Causes

Many types of problems, ranging from traumatic injuries to diseases and other conditions, can cause a swollen knee.

Injuries

Damage to any part of your knee can cause excess joint fluid to accumulate. Injuries that can cause fluid buildup in and around the knee joint include:

• Torn ligament, particularly the anterior cruciate ligament (ACL)
• Cartilage (meniscus) tear
• Irritation from overuse
• Broken bones

Diseases and conditions

Underlying diseases and conditions that can produce fluid buildup in and around the knee joint include:

• Osteoarthritis
• Rheumatoid arthritis
• Infection
• Gout
• Pseudogout
• Bursitis
• Cysts
• Tumors