Most knee bruises are mild and heal on their own, but some can be severe. Steps that can support healing include rest, ice, compression, and elevation (RICE). However, some bruises may need medical attention.
Bruises are a type of injury that typically appear as an area of skin discoloration. They often occur following trauma or impact, which causes damage to the underlying blood vessels.
The knee is a fairly common site to develop a bruise. As well as discoloration, a bruised knee may cause pain and difficulty walking. In most cases, a bruised knee is treatable with sufficient rest and support, and a person will usually recover in a few weeks.
What is a bruise?
A bruise or contusion forms when small blood vessels under the skin break, but the skin remains intact. Blood leaks out of these broken capillaries into the surrounding soft tissues, which causes discoloration.
There are three types of bruises:
• subcutaneous, which occur just under the skin’s surface
• intramuscular, occurring within the underlying muscle
• periosteal, or bone bruises, which are an injury to the bone
A bone bruise is typically the most painful type of bruise. Doctors can only detect these using magnetic resonance imaging (MRI), as they are not easily visible on X-rays.
A bruise on the knee may occur because of damage to the skin, tendons, ligaments, or the bone of the knee cap. For example, a knee injury may cause a tear in the anterior cruciate ligament, in addition to bruising.
What do knee bruises look and feel like?
A bruise on the knee may appear black, blue, or purple on lighter skin, or dark purple or brown on darker skin. Bruises may change color as they heal, turning yellow or green.
In addition to discoloration, the most common signs of bruising include pain and swelling. A knee bruise may also trigger other symptoms such as:
• tenderness
• stiffness
• weakness
• a lump, or hematoma, caused by blood pooling in the area
If there is a bone bruise, the knee may be particularly stiff, swollen, and take longer to heal. However, with no other symptoms, most bruises are usually not serious and typically heal on their own.
Causes of knee bruises
Bruises to the knee generally occur from direct blows to the knee area involving something blunt. This may occur due to a fall or when a person bangs their knee into something hard.
Bruising can also develop alongside other types of common knee injuries, such as:
• meniscus injuries
• anterior cruciate ligament (ACL) injuries
• lateral collateral ligament (LCL) injuries
• medial collateral ligament (MCL) injuries
• dislocating the kneecap
Older adults are more likely to bruise than younger adults. Additionally, people may bruise more easily than others. This may be due to taking certain medications or having certain nutritional deficiencies.
Bruises without any injury
Sometimes, people develop bruises and forget how they occurred. However, some bruise-like markings on the skin that do not result from an injury may be due to blood spots, also known as purpura.
Purpura is not the same as bruising, although they look similar. This symptom can occur due to a range of conditions, including:
• medications that thin the blood, such as aspirin or warfarin
• malnutrition and vitamin deficiencies
• inflammatory conditions, such as lupus
• inflamed blood vessels, or vasculitis
• a bleeding or clotting disorder, such as hemophilia
• liver disease, such a cirrhosis
• infections that cause toxins to build up in the blood, such as sepsis
• some types of cancer, such as leukemia
If a person notices red or purple patches under the skin that they cannot explain, it is best to consult a doctor.
How to treat a bruised knee
The RICE method is an appropriate treatment for bruising, as it may help reduce symptoms and aid healing. The RICE method stands for:
• Rest: rest the knee joint
• Ice: cool the area with a compress or ice pack wrapped in a towel for 20 minutes at a time, several times per day
• Compression: lightly wrap the knee in a soft bandage
• Elevation: Raise the knee above the level of the heart, if possible, to prevent blood from pooling
• Do not apply ice directly to the skin, or try to drain the bruise of blood using a needle. If there is a large lump that does not decrease in size after several days, a doctor may need to drain it.
• How long do bruised knees take to heal?
In many cases, most bruises are minor and may heal within a few days. However, more serious bruising will require a longer recovery time and will take longer to before a person can return to their activities.
Depending on the extent of damage to the knee, it may take up to 6 weeks to recover. For example, a bone bruise may take as long as 1 to 2 months or longer if the bruise is large.
How to tell the difference between a bruised knee and a fracture
Sometimes, a direct blow to the knee causes a sprain or a kneecap fracture. It may be difficult to tell the difference between these injuries.
A kneecap or patella fracture can cause:
• pain on and around the kneecap
• pain when moving the knee in any direction
• Swelling
• difficulty extending the leg
• a deformed appearance due to broken pieces of bone
If a person has a sprain or kneecap fracture, severe pain, bruising, or swelling will set in quickly after the injury. A doctor can determine if someone has a fracture with an X-ray.
Treatment for a fractured kneecap may involve surgery to repair the broken bones or replacing all or part of the kneecap.
When to seek medical help
A person should consult a doctor if:
• a knee bruise does not improve within 6 weeks
• they develop a large hematoma on the knee that does not decrease in size after a few days
• their knee shows signs of a fracture or more serious injury, such as severe pain or swelling
• they develop red or purple or discolored patches that are not due to an injury
• the knee shows signs of infection, such as swelling, pus, and warmth
A person should seek emergency medical care if they experience extremely painful swelling in the muscles in the foot, leg, buttocks, or arms.
This may be the result of compartment syndrome, a rare but serious condition that requires immediate treatment.
Summary
A bruised knee is typically a minor injury that heals on its own in a few weeks. A bone bruise may cause more pain and take longer to heal.
The RICE approach may help relieve symptoms and promote healing in knee injuries. However, if there is severe pain and swelling, or the bruise is not due to an injury, a person should speak with a doctor.
