Updated November 03, 2014.

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

The words 'bone bruise,' also bone marrow edema or bone contusion, are often used by doctors or read in medical reports.  Many patients find these words confusing and wonder what it means to have a bone bruise?

Bone Bruise

There is controversy about exactly what a bone bruise is, are they all the same, and why did they occur?  Prior to MRIs being performed, there was no test for a bone bruise, and therefore, the condition was not well recognized.

  When MRI tests started to be performed, doctors were able to 'see' an abnormality in the bone that was described as bone bruising.

A bone bruise is thought to occur when there is microscopic fracturing of the internal bone structure.  While these microfractures don't significantly weaken the bone, it can cause bleeding and inflammation within the bone.  This can lead to pain and symptoms similar to a more familiar soft-tissue bruise.  The most appropriate way to refer to this finding on an MRI is "bone marrow edema."

Causes of Bone Marrow Edema

There are three main reasons why people can get bone marrow edema.

• Traumatic Injury.  Trauma is a common cause of bone marrow edema.  The trauma may be the result of repetitive overuse, or it may be the result of an acute injury.  One of the most common causes of a bone bruise seen on a knee MRI is a ligament injury such as an ACL tear.  When the ACL is torn, the bones suddenly shift causing a compression injury and a very specific pattern of bone marrow edema.  In fact, when MRIs were less clear, and the ACL was harder to visualize, doctors looked for this pattern of bone bruise to diagnose a torn ACL.  Today's MRIs are much better quality, and seeing the torn ACL is much easier, but the bone bruise pattern is still helpful to confirm the injury.

• Arthritis.  Arthritis causes damage to the cartilage surface of the joint.  This protective surfaces helps to shield and cushion the underlying bone.  When this cartilage surface is damaged or worn this, the bone around the joint may be exposed to higher stress and may succumb to the increased burden.  Patients with arthritis often have evidence of bone bruising in the areas most affected by their condition.
• Osteonecrosis.  Osteonecrosis is a specific condition that causes interruption of the blood supply to the bone.  The lack of blood flow can lead to weakening on the bone.  If the bone becomes weak, it may sustain the microfractures from lack of strength of the structure of the bone.  These microfractures may cause bone marrow edema surrounding the area of osteonecrosis.

Treatment of Bone Bruising

Damaged bone needs rest and relief from stress.  When bone bruising is seen on an MRI, the bone is damaged and should be allowed to heal.  It is very difficult to predict how long bone bruising takes to resolve, and there are some conditions where the bone bruising may be indefinitely persistent.  The bone bruising after an ACL tear may be present for several months after the injury, and the bone bruising of arthritis or osteonecrosis may persist so long as those conditions are present.

Most surgeons recommend limiting activity when bone bruising is found around a joint.  In these cases, there is often concern about damage to the cartilage of the joint.  Further damage to the bone supporting the cartilage can lead to a condition called post-traumatic arthritis.  Therefore, most orthopedists will recommend allowing the symptoms of a bone bruise to completely resolve before resuming athletic activity.