Overview

Swollen knee, medically known as knee effusion, refers to the accumulation of excess fluid in or around the knee joint. This condition can develop suddenly due to an injury or progressively as a result of underlying medical conditions. A swollen knee can cause pain, stiffness, and difficulty in movement, significantly impacting a person’s ability to perform daily activities. It is a common complaint among individuals of all ages, especially athletes and older adults. While some cases resolve with home treatment, others may require medical intervention to address the underlying cause and prevent long-term joint damage.

Causes

Swelling of the knee can occur due to a variety of reasons, which can be broadly categorized into injuries, medical conditions, and infections:

• Injuries:
  • Ligament injuries (e.g., ACL tear)
  • Meniscus tear
  • Fractures or dislocations
  • Overuse injuries from repetitive stress
• Arthritis:
  • Osteoarthritis, due to cartilage degeneration
  • Rheumatoid arthritis, an autoimmune condition
  • Gout, caused by uric acid crystal buildup
  • Pseudogout, caused by calcium pyrophosphate crystals
• Infections: Septic arthritis, where the joint becomes infected, causing rapid swelling and severe pain.
• Bursitis: Inflammation of the small fluid-filled sacs (bursae) near the knee joint, commonly from pressure or overuse.
• Cysts: Baker’s cyst, a fluid-filled swelling behind the knee, can cause noticeable swelling especially during movement.
• Obesity: Excess body weight increases stress on the knee joint, contributing to wear and tear and inflammation.

Symptoms

The primary symptom of a swollen knee is visible enlargement of the knee joint. Other associated symptoms may include:

• Pain: Ranging from mild discomfort to severe pain, especially when putting weight on the knee.
• Stiffness: Reduced range of motion, making it difficult to bend or straighten the knee fully.
• Warmth and redness: The swollen area may feel warm to touch and appear red, particularly in infections or inflammation.
• Instability: The knee may feel weak or unstable, especially after an injury.
• Difficulty walking: Limping or inability to bear weight due to pain and swelling.

Diagnosis

Diagnosing the cause of a swollen knee involves a detailed medical history, physical examination, and diagnostic tests:

• Physical examination: The doctor checks for swelling, tenderness, warmth, and range of motion in the knee.
• Medical history: Information about recent injuries, physical activity, medical conditions, and previous joint issues is collected.
• Imaging tests:
  • X-rays: To identify fractures, arthritis, or joint alignment issues.
  • MRI: Provides detailed images of soft tissues like ligaments, tendons, and cartilage.
  • Ultrasound: Useful for detecting fluid accumulation and cysts.
• Joint aspiration (arthrocentesis): A sample of fluid from the knee joint is withdrawn and analyzed to check for infection, crystals, or inflammation markers.
• Blood tests: Used to identify underlying conditions such as gout, rheumatoid arthritis, or infections.

Treatment

Treatment for a swollen knee focuses on relieving symptoms, addressing the underlying cause, and restoring function:

• Home care:
  • Resting the knee and avoiding activities that worsen the pain.
  • Applying ice packs to reduce swelling and inflammation.
  • Compression bandages to control swelling.
  • Elevation of the leg to minimize fluid accumulation.
• Medications:
  • Non-steroidal anti-inflammatory drugs (NSAIDs) like ibuprofen for pain and swelling.
  • Corticosteroid injections for severe inflammation.
  • Antibiotics if an infection is diagnosed.
• Physical therapy: Exercises to improve strength, flexibility, and joint stability after the acute swelling reduces.
• Joint aspiration: Removing excess fluid can relieve pressure and aid in diagnosis.
• Surgery: In cases of severe injury, advanced arthritis, or persistent swelling, procedures like arthroscopy or joint replacement may be necessary.

Prognosis

The prognosis for a swollen knee depends on its underlying cause and timely treatment. For minor injuries or overuse cases, full recovery is common with rest and conservative management within a few weeks. Chronic conditions like arthritis may require ongoing care to manage symptoms and prevent flare-ups.

When promptly diagnosed and treated, infections and inflammatory causes can be resolved without long-term consequences. Untreated or recurrent swelling may lead to joint stiffness, weakness, and long-term mobility issues. Following medical advice, maintaining a healthy weight, and engaging in joint-friendly activities can significantly improve long-term outcomes and joint health.