Runner's Knee: What Patellofemoral Pain Is and How to Fix It

The patellofemoral joint is where the back of the kneecap meets the groove in the front of the femur (the trochlear groove). The patella is a sesamoid bone embedded in the quadriceps tendon; it acts as a pulley, increasing the mechanical advantage of the quadriceps during knee extension. During a squat or stair descent, the compressive force across the patellofemoral joint can reach several times body weight. The depth of the trochlear groove, the alignment of the quadriceps tendon, and the balance of forces pulling on the patella all determine whether it tracks smoothly through this groove or drifts to one side under load.

Patellofemoral pain syndrome is the clinical term for pain around or behind the kneecap. It is the most common running injury and one of the most common knee problems in the general population. The pain is typically worse with stairs, squatting, prolonged sitting (the “movie theater sign”), and running, especially downhill. The pattern is consistent: activities that increase the compressive load across the patellofemoral joint reproduce the symptoms. A deep squat loads the joint more than a shallow one; a downhill run loads it more than a flat run.

What Is Happening

The pain results from abnormal loading of the patellofemoral joint. Two main mechanisms contribute, and in most runners both are present to some degree:

Quadriceps weakness, particularly in the vastus medialis oblique (VMO), allows the patella to track laterally during knee flexion. This increases the contact pressure on the lateral facet of the patella. The VMO is the only quadriceps muscle that pulls the patella medially; when it is weak relative to the vastus lateralis, the patella drifts. The result is not evenly distributed load across the joint surface, but concentrated pressure on a smaller area of cartilage. Over repeated loading cycles, this produces the characteristic aching pain behind the kneecap.

Hip abductor weakness allows the femur to adduct and internally rotate during weight-bearing activities. This changes the angle between the femur and the patella, effectively shifting the femoral groove underneath the patella and increasing lateral contact pressure [4]. Biomechanical studies have shown that runners with patellofemoral pain have greater hip adduction angles during running than pain-free runners. The joint-by-joint model is useful here: the hip is a mobility joint that also needs to produce stability in the frontal plane. When the gluteus medius and other hip abductors cannot control the femur during single-leg stance, the knee, which is designed for sagittal plane motion, absorbs forces it was not built to manage.

The 2016 consensus statement on patellofemoral pain identified both quadriceps and hip muscle weakness as the primary modifiable risk factors [1]. Other contributing factors include increased Q-angle, excessive foot pronation, and training errors (rapid increases in mileage or intensity), but the muscle weakness is the most addressable and the most consistently supported by the evidence.

What the Evidence Supports

Exercise is the most strongly supported treatment. A Cochrane review of 31 trials found that exercise therapy reduces pain and improves function in patellofemoral pain, with benefits sustained at long-term follow-up [5]. The evidence is strong enough that the consensus statement lists exercise as the cornerstone of management.

The specific question of hip vs knee strengthening has been studied directly. A 2015 meta-analysis of 14 RCTs found that proximal (hip-focused) strengthening programs produced larger reductions in pain than knee-focused programs alone in the short term [2]. A 2018 review confirmed that combined hip and knee strengthening is more effective than either alone [3]. The mechanism is straightforward: strengthening the hip abductors controls femoral rotation, while strengthening the quadriceps controls patellar tracking. Both components of the problem need to be addressed.

Patellar taping (McConnell taping) can provide immediate short-term pain relief by manually shifting the patella medially, reducing lateral contact pressure. It is a useful adjunct during rehabilitation, particularly in the early weeks when strengthening has not yet produced significant gains, but it does not replace strengthening.

Foot orthoses have moderate evidence for short-term pain relief in some subgroups, particularly those with excessive pronation. They are not universally effective and should not be the sole treatment. For runners with visible overpronation, addressing it may reduce one contributing factor, but the hip and quadriceps weakness remain the primary targets.

Running retraining is an emerging area. Increasing step rate by 5 to 10 percent reduces the load on the patellofemoral joint per stride by shortening the ground contact time and reducing the braking force at heel strike. Some clinicians also cue runners to avoid letting the knee cross the midline during stance phase, which reduces the hip adduction component. Others work on trunk lean and pelvic drop, both of which influence the forces acting on the patellofemoral joint during single-leg stance. The evidence for these gait modifications is less mature than the evidence for strengthening, but the biomechanical logic is sound and the modifications are low-risk to implement.

Exercises to Try

Wall sit at 60 degrees. Stand with your back against a wall. Slide down to approximately 60 degrees of knee flexion (not a full 90-degree squat). Hold for 30 to 45 seconds. This loads the quadriceps isometrically in a range that is tolerable for most patellofemoral pain, because the patellofemoral contact pressure is lower at 60 degrees than at deeper flexion angles. Three sets. Progress by increasing hold time to 60 seconds before adding any external load.

Side-lying hip abduction with band. Lie on your uninvolved side with a resistance band around the ankles. Raise the top leg to 30 degrees, keeping the toes pointed slightly downward to bias the gluteus medius over the tensor fasciae latae. Hold two seconds. Lower slowly. Three sets of 15. This is a primary gluteus medius exercise. If this is easy, progress to standing with a band around the ankles and stepping laterally (banded side steps), which loads the hip abductors in a more functional position.

Step-up with control. Stand in front of a step, 15 to 20 cm high. Step up with the affected leg, focusing on keeping the knee aligned over the second toe (do not let it collapse inward). Step down slowly with the opposite leg. Three sets of 10. The emphasis is on control and alignment, not speed. Watch the knee in a mirror if possible: the inward collapse during a step-up is often invisible without visual feedback.

Single-leg bridge. Lie on your back, one foot flat on the floor, the other leg extended. Drive through the planted foot to lift the hips. Hold two seconds at the top, pelvis level. Three sets of 10 each side. This loads the gluteus maximus and medius in hip extension. A pelvis that drops on the unsupported side indicates gluteus medius weakness, which is precisely the deficit this exercise targets.

Quadriceps stretch. Stand on one leg, holding the opposite ankle behind you. Pull gently until you feel a stretch on the front of the thigh. Hold 30 seconds. Repeat both sides. This helps maintain quadriceps flexibility, which reduces patellar tendon tension. Pair it with a hip flexor stretch (half-kneeling lunge position, squeezing the glute on the kneeling side) for runners who sit at a desk for long periods.

Managing Training Load

Complete rest is rarely necessary and often counterproductive. The muscles that need strengthening will decondition further with inactivity. The approach that the evidence supports is relative rest: reduce running volume and intensity to a level that does not increase pain during or within 24 hours after the run, and supplement with the strengthening program above.

Avoid steep hills and deep stair descents in the early weeks, as these activities generate the highest patellofemoral joint loads. Flat running at a moderate pace is usually tolerable. If running is painful even at reduced volume, cycling or swimming can maintain cardiovascular fitness while the strengthening program takes effect. The goal is to return to full training gradually, typically over 3 to 4 months, with the strengthening program continuing alongside.

Patellofemoral pain has a notable recurrence rate. Runners who return to full volume but discontinue strengthening often see the problem return within months. The consensus statement identifies this as one of the most important points in management: patellofemoral pain is not a condition that resolves permanently with a short course of exercise [1]. The underlying biomechanical factors (hip abductor capacity, VMO strength relative to vastus lateralis, patellar tracking) require ongoing maintenance. A program of two hip and quadriceps sessions per week, even after symptoms resolve, is the best protection against recurrence.

When to See a Doctor

See a doctor or physical therapist if:

• Pain is worsening despite 6 to 8 weeks of consistent strengthening
• The knee swells after activity
• The knee gives way or locks
• Pain is sharp and localized rather than diffuse (may indicate a different pathology)
• There was a specific injury (a twist or blow to the knee) before the pain started

When to see a doctor. If joint pain follows a significant injury, is accompanied by swelling, giving way, locking, or loss of range of motion, or if you have neurological symptoms (numbness, tingling, weakness), see a doctor or physical therapist. They can assess whether imaging or specialist input is appropriate.