Front-of-knee pain is one of the most common musculoskeletal complaints, and the most likely cause is patellofemoral pain syndrome, sometimes called runner’s knee. But several other conditions can produce pain in exactly the same spot, and telling them apart comes down to where the pain sits, what triggers it, and whether there’s visible swelling. Here’s what’s probably going on and what you can do about it.
Patellofemoral Pain Syndrome
This is the single most common reason for pain at the front of the knee. It’s a dull, aching pain that feels like it’s behind or around your kneecap, and it typically gets worse when you squat, climb stairs, sit for a long time with bent knees, or run. The underlying problem is excessive stress on the joint where your kneecap meets the thigh bone.
Your kneecap sits in a groove on the front of your femur and glides up and down as you bend and straighten your leg. The compression force on that joint increases dramatically with deeper knee bends, because both the angle and the muscle tension pulling on the kneecap go up. When the kneecap tracks slightly off-center, or when the contact area between the kneecap and the groove is small, the stress per square inch on the cartilage spikes. That’s what produces pain.
Several things can push the kneecap off track. Two muscles on the inner and outer sides of your thigh (the vastus medialis oblique and vastus lateralis) are supposed to pull on the kneecap with equal force, keeping it centered. In people with patellofemoral pain, the inner muscle is often weaker, so the outer muscle wins the tug-of-war and drags the kneecap slightly outward. That lateral shift concentrates pressure on one side of the cartilage surface. Weakness in the hip muscles, particularly the glutes and hip rotators, also plays a role: when those muscles can’t stabilize your pelvis and thigh during movement, the knee collapses inward with each step, which pushes the kneecap further off its ideal path.
Why Women Are More Affected
Women develop front knee pain more often than men, and anatomy is a big part of the reason. The Q-angle, a measurement of the angle between your hip, kneecap, and shinbone, tends to be larger in women because of wider hips. A larger Q-angle increases the sideways pull on the kneecap, promoting the kind of maltracking that leads to pain. Women also tend to have relatively weaker quadriceps, hip rotators, and hip abductors compared to men, compounding the mechanical disadvantage.
Jumper’s Knee (Patellar Tendonitis)
If the pain is very specifically located just below your kneecap, right where the kneecap connects to the shinbone via a thick tendon, you may be dealing with patellar tendonitis. This is an overuse injury caused by repeated stress on the patellar tendon, which creates tiny tears that accumulate over time. It’s extremely common in basketball and volleyball players, but anyone who does a lot of jumping, sprinting, or deep squatting can develop it.
Patellar tendonitis follows a fairly predictable progression. Early on, you only notice pain during or right after intense activity. In the next stage, the pain shows up at the start of exercise, disappears once you’ve warmed up, then returns when you’re fatigued. If it keeps progressing, the pain becomes constant during activity and eventually bothers you at rest too. The tenderness is very specific: pressing on the bottom tip of the kneecap with the knee straight reproduces the pain, and it eases when the knee is bent.
Cartilage Softening (Chondromalacia)
The cartilage lining the underside of your kneecap can soften and break down over time, a condition called chondromalacia patellae. It starts with softening and swelling of the cartilage (Grade I), progresses to small cracks and fissures in the surface (Grade II), then to larger partial-thickness defects (Grade III), and finally to full-thickness loss that exposes the bone underneath (Grade IV).
The pain from chondromalacia is often vague and hard to pinpoint. People describe it as a deep ache behind the kneecap that comes on gradually rather than appearing after one specific injury. A healthcare provider can check for this using a simple test: they press down gently on your kneecap while you tighten your thigh muscle. Grinding, pain, or an inability to hold the contraction suggests the cartilage underneath is breaking down.
Bursitis at the Front of the Knee
A fluid-filled sac called the prepatellar bursa sits directly in front of your kneecap, cushioning it from the skin. When this bursa gets irritated, typically from repeated kneeling, it fills with fluid and swells visibly. You can actually see and feel the puffy, squishy swelling right over the kneecap. This is why the condition is sometimes called housemaid’s knee. It’s common in people who kneel for work: carpet layers, gardeners, plumbers, wrestlers, and surfers.
Unlike patellofemoral pain, which is felt deep behind the kneecap, bursitis pain and swelling sit right on the surface. In chronic cases, the swelling is more prominent than the pain, and you may notice stiffness or reduced range of motion simply because the swollen sac gets in the way.
Less Common Causes
A few other structures at the front of the knee can be the source of pain. The fat pad, a cushion of fatty tissue that sits just behind the patellar tendon, can get pinched between the kneecap and the thigh bone during full extension. This produces a burning or aching pain deep to and on either side of the tendon, often with a grinding sensation. People with fat pad impingement sometimes find that standing with their knees slightly hyperextended actually feels better.
Plica syndrome is another possibility. Plicae are folds of tissue left over from fetal development that line the inside of the knee joint. When a plica gets irritated, it causes pain along with snapping, clicking, or catching sensations during bending and straightening. The pain tends to flare with repetitive motion or after sitting with the knee bent for a long time.
Quadriceps tendonitis, which affects the tendon just above the kneecap rather than below it, produces pain at the top of the kneecap that worsens with deep bending.
What Actually Helps
For the most common cause, patellofemoral pain, the strongest evidence supports targeted strengthening exercises. The key muscle to rehabilitate is the vastus medialis oblique (VMO), the teardrop-shaped muscle on the inner side of your thigh just above the kneecap. In healthy knees, the VMO and its counterpart on the outer thigh fire with a 1:1 ratio. In people with front knee pain, that balance is off, and restoring it is the primary goal of rehab.
Hip strengthening is equally important. Exercises targeting the glutes and hip rotators reduce pain and improve function, whether done alone or combined with knee-focused work. Hip adduction exercises (squeezing the thighs together against resistance) are particularly useful because the VMO’s muscle fibers actually connect to the hip adductor muscles, so strengthening one helps activate the other.
Patellar taping and foot orthotics can also reduce pain in the short term by changing how the kneecap tracks or how forces travel up from the foot. Bracing has been studied primarily for more advanced cases involving early arthritis. Passive treatments like ultrasound and electrical stimulation have not shown benefit compared to controls.
Most people with patellofemoral pain need one to two months to recover with consistent rehabilitation. You should expect to modify or pause the activities that provoke your pain during that time. Returning to sport or exercise is generally safe once you’re pain-free and have rebuilt strength in the muscles around the knee and hip.
Signs That Need Prompt Attention
Most front-of-knee pain responds well to activity modification and strengthening, but certain symptoms point to something more serious. You should be evaluated promptly if your knee gives out or feels unstable, if it swells significantly, if you can’t fully straighten or bend it, if there’s an obvious deformity, or if you have a fever along with redness, pain, and swelling. Severe pain following an acute injury also warrants immediate evaluation.