pain syndrome focuses on relieving pain, improving knee function, and addressing factors that contribute to the problem. Most people improve with nonsurgical treatments. Treatment options include:

• Activity modification, which involves reducing or avoiding activities that cause pain, such as running or squatting, to allow the knee to recover
• Physical therapy, which includes exercises to strengthen the thigh, hip, and core muscles that help support and stabilize the knee
• Stretching, which improves flexibility in the quadriceps, hamstrings, and iliotibial band to reduce stress on the kneecap
• Short-term use of nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen or naproxen, can help reduce pain and swelling for a few weeks, but they are not recommended for long-term use
• Ice, which involves applying ice packs to the front of the knee to relieve pain after activity
• Patellar taping, which involves applying a special tape to the kneecap and may reduce pain and improve function when used with exercise
• Foot orthoses (shoe inserts), which may help some people, especially those with flat feet or abnormal foot movement, by improving alignment and reducing stress on the knee
• Education and reassurance, which help people learn about the condition and its management, stay active, and stick with an exercise program
• Gradual return to activity, which involves slowly reintroducing activities once pain improves, with attention to proper technique and muscle strength

Other treatments, such as ultrasound, electrical stimulation, or injections, have not been shown to provide lasting benefit for most people with patellofemoral pain syndrome. Surgery is rarely needed and is considered only if symptoms do not improve after a long period of nonsurgical care and a clear structural problem is found.

Complications of patellofemoral pain syndrome are uncommon, but some people may experience ongoing problems. Possible complications include:

• Persistent or chronic pain, which may limit daily activities or sports participation and can last for months or years, or come and go over time
• Reduced knee function, leading to difficulty with exercise or work tasks
• Patellofemoral osteoarthritis, a type of joint wear that may develop in some people with abnormal kneecap tracking
• Needing to stop or change sports or activities due to pain

People should seek medical advice if symptoms worsen, do not improve with treatment, or new symptoms such as severe swelling, redness, or inability to move the knee develop.

Some cases of patellofemoral pain syndrome may be prevented by taking steps to reduce stress on the knee and improve muscle strength. Prevention strategies include:

• Gradually increasing the intensity and duration of physical activity, rather than making sudden changes
• Doing regular exercises to strengthen the thigh, hip, and core muscles, which support the knee
• Including stretching for the quadriceps, hamstrings, and calves to maintain flexibility
• Using proper technique during sports and exercise
• Wearing appropriate footwear and considering shoe inserts if recommended for foot problems
• Taking breaks from repetitive activities that strain the knee

The outlook for people with patellofemoral pain syndrome is generally good, especially with early and consistent treatment. Many people recover fully or have only mild, occasional symptoms after following a rehabilitation program focused on exercise and activity modification.

However, about 40% of people may continue to have some symptoms one year after starting treatment. Long-term studies show that most people report successful outcomes after several years, especially if they continue with strengthening exercises and avoid overloading the knee.

Factors that may lead to a less favorable outlook include having a very mobile kneecap, older age, symptoms in both knees, or not following the recommended exercise program. Addressing psychological factors, such as fear of movement, can also improve recovery.

This article was medically reviewed in July 2026.