A pressure sensation or pressure pain in the knee usually occurs with fluid accumulation in the joint. This is known as a joint effusion. It is usually accompanied by some degree of stiffness as well as visible swelling of the knee. There are several reasons why this may occur. Most of the time it is due to inflammation which in turn can be caused by a host of different factors such as with injury, infections and autoimmune diseases.
The knee is a synovial joint where bones of the thigh and lower leg articulate with each other, along with the kneecap (patella). The ends of the bones are capped with cartilage which is constantly regenerated to counteract the wear and tear. It is lined with a membrane known as the synovium. This membrane secretes synovial fluid into the joint cavity which acts as a lubricant. Pressure within a joint is usually stable but can increase when the joint is diseased.
Pressure when Walking, Standing and Bending
Knee effusion means that excess fluid has accumulated within the knee joint cavity. This fluid accumulation may be palpable meaning that there may be a feeling of fullness or pressure within the joint. If there is severe fluid accumulation then it can cause pain but usually the pain is due to inflammation. Sometimes there may be blood within the joint cavity and this blood can further irritate the joint lining and lead to pain.
Read more on aching knee.
Pressure on the joint increases in certain positions. The knee has to bear the weight of the entire upper body and thighs when standing. This pressure is further heightened when walking and especially when running. Normally there may not be any symptoms but in the diseased joint this pressure can elicit further discomfort and pain.
Bending of the lower limbs at the knee joint should not normally cause any discomfort or pain. However, when the joint fluid is excessive (effusion), filled with crystals (gout or pseudogout), has a foreign body within it (broken cartilage or bone) or when the joint lining (synovium) is inflamed then bending at the knee joint may cause a fullness sensation or even pressure pain.
Causes of Knee Pressure
As mentioned, pressure in the knee is a sensation that usually arises with fluid accumulation (effusion) in the joint. The most likely causes of knee effusions have been discussed below. Some of these conditions are acute where it arises suddenly and resolves quickly with proper treatment. However, the more common causes are often chronic meaning that it persists for a long period and sometimes even throughout life.
The pressure sensation or pressure pain is usually accompanied y a limited range of motion, often described as knee stiffness. There may also be other symptoms like a grating or clicking sound when there is movement of the leg at the knee joint.
Read more on knee stiffness.
Injury to the knee may occur through various ways. It may be blunt force or a penetrating injury. A blow to the knee is a relatively common type of injury, mostly arising from falls and contact sports. The surrounding tissue (ligaments, myscles and tendons) are also injured in most cases. Fractures may also occur, especially of the patella.
Repetitive stress injury is where there is minor trauma from repeated strain on the knee joint. This is also known as overuse injuries and may also contribute to joint degeneration in the long term. Sometimes the injury and strain may not always be obvious as may arise with a high body weight (being overweight or obese).
Osteoarthritis (OA) is the most common type of arthritis although there is no inflammation of the joint. Instead the cartilage lining the ends of the bones in the joint become worn out. Eventually the bone is exposed and parts of the bone can break off into the joint space.
Osteoarthritis is more common in older people once the regenerative capacity of the cartilage is insufficient to repair joint wear and tear. Overuse of the knee joint may also cause similar symptoms even without osteoarthritis being present. This is more likely in people who are running and standing for long hours on a daily basis.
Rheumatoid arthritis is joint inflammation that occurs due to autoimmune factors. The immune system malfunctions and attacks the joint lining. An inflamed joint may also occur with other autoimmune diseases like systemic lupus erythematosus (SLE) and psoriasis.
Reactive arthritis is another autoimmune joint condition. It is also known as Reiter’s syndrome and arises with certain infections, particularly of the digestive system and urinary tract. The joint symptoms are an autoimmune response to the infection and not a joint infection.
An infection of the knee is more likely to occur when infectious agents like bacteria enter the joint space directly. It tends to follow an injury to the knee area where there is a break in the skin. As with an infection elsewhere in the body, there is usually inflammation. Therefore a joint infection is also referred to as septic arthritis.
Staphylococcus aureus is the most common cause of septic arthritis. Gonorrhea, Lyme disease, tuberculosis (TB) and brucellosis are some of the other infections where fluid accumulation occur in the knee joint. The symptoms of these infections usually arise suddenly and are intense.
Gout and pseudogout are two disorders of metabolism that can cause joint inflammation. Uric acid and calcium pyrophosphate are two substances that can cause inflammation of the joint in gout and pseudogout, respectively. These substances form crystals in the joint which leads to inflammation.
The knee is the most commonly affected joint in pseudogout although this condition is less common than gout. The toes and specifically the big toe is the most frequently affected in gout but the knee can also sometimes be involved. Both pseudogout and gout are more common among older people.
As with any part of the body, abnormal growths may arise in the knee joint. This can lead to fluid accumulation in the knee joint along with other symptoms like pain and decreased range of motion. Tumors may be benign (non-cancerous) or malignant (cancerous).
Cancers like chondroblastoma, osteosarcoma and synovial sarcoma can cause effusion (fluid accumulation) in the knee joint. Benign tumors like fibrous dysplasia, osteochondroma and osteoid osteoma may also be responsible for fluid accumulation.