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The word bone bruise probably conjures images of some purpling discolouration of the skin. But the word "bone bruise" is a misnomer, making the injury seem less traumatic than it actually is. While we often think of a "bruise" as being a minor injury of the skin, a bone bruise is a more serious and painful injury, involving the bone and muscle, that can take a long time to heal and could even lead to the death of the bone.
What is a "bone bruise"?
A bone bruise is actually a small fracture of an inner-layer of bone.
Broadly speaking, you have two layers of bone:
- The outer-layer is called the "compact" bone. It is extremely strong.
- The innermost layer of bone is called the cancellous bone. It is spongy and, unlike the outer-layer (which is arranged in concentric layers), is arranged in plates. These plates form an irregular mesh, which isn't as strong as the "compact" outer-layer and chips easily.
In a bone bruise, tiny fractures (like cracks or chips) form in the cancellous bone as a response to stress or injury. If enough of the small small fibres that comprise a bone break apart, there will be a bone bruise.
Three possible types of bone bruise
There are three possible types of bone bruise:
- Subperiosteal Hematoma: where blood builds up in the area beneath your periosteum (a thin layer that covers most bones, except the long bones).
- Subchondral bone bruise: where there is bleeding and swelling in the area between your cartilage and the bone beneath.
- Interosseous bone bruise: where bleeding and swelling occurs in the marrow of your bone.
Causes of a bone bruise?
A bone bruise can result from any injury where there is direct force, but not force enough to break the outer-bone. The following kinds of injuries may cause a bone bruise:
- Sports injuries: especially when players collide at high velocity. Football and rugby players are especially prone to bone bruises.
- Twisting injuries: When you sprain an ankle or knee, bones collide forcefully causing a bone bruise.
- High velocity trauma: any blunt force injury may cause a bone bruise (a car accident, a fall, or something falling onto you from a height).
Arthritis patients are also prone to bone bruises. This is because bone surfaces are unprotected in arthritis, leading bones to grind against each other.
Where do bone bruises occur?
Bone bruises most commonly occur in the knee or femur (thighbone). They are also very common in the ankle. However, they can also occur in the: hipbone, wrist, heel, foot, and shoulder.
Symptoms of Bone Bruise
- Pain: As with all trauma, bone bruises hurt. They hurt far more than just regular bruising on the skin and muscle, and pain may be the first sign that your injury is more than a minor sprain. With bone bruises, the pain can last for weeks, or even months.
- Soft tissue swelling
- Discolouration: At first your skin may look blue or purple, due to the blood pooling beneath the skin (but may not if the injury is especially deep); as the injury is healing, the discolouration will be yellow or green in hue.
- Swelling or stiffness of the injured joint
Risks of Bone Bruises
With correct treatment, most bone bruises heal very well. However, a very large untreated bone bruise may cause problems in getting blood flow to the area. This could lead to "avascular necrosis" and the eventual death of the bone. If you don't rest and take the appropriate steps, there's also the risk that your bone bruise may lead to a full fracture.