It is possible to get a bone bruise in your knee. A bone bruise, also known as a bone contusion, occurs when the bone itself sustains an injury, distinct from a typical skin bruise. This article will explain what a bone bruise is, how these injuries typically happen in the knee, the symptoms to look for, and methods for diagnosis and treatment.
What Exactly is a Bone Bruise?
A bone bruise, or bone contusion, is an injury to the bone that does not involve a complete break or fracture. Instead, it represents microscopic damage to the bone’s internal structure, specifically the tiny, beam-like supports called trabeculae, and the small blood vessels within the bone. This damage leads to bleeding and fluid accumulation, or edema, inside the bone, which causes pain and swelling. While less severe than a fracture, a bone bruise can still cause significant discomfort and require time to heal.
There are different types of bone bruises, categorized by their location within the bone structure. A subchondral bone bruise occurs beneath the cartilage that covers the ends of bones in a joint, often due to extreme compression or rotational forces. An interosseous or medullary bone bruise involves bleeding and swelling within the bone marrow, the inner part of the bone containing fibrous tissue and blood supply. Lastly, a periosteal bone bruise, also called a subperiosteal hematoma, involves blood collecting beneath the periosteum, which is the dense, fibrous membrane covering most of the bone’s surface.
A key distinction between a bone bruise and a bone fracture lies in the extent of damage. In a bone bruise, only some of the internal bone trabeculae are damaged, sometimes referred to as microfractures, without a visible break line. A fracture, however, means that all the trabeculae in a specific region have broken, resulting in a more severe injury. The force required to bruise a bone is greater than that needed to bruise skin, reflecting the bone’s greater structural integrity.
How Bone Bruises Occur in the Knee
Bone bruises in the knee commonly result from specific mechanisms of injury that exert significant force on the joint. Direct impact, such as falling directly onto the knee or receiving a blunt blow during sports, can cause the bones to sustain internal damage. This type of force can compress the bone tissue, leading to the bleeding and swelling characteristic of a bone bruise.
Twisting injuries are another frequent cause, particularly in sports like soccer or basketball where sudden pivots or changes in direction are common. These rotational forces can cause the bones within the knee joint—the femur (thigh bone), tibia (shin bone), and patella (kneecap)—to impact each other, resulting in bone-on-bone trauma. Hyperextension or hyperflexion of the knee joint, where the knee is forced beyond its normal range of motion, can also lead to bone bruises.
Bone bruises in the knee frequently occur alongside other knee injuries, indicating the high forces involved. For instance, a significant percentage of individuals who tear their anterior cruciate ligament (ACL) also experience a bone bruise in the knee joint, often in the lateral femur and lateral tibia. While often associated with ligament or cartilage damage, bone bruises can also occur as isolated injuries due to trauma or even from repetitive low impacts, such as those sustained during endurance running.
Recognizing and Diagnosing a Bone Bruise
Individuals typically experience localized pain that is deep and persistent, and can be more intense than expected. Swelling around the knee joint and tenderness to the touch over the affected bone are common indicators.
Limited range of motion in the knee or difficulty bearing weight on the injured leg can also indicate a bone bruise. These symptoms can sometimes mimic those of more severe injuries like fractures or ligament tears. A healthcare professional will typically perform a physical examination to assess the knee’s condition and identify areas of pain or swelling.
For a definitive diagnosis, imaging tests are important. While X-rays are often used initially to rule out bone fractures, they do not show bone bruises because these injuries involve microscopic damage rather than a visible break. Magnetic Resonance Imaging (MRI) is the primary method for diagnosis. An MRI can visualize the internal bone edema and bleeding.
Treatment and Recovery
Managing a bone bruise in the knee involves conservative treatment to reduce pain and promote healing. The RICE protocol—Rest, Ice, Compression, and Elevation—is recommended to decrease swelling and discomfort. Resting the knee by avoiding activities that worsen pain allows healing. Over-the-counter pain relievers can help manage any discomfort.
Activity modification plays a role in recovery, avoiding high-impact activities or movements that stress the injured knee. Once the initial pain subsides, physical therapy may be recommended to regain strength, flexibility, and range of motion in the knee joint. Movement, even gentle, is important for nutrient exchange within the joint, which aids the healing process.
Patience is an important aspect of recovery, as bone bruises can take significant time to fully heal. Depending on the severity and location of the bruise, recovery can range from several weeks to many months, often between 4 weeks and 6 months or even longer. Most bone bruises heal without long-term complications, though severe cases can rarely impact blood flow to the bone. It is important to seek medical attention if symptoms persist, pain becomes severe, or if there is an inability to bear weight on the leg, as these could indicate a more serious underlying issue or complications.