Swollen Knee: Symptoms, Causes and Treatment

A swollen knee—sometimes called "knee effusion" or "water on the knee"—is a common condition that can affect people of all ages and activity levels. Whether your swelling comes on suddenly after an injury, or has been building up slowly due to chronic conditions, understanding the symptoms, causes, and best treatment options is essential for effective management and a faster return to mobility.

In this comprehensive guide, we'll explore what to look for, why knees swell, and the most up-to-date, evidence-based treatments available.

Symptoms of Swollen Knee

A swollen knee often announces itself with unmistakable signs, but there are subtle clues you shouldn’t ignore. Early recognition of symptoms can be crucial—helping you seek timely medical care, prevent complications, and ensure the best outcomes for your joint health. Sometimes, swelling is accompanied by pain, warmth, or redness, while in other cases, the knee may simply feel stiff or "full."

Below is a concise summary of the key symptoms associated with a swollen knee.

Symptom	Description	Additional Signs	Source(s)
Swelling	Noticeable increase in knee size	May be localized or diffuse	3 5 10
Pain	Discomfort or aching in the knee	Can be sharp or dull	5 10
Warmth	Knee feels warmer to the touch	Sometimes with redness	3 5 10
Stiffness	Reduced flexibility or range of motion	Difficulty bending/straightening	6 9
Redness	Skin appears redder over the knee	Often with warmth/swelling	5 10
Limited Motion	Difficulty moving the knee	Stiffness, locking	9 10
Tenderness	Soreness to touch	Especially on pressure	10

Table 1: Key Symptoms of Swollen Knee

Swelling

Swelling is the hallmark symptom. It can be obvious, with the knee looking puffy, or more subtle, with just a bit of fullness. Swelling can occur inside the joint (effusion) or in the surrounding soft tissues. Sometimes, swelling is most evident above the kneecap or on either side of the joint 3 5 10.

Pain and Tenderness

Pain often accompanies swelling, but not always. The discomfort may range from a dull ache to sharp, intense pain, especially with movement or when pressing on the knee. Tenderness is often felt when the knee is touched or when weight is placed on it 5 10.

Warmth and Redness

A swollen knee might feel warmer than the surrounding skin. Redness can also develop, especially if inflammation or infection is present. These signs usually mean that the body is mounting a response to injury, infection, or another underlying issue 5 10.

Stiffness and Limited Motion

As fluid builds up, the knee can become stiff and difficult to bend or straighten. People often report a "tight" feeling or a sense of fullness that limits everyday activities, such as walking, climbing stairs, or squatting 6 9.

Other Notable Symptoms

• Locking or Catching: Sometimes the knee gets stuck in a certain position due to swelling or structural problems.
• Clicking or Popping: Audible sensations may occur with movement.
• Weakness or Instability: Chronic swelling can weaken the muscles around the knee, leading to a sense of instability.

Recognizing the pattern and combination of symptoms can help guide further evaluation and management.

Causes of Swollen Knee

A swollen knee is not a diagnosis by itself—it’s a sign of an underlying problem. The causes are varied, ranging from injuries, infections, and inflammatory diseases to less common issues such as rare tumors or systemic conditions. Identifying the right cause is critical for targeted treatment.

Here's a summary table of the common and some rare causes of swollen knees.

Cause Type	Example(s)	Typical Features	Source(s)
Traumatic	Ligament tears, fractures, meniscus injury	Sudden onset after injury	5 10
Inflammatory	Rheumatoid arthritis, gout	Red, hot, tender, recurrent episodes	3 5 10
Infectious	Septic arthritis	Severe pain, fever, rapid swelling	5 10
Degenerative	Osteoarthritis	Chronic, intermittent swelling	6 9
Post-Surgical	After total knee arthroplasty (TKA)	Persistent swelling post-operation	1 8 9
Vascular	Poor venous return, DVT	Swelling with/without pain, risk of clot	1 8
Hematoma	Joint bleeding (hemarthrosis)	Swelling after injury or surgery	1 4 5
Rare Conditions	Synovial hemangioma, endometriosis	Unusual, may require imaging/biopsy	2 4

Table 2: Common and Rare Causes of Swollen Knee

Traumatic Causes

• Acute Injury: Most commonly, swelling develops after trauma such as falls, sports injuries, or accidents. Ligament sprains, meniscus tears, and fractures are leading culprits 5 10.
• Hemarthrosis: Bleeding into the joint space (often after severe injury or in people with bleeding disorders) can rapidly cause a tense, swollen knee 5.

Inflammatory Causes

• Rheumatoid Arthritis: A systemic autoimmune disease that often causes swelling, pain, and warmth in multiple joints, including the knee 3.
• Gout and Pseudogout: Crystal-induced inflammation can cause dramatic, sudden-onset swelling, redness, and intense pain in the knee 3 5 10.
• Other Systemic Conditions: Psoriatic arthritis, lupus, and reactive arthritis are less common but can also cause knee effusions.

Infectious Causes

• Septic Arthritis: Infection within the knee joint is a medical emergency. It presents with severe pain, marked swelling, heat, and often fever 5 10.
• Lyme Disease: In some regions, Lyme arthritis can cause recurrent knee swelling.

Degenerative Causes

• Osteoarthritis: The most common chronic knee condition, osteoarthritis leads to intermittent swelling, stiffness, and pain, especially after activity 6 9.
• Chronic Meniscal Injury: Long-standing cartilage damage can result in repeated episodes of swelling.

Post-Surgical and Iatrogenic Causes

• Post-TKA Swelling: Swelling is common after total knee arthroplasty (TKA), caused by inflammation, hematoma, muscle damage, or poor venous return 1 8 9.
• Other Surgeries: Any knee surgery can cause swelling as part of the healing process.

Vascular and Hematologic Causes

• Deep Vein Thrombosis (DVT): Clot formation in the leg veins may cause swelling, sometimes in the knee area 1 8.
• Poor Venous Return: Chronic venous insufficiency can also contribute to persistent swelling.

Rare and Unusual Causes

• Synovial Hemangioma: A rare benign vascular tumor inside the joint may mimic other causes of swelling and is best diagnosed with imaging 4.
• Intra-articular Endometriosis: Rarely, endometrial tissue can be found in the knee, causing cyclical swelling associated with menstruation 2.
• Menstrual Arthritis: Another rare condition where knee swelling recurs with the menstrual cycle due to inflammatory mediators 2.

Diagnostic Approach

• History and Examination: Detailed questioning about the onset, duration, and associated symptoms, along with thorough physical examination, are crucial 3 10.
• Laboratory Tests: Blood tests may reveal inflammation, infection, or systemic disease 1.
• Imaging: X-rays, ultrasound, and MRI can help identify structural, infectious, or neoplastic causes 1 4 10.
• Joint Aspiration (Arthrocentesis): Removing and analyzing joint fluid can be diagnostic and sometimes therapeutic, especially in suspected infection or crystal disease 10.

Treatment of Swollen Knee

Treating a swollen knee is not a one-size-fits-all process. The underlying cause, severity, and patient’s overall health influence the best approach. From home remedies to advanced medical and surgical interventions, the goal is to reduce swelling, relieve pain, and restore function as quickly—and safely—as possible.

Below is a summary table of evidence-based treatment strategies.

Treatment Type	Examples/Approaches	Best Used For	Source(s)
Conservative	Rest, ice, compression, elevation (RICE); NSAIDs	Mild-moderate swelling, most initial cases	5 6 8 9
Physical Therapy	Exercise, range-of-motion, strength training	Chronic or post-surgical swelling	6 8 9
Compression Therapies	Intermittent pneumatic compression, compression garments, Kinesio taping	Post-surgical, osteoarthritis-related swelling	6 8 9
Medical Management	Antibiotics, anti-inflammatories, colchicine, steroids	Infection, inflammatory arthritis, gout	5 10
Aspiration	Joint fluid removal	Severe swelling, diagnostic/therapeutic	10
Surgical Intervention	Arthroscopy, hemangioma excision, joint replacement	Structural, neoplastic, or refractory cases	4 5 10

Table 3: Treatment Options for Swollen Knee

Conservative and Home-Based Care

• RICE Protocol: Rest, ice application, compression (with bandages or wraps), and elevation are foundational for managing most acute or mild cases of knee swelling 5.
• Nonsteroidal Anti-inflammatory Drugs (NSAIDs): These medications help reduce pain and inflammation.

Physical Therapy and Rehabilitation

• Exercise & Movement: Early, guided range-of-motion and strengthening exercises help restore function and reduce swelling over time, especially after surgery or injury 6 8 9.
• Manual Lymphatic Drainage (MLD): Specialized massage techniques can help move excess fluid out of the knee after surgery 8.

Compression Therapies

• Intermittent Pneumatic Compression (IPC): Devices that rhythmically squeeze the leg can significantly reduce swelling in osteoarthritis and after TKA, outperforming cold-pack therapy 6 7.
• Compression Garments: Adjustable, inelastic compression braces can help maintain reduced swelling and support healing 8.
• Kinesio Taping: Applied by trained professionals, this elastic tape technique aids subcutaneous fluid drainage, especially following knee surgery 9.

Medical Management

• Antibiotics: Essential in treating septic arthritis or when infection is confirmed or suspected 5 10.
• Steroids and Disease-Modifying Agents: Used for autoimmune or inflammatory causes like rheumatoid arthritis or gout 3 5.
• Colchicine or Other Specific Medications: For crystal-induced arthritis such as gout.

Joint Aspiration (Arthrocentesis)

• Fluid Removal: Drawing fluid from the knee can relieve pressure, reduce pain, and provide a sample for diagnosis 10.

Surgical Options

• Arthroscopy: Minimally invasive surgery can treat meniscal tears, remove loose bodies, or address persistent effusions.
• Tumor Excision: For rare causes like synovial hemangioma, surgical removal is definitive 4.
• Total Knee Replacement: For end-stage osteoarthritis or when structural damage is severe.

Post-Surgical & Chronic Swelling Management

• Multimodal Swelling Interventions: Combining compression, manual lymph drainage, and home exercise has been shown to reduce swelling and improve outcomes after total knee replacement 8.
• Patient Education: Knowing when to seek urgent care (e.g., for signs of infection or severe pain) is critical.

Special Notes on Monitoring and Prevention

• Regular Follow-Up: Especially important after knee surgery or if underlying conditions (like rheumatoid arthritis) are present.
• Early Mobilization: Helps prevent complications like deep vein thrombosis (DVT) and accelerates recovery 8.

Conclusion

Swollen knees are a common problem, but their impact on daily life and long-term joint health should not be underestimated. By recognizing key symptoms, understanding the diverse causes, and applying targeted, evidence-based treatments, you can take effective steps toward relief and recovery.

Key takeaways:

• Knee swelling is a symptom, not a diagnosis. Identifying the cause is critical for proper management.
• Symptoms include swelling, pain, warmth, stiffness, redness, and limited motion.
• Causes range from injuries and arthritis to rare conditions and post-surgical changes.
• Treatment must be tailored—from RICE and physical therapy to advanced interventions like pneumatic compression or surgery.
• Prompt medical evaluation is needed for severe pain, rapid swelling, fever, or suspicion of infection.
• New treatments like intermittent pneumatic compression and multimodal interventions offer promising results for chronic and post-surgical swelling.
• Patient education and ongoing monitoring are essential for long-term knee health and function.

With the right knowledge and approach, most people can manage a swollen knee effectively and return to the activities they love.