Knee swelling, also known as knee effusion, isn’t it a pain in the butt? It is usually caused by injuries, overuse, arthritis, and other conditions that can limit your mobility and cause discomfort in your daily life. In fact, studies show that nearly 30% of adults experience knee swelling at some point.
For this reason, I’m here to guide you the common causes, symptoms and treatments to help you understand and manage swelling on side of knee.
What is Swelling on the Side of the Knee
Swelling on the side of the knee, also known as knee effusion, is when excess fluid accumulates around the knee joint. This fluid buildup can be very painful and causes knee pain and makes it difficult to move the affected knee.
Various knee problems such as knee injury or overuse can cause this condition. The pain and swelling can be immediate or develop over time and if left untreated can become chronic swelling.
Common symptoms of a swollen knee are pain, stiffness and tightness around the knee joint. In some cases this swelling can also cause a Baker’s cyst to form which is a fluid filled sac behind the knee.
Causes of Lateral Knee Swelling
Swelling in the knee can arise from various factors, including trauma, overuse, and underlying medical conditions.
While some individuals may experience sudden swelling due to an injury, others might notice gradual swelling linked to overuse or chronic conditions.
Several conditions can lead to knee swelling, each with its own symptoms and treatment options. Common culprits include knee injuries, arthritis, and acute injuries, but other conditions like bursitis and Baker’s cyst can also contribute.
Let’s explore these causes in detail.
Knee Injuries
Knee injuries are a common cause of swelling on the lateral side of the knee. One common injury is a meniscus tear which is when the cartilaginous structure within the knee joint is damaged and causes pain and swelling.
Another common injury is the medial collateral ligament (MCL) which can be damaged by a fall or impact and causes swelling and pain on the inner side of the knee but can also extend to the lateral side.
Soft tissue injuries such as sprains or strains around the knee can also cause swelling. These injuries can cause inflammation and fluid accumulation and contributes to the swelling and discomfort around the knee joint.

Torn ACL
A torn anterior cruciate ligament (ACL) is a severe knee injury that can cause a lot of knee pain and swelling. One of the signs of an ACL tear is a sudden loud popping sound when you get injured. Many people with ACL injury can’t bear weight on the affected leg and the knee joint is unstable. A torn meniscus and a torn ligament can hinder recovery and rehabilitation.
Despite the severity of the injury some people may experience minimal pain and swelling and can continue to do activities temporarily. But the underlying damage can cause significant instability and chronic problems if not treated properly.
Athletes are more prone to ACL injuries which often occurs due to sudden lateral movements.
Read More: knee pain diagnosis chart
Arthritis
Arthritis is a common cause of chronic knee swelling. Rheumatoid arthritis is an autoimmune disorder that can cause significant swelling around the knee joint due to chronic inflammation. This condition not only causes knee pain but also causes swelling and stiffness that can severely limit mobility.
Knee osteoarthritis is another form of arthritis which is caused by the gradual wear and tear of the joint cartilage. This degeneration causes severe knee pain, knee effusion and pain and makes it hard to do daily activities.
Acute injuries
Acute injuries to the knee such as torn ligaments and cartilage can cause immediate and severe swelling. These injuries are common during sports activities that involves sudden stops or twists. Symptoms of acute knee injuries are sudden swelling, sharp pain and difficulty in moving the knee.
The R.I.C.E. method rest, ice, compression with an elastic bandage and elevation is used immediately to treat acute injuries and reduce swelling and pain.
Other Conditions
Other conditions can also cause swelling on the side of the knee. Bursitis for example is the inflammation of the fluid-filled sacs (bursae) that cushion the knee joint which can cause significant swelling and discomfort.
A Baker’s cyst is when the joint fluid leaks into the back of the knee and forms a painful and swollen lump.
Swelling on the Side of the Knee Diagnosis
A physical examination by a healthcare provider is often the first step. This includes a thorough review of your medical history and a hands on examination of the knee and surrounding joints. Doctors will look for signs of pain and swelling and will ask specific questions to pinpoint the cause.
In addition to the physical examination, imaging and joint aspiration may be needed to determine the underlying cause.
Physical Examination
During the physical examination, doctors will first discuss your symptoms and review your medical history.
They will then do a thorough examination of the knees, hips, legs and other joints to look for any issues. Conditions like arthritis which can cause chronic knee swelling are often evaluated during this initial examination.
The physical examination also looks for excess fluid in the knee joint which can be due to trauma or overuse. This hands on examination will determine the next step in the diagnostic process.
Imaging Tests
Imaging tests such as X-rays, MRIs and ultrasounds are important in diagnosing the underlying cause of knee swelling. These tests will give detailed information of the knee joint, the bones, cartilage, tendons and ligaments.
Joint Aspiration
Joint aspiration also known as arthrocentesis is a procedure where fluid is removed from the knee joint for analysis.
This procedure will help diagnose the cause of knee swelling by analyzing the extracted fluid for infections or other underlying conditions.
Joint aspiration can also give immediate relief from pain and stiffness caused by fluid buildup.
In some cases, corticosteroids may be injected into the knee joint after fluid removal to further manage inflammation and pain. ( Ask your doctor first )

Treatment for Swelling on the Side of the Knee
Treating lateral knee swelling requires a multi-faceted approach which includes medications, physical therapy and sometimes surgical interventions. The goal is to reduce pain and swelling, improve knee function and prevent future problems. Depending on the cause and severity of the swelling, different treatment may be recommended.
Medications can manage pain and inflammation, physical therapy can strengthen the knee and improve mobility.
In severe cases, surgical intervention may be needed to repair or replace damaged structures. Let’s take a look at these treatment options.
Medications
NSAIDs like ibuprofen can help relieve pain and reduce knee inflammation. Over the counter pain relievers like acetaminophen can also help in managing knee pain. For severe pain and inflammation, corticosteroid injection into the knee joint may be considered.
These medications will give significant relief and are the first line of treatment for knee swelling. But always consult with a healthcare provider to ensure proper use and dosage especially if you have underlying medical conditions.
Take Note: Avoid taking any medications without consulting your doctor or having a prescription. We strongly recommend getting your doctor’s advice first.
Physical Therapy
Physical therapy is part of the treatment plan for knee swelling. Targeted exercises will enhance knee strength and function and relieve pain and improve mobility. Stretching and strengthening exercises are usually recommended to support knee stability and function.
A study in the journal Physical Therapy found that after four weeks, people with knee osteoarthritis who went to physical therapy in a clinic saw a 52% increase in their Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) scores, while people who did exercises at home saw a 26% increase.
Therapists may also use modalities like ultrasound or electrical stimulation to enhance treatment outcome and reduce pain.
Surgical Interventions
Sometimes surgery is needed to address knee problems that don’t respond to conservative treatments. Arthroscopic surgery allows for minimally invasive repair of various knee conditions like meniscus tears or ligament damage. This surgery involves small incisions and uses a camera to guide the procedure.
For severe or chronic knee problems, knee replacement surgery may be the last resort. This involves replacing the damaged knee joint with an artificial one to restore function and reduce pain.
Home Care
Rest is important to prevent further irritation and allow the knee to heal. Applying ice will reduce swelling and is a home remedy.
Here are some more home care tips:
- Use a knee brace or compression sleeve to support and prevent fluid accumulation. Elevate your leg above heart level to reduce swelling. This will give relief.
- Gentle stretching and self-massage to maintain knee mobility and drain fluid from the joint.
- Apply heat after 72 hours of icing if swelling doesn’t get worse; this will help in recovery.
- Do knee exercises to strengthen the muscles around the joint.
- Be healthy to reduce stress on the knee joints.
- Avoid activities that will worsen the pain and swelling.
- Wear supportive shoes to reduce impact on your knees.
- Stay hydrated and eat balanced diet to support overall joint health.
- Over the counter anti-inflammatory creams or gels may also help.
These home care will help manage knee swelling and prevent it from becoming chronic.
Preventing Future Knee Problems
One of the best way to reduce the risk of knee problems is to be healthy. Excess weight puts additional stress on the knee joints, carrying weight and increasing the chances of swelling and injury. Regular exercise and balanced diet are key to being healthy.
Besides weight management, wearing proper shoes, avoiding high impact activities and doing regular stretching and strengthening exercises can reduce the risk of knee injuries.
These will maintain the strength and flexibility of the knee joint and make it less prone to damage.
When to See a Doctor
While many cases of knee swelling can be managed at home, there are times when you need professional medical attention. See a doctor immediately if you have severe pain, significant swelling or can’t bear weight on the affected knee. These are signs of severe injury or underlying medical condition that needs to be evaluated immediately.
If symptoms persist after a few days of home care, see a healthcare provider. Signs of infection like redness, warmth and fever with knee swelling needs urgent evaluation.
Consulting a specialist in musculoskeletal and joint problems will give you a targeted evaluation and treatment plan for your condition. Seeking professional care when needed will give you the best outcome for your knee health.