Swelling on top of the knee is a common problem.
Fluid may pool in the lower thigh, just above the kneecap or at the front of the knee, right on top of the knee cap.
There are lots of possible causes of swelling above the knee such as soft tissue injuries, underlying medical conditions and localised inflammation.
There may be a defined pocket of swelling, a hard lump above the knee or more generalised swelling around the knee. And the swelling may be constant or may fluctuate, depending on the underlying cause.
There are a number of possible causes of swelling on top of the knee and each will present slightly differently.
Here we start by looking at the five most common causes of swelling above the knee and the causes and symptoms of each. We will there go on to look at other possible causes of swelling above the knee and how to treat them.
The most common cause of swelling on top of the knee is patellar bursitis.
Bursa are small, fluid-filled sacs that sit between bones and soft tissues to allow the structures to glide smoothly over each other without any friction.
There are two bursa at the front of the knee that, when irritated, can cause swelling on top of the knee:
Inflammation of the suprapatellar and prepatellar bursa is caused by repetitive pressure or friction on the bursa. Common activities that cause bursitis swelling on top of the knee include prolonged or frequent kneeling, squatting, jumping and kicking, particularly if the muscles at the front of the knee are tight.
The bursa produce excess fluid in an attempt to protect the knee from injury, which form pockets of swelling above or in front of the knee. With bursitis, the area of swelling is typically well defined and people often describe it as being like a squashy orange.
In most cases, swelling on top of the knee from patellar bursitis can be treated at home, but in some cases, your doctor may recommend further intervention. If there is significant swelling on top of the knee from bursitis, the fluid can be drained, known as aspiration, but it is important to address the underlying cause of the bursitis otherwise the fluid will recollect causing further bouts of swelling above the knee.
You can find out lots more about the causes, symptoms, treatment and prevention options in the Knee Bursitis section.
Another common cause of swelling on top of the knee is quadriceps tendonitis.
Quadriceps tendonitis is caused by inflammation and degeneration of the quadriceps tendon, just above the kneecap.
Strain and overuse of the quadriceps can lead to inflammation and tearing in the quadriceps tendon, resulting in pain and swelling above the knee.
In most cases, swelling on top of the knee from quadriceps tendonitis is due to overuse, typically with sports that involve quick starts, stops and turns, running and jumping e.g. basketball, tennis and football.
There are several things that can make you more prone to quadriceps tendonitis such as muscle imbalance, sudden increases in training levels, altered foot biomechanics and unsupportive footwear.
Quadriceps tendonitis tends to initially cause pain and tenderness just above the kneecap with activity. You may also so start to develop some swelling on top of the knee, just above the kneecap, particularly after physical activity e.g. running or sports. Over time, the knee may become stiff and weak.
Swelling above the knee from quadriceps tendonitis tends to be mild to moderate, localised and may fluctuate with activity.
In most cases, swelling on top of the knee from quadriceps tendonitis can be treated at home and will settle within a few weeks. But without proper treatment and sufficient rest, there may be further tearing in the tendon which can lead to moderate to severe pain and swelling above the knee and weakness. In severe cases, the tendon may rupture completely.
You can find out more about the causes, symptoms and treatment options in the Quadriceps Tendonitis section.
Another possible cause of mild swelling on top of the knee is patellofemoral pain syndrome, aka Runners Knee. But don’t let the name fool you – it is just as likely to affect office workers as runners!
With patellofemoral pain syndrome, there is a problem with how the kneecap glides up and down at the front of the knee. This places increased pressure and friction on the cartilage lining the back of the kneecap.
Symptoms usually develop gradually and typically include aching anterior knee pain and mild swelling on top of the knee cap and around the front of the knee. Some people also notice a grating/grinding sensation when moving their knee.
Patellofemoral pain syndrome is usually caused by a combination of muscle weakness and tightness, altered foot biomechanics and anatomy. Symptoms are typically worse when you first get up after sitting for long periods, or with prolonged activity, especially long distance running, walking/running downhill and coming down stairs.
You can find out all about the common causes, symptoms, diagnosis and best treatment options in the Runners Knee section.
Swelling on top of the knee can also be due to a meniscus tear – the thick cartilage that line the knee joint.
Swelling above the knee from a meniscus tear can develop:
Knee swelling from a meniscus tear will vary depending on how large the tear is and which part of the meniscus is affected. Often there is generalised swelling on top of the knee and when you press on the area it often feels slightly “boggy” or “springy”. In some cases there may be a more specific area of swelling at the side of the knee.
You can find out loads more about the causes, symptoms and treatment options in the Meniscus Tear section.
If you can feel a lump above the knee cap, it may be from suprapatellar plica syndrome.
Plica are folds in the lining of the knee joint, known as the synovial membrane. Only around 10% of the population have knee plica and in most cases, they don’t cause any problems. But, if the suprapatellar plica which sits just above the kneecap get inflamed or irritated, then it can cause pain and instability in the knee.
Suprapatellar plica syndrome occurs when there is excessive friction on the plica or if it gets squashed. This leads to inflammation in the plica which gradually thickens and can harden over time, forming a lump above the knee.
Typical activities which can lead to swelling on top of the knee from plica syndrome are a blow to the knee, activities requiring repetitive knee flexion/extension e.g. running and cycling or suddenly increasing your activity levels.
Muscle weakness, underlying medical conditions and previous knee injuries can make the knee more prone to plica syndrome.
There are four areas of knee plica and plica syndrome can develop in any of them
In some cases of plica syndrome, adhesions may also form between the suprapatellar plica and the knee bones which can limit knee movement.
If you think this is the cause of you lump on top of your knee the find out more in the Knee Plica Syndrome section.
So far we have looked at the five most common causes of swelling on top of the knee, but there are a number of other things that can cause swelling at the front and sides of the knee, as well as above it.
The best treatment for swelling on top of the knee will depend on the underlying cause of the swelling, but the initial aim is to reduce the amount of excess fluid. Treatment for swelling above the knee will often involve a combination of:
You can find out all about the different ways to reduce swelling on top of the knee in the Swollen Knee Treatment section.
There are lots of possible causes of knee swelling.
If there is a distinct pocket of swelling or lump on top of the knee it is likely due to patellar bursitis, suprapatellar plica syndrome or a quads tendon rupture.
If there is mild to moderate swelling above the knee only, it is likely due to quadriceps tendonitis, meniscus tear or patellofemoral pain syndrome.
If there is more generalised swelling around the knee joint as a whole, it may be due to arthritis, a large meniscus tear or a ligament tear.
If the swelling above your knee is accompanied by redness and warmth, it may be due to gout, an infection or a DVT – seem medical assistance as soon as possible.
Swelling isn’t always confined to the top of the knee and different things cause knee swelling in different places. Find out more in the following sections:
Page Last Updated: 18/01/23
Next Review Due: 18/01/25