What Is Bone Marrow Edema in the Knee?

Bone marrow is a fatty substance found in the center of bones that helps produce new blood cells. Bone marrow edema, also referred to as a bone marrow lesion, is a condition where the normal fatty bone marrow is replaced with a watery material when there is damage to normal bone structure.

This abnormal watery material within the bone marrow results from the leakage of fluid and blood into the bone due to damage to the walls of surrounding capillaries and changes in blood flow to and from the bone marrow. Fluid is more likely to accumulate in the bone marrow when there is also damage to the cortical bone that surrounds the bone marrow cavity.

While bone marrow edema can occur in any bone, it is most frequently observed in the lower limbs, especially within the bones that form the knee joint. Bone marrow edema of the knee can be asymptomatic or painful and is diagnosed via magnetic resonance imaging (MRI).

Causes

Bone marrow edema can result from a variety of different conditions and is classified based on the underlying cause:

• Traumatic: Traumatic bone marrow edema is caused by a traumatic injury to the knee joint resulting in fractures of the tibia or femur, the leg bones that form the knee joint. Fracture of the underlying bones causes increased fluid levels within the knee joint from inflammation and swelling that result from injury as well as damage to the surrounding blood vessels. This excess fluid can replace the normal fatty bone marrow tissue within the leg bones. Dislocation of the kneecap or injuries to the menisci or ligaments of the knee can also increase the risk of developing bone marrow edema in the knee.
• Mechanical or degenerative: Mechanical or degenerative bone marrow edema results from physical changes that damage the bones that form the knee joint and underlying bone marrow. These changes include the development of osteoarthritis, cartilage injury, and bone stress injuries like bone bruises.
• Inflammatory or rheumatic: Systemic, inflammatory rheumatic conditions such as rheumatoid arthritis, psoriatic arthritis, and ankylosing spondylitis that attack the joints and produce widespread inflammation throughout the body can cause inflammation of the bone. This inflammation results in the infiltration of blood cells like lymphocytes, plasma cells, and macrophages into the subchondral bone, which damages the bone marrow tissue, resulting in inflammatory rheumatic bone marrow edema.
• Septic: Septic bone marrow edema can result from infections such as osteomyelitis and septic arthritis, which alter the structure of healthy bone marrow. Factors that increase the risk of developing septic bone marrow edema within the knee include recent joint surgery or injection within the knee joint, presence of a knee replacement, intravenous drug use, and conditions that affect the ability to heal, including diabetes.
• Ischemic: Ischemic bone marrow edema of the knee results from avascular necrosis, where there is a disruption in blood flow to the knee joint. Avascular necrosis can occur following a fracture that damages nearby blood vessels. It can also occur in the absence of trauma and is linked to certain risk factors such as prolonged corticosteroid use, alcohol consumption, chemotherapy, and abnormal blood clotting conditions such as sickle cell disease.
• Neoplastic: Bone tumors within the knee joint can cause neoplastic bone marrow edema as a response to the abnormal, cancerous mass that infiltrates healthy bone tissue. Primary bone cancer, such as osteosarcoma, chondrosarcoma, and Ewing’s sarcoma, is quite rare and primarily occurs in children. Metastasis, or spreading of cancer cells that originate in another part of the body, occurs more frequently from breast, prostate, and renal cancer.

Symptoms

The most common symptom of bone marrow edema in the knee is pain. Bone marrow edema can stimulate nerve fibers in the periosteum, a membrane surrounding the outside of bones, that transmit pain signals. This pain often increases with weight-bearing of the knee joint—with standing, walking, and going up and down stairs—and can limit the overall function of the knee joint.

Bone marrow edema in the knee has been associated with the presence and progression of osteoarthritis in the knee, which can cause further knee pain, stiffness, swelling, weakness, and difficulty performing everyday tasks. Bone marrow edema is also strongly associated with inflammatory autoimmune conditions that attack joints.

Diagnosis

Diagnosis of bone marrow edema is based on the following criteria:

• Thorough medical history to assess risk factors such as prior history of injury to the knee, smoking or alcohol abuse, blood clotting, weight loss, night sweats, infection, or glucocorticoid treatment
• Physical examination to assess vital signs, joint effusion, and signs of local infection such as redness, warmth, swelling, and pain
• Blood work to assess blood cell count and levels of inflammatory markers such as C-reactive protein and erythrocyte sedimentation rate, which are found to be elevated with infections and autoimmune conditions 
• MRI to check for bone marrow edema

The presence of the following factors can help lead to a diagnosis of bone marrow edema in the knee:

• Need for arthrocentesis, a procedure done to remove excess synovial fluid accumulated around a swollen joint
• Presence of osteoarthritis or inflammatory rheumatic diseases such as rheumatoid arthritis, psoriatic arthritis, or ankylosing spondylitis
• Elevated white blood cell count

Imaging

The most effective way to diagnose bone marrow edema is through MRI, which produces an image of bones showing significant contrast in intensity between cells with differing fat and water content. Fluid-containing tissues will appear dark grey or black on T1-weighted (T1W) imaging and bright white on T2-weighted (T2W) imaging.

Because bone marrow is normally a fatty tissue, the presence of bone marrow edema can be detected on an MRI if the bone marrow tissue appears grey on T1W imaging and white on T2W imaging due to the replacement of fat cells with watery material.

Computed tomography (CT) scans can supplement MRI imaging to help determine the possible causes of bone marrow edema by revealing bone fractures, stress fractures, osteochondral lesions, osteonecrosis, or bone tumors like osteoid osteoma.

While they cannot be used to diagnose bone marrow edema, dual energy X-ray absorptiometry (DXA) scans examine bone mineral density levels and can be used to diagnose osteoporosis, a risk factor for developing bone marrow edema.

Conventional X-rays lack sufficient clarity to be able to diagnose bone marrow edema, but can show the presence of osteoarthritis and avascular necrosis, both of which can also lead to the formation of bone marrow edema.

Treatment

Several treatment options, including surgical, physical, and pharmacological methods, exist to help alleviate pain from bone marrow edema within the knee.

Core Decompression

Because bone marrow edema often results from disrupted circulation to the bone marrow, resulting in increased pressure within the bone, surgery can help improve blood flow.

With a core decompression procedure, holes are drilled in the area of the bone with bone marrow edema to help relieve pressure, improve blood flow, reduce bone destruction, and reduce pain. Core decompression is commonly performed to manage or prevent avascular necrosis or osteonecrosis, death of bone cells due to lack of adequate blood supply.

Extracorporeal Shock Wave Therapy

Extracorporeal shock wave therapy involves sending shock waves (sound waves produced by a radial transducer placed on the skin) into the area of the bone with bone marrow edema to increase circulation, promote healing, and decrease the intensity of nerve signals to improve pain and function of the knee joint. A large treatment probe is placed on the outside surface of the skin around the knee joint to deliver shock waves into the bone through the overlying skin and muscles. Extracorporeal shock wave therapy is a noninvasive procedure performed on an outpatient basis.

Medications

Certain medications can be prescribed to help manage symptoms and prevent progression of bone marrow edema. These include:

• Bisphosphonates, which slow bone loss
• Prostaglandin derivatives, which promote bone regeneration and improve circulation
• TNF-inhibitors, which lower the levels of tumor necrosis factor (TNF) to reduce inflammation and disease progression of inflammatory conditions that affect joints and bones like rheumatoid arthritis, psoriatic arthritis, and ankylosing spondylitis

Treatment of bone marrow edema also involves management of the underlying cause, such as:

• Immobilization for fractures of the bones that form the knee joint to promote healing
• Surgical procedures to repair fractures; repair damaged structures like cartilage, ligaments, or menisci within the knee; or remove cancerous growths
• Physical therapy to improve knee strength, mobility, and function after injury
• Pain-relieving and anti-inflammatory medications
• Corticosteroids, disease-modifying anti-rheumatic drugs (DMARDs), and biologic medications like TNF-inhibitors to treat inflammatory autoimmune conditions such as rheumatoid arthritis, psoriatic arthritis, and ankylosing spondylitis
• Antibiotics to treat infections
• Cancer treatment like chemotherapy and radiation to decrease bone tumors

A Word From Verywell

Bone marrow edema in the knee can occur from a variety of causes through physical stress, inflammation, or decreased blood supply to the bone marrow. If left untreated, bone marrow edema can progress and cause further bone damage that can be very painful and significantly impact your functional abilities.

It is important to seek appropriate treatment to manage the underlying cause of your bone marrow edema to decrease your knee pain and protect your knee joint from further damage.