Pain just below the kneecap most often comes from the patellar tendon, the thick band of tissue connecting your kneecap to your shinbone. This is the most common site of trouble, but several other structures sit in the same small area and can produce similar pain. The cause depends on your age, activity level, and exactly where and when the pain shows up.
Patellar Tendonitis (Jumper’s Knee)
The most likely explanation for pain below your kneecap is patellar tendonitis, sometimes called jumper’s knee. The patellar tendon runs from the bottom of your kneecap straight down to the top of your shinbone, and pain typically sits right in that gap between the two bones. It develops when repetitive stress, especially from jumping, running, or squatting, causes small-scale damage that accumulates faster than the tendon can repair itself.
The progression is predictable. At first, you only notice pain when you start an activity or just after a hard workout. Over time it creeps into the activity itself. Eventually it interferes with everyday movements like climbing stairs or standing up from a chair. The pain tends to feel like a deep ache or burning sensation near the bottom edge of the kneecap, and it often gets worse when you push off, land from a jump, or straighten your leg against resistance.
Patellar tendonitis is most common in sports that involve explosive jumping (basketball, volleyball) but also shows up in runners, cyclists, and anyone who significantly increases their training load too quickly.
Fat Pad Impingement (Hoffa’s Syndrome)
Sitting just behind the patellar tendon is a pad of fatty tissue called the infrapatellar fat pad. When this tissue gets pinched between the kneecap and the thighbone, it swells, stiffens, and produces a burning or aching pain that feels almost identical to patellar tendonitis. The key difference: fat pad pain tends to be worst in the last few degrees as you fully straighten your knee, and it can also flare during prolonged sitting with the knee bent.
Fat pad impingement often follows a direct blow to the front of the knee or develops gradually after another knee injury. On examination, pressing firmly on either side of the patellar tendon while slowly straightening the knee reproduces the pain. Patients with this condition also tend to have some restriction in how far they can bend or straighten the knee, and the area below the kneecap may feel thicker or firmer than the other side.
Osgood-Schlatter Disease in Young People
If the person with pain below the kneecap is between roughly 10 and 15 years old, Osgood-Schlatter disease is a strong possibility. This condition targets the bony bump (tibial tubercle) where the patellar tendon attaches to the shinbone. During growth spurts, the tendon pulls on a still-developing growth plate, causing inflammation and sometimes a visible bony lump just below the knee. Prevalence in the 12-to-14 age range runs between about 10 and 13 percent, and it affects boys and girls at similar rates.
The hallmark sign is a tender, swollen bump you can see and feel at the top of the shinbone. It hurts most during running, jumping, and kneeling. X-rays sometimes show a small bony projection at the tibial tubercle. The condition is self-limiting, meaning it resolves once growth is complete, though the bony bump may remain permanently.
Infrapatellar Bursitis
Two small fluid-filled sacs (bursae) sit near the patellar tendon: one just under the skin and one deeper, behind the tendon. When either becomes inflamed, you get localized swelling and tenderness below the kneecap. The superficial version, historically called “clergyman’s knee,” develops from repetitive kneeling. The deeper version produces tenderness on either side of the patellar tendon and thickening of the soft tissue you can sometimes feel with your fingers.
Bursitis pain tends to be more constant and less tied to specific movements than tendonitis. The swelling is often the most noticeable feature.
Poor Kneecap Tracking
Sometimes the pain below the kneecap is a downstream effect of how the kneecap itself moves. When the kneecap sits too high in its groove (a condition called patella alta) or drifts to one side during bending and straightening, it changes the angle of pull on the patellar tendon and concentrates stress on a smaller area of cartilage. Research on patients with kneecap maltracking has found that the vertical position of the kneecap is the single strongest predictor of how much cartilage contact area the joint uses. A high-riding kneecap leaves the groove too early during straightening, allowing it to shift and tilt laterally. When it re-enters the groove during bending, the contact forces spike, producing pain both behind and below the kneecap.
This pattern is more common in people with naturally loose ligaments and tends to cause pain during stairs, squatting, and prolonged sitting.
How These Conditions Are Diagnosed
A physical exam is the starting point. Your doctor will press on specific spots around the patellar tendon, check for swelling, test your range of motion, and have you squat or extend your leg against resistance. These hands-on tests can usually distinguish between tendon pain, fat pad impingement, and bursitis.
When imaging is needed, ultrasound is often more useful than MRI for confirming patellar tendon problems. One comparative study found ultrasound was 83% accurate at confirming patellar tendonitis, compared to 70% for MRI. Ultrasound also caught more true cases (87% sensitivity versus 57% for MRI). It’s faster, cheaper, and lets the examiner look at the tendon in real time as you bend and straighten your knee. MRI is still valuable when the diagnosis is unclear or when deeper structures like the fat pad or meniscus need a closer look.
Managing the Pain at Home
For patellar tendon pain specifically, isometric exercises (static holds where the muscle contracts without the joint moving) can provide immediate relief. A practical version: hold a wall sit or static squat position for 30 seconds, rest, and repeat five times. Research on athletes with patellar tendonitis found that this type of isometric hold reduces pain right away and actually improves muscle performance afterward, likely by dialing down pain-related inhibition in the brain. This makes isometrics useful as a warm-up before activity, not just a rehabilitation tool.
Ice applied for 15 to 20 minutes after aggravating activities helps control inflammation, particularly with bursitis or fat pad irritation. Reducing or modifying the activity that triggers the pain is essential in the short term. For runners, that might mean temporarily cutting mileage. For jumpers, it might mean limiting plyometric drills.
Long-Term Tendon Rehabilitation
If your pain is from patellar tendonitis, short-term rest alone won’t fix the underlying tendon damage. The gold standard for long-term recovery is a progressive eccentric loading program, which means slowly lowering your body weight through a squat while the tendon lengthens under tension. Performing these squats on a 25-degree decline board increases the load on the patellar tendon by 25 to 30 percent compared to flat-ground squats, making the exercise more targeted.
The standard protocol calls for 3 sets of 15 repetitions, twice daily, over a 12-week period. Squatting depth should stay in the 60-to-70-degree range to avoid excessive stress on the joint. The progression follows a logical sequence: start with both legs sharing the load (or in a pool or on a partial-weight-bearing machine), advance to single-leg work on the affected side, and eventually add weight in small increments starting at about 10% of your body weight. You’re ready to progress when you can complete all sets pain-free.
This process requires patience. Tendons remodel slowly, and skipping ahead or returning to full activity too soon is the most common reason people end up with chronic problems.
Signs That Need Prompt Attention
Most causes of pain below the kneecap are overuse injuries that respond to conservative treatment. But a sudden, sharp event is different. A patellar tendon rupture, where the tendon tears partially or completely, produces a distinct popping or tearing sensation followed by immediate swelling. The clearest sign: you cannot straighten your knee. Without the tendon anchoring it, the kneecap shifts upward into the thigh, and you may be able to feel an indentation where the tendon used to be. Walking becomes difficult because the knee buckles or gives way. This is a surgical emergency and needs same-day evaluation.
Significant swelling that appears rapidly, inability to bear weight, or pain that wakes you at night are also reasons to get evaluated sooner rather than later, as these patterns can point to fractures, infections, or internal joint damage that won’t improve with rest alone.