When patients think about knee osteoarthritis, they often think mainly about cartilage.
They may say:
“My cartilage is wearing out.”
Or:
“Is it bone-on-bone?”
But MRI sometimes reveals another important finding:
bone marrow lesions, often shortened to BMLs.
These can sound alarming.
Patients may wonder:
- Are bone marrow lesions dangerous?
- Do they mean cancer?
- Are they the reason my knee hurts?
- Do they mean arthritis is severe?
- Can they heal?
- Should treatment change?
These are important questions.
Bone marrow lesions can be relevant in knee osteoarthritis, but they need careful interpretation.
What Are Bone Marrow Lesions?
Bone marrow lesions are MRI findings seen within the bone beneath the joint surface.
In knee osteoarthritis, they are often found in the subchondral bone, meaning the bone just under the cartilage.
They may reflect a mixture of tissue changes, such as:
- bone stress
- fluid-related signal changes
- microstructural change
- local inflammatory activity
- mechanical overload response
- bone remodeling
They are not the same as cancer.
They are also not a diagnosis by themselves.
They are imaging findings that must be interpreted in clinical context.
Why Bone Marrow Lesions Matter In Osteoarthritis
For a long time, osteoarthritis was oversimplified as cartilage loss.
But modern understanding recognises osteoarthritis as a whole-joint condition involving cartilage, bone, synovium, meniscus, muscles, and mechanics.
Bone marrow lesions matter because the bone beneath the cartilage may contribute to pain.
A widely cited study in Annals of Internal Medicine reported that MRI-detected bone marrow lesions were strongly associated with pain in knee osteoarthritis. (PubMed)
This does not mean every BML causes pain.
But it does mean BMLs deserve attention when interpreting MRI findings.
Why Bone Can Hurt Even When Cartilage Cannot
Cartilage itself has limited pain sensitivity.
This surprises many patients.
Pain in osteoarthritis may come from other structures, including:
- subchondral bone
- synovium
- joint capsule
- ligaments
- tendon structures
- surrounding soft tissues
Bone marrow lesions may be relevant because bone is richly supplied with nerves and blood vessels compared with cartilage.
This helps explain why “cartilage wear” alone is often an incomplete explanation for pain.
Are Bone Marrow Lesions Always Painful?
No.
This is important.
BMLs may be associated with pain, but association is not the same as certainty.
Some patients may have BMLs with significant symptoms.
Others may have BMLs that are less clinically relevant.
Factors that may influence meaning include:
- size
- location
- change over time
- mechanical loading pattern
- surrounding cartilage status
- swelling
- synovitis
- symptom pattern
A 2023 review in Osteoarthritis and Cartilage reported that osteoarthritis-related BMLs are associated with pain, may fluctuate with pain, and may also relate to prognosis and treatment outcomes. (oarsijournal.com)
Why BML Location Matters
Not all BMLs mean the same thing.
A lesion in a heavily loaded part of the knee may have different practical relevance from a small incidental finding elsewhere.
Location may matter because knee pain is often load-related.
For example, pain during:
- walking
- stairs
- standing
- weight-bearing
- turning
may raise different questions from pain that occurs mainly at rest.
Research in Arthritis Research & Therapy has explored how BML location and size may relate to weight-bearing knee pain in knee osteoarthritis. (Springer)
BMLs And Synovitis May Interact
Pain rarely has one single source.
Some research suggests that synovitis—irritation or inflammation of the joint lining—may partly mediate the relationship between BMLs and pain.
This means BML-related pain may not be purely a “bone problem.”
The whole joint environment may matter.
A study in Osteoarthritis and Cartilage found that synovitis partially mediated the association between medial femorotibial BMLs and knee pain. (ScienceDirect)
Why Patients Should Not Panic Over MRI Wording
MRI reports often use technical language.
Terms such as:
- marrow oedema
- bone marrow lesion
- subchondral change
- cystic change
- bone attrition
- reactive change
can sound frightening.
But MRI language describes appearances.
It does not automatically determine prognosis, pain severity, or treatment pathway.
Clinical interpretation matters.
Bone Marrow Lesions vs Bone Bruise
Patients sometimes ask whether BMLs are the same as a bone bruise.
The answer depends on context.
In acute injury, MRI may show bone bruising related to trauma.
In osteoarthritis, BMLs are usually discussed differently, often as part of degenerative joint disease and mechanical-biological joint stress.
The clinical story matters.
A sudden traumatic injury is different from gradual osteoarthritis-related change.
Do Bone Marrow Lesions Mean Arthritis Is Progressing?
Sometimes BMLs may be relevant to progression risk.
But they should not be interpreted in isolation.
Progression depends on many factors:
- alignment
- loading
- cartilage status
- meniscus condition
- inflammation
- muscle strength
- body weight
- activity pattern
- symptom behaviour
A BML may be one important clue—but not the whole diagnosis.
Common Misunderstandings
“Bone marrow lesion means cancer.”
No.
In osteoarthritis, BMLs are MRI signal findings related to joint disease context.
“If I have a BML, that explains all my pain.”
Not necessarily.
It may be relevant, but symptoms are usually multifactorial.
“BML means I need surgery.”
No.
Treatment decisions depend on the full clinical picture.
“Cartilage is the only thing that matters.”
No.
Subchondral bone, synovium, meniscus, muscles, and loading all matter.
What This Means For Patients
Useful practical questions include:
- Where is the BML located?
- Does it match the pain pattern?
- Is pain mainly weight-bearing?
- Is swelling also present?
- Are there meniscus or cartilage findings?
- Is the finding new or changing?
- Would it alter management?
The better question is:
“Is this bone marrow lesion clinically meaningful in my case?”
not simply:
“Is there a lesion on MRI?”
Practical Decision-Making Considerations
Considerations may include:
- symptom location
- pain during weight-bearing
- MRI context
- swelling or synovitis
- cartilage status
- meniscus status
- alignment
- functional limitation
- treatment goals
Based on over 20 years of clinical practice, Dr Terence Tan, founder of The Pain Relief Clinic Singapore, notes that patients may become alarmed by the phrase “bone marrow lesion,” when the more useful clinical question is whether the MRI finding matches the patient’s symptoms, function, and loading pattern.
When Further Assessment May Matter
Further review may be particularly important when:
- pain is severe during weight-bearing
- symptoms worsen rapidly
- MRI findings seem disproportionate
- swelling is persistent
- night pain is concerning
- diagnosis remains uncertain
- treatment repeatedly fails
- there is a history of recent trauma
Frequently Asked Questions
Are bone marrow lesions dangerous?
In osteoarthritis, they are usually interpreted as MRI findings within the joint disease context, not automatically as dangerous disease.
Do BMLs cause pain?
They may be associated with pain, but not every BML explains symptoms.
Are BMLs the same as cancer?
No.
The term can sound alarming, but osteoarthritis-related BMLs are not the same as cancer.
Can BMLs change over time?
Yes.
They may fluctuate, and interpretation depends on context.
Do BMLs mean I need surgery?
No.
Surgery decisions depend on broader clinical assessment.
Are BMLs more important than cartilage loss?
Not necessarily.
They are one part of the whole-joint picture.
Should BMLs change treatment?
Sometimes they may influence clinical reasoning, but management depends on the full patient context.
About the contributor
Dr Terence Tan is a Singapore licensed medical doctor with over 20 years of clinical practice and founder of The Pain Relief Clinic Singapore (https://painrelief.com.sg).
Medical Disclaimer
This article is for educational purposes only and does not constitute personalised medical advice, diagnosis, or treatment recommendations. Individual medical decisions should be made in consultation with an appropriately licensed healthcare professional.
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