Swollen Knee: Everything You Need To Know

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A swollen knee occurs when excess fluid accumulates in or around the knee joint. This fluid, known as synovial fluid, can build up due to various causes, including injury, infection, arthritis, or overuse.

Some causes of knee swelling can be treated with at-home remedies. However, this symptom may sometimes indicate a serious underlying condition requiring more complex intervention.

Considering all available treatments and exploring less invasive options can help patients address their swollen knees effectively, potentially reducing the need for medications or surgery.

What Is Knee Swelling?

Swelling refers to the accumulation of fluids in and around the joint space. This fluid build-up occurs as part of the body’s inflammatory response. In the event of injury or irritation, the body attempts to contain tissue damage by redirecting fluids to the injured area.

This fluid accumulation can cause the knee to appear puffy and feel stiff or painful.

There are different types of swelling:

Effusion: The knee is a synovial joint surrounded by a capsule containing 2-3 milliliters (0.06-0.10 oz) of lubricating fluid, called synovial fluid. Conditions like overuse, injury, or arthritis can cause this fluid to increase in volume, leading to a type of swelling called effusion.
Edema: Edema occurs when blood vessels leak fluid into nearby tissues, causing the outer area of the joint to swell.
Hemarthrosis: Hemarthrosis occurs when blood from broken blood vessels leaks into the joint and accumulates. It can result from trauma, bleeding disorders, or surgical complications.

Knee swelling can also be categorized based on the type of inflammation that is causing it.

Acute swelling: Acute swelling is caused by acute inflammation, which is the body’s response to infection or trauma. It occurs suddenly after an injury and disappears when the injury has healed.
Chronic swelling: Chronic swelling indicates low-grade systemic inflammation. This type of inflammation develops over time and lasts for prolonged periods, usually several months to years. It can occur due to osteoarthritis, rheumatoid arthritis, or infections.

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Parts Of The Knee Affected During Swelling

Knee swelling can affect multiple components of the joint, including the following:

Bursa: Bursae are small fluid-filled sacs that cushion the knee. They reduce friction between tissues. Typically, the bursae swell when they become inflamed from overuse or injury.
Bones: The knee connects the femur (thigh bone), tibia (shin bone), and patella (kneecap). Arthritis can also cause friction damage and cartilage loss, leading to inflammation and swelling.
Ligaments: Ligaments are tough bands of tissues that connect bones and stabilize the knee. Swelling happens if they stretch or tear due to sports activities, overuse, or injury.
Cartilages: Cartilages are smooth tissues covering the ends of bones. They cushion the knee joint and allow smooth movement. They swell from damage or wear, as seen in osteoarthritis.
Tendons: Tendons connect muscles to bones and assist knee movement. Tendons can swell due to overuse or due to inflammatory conditions like tendonitis.

Symptoms Of A Swelling Knee

Depending on the underlying cause, swelling can be accompanied by several symptoms. These stem from active inflammation:

Knee pain, stiffness, and visible swelling: Pain and stiffness often accompany swelling because the accumulation of fluids makes it difficult or painful to move the knee. The swollen knee will also be different in appearance from the healthy one, usually appearing puffy or larger.
Warmth: A sensation of warmth results from the increased blood flow to the affected area as the body begins healing. This symptom suggests active inflammation or infection. It may also be accompanied by skin discoloration. The knee may feel warm to touch even when the rest of the body is cool.
Difficulty bearing weight. Swelling makes knee movements painful or unreliable, leading to loss of function. This makes it difficult to perform daily activities or bear weight on the affected leg.

Causes Of Swelling In The Knee

As noted, swelling is a primary symptom of active inflammation. Causes of inflammation in the knee joint include:

Physical injuries: Injuries occur when the knee is put under excessive pressure. They can occur due to direct trauma, such as receiving a blow to the knee or falls. Common knee injuries include fractures and dislocations, as well as tears:
- Ligament tears: Ligament tears can result from sudden twists or impacts, commonly seen in sports. Depending on the severity of the tear, this injury can cause swelling, pain, knee instability, reduced range of motion, and loss of function. The anterior cruciate ligament (ACL) is the most commonly affected ligament, an injury estimated to affect 1 in 3500 people in the US.
- Meniscus tears: Each knee has two menisci, C-shaped cushions of cartilage that act as shock absorbers and stabilizers. Tears occur from sharp turns or heavy lifting. Symptoms include pain, swelling, and the inability to bend or straighten the knee fully. Patients also experience knee locking and grinding sounds during movement.
Overuse: Repetitive movements like jumping can strain the knee. Over time, this wear and tear on knee tissues leads to chronic inflammation and swelling. Risk factors include participating in certain activities. These include sports and jobs that involve forceful or repetitive knee movement.
Infections: Bacterial infections in the knee joint occur when bacteria enter the joint through a cut in the skin. It can be a complication of open fractures, injury, or surgery. Swelling occurs when the immune response increases synovial fluid volume to fight the infection.
Pre-existing medical conditions. Certain medical conditions can contribute to the wear and tear of the joint’s components. Over time, this leads to inflammation and swelling. These are autoimmune conditions, connective tissue disorders, and anatomical defects, such as being born with thinner cartilage.

Conditions Associated With Knee Swelling

Estimations show that around 27% of people will eventually experience a swollen knee. Sometimes, this symptom is due to mild blows or injuries to the knee. In this case, the swelling will likely ease with rest and at-home care.

However, sometimes, ongoing or severe knee swelling indicates a more severe underlying condition. This makes it critical to obtain an accurate diagnosis and begin treatment. Below are some of the conditions that could lead to knee swelling.

Arthritis

Arthritis is an umbrella term for several inflammatory conditions that affect the joints, causing inflammation, pain, and damage.

As a result of inflammation, the joints can become swollen due to the buildup of fluid and increased blood flow to the affected area. Other arthritis symptoms include pain, restricted joint movement, and deformities, such as bone spurs.

There are different types of arthritis:

Osteoarthritis: Osteoarthritis is a degenerative disease due to age-related wear and tear. It involves the gradual breakdown of cartilage in the knee joint. When cartilage wears away, bones rub together, causing pain and inflammation. The body responds by producing excess synovial fluid, leading to swelling. A 2021 study estimates that 30% of people with knee osteoarthritis experience knee swelling.
Rheumatoid arthritis: Rheumatoid arthritis is an autoimmune disorder. The immune system mistakenly attacks the knee joint lining, causing inflammation and, in turn, swelling.
Psoriatic arthritis: Psoriatic arthritis is an inflammatory condition that affects some people with psoriasis. It causes the immune system to attack the joints, leading to pain, inflammation, and swelling.

Baker’s Cyst

A Baker’s cyst, a popliteal cyst, is a fluid-filled sac that forms behind the knee. This occurs when excess synovial fluid is pushed into a bursa, a small sac that cushions and lubricates joints. The cyst can swell and cause discomfort, especially when bending or extending the knee.

A Baker’s cyst often indicates the presence of underlying conditions that cause the knee to produce extra synovial fluid. These include arthritis and knee injuries.

Tendinitis

Tendinitis refers to the inflammation of tendons. These are flexible cords of tissues that connect muscles to bones. In the knee, this condition often results from overuse or repetitive strain. Common causes include running, jumping, or rapid exercise intensity. Symptoms include pain, swelling, and tenderness around the affected tendon.

The body sends blood and immune cells to repair the damage when tendons are overworked or injured. This process increases fluid in the tissue, leading to swelling.

Types of tendonitis affecting the knee include:

Patellar tendonitis or jumper’s knee affects the patellar tendon, which connects the kneecap to the shinbone.
Popliteus tendonitis affects the tendon connecting the popliteus muscle to the back of the shin bone.
Pes anserine tendonitis affects the tendons connecting the inner knee to the shin bone.
Quadriceps tendonitis affects the tendon connecting the quadriceps muscle to the kneecap.
Iliotibial band (IT band) tendonitis affects the tendon running outside the thigh, from the hip to the knee.

Bursitis

Bursitis is the inflammation of the bursae, small fluid-filled sacs that cushion the bones, tendons, and muscles near the joints. In the knee, bursitis typically affects the prepatellar bursa and pes anserine over the inside of the knee, located in front of the kneecap. Causes of knee bursitis include prolonged kneeling, repetitive motions, or direct trauma.

Symptoms include sharp pain, swelling, and skin color changes over the knee. Swelling occurs because the inflamed bursa produces excess synovial fluid. This may cause a noticeable bulge that can be tender and warm to the touch. Long-term irritation or infection can worsen these symptoms. Over time, this can cause significant discomfort and restricted movement.

Patellofemoral Pain Syndrome

Patellofemoral pain syndrome (PFPS) is also known as “runner’s knee.” It is a condition characterized by pain around the kneecap (patella). This syndrome often results from overuse, misalignment of the knee joint, or muscular imbalances. Risk factors include activities like running, squatting, or climbing stairs.

Symptoms include aching pain and sometimes swelling behind or around the kneecap. These symptoms tend to intensify when bending the knee. The swelling in PFPS is due to the increased stress and friction between the patella and the femur. This mechanical irritation triggers inflammation, leading to fluid buildup in the knee joint.

What Are The Common Treatments For Knee Swelling?

Common treatments for knee swelling include at-home care and conservative therapies. Sometimes, physicians may prescribe surgery. This could be suggested if damage to the knee is extensive and gets in the way of daily activities.

Home Remedy: RICE Method

The RICE method is a commonly recommended home remedy for knee swelling. RICE involves steps to target specific aspects of inflammation and swelling:

Rest: Resting the knee minimizes movement and prevents further injury. Reduced activity helps limit additional fluid build-up in the joint.
Ice: Applying ice reduces blood flow to the affected area, decreasing inflammation and numbing pain.
Compression: Using an elastic bandage to compress the knee helps reduce swelling by limiting fluid accumulation. It also supports the knee, providing stability.
Elevation: Elevating the knee above heart level encourages fluid drainage away from the joint, reducing swelling.

The combination of these steps helps control the body’s inflammatory response. In turn, this alleviates pain and swelling. However, one recent study highlights the downsides of reducing blood flow to the injured area, including delayed healing.

Assistive Devices

Assistive devices can significantly reduce knee swelling by providing support, stability, and reducing pressure on the affected knee. Used correctly, they can aid recovery and lessen pain. Commonly used devices include:

Knee braces: Knee braces stabilize and compress the knee joint. This limits movement, prevents further injury and reduces swelling. However, over-reliance can weaken surrounding muscles, potentially worsening long-term joint stability.
Crutches: Crutches transfer weight from the legs to the upper body, reducing knee strain during movement. The downside is the physical strain on the arms and upper body.
Canes: Like crutches, canes help redistribute weight, providing stability and reducing knee pressure. They are less cumbersome than crutches but offer less support. Correct cane height and usage are crucial to avoid additional strain on the body.
Shoe inserts: Shoe inserts or orthotics improve foot alignment, reducing knee strain during walking. They can help prevent recurring knee issues by addressing leg alignment problems. However, they may require customization and can be expensive.
Splints: Splints immobilize and protect the knee, maintaining alignment and reducing strain. However, they can be uncomfortable and limit mobility. They can also cause muscle atrophy if used for prolonged periods.

Physical Therapy

Physical therapy plays a crucial role in managing knee swelling. It works through a combination of targeted exercises and manual techniques. These aim to reduce inflammation, improve joint mobility, and rebuild muscle strength. These exercises improve blood flow, reduce stiffness, and minimize fluid accumulation in the knee joint.

Risks of physical therapy include potential discomfort or injury, especially if exercises are not performed correctly. The guidance of a specialized physical therapist is essential.

Medications

Medications often address knee swelling by targeting pain and inflammation:

NSAIDs (non-steroidal anti-inflammatory drugs): These are common medications like ibuprofen or naproxen. They reduce pain and inflammation by blocking inflammatory agents in the body, like prostaglandins. However, prolonged use can increase the risk of heart attack, peptic ulcers, stroke, and kidney disease.

Corticosteroids: Corticosteroids mimic anti-inflammatory hormones in the body to reduce inflammation. Long-term use can cause cartilage loss and disrupt normal cortisol production.

Surgery

Surgery may be used to diagnose the cause of knee swelling or address joint damage. Potential interventions include:

Synovectomy: This involves the removal of the inflamed synovium, the thin membrane that lines the joints. It helps reduce inflammation and pain from conditions like rheumatoid arthritis. The risks include recurrence of swelling, joint stiffness, and standard surgical complications such as infection. A 2023 study found that just under 40% of patients undergoing this surgery required revision surgery after 10 years.
Arthroscopy: This surgery uses a small camera to view the inside of the knee. Small incisions also allow the surgeon to repair damaged tissues. Risks include infection, blood clots, and continued pain.
Partial knee replacement: In this procedure, a surgeon replaces the damaged part of the knee. It involves removing the damaged bone and cartilage and replacing them with metal and plastic components. Downsides include potential implant issues, infection, and wear and tear over time.
Total knee replacement: In this surgery, the entire knee joint is replaced with a prosthetic joint. This is a large-scale surgery that comes with lengthy recovery times and risks of infection, reduced joint function, and the possible need for revision surgery. A 2021 study examined 33,292 revision knee replacements. It found that 19·9% of revisions needed another revision within 13 years.

How Regenexx May Help With Knee Swelling

The body has the natural ability to heal its own tissues, but this ability can decrease with injury or aging.

The Regenexx approach uses interventional orthobiologics to support this healing ability without medications or surgery. A physician in the licensed Regenexx network will review MRIs and scans and perform physical exams to identify the root cause of pain and design a customized treatment plan.

The interventional orthobiologic procedures using Regenexx lab processes routinely achieve cell concentrations of up to 20X—much higher volume than what other providers can typically achieve. Additionally, the cells are counted using specialized Regenexx proprietary methods, allowing physicians to customize the dose for each patient’s specific condition.

The Regenexx Alternative

The Regenexx approach combines several interventional orthobiologics, including:

Regenexx-SD Injectate

Procedures using Regenexx-SD injectate include a patented protocol that utilizes Bone Marrow Concentrate (BMC), which contains the patient’s own mesenchymal stem cells. The cell processing for a Regenexx-SD injectate routinely achieves 20x concentration— far above what non-Regenexx cell processing can achieve.

Regenexx-SCP Injectate

Procedures using Regenexx-SCP injectate represent a supercharged version of platelet-rich plasma (PRP). In this process, blood is drawn and then processed to isolate the platelets and growth factors. The growth factors are then purified, concentrated, and injected into the knee area using imaging guidance for precision. Regenexx-SCP injectate provides a higher concentration of growth factors compared to typical PRP procedures.

Regenexx-PL Injectate

Procedures using Regenexx-PL injectate are a highly specialized derivative of platelet-rich plasma (PRP) with a faster and more concentrated release of growth factors compared to typical PRP. The PL injectate is often combined with other orthobiologics, such as PRP and bone marrow concentrate.

Address Your Knee Swelling Early

Ignoring knee swelling can lead to further complications and chronic pain. Discover how non-surgical treatments may help support your knee health. Schedule a consultation with a physician specializing in Regenexx today!