What Is Bone Marrow Edema?

Older Term for Bone Marrow Lesions

An X-ray of a knee with arthritis.
An X-ray of a knee with arthritis. Science Photo Library - DR P. MARAZZI/Getty Images

The term "bone marrow edema," first used in 1988, refers to a build up of fluid (edema) in the bone marrow. Bone marrow edema is now considered an older term, replaced by the term bone marrow lesions. It is seen on magnetic resonance imaging or ultrasound as the presence of more water than usual in the bone marrow. Several conditions, including osteoarthritis or fracture, can cause bone marrow edema.

Bone Marrow Edema and Prognosis in Osteoarthritis

Not only is bone marrow edema characteristic of osteoarthritis, it also indicates a poor prognosis. An increase in bone marrow edema is strongly associated with worsening condition of the cartilage associated with the bone. The extent of edema often increases over time as well. There appears to be a connection between bone marrow edema and subchondral cysts. Most subchondral cysts develop in areas where there already was subchondral bone marrow edema.

MRI of the affected joint may show bone marrow lesions and edema, which can indicate progression of osteoarthritis. Some researchers believe that the bone marrow edema may be part of the source of pain in knee osteoarthritis, as the bone marrow has many pain receptors while the cartilage does not.

Significance of Bone Marrow Edema to Osteoarthritis

At one point in the history of research, it was unclear if bone marrow edema was associated with worsening knee osteoarthritis.

According to one study, conducted at the Veterans Administration hospital in Boston, Massachusetts, patients with bone marrow edema on an MRI were more likely to develop worsening osteoarthritis over a period of 15 to 30 months than patients without bone marrow edema.

Researchers also found that knee osteoarthritis with malalignment was associated with bone marrow edema and with worsening osteoarthritis.

Bone marrow lesions predicted worsening of osteoarthritis even after researchers accounted for the role malalignment may have played.

In a cohort of study participants from yet another study, known as the Mechanical Factors in Arthritis of the Knee 2 (MAK-2) study, it was found that among patients with knee osteoarthritis, bone marrow lesions were rare in the early stages of osteoarthritis but they were predictive of cartilage loss, even after taking into account other types of bone lesions present within the same region.

Bone Marrow Edema Can Be Associated with Pain in Knee Osteoarthritis

Bone marrow edema may be part of the answer to the question of what is causing pain in knee osteoarthritis. In that process, the articular cartilage is degenerated but it has no nerve fibers that detect pain. It can't hurt because it doesn't have the nerves that would send that signal to the brain.

However, the subchondral bone marrow beneath the cartilage is packed with pain nerve fibers. Edema and other disorders in the bone marrow could clearly be the source of pain. Studies have looked at whether subchondral bone marrow edema is associated with degeneration of the articular cartilage and knee pain.

Bone marrow lesions and edema, as seen on MRI, are associated with the presence of pain and worse articular cartilage defects.


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