A bruise, also known as a contusion, occurs when tiny blood vessels beneath the skin rupture, leading to blood leaking into the surrounding tissues. This pooling of blood causes the characteristic skin discoloration. Knees are particularly susceptible to bruising due to their exposed position and the minimal layers of fat and muscle that protect the underlying bone structure. This makes them prone to injury from direct impact during daily activities.
Everyday Reasons for Knee Bruises
Knees frequently encounter minor impacts. A common cause is bumping into objects like furniture or doorframes, which can damage small capillaries beneath the skin. Even a slight impact can lead to a visible bruise, especially if the individual has skin that bruises easily.
Minor falls are another frequent source of knee bruises. Landing on a hard surface can cause significant impact, leading to a contusion. These injuries often resolve with home care like rest and ice.
Sports and physical activities also contribute to knee bruising. Activities involving kneeling, such as gardening, cleaning, or certain sports, can cause repetitive pressure or direct trauma. The lack of thick padding over the kneecap means the skin is under considerable stress, and direct pressure can rupture small blood vessels.
Repetitive strain on the knee can also lead to bruising over time. These everyday occurrences highlight the knee’s vulnerability. Most bruises from these activities are superficial and heal naturally within days to weeks.
Underlying Medical Considerations
While many knee bruises result from everyday impacts, some medical factors can contribute to easy or unexplained bruising. Certain medications can interfere with the body’s ability to clot blood, increasing the likelihood of bruising. These include blood thinners like warfarin, rivaroxaban, and apixaban, which are prescribed to prevent blood clots. Nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen and naproxen, along with certain antidepressants, can also affect platelet function, making bruising more common. Corticosteroids, which reduce inflammation, may thin the skin, increasing bruising susceptibility.
Nutritional deficiencies can also play a role in easy bruising. A lack of vitamin C, for instance, can weaken blood vessel walls, making them more prone to rupture, a condition historically associated with scurvy. Insufficient vitamin K can impair clotting mechanisms, as it is essential for producing coagulation proteins.
Underlying medical conditions may also lead to increased bruising. Bleeding disorders, such as hemophilia or von Willebrand disease, directly affect blood clotting and can cause frequent or large bruises. Conditions like low platelet count (thrombocytopenia), liver disease, and certain autoimmune conditions (e.g., lupus, vasculitis) can also increase bruising due to compromised blood vessel integrity or clotting.
When to Seek Medical Attention
While most knee bruises are harmless and resolve on their own, certain signs warrant medical evaluation. Seek attention if a bruise is unusually large, causes severe pain, or has significant, persistent swelling. Bruises appearing without a clear reason, especially if frequent or in unusual areas (e.g., chest, abdomen, back), should be investigated.
Medical attention is advised if a bruise does not improve within a few weeks (2 to 4 weeks), or if it gets larger or more painful. Additional symptoms like fever, redness, warmth, or pus around the bruised area could indicate infection. If bruising occurs alongside other symptoms like nosebleeds, bleeding gums, blood in urine or stool, or extreme fatigue, these may signal a widespread issue. Any bruising following significant trauma or suspected broken bone also warrants a medical visit.
Caring for a Bruised Knee
Caring for a bruised knee involves simple self-care measures to manage symptoms and support healing. Immediately after the injury, applying ice to the affected area can help reduce swelling and discomfort by constricting blood vessels. Apply an ice pack, wrapped in a thin towel, for 15 to 20 minutes at a time, several times daily.
Resting the injured knee by avoiding painful activities is beneficial. Elevating the knee above heart level, if possible, can minimize swelling by assisting fluid drainage. Light compression, such as wrapping with a soft bandage, can also limit swelling, but avoid wrapping too tightly to prevent restricted circulation.
Over-the-counter pain relievers (e.g., acetaminophen, ibuprofen) can manage pain and inflammation. As the bruise heals, it typically changes colors from reddish-purple to bluish-black, then greenish-yellow, eventually fading to light brown. This color progression indicates the body’s natural process of breaking down and reabsorbing pooled blood. Most bruises heal within a few weeks; bone bruises can take longer, potentially one to two months, and may be more painful.