A subchondral bone marrow lesion, usually shortened to BML, is an area of abnormal signal in the bone just beneath the cartilage on a knee MRI. It is a finding, not a diagnosis. The Multicenter Osteoarthritis Study (MOST) looked at 1,025 knees. The adults either had knee osteoarthritis or were at high risk for it. In that group, 9.2% of the knee areas studied showed a BML.1
The more useful fact is that these lesions move. A separate MOST study followed 395 knees for 30 months. In that time, 66% of existing BMLs changed size, and 50% either shrank or went away.2 That is why the wording on your report starts a conversation. It is not a sentence.
Key takeaways
- A BML is an MRI signal change in the bone under the cartilage. It is not a diagnosis by itself.
- In a MOST group of adults with knee osteoarthritis or at high risk for it, 9.2% of the knee areas studied showed a BML.
- Over 30 months, most existing lesions changed size, and half shrank or went away.
- Which way a lesion is changing says more about risk than whether a lesion is there.
- Nothing offered at Regen.MD regrows cartilage, and we will not describe an orthobiologic that way. See what orthobiologics actually are.
What does bone marrow edema on a knee MRI mean?
“Subchondral” and “bone marrow lesion” in plain language
“Subchondral” describes location: the bone just under the joint cartilage. “Bone marrow lesion” describes what the scanner saw there. It is an area whose signal looks different from the marrow around it on certain MRI settings. Older reports sometimes call the same finding bone marrow edema. That is why the two phrases show up as if they mean the same thing.
How the finding is scored
In the MOST research, the knee is split into small areas. Each area is scored on its own for lesion size and cartilage health. That is why the numbers are given per area, not per knee.1 A normal radiology report will not use that scoring system. But it will usually name a section or location of the knee. That location is the part worth talking about.
How serious is a bone marrow lesion on a knee MRI?
Progressing and newly developing lesions carry the highest risk
The 30-month MOST study of 395 knees compared cartilage loss in the same area against stable lesions. Areas with growing BMLs had an adjusted odds ratio of 2.8 (95% CI 1.5 to 5.2) for cartilage loss. Areas with new BMLs had an adjusted odds ratio of 3.5 (95% CI 2.1 to 5.9).2
The reverse held too. Areas with no BML on either scan had an adjusted odds ratio of 0.2 (95% CI 0.1 to 0.3) for cartilage loss.2 In that group, having no lesion was a good sign.
A stable or shrinking lesion is a different message
In the same study, shrinking lesions had an adjusted odds ratio of 1.2, and lesions that went away had 0.9. Neither was different from the stable group.2 So two reports six months apart say far more than one report does.
What these numbers are not
These are group-level links from a study that watched people over time. Those people already had knee osteoarthritis or were at high risk for it. The numbers do not predict any one knee. They say nothing about whether a given treatment changes the lesion. We will not present them as if they do.
How is a knee bone marrow lesion treated at Regen.MD?
The finding is interpreted alongside the examination
The real question is whether the lesion’s location matches where your knee hurts, and how it acts under load. That match, plus the exam, is what a plan is built on. How we set up that review is described in our approach.
Where orthobiologics enter the conversation
Regen.MD offers platelet-rich plasma into the joint and into tendons. We also offer intraosseous and subchondral PRP (into the bone under the cartilage), bone marrow aspirate concentrate, Lipogems, and orthobiologics into the disc. For advanced knee osteoarthritis, PRP is framed as a safe bridge therapy before joint replacement. Its aim is less pain and better function. It is not a claim that lost cartilage grows back. No honest reading of the evidence supports that claim.
Whether any of these fits depends on the joint, the stage, and the exam. It does not depend on the wording of an MRI report. The problems we assess are listed under the conditions we evaluate.
For more information, get our free guide to knee pain and treatment options.
Questions worth asking at your next appointment
- Where exactly is the lesion, and does that spot match the pain I really feel?
- Is there an older MRI to compare, and did the lesion grow, shrink, or hold steady?
- What is the first conservative step, and how will we measure whether it worked?
- What findings would change the plan, and when does surgery become the right conversation?
When those lesions follow a specific injury, the longer path is laid out in post-traumatic osteoarthritis after an injury.
Have your MRI read against your examination, not in isolation
Regen.MD begins with a physician-led Clinical Evaluation — a review of your history, imaging, and metabolic data, and a written terrain roadmap. Evaluation is contingent upon review of your data.
Questions? Call or text us.
Frequently Asked Questions
Are subchondral bone marrow lesions on a knee MRI permanent?
Often not. A 30-month MOST study followed 395 knees. In that time, 66% of existing bone marrow lesions changed size, and 50% either shrank or went away. That is a group result from research, not a prediction about your knee. But it is why one MRI should not be read as a final verdict. More of our writing on imaging and terrain is in the Regen.MD library.
Does a bone marrow lesion mean I am going to lose cartilage?
It raises the odds, and which way it is changing matters more than whether it is there. In the same MOST study, areas with growing lesions had 2.8 times the adjusted odds of cartilage loss. New lesions had 3.5 times the odds. Both were compared with stable lesions. Your exam and symptom pattern still decide what it means. That is the point of the physician-led review.
Will PRP or BMAC make the lesion disappear on a repeat MRI?
We cannot tell you that, and no orthobiologic offered here regrows cartilage. For advanced knee osteoarthritis, platelet-rich plasma is framed as a bridge therapy before joint replacement. It aims at symptoms and function, not at changing an image. Adding load in steps after any such procedure is covered in Return to Activity Without Surgery.
What if conservative care and orthobiologics do not work?
Then surgery is discussed on its merits. Dr. Gurpreet Singh Padda, MD, MBA, MHP is a surgeon, and Regen.MD provides surgery once conservative care has run its course. It is the step after a structured plan has been tried, not the opening move. Our office is at 4477 Woodson Rd, Suite 103, St. Louis, MO 63134, with details on the locations page.
How serious is bone marrow edema in the knee?
It is a finding, not a diagnosis. How serious it is depends on which way it is moving. In the MOST group, growing and new lesions carried the highest odds of cartilage loss. Shrinking lesions, or ones that went away, were no different from stable ones. Knee areas with no lesion on either scan had the lowest odds. Your exam, and where you really hurt, decide what the finding means for you.
How long does it take for bone marrow edema to go away?
There is no fixed timeline. A MOST study followed 395 knees for 30 months. Half of the lesions already there either shrank or went away, and two out of three changed size. That is a group result, not a forecast for your knee. It is why two MRI reports taken six months apart tell us much more than one report does.
Sources
- Roemer FW, Neogi T, Nevitt MC, Felson DT, Zhu Y, Zhang Y, Lynch JA, Javaid MK, Crema MD, Torner J, Lewis CE, Guermazi A. “Subchondral bone marrow lesions are highly associated with, and predict subchondral bone attrition longitudinally: the MOST study.” Osteoarthritis and Cartilage, 2010 Jan;18(1):47–53. https://pmc.ncbi.nlm.nih.gov/articles/PMC2818146/
- Roemer FW, Guermazi A, Javaid MK, Lynch JA, Niu J, Zhang Y, Felson DT, Lewis CE, Torner J, Nevitt MC; MOST Study investigators. “Change in MRI-detected subchondral bone marrow lesions is associated with cartilage loss: the MOST Study. A longitudinal multicentre study of knee osteoarthritis.” Annals of the Rheumatic Diseases, 2009 Sep;68(9):1461–5. https://pmc.ncbi.nlm.nih.gov/articles/PMC2905622/