A sprained knee occurs when one or more of the ligaments that stabilize the joint are stretched or torn, usually due to a sudden twisting or impact. The body’s immediate reaction to this internal damage is to initiate an inflammatory response, which manifests visibly as swelling. Understanding the duration of this swelling is often a primary concern for those managing a knee injury, but the timeline is highly variable and directly linked to the extent of the ligament damage.
What Causes Swelling in a Sprained Knee
Swelling following a knee sprain is the direct result of acute inflammation. When a ligament is damaged, tiny blood vessels rupture, causing blood and fluid to leak into the surrounding joint space and soft tissues. Fluid accumulation inside the joint capsule is specifically called an effusion, while buildup in the surrounding soft tissues is edema.
The leaked fluid contains water, proteins, and immune cells that rush to the injury site to begin healing. This influx causes the knee to become visibly puffy, warm, and tender. In more severe sprains, a significant amount of blood can pool inside the joint, a condition called hemarthrosis, resulting in rapid and extensive swelling. The pressure from this swelling contributes to pain and stiffness, limiting the joint’s ability to bend or straighten fully.
Sprain Severity and the Swelling Timeline
The length of time a knee remains swollen is directly dependent on the severity of the ligament injury, which healthcare providers categorize into three grades. Swelling for any acute injury typically peaks within the first 24 to 48 hours, regardless of the grade.
Grade I Sprain
A Grade I sprain involves only a mild stretching of the ligament fibers with microscopic tearing, and the knee joint remains stable. Swelling is often minimal and localized, beginning to resolve quickly after the first two days. Significant swelling typically disappears within three to seven days, although slight residual puffiness may linger for up to two weeks.
Grade II Sprain
In a Grade II sprain, there is a partial tear of the ligament, leading to noticeable swelling and some joint instability. The swelling is more pronounced and takes a longer time to subside, often persisting for one to two weeks. Full resolution of this moderate swelling can take three to six weeks, depending on how the injury is managed.
Grade III Sprain
A Grade III sprain represents a complete tear of the ligament, resulting in massive and often immediate swelling due to internal bleeding (hemarthrosis). Because this is a severe injury, the resolution timeline is much slower and unpredictable, often taking months, especially if surgical intervention is required. The swelling in a Grade III injury requires immediate medical attention to manage the joint fluid and initiate the correct treatment plan.
Strategies for Reducing Knee Swelling
Managing acute swelling effectively in the first few days can significantly shorten the overall duration of the symptom. The initial approach to controlling inflammation centers on the R.I.C.E. method: Rest, Ice, Compression, and Elevation.
Rest and Ice
Rest involves avoiding activities that cause pain and may require the use of crutches to prevent putting weight on the injured leg. Applying a cold compress or ice pack for 15 to 20 minutes every one to two hours helps to constrict blood vessels. This constriction reduces internal bleeding and fluid leakage into the joint space.
Compression and Elevation
Compression, typically achieved with an elastic bandage, provides external support and helps to limit the amount of fluid accumulation. Care must be taken to ensure the bandage is firm but does not restrict circulation. Elevation works by using gravity to drain excess fluid away from the knee. The knee should be elevated above the level of the heart as frequently as possible throughout the day, especially during periods of rest. Additionally, over-the-counter nonsteroidal anti-inflammatory drugs (NSAIDs) can be used to help reduce both the pain and the underlying inflammatory process contributing to the swelling.
Warning Signs That Require Medical Attention
While mild swelling is expected after a knee sprain, certain signs indicate a potentially more serious injury that requires prompt professional evaluation. Swelling that is severe, rapid in onset, or continues to increase or spread beyond 72 hours should be assessed by a healthcare provider.
Inability to bear weight on the injured leg or a feeling that the knee is unstable or “giving way” are signs of a significant ligament tear. Other red flags include a popping sound felt or heard at the time of the injury, or the knee appearing visibly deformed. Watch also for signs of infection, such as fever, increasing warmth, or redness around the joint, as these symptoms require immediate medical intervention.