Bone Marrow Edema in the Knee

Bone Marrow Edema sounds scary.  Many people come into the office with their MRI reports and worry that something is wrong with their bone marrow.

Bone Marrow Edema is simply a condition where fluid is found within the bone.  That’s it.  It’s a very non-specific finding.  In the vast majority of circumstances it is not dangerous.   Like our muscles after a long run or our joints if they are wearing out, the bone can become sore too. In the picture to the right, you are looking at a knee, and the arrows are pointing to the fluid in the bone, or bone marrow edema. Bone marrow edema can however be very painful.

What Causes of Bone Marrow Edema?

Bone marrow edema occurs for three main reasons.

• The first is trauma.  If you suffer a significant injury something may hit your bone, or the two bones might be crushed together.  Either way, the bones will not be happy.  They will develop fluid within them in response to the injury.  Bone, in that respect, is not very different from our other tissues like muscles which collect fluid after an injury.
• The second most common cause of bone marrow edema is osteoarthritis.  In a healthy knee, the bones are covered in cartilage.  In an arthritic knee that cartilage has become thin, or absent. In that situation, the bone is under more stress. If the stress exceeds the capacity of the bone to support the weight then a stress reaction, or stress fracture occurs.  That stress reaction or fracture shows up as bone marrow edema.
• “Osteonecrosis”: Osteonecrosis literally means “bone death”.  That means that a small blood vessel in the bone was choked off somehow, and a small piece of bone dies.  It is not as catastrophic as it sounds, but it produces a lot of bone marrow edema… and it can be quite painful.

Does Bone Marrow Edema Hurt?

When your muscles are injured, and fluid collects in the muscle — the muscle will swell.  You have all had this at one time or another.  Well.. bones are hard. Bones can not swell. So if there is fluid in the bone, the pressure inside the bone goes up.  When the pressure in the bone rises because of the bone marrow edema, severe pain will occur.  For those of you who have had a tooth abscess … that is what pressure pain feels like.

In many patients with osteoarthritis, especially those of you with very little swelling in the knee, it is likely that the bone marrow edema is bothering you more than the osteoarthritis, or inflammation in the knee joint.  Usually, a physical exam will show that you are more tender over the bone, as opposed to being tender over the joint where the two bones meet.

Does Bone Marrow Edema Need to be Treated?

After trauma, the bone marrow edema will subside on its own.  Just like most any other bruise you have had.   In osteonecrosis, the bone marrow edema will also subside.  In many cases of osteonecrosis, the bone will grow new blood vessels and regrow itself.  Sometimes the area involved is too large, and it may not regrow. Osteoarthritis, on the other hand, is a progressive condition. Sadly, it only gets worse over time.  That means that the edema in the bone is unlikely to improve either. In cases of severe pain that are thought to be due to bone marrow edema, certain treatments might improve your pain dramatically. Therefore treatment is not always necessary for bone marrow edema, it depends on the cause of the edema and the severity of your pain.

How is Bone Marrow Edema Treated?

The initial treatment of bone marrow edema is not very different from the treatment of most bruises. Rest, ice, medications, activity limitation, and possibly a crutch or a cane. In cases of trauma, and many cases of osteonecrosis, that will suffice.  In patients with bone marrow edema due to osteoarthritis, the pain might not improve on its own.  If your pain has not improved and your quality of life is suffering, you may prove to be a candidate for a procedure known as a “Subchondroplasty”.

During  a subchondroplasty, we use an X-ray machine to find the area of bone where the edema is.  A small needle is placed  into the bone (under sedation), and a paste is injected.  That paste will harden shortly after the procedure.  Once the paste has hardened, it will give the bone significantly more strength.  By improving the strength of the bone, it will enable the bone to deal with the added stress due to the osteoarthritis.  If the procedure is successful, and the bone is stronger, then the bone marrow edema will subside.  Once the bone marrow edema subsides, your pain should improve dramatically. The early clinical trials and our experience show this to be a safe and effective procedure.  Of course, complications can arise,  so you will need to determine if the potential risks are worth it.  We need more research, and more time to determine if this could be a long term solution for pain due to bone marrow edema.