Noticing swelling in only one knee can be unsettling, especially when the other knee feels completely normal. Unlike swelling in both knees, which often suggests a systemic issue like arthritis, swelling in just one knee usually points to a localized cause that may need closer attention.

Several common conditions can lead to swelling in a single knee. Injuries such as ligament or meniscus tears are frequent culprits, particularly in active individuals. Repetitive stress can also cause bursitis, where fluid-filled sacs around the joint become inflamed. Another possible cause is a Baker’s cyst, which can result from fluid buildup in the joint.

In some cases, inflammatory conditions like gout or pseudogout may trigger sudden knee swelling. These conditions often cause intense pain and stiffness. Additionally, while arthritis is typically bilateral, it can sometimes affect just one knee, particularly if there has been prior injury or overuse. Tendonitis may also develop for similar reasons.

One particularly serious cause to consider is infection, such as septic arthritis. This can lead to sudden, severe swelling and should be treated as a medical emergency. If the swelling is accompanied by fever, extreme pain, or redness, immediate medical attention is crucial.

For less severe swelling, at-home care using the RICE method (Rest, Ice, Compression, Elevation) can be helpful. Over-the-counter anti-inflammatories may also reduce discomfort. However, if symptoms persist or worsen, consulting a healthcare provider is important to ensure proper diagnosis and prevent long-term damage. Early intervention often leads to better outcomes.