Bone marrow edema in the knee is an area of increased fluid inside the bone near the joint, seen on an MRI scan. It is not a disease on its own but a sign that the bone is reacting to something, most often an injury, overload, osteoarthritis or, less commonly, a problem with the bone’s blood supply. Most cases settle as the underlying cause is treated, typically over weeks to months.
In my practice, I often see patients who are worried after reading this phrase on an MRI report, especially when it was not expected. The finding is common, and understanding the pattern and the cause usually makes the path forward much clearer. For a broader discussion beyond the knee, see our article on bone marrow edema and its causes and treatment.
What Is Bone Marrow Edema in the Knee?
The ends of the thigh bone (femur), shin bone (tibia) and kneecap (patella) contain spongy bone filled with marrow. In adults, this marrow is largely fatty. To appreciate what changes in edema, it helps to know the normal composition and function of bone marrow.
When bone is stressed or injured, the marrow space fills with extra fluid, and sometimes with tiny fractures of the bony struts (trabeculae), bleeding or inflammation. Radiologists often use the term bone marrow lesion because the MRI signal reflects a mix of these changes rather than fluid alone.
On MRI, the affected area appears bright on fluid-sensitive sequences (such as STIR or fat-suppressed T2) and darker on T1-weighted images. X-rays cannot show it, which is why it is often discovered only when an MRI is done for knee pain.
Common Causes of Knee Bone Marrow Edema
The cause usually becomes clear from the story of how the pain started, the patient’s age and the location and shape of the edema on MRI.
| Cause | Typical setting | Usual MRI clues |
|---|---|---|
| Bone bruise (contusion) | Twisting injury, fall or direct blow | Edema in a pattern matching the injury; after ACL tears, often the outer femoral condyle and back of the outer tibial plateau |
| Stress reaction or stress fracture | Runners, military recruits, sudden increase in training | Edema with or without a fine fracture line |
| Osteoarthritis | Middle-aged and older adults with worn cartilage | Edema under areas of cartilage loss |
| Subchondral insufficiency fracture (formerly called spontaneous osteonecrosis, SONK) | Often older adults, sometimes with low bone density; sudden pain without major injury | Edema with a thin line just beneath the joint surface, commonly the inner femoral condyle |
| Avascular necrosis | Steroid use, heavy alcohol intake, sickle cell disease | Well-defined dead-bone area surrounded by edema |
| Transient bone marrow edema syndrome | Spontaneous pain without injury | Diffuse edema that resolves over months |
| Inflammatory arthritis or infection | Rheumatoid arthritis, other inflammatory disease, or osteomyelitis | Edema with joint fluid, synovitis or other signs of infection |
Rarely, marrow changes on MRI reflect a tumor or marrow infiltration, which is why unexplained patterns are always reviewed carefully by a radiologist.
Symptoms and Risk Factors
Symptoms depend on the cause, but most people notice:
- Deep, aching knee pain, often worse with standing, walking or stairs
- Pain at night or at rest in some cases, especially with insufficiency fractures
- Swelling and stiffness
- Reduced range of motion or difficulty bearing weight
- Tenderness over a specific part of the bone
Risk factors include high-impact or pivoting sports, a sudden jump in training load, excess body weight, poor knee alignment, existing osteoarthritis and low bone density. Long-term steroid use, heavy alcohol intake and certain blood disorders raise the risk of the less common vascular causes.
How It Is Diagnosed
MRI is the key test, because it is the only routine imaging that shows marrow edema clearly. It also reveals related damage to ligaments, menisci and cartilage, which often matters more for treatment than the edema itself.
A good assessment combines the scan with a careful history and examination. Plain X-rays are still useful to look for arthritis, alignment problems or established fractures. Blood tests may be ordered if infection, inflammatory arthritis or a marrow disorder is suspected, and a bone density scan can help when an insufficiency fracture is found.
Part of the diagnosis is distinguishing true marrow edema from look-alikes, such as normal red marrow in younger people, cysts near the meniscus or artifacts on the scan.
Treatment Options and Recovery
Treatment is directed at the underlying cause. For most people, it is conservative and centered on letting the bone recover.
Conservative care
- Load reduction: modifying activity, and sometimes using crutches for protected weight-bearing, to take stress off the affected bone.
- Pain relief: simple analgesics or NSAIDs, used as advised by a clinician.
- Physical therapy: strengthening the quadriceps, hip and core muscles to share load across the joint, with a gradual return to impact.
- Weight management: reducing load on the knee in people with osteoarthritis.
Treating the underlying condition
Ligament or meniscal injuries may need their own treatment, sometimes surgery. Inflammatory arthritis is managed with appropriate disease-controlling medication, and infection with antibiotics. If an insufficiency fracture is found, bone health should be checked and treated.
Medications and procedures
For stubborn or severe cases, some specialists use medications that affect bone turnover, such as bisphosphonates, although evidence is still developing. Procedures such as core decompression or subchondroplasty are reserved for selected cases, for example avascular necrosis or persistent lesions that have not responded to conservative care.
How long does it take to heal?
Bone bruises from injury commonly improve over a few months, though the MRI can lag behind symptoms. Transient edema syndrome also tends to resolve over several months. Edema linked to osteoarthritis may fluctuate with joint loading rather than disappear completely.
Complications and Prevention
Most bone marrow edema resolves without lasting harm. When the cause is not addressed, however, problems can follow: a stress reaction can progress to a complete fracture, an insufficiency fracture can lead to collapse of the joint surface, and persistent edema in osteoarthritis is associated with ongoing pain and cartilage loss.
Not every case can be prevented, but these steps reduce risk:
- Increasing training volume gradually and building in rest days
- Strength and balance training to support the knee
- Maintaining a healthy weight
- Using appropriate footwear and protective gear in sport
- Looking after bone health with adequate calcium, vitamin D and weight-bearing exercise
For more on marrow biology and related conditions, visit our bone marrow guide.
When to See a Doctor
See a doctor if knee pain persists beyond a couple of weeks, keeps you awake at night, or makes it hard to bear weight. Seek prompt care if the knee is hot, red and swollen with fever, which can signal infection, or if pain began suddenly without injury in someone with risk factors for osteonecrosis.
Frequently Asked Questions
Is bone marrow edema in the knee serious?
Usually not. Most cases reflect a bone bruise, overload or arthritis and improve with time and load management. It becomes more serious when it signals a fracture, osteonecrosis or infection, which is why the cause always needs to be identified.
Can I walk with bone marrow edema in my knee?
Many people can walk, but painful activities should be reduced. Your clinician may recommend crutches for a period if the edema is extensive or linked to a stress or insufficiency fracture. Letting pain guide activity is a sensible general rule.
Does bone marrow edema show up on X-ray?
No. Plain X-rays cannot show marrow edema, although they may reveal related problems such as arthritis or a fracture. MRI is the standard test for detecting it.
Will I need a repeat MRI?
Not always. Many patients are followed by symptoms alone. A repeat scan is more likely if pain does not improve as expected or if a fracture or osteonecrosis was suspected.
