A swollen knee is a common problem that occurs when excess fluid builds up in or around the knee joint. Other names for this condition include “knee effusion” and “water on the knee”.

A swollen knee may be the result of overuse injuries, a sudden blow to the knee or an underlying disease or condition.Depending on the underlying condition, it may display no other symptoms or may feel painful and stiff. 

To determine the exact cause of the swelling, a proper diagnosis from a doctor is required. Once the diagnosis is confirmed, appropriate treatment can be recommended.  



When the knee joint contains excess fluid, it may be difficult to bend or straighten the leg completely. Signs and symptoms of water on the knee typically include:


  • Pain in the knee
  • Stiffness in the knee
  • Swelling of the affected knee



There are many factors which can cause a swollen knee. The most common causes are: injuries to the knee and diseases.

Injuries to the knee which can produce excess fluid buildup in and around the knee joint include:


  • Broken bones
  • Irritation from overuse of the knee
  • A torn ligament
  • Cartilage tear


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


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


Risk factors

A few factors that can increase the risk of a swollen knee include the following:


  • Increase in age: The chances of developing a swollen knee related to arthritis increases with age.
  • Participation in certain sports: Distortion of the knee or a sudden blow to the knee from playing certain sports can lead to knee injuries that cause swelling.
  • Being overweight: Excess weight can add pressure to the knee joint and in turn lead to a swollen knee.



Complications of a swollen knee can include:


  • Loss of muscle function
  • Baker’s cyst: A painful fluid filled sac that occurs from buildup of fluid in the knee



A few recommendations that can help manage overall health and prevent injuries include: 


  • Maintaining a healthy weight to ensure no added stress to the knee joint
  • Exercising regularly by participating in certain activities such as water aerobics and swimming
  • Strengthening the muscles around the knee to prevent injuries