A subchondral bone marrow lesion, usually abbreviated BML, is an area of abnormal signal in the bone directly beneath the cartilage on a knee MRI. It is a finding, not a diagnosis. In the Multicenter Osteoarthritis Study (MOST), an analysis of 1,025 knees in adults who had knee osteoarthritis or were at high risk of developing it found that 9.2% of the analyzed knee subregions showed a prevalent subchondral BML.1
The more useful fact is that these lesions move. In a separate MOST analysis of 395 knees followed for 30 months, 66% of pre-existing BMLs changed size and 50% either regressed or resolved.2 That is why the wording on your report is a starting point for a conversation rather than a sentence.
Key takeaways
- A BML is an MRI signal change in bone under the cartilage. It is not by itself a diagnosis.
- In a MOST cohort of adults with or at high risk for knee osteoarthritis, 9.2% of analyzed knee subregions showed a prevalent BML.
- Over 30 months, most pre-existing lesions changed size and half regressed or resolved.
- The direction of change carries more risk information than the presence of a lesion.
- Nothing offered at Regen.MD regrows cartilage, and we will not describe an orthobiologic that way. See what orthobiologics actually are.
What the MRI report is describing
“Subchondral” and “bone marrow lesion” in plain language
“Subchondral” describes location: the bone immediately under the joint cartilage. “Bone marrow lesion” describes what the scanner saw there, an area whose signal differs from surrounding marrow on fat-suppressed sequences. Older reports sometimes call the same finding bone marrow edema, which is why the two phrases appear interchangeably.
How the finding is scored
In the MOST research setting the knee is divided into subregions and each is scored separately for lesion size and cartilage status, which is why prevalence is reported per subregion rather than per knee.1 A clinical radiology report will not use that scoring system, but it will usually name a compartment or location, and that location is the part worth discussing.
What BMLs predict, and what they do not
Progressing and newly developing lesions carry the highest risk
In the 30-month MOST analysis of 395 knees, cartilage loss in the same subregion was compared against stable lesions as the reference group. Subregions with progressing BMLs had an adjusted odds ratio of 2.8 (95% CI 1.5 to 5.2) for cartilage loss, and newly developing BMLs an adjusted odds ratio of 3.5 (95% CI 2.1 to 5.9).2
The reverse held as well. Subregions with no BML at either baseline or follow-up had an adjusted odds ratio of 0.2 (95% CI 0.1 to 0.3) for cartilage loss.2 Absence of a lesion was protective information in that cohort.
A stable or shrinking lesion is a different message
In the same analysis, regressing lesions carried an adjusted odds ratio of 1.2 and resolving lesions 0.9, neither of which was distinguishable from the stable reference group.2 Two reports six months apart therefore say considerably more than one report does.
What these numbers are not
These are group-level associations from an observational cohort of people who already had knee osteoarthritis or were at high risk for it. They do not forecast an individual knee, and they say nothing about whether any particular treatment changes the lesion. We will not present them as though they do.
Why this matters for a conservative-first knee plan
The finding is interpreted alongside the examination
The practical question is whether the lesion location matches where your knee actually hurts and how it behaves under load. That comparison, plus the examination, is what a plan is built on. How we structure that review is described in our approach.
Where orthobiologics enter the conversation
Regen.MD offers intra-articular and tendon platelet-rich plasma, intraosseous and subchondral PRP, bone marrow aspirate concentrate, Lipogems, and intradiscal orthobiologics. For advanced knee osteoarthritis, PRP is framed as a safe bridge therapy prior to joint replacement. It is a symptom-and-function strategy. It is not a claim that lost cartilage grows back, and no honest reading of the evidence supports that claim.
Whether any of these is appropriate depends on the joint, the stage, and the examination, not on the wording of an MRI report. The range of presentations we assess is listed under the conditions we evaluate.
Questions worth asking at your next appointment
- Where exactly is the lesion, and does that location match the pain I actually feel?
- Is there a prior MRI to compare against, 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 at what point does surgery become the right conversation?
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 (314) 295-3000 or text (314) 886-5902.
Frequently Asked Questions
Are subchondral bone marrow lesions on a knee MRI permanent?
Often not. In a 30-month MOST analysis of 395 knees, 66% of pre-existing bone marrow lesions changed size and 50% either regressed or resolved. That is a group result in a research cohort rather than a prediction about your knee, but it is the reason a single MRI should not be read as a fixed verdict. More of our written imaging and terrain education sits in the Regen.MD library.
Does a bone marrow lesion mean I am going to lose cartilage?
It raises the odds, and the direction of change matters more than the presence of a lesion. In the same MOST analysis, subregions with progressing lesions had 2.8 times the adjusted odds of cartilage loss and newly developing lesions 3.5 times the odds, compared with stable lesions. Your examination and symptom pattern still carry the interpretation, which 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, aimed at symptoms and function rather than at changing an image. Staged loading 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 measures have been exhausted. 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.
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/