Patellofemoral pain syndrome is pain at the front of the knee, around or behind the kneecap. It produces a dull, aching sensation that worsens with activities like climbing stairs, squatting, kneeling, or sitting with bent knees for long periods. Sometimes called runner’s knee, it’s one of the most common knee complaints: roughly one in five adults experiences it, and prevalence in adolescents runs between 20 and 40%.
What Causes the Pain
The kneecap sits in a groove on the front of the thighbone and glides up and down as you bend and straighten your leg. When that tracking is smooth, the forces spread evenly across the joint surfaces. In patellofemoral pain syndrome, the kneecap shifts slightly off course, either sitting in an abnormal position at rest or drifting out of alignment during movement. That lateral drift concentrates pressure unevenly on the cartilage underneath the kneecap and the surrounding soft tissues, which generates pain.
The cause is considered multifactorial, meaning no single problem is responsible. Weakness in the quadriceps (the front thigh muscles) is a major contributor because those muscles are the primary stabilizers of the kneecap. Weakness or poor control at the hip matters too, since the hip muscles influence how the entire leg lines up during weight-bearing activities. Other factors include tightness in the hamstrings or calf muscles, flat feet or excessive foot pronation, and sudden increases in training volume or intensity.
Women develop patellofemoral pain at nearly twice the rate of men. Annual prevalence in women is about 29%, compared to roughly 16% in men. Wider hips create a sharper angle where the thighbone meets the kneecap, which may explain part of that difference. Military recruits, runners, and cyclists are also disproportionately affected. One study of male cyclists found that over a third reported knee pain symptoms each year.
How It Feels Day to Day
The hallmark is a vague ache around the front of the knee rather than a sharp, pinpoint pain. It tends to build gradually instead of appearing after a single injury. Stairs are a common trigger, both going up and coming down, because those movements load the kneecap joint with several times your body weight. Squatting and lunging produce similar stress. One of the more frustrating features is “theater sign,” where pain increases simply from sitting with your knees bent for an extended time, like during a movie or a long car ride.
Some people also notice a grinding or crunching sensation when bending the knee. Mild swelling around the kneecap can occur but isn’t always present. The pain usually affects one knee more than the other, though it can be bilateral.
How It’s Diagnosed
Patellofemoral pain syndrome is primarily diagnosed through a physical exam rather than imaging. A clinician will check your kneecap alignment, test the strength and flexibility of your hip and thigh muscles, assess how your kneecap moves when you bend and straighten the leg, and press along the edges of the kneecap to locate tenderness.
Two findings are particularly telling. Pain during a squat is the most sensitive screening test, catching about 91% of cases. The patellar tilt test, where the examiner tips the kneecap to assess how tightly it’s held in place, is the most specific: if that test is positive, the odds strongly favor a patellofemoral diagnosis.
X-rays are commonly ordered, not to confirm patellofemoral pain itself but to rule out bone damage or other structural problems. An MRI is typically reserved for cases that don’t improve after a course of physical therapy, since it can reveal cartilage damage or soft tissue issues that might change the treatment plan. In some cases, a related condition called chondromalacia patella is found, where the cartilage on the underside of the kneecap has started to soften and break down. Chondromalacia can coexist with patellofemoral pain syndrome but isn’t always present.
Conditions That Look Similar
Front-of-knee pain has several possible causes, and distinguishing them matters for treatment. Patellar tendonitis (sometimes called jumper’s knee) produces pain just below the kneecap, at the point where the patellar tendon attaches to the shinbone. The tenderness is very localized, whereas patellofemoral pain is more diffuse around the kneecap itself. IT band syndrome causes pain on the outer side of the knee, not the front, and is most common in runners. During an exam, a clinician checks alignment, hip rotation, range of motion, and the specific location of tenderness to separate these conditions.
Treatment: Exercise Comes First
Exercise therapy paired with patient education is the recommended first-line treatment. A 2024 best practice guide published in the British Journal of Sports Medicine calls this the primary intervention, with strong evidence behind it. Knee-targeted exercises, particularly quadriceps strengthening, show the most robust pain-reduction benefits. When someone can’t tolerate loaded knee bending early on, starting with hip-strengthening exercises (targeting the glutes and hip stabilizers) and gradually adding knee work is a practical alternative.
The specific exercises are tailored to the individual. Someone with visible quadriceps wasting who can tolerate squats and leg presses will follow a different program than someone whose knee flares up with any loaded bending. A physical therapist typically assesses symptom severity and irritability before setting the starting point, then progresses the load and complexity over time.
Several supporting interventions can be layered on top of exercise. Patellar taping, where adhesive tape is applied to shift the kneecap’s position slightly, has consistent evidence for reducing pain and improving quadriceps function. It can be especially useful in the early stages when pain limits your ability to exercise. Prefabricated foot orthoses (off-the-shelf shoe inserts) are another option for people with foot alignment issues contributing to the problem. Manual therapy and gait or running retraining are additional tools a therapist may use depending on your situation.
Recovery Timeline
Most people need one to two months of consistent rehabilitation to see meaningful improvement. That timeline varies based on how long symptoms have been present, your starting strength, and your activity level. The key word is “consistent.” Patellofemoral pain responds to progressive loading over weeks, not days, and dropping out of a rehab program early is one of the most common reasons symptoms return.
Returning to sport or high-impact activity usually happens gradually. A therapist will look for pain-free performance of single-leg squats, step-downs, and sport-specific movements before clearing you for full return. Some people manage symptoms long-term with a maintenance strength program, particularly if they have underlying alignment or flexibility issues that contributed to the problem in the first place.