Knee tendonitis is an overuse injury affecting one of the tendons that connect muscle to bone around the knee joint. In most cases, the term refers to irritation or damage in the patellar tendon, the thick band of tissue that runs from the bottom of the kneecap down to the shinbone. The quadriceps tendon, which sits just above the kneecap and anchors the thigh muscles, can also be affected but is less commonly involved. Because jumping sports are a major trigger, patellar tendonitis is often called “jumper’s knee.”
Where It Happens and Why
The patellar tendon works like a lever every time you straighten your knee. When you jump, land, sprint, or squat, this tendon absorbs a tremendous amount of force. Problems begin when the tendon is loaded repeatedly without enough recovery time. Tiny tears accumulate faster than the body can repair them, and over weeks or months the tendon’s internal structure starts to change.
What most people call “tendonitis” is actually, at the microscopic level, more often a process of degeneration than active inflammation. Healthy tendon tissue is made of tightly organized, mature collagen fibers aligned in parallel to handle pulling forces. In a damaged tendon, those mature fibers are gradually replaced by weaker, immature collagen that loses its organized alignment. The fibers stop linking together properly, blood vessels grow in haphazardly, and the tissue becomes less capable of bearing load. Inflammatory cells are rarely present in tissue samples from chronic cases, which is why many specialists prefer the term “tendinopathy” over “tendinitis.” The distinction matters because treatments aimed at reducing inflammation, like ice and anti-inflammatory drugs, don’t address the underlying collagen breakdown in a chronic case.
Who Gets It
Knee tendonitis is overwhelmingly a problem for athletes in sports that demand repeated jumping and landing. Prevalence data from elite-level sports paints a striking picture: up to 50% of high-level male volleyball players and roughly 32% of elite male basketball players develop patellar tendinopathy. Even among collegiate basketball players, more than 20% showed both tendon abnormality and pain on ultrasound before the season had even started. Teenage and junior athletes aren’t spared either, with reported rates of 7% in elite teen basketball players and 18% in elite junior volleyball players.
Outside of organized sports, knee tendonitis also shows up in runners, recreational cyclists who ramp up mileage too fast, hikers, and people whose jobs involve frequent squatting, kneeling, or stair climbing. Any activity that repeatedly loads the patellar tendon beyond its current capacity can trigger the process.
What It Feels Like
The hallmark symptom is a focused, sharp or aching pain right at the front of the knee, typically at the bottom tip of the kneecap or along the tendon just below it. Pain usually creeps in gradually rather than starting from a single incident. Early on, you might only notice it at the beginning of exercise, and it may fade once you warm up. As the condition progresses, pain persists throughout the activity and eventually starts limiting what you can do.
In more advanced stages, everyday tasks become uncomfortable. Sitting for long periods with a bent knee can produce a dull ache. Walking downhill or descending stairs often hurts more than going up because the tendon works harder to control your descent. Pressing directly on the lower edge of the kneecap or on the bony bump at the top of the shinbone typically reproduces the pain. If you’ve reached the point where pain is affecting your daily routine, not just your workouts, the tendon has likely been deteriorating for some time.
How It’s Diagnosed
Diagnosis starts with a physical exam. Your doctor or physical therapist will press along the tendon to find the exact point of tenderness and will likely ask you to perform loaded movements, such as a single-leg squat on a decline surface. This decline squat test is one of the most sensitive ways to provoke and measure tendon pain, and it’s commonly used to track progress during rehab as well.
Imaging isn’t always necessary, but when confirmation is needed, ultrasound tends to outperform MRI for this particular condition. One study comparing the two found ultrasound was 87% sensitive at detecting patellar tendinopathy compared to just 57% for MRI, while both had similar specificity around 82%. Ultrasound also has the advantage of being faster, cheaper, and performed in real time so the clinician can see the tendon while moving the knee. MRI is typically reserved for cases where the diagnosis is uncertain or surgery is being considered.
Treatment Through Loading
The cornerstone of treatment is progressive tendon loading through structured exercise. This might sound counterintuitive for an overuse injury, but controlled loading is what stimulates the tendon to rebuild stronger collagen. The two most studied approaches are eccentric exercises and heavy slow resistance training.
Eccentric exercises focus on the lowering phase of a movement. A classic example is a slow, controlled decline squat where you lower yourself over several seconds. Heavy slow resistance training uses both the lifting and lowering phases with progressively heavier weight and a deliberately slow tempo. A randomized trial comparing the two approaches in tendinopathy patients found that both produced equally strong clinical improvements that lasted through a full year of follow-up. The notable difference was in how patients experienced the programs: compliance was significantly higher in the heavy slow resistance group (92% vs. 78%), and patient satisfaction trended higher as well (100% vs. 80% at 12 weeks). For many people, the heavy slow approach simply feels more tolerable and sustainable.
Whichever method you use, expect the rehab process to take months, not weeks. A physical therapist will typically progress you through phases: reducing pain with modified activity first, then gradually increasing tendon load, and finally reintroducing sport-specific movements. Rushing back before the tendon has adapted is one of the most common reasons people end up with a recurring problem.
Other Treatments and What to Expect From Them
Shockwave therapy is sometimes offered for cases that haven’t responded to exercise alone. The treatment delivers focused pressure waves to the tendon with the goal of stimulating a healing response. The evidence, however, is mixed. A systematic review found that when shockwave therapy was compared directly to a placebo, there was no clear superiority for reducing pain in the short term. When combined with exercise, it still showed negligible additional benefit over exercise with a placebo. Where shockwave therapy did show a large effect was when compared to other conservative treatments like rest or bracing alone, which suggests it may work but not much better than a well-designed exercise program.
Corticosteroid injections can provide short-term pain relief, but they come with real risks for tendon tissue. Steroids can cause tissue atrophy and weaken the tendon structure, which is the opposite of what a degenerating tendon needs. Most sports medicine specialists use them sparingly, if at all, for patellar tendinopathy. When injections are used, clinicians reduce the risk by choosing lower concentrations, using ultrasound guidance for precise placement, and limiting the number of injections.
Recovery Timeline
Mild cases caught early, where pain only appears at the start of exercise and doesn’t affect daily life, often improve within a few weeks of modifying activity and beginning a loading program. Moderate cases where pain persists throughout exercise typically require three to six months of consistent rehab before a return to full sport. Severe or long-standing cases can take longer, and the timeline depends heavily on how much structural change has occurred in the tendon.
The most important factor in recovery speed is patience. Tendons heal slowly because they have a limited blood supply compared to muscle. Collagen remodeling takes time, and the tendon needs progressive, sustained loading to lay down organized fibers that can handle high forces again. Returning to jumping, sprinting, or heavy squatting before the tendon is ready doesn’t just stall progress; it can cause further degeneration that sets you back months. Your recovery timeline should be guided by how the tendon responds to increasing load, not by how long you’ve been waiting.