Bone Marrow Edema in the Knee

What the scan is showing. On the fluid-sensitive sequences of an MRI, healthy bone marrow looks dark. An area that looks bright is reported as bone marrow edema or a bone marrow lesion. The name describes the picture. The tissue is not simply waterlogged, and the same bright patch can come from very different causes, which is why the report usually adds where it is and what sits next to it.

The words that come with it. These are the terms you are most likely to see around it.

It is common in knees that do not hurt. In the Framingham study, 52 percent of adults whose X-rays showed no osteoarthritis had a bone marrow lesion on MRI, and 86 to 88 percent of painless knees had at least one abnormality of some kind (Guermazi et al., 2012). In 230 knees of asymptomatic adults scanned at 3 tesla, bone marrow abnormalities were found behind the kneecap in 48 percent (Horga et al., 2020). Across 63 studies of uninjured adults without symptoms, the pooled prevalence was 18 percent (Culvenor et al., 2019).

In an arthritic knee, it is linked with pain. Among people with knee osteoarthritis, lesions were present in 77.5 percent of painful knees and 30 percent of painless ones, and large lesions were found almost only in painful knees (Felson et al., 2001). Among people who did have pain, the lesion did not predict how severe the pain was.

It changes, and pain tends to change with it. When a lesion grew between two visits, the odds of frequent knee pain rose with the size of the change, and shrinking lesions went with pain settling (Zhang et al., 2011). New knee pain was more likely in knees where a lesion appeared or enlarged (Felson et al., 2007). This is the useful part: the finding is not fixed.

It is a marker of load. Lesions on the inner side of the knee were mostly found in bow-legged limbs and lesions on the outer side in knock-kneed limbs, and knees with a medial lesion were more likely to show medial progression on later X-rays. Much of that risk was explained by alignment (Felson et al., 2003). In plain terms, the lesion often marks the part of the joint carrying the most load.

It is not a diagnosis. The same bright signal appears after a twisting injury, in a runner who has added mileage, in an arthritic joint, and in an insufficiency fracture. The history and the examination decide which, and the report’s own wording about fracture lines, cartilage and ligaments points the way.

• After an injury. A twist, a fall or a tackle can bruise the bone where two surfaces struck each other. These lesions usually sit with a ligament or meniscus injury on the same scan, and the plan follows that injury.
• With osteoarthritis. In a worn compartment the lesion sits under thinned cartilage, often on the side that carries more load because of alignment. Here it behaves as a marker of how the joint is coping rather than a separate problem.
• From a change in training. Runners, military recruits and people who have quickly increased impact or hill work can develop a stress response in the shin bone or thigh bone near the knee. Caught early, it settles with a change in load.
• Without an injury, in older or osteoporotic bone. Sudden pain in an older adult with no clear cause, especially on the inner side of the knee, raises the question of a subchondral insufficiency fracture. This is the one to take to a doctor promptly, because early protection matters (Yamamoto and Bullough, 2000).

There is no routine treatment aimed at the lesion itself. Care follows the cause, and for the commonest cause, osteoarthritis, the guidelines are clear.

• Osteoarthritis. Information, tailored exercise and weight management where weight is a factor are the first line at every stage (NICE, 2022). A bone marrow lesion on the scan does not change that advice.
• Injury and overload. The plan is built around the injured structure and the load that provoked it: a period of reduced impact, then a graded return. The lesion is expected to fade behind the symptoms rather than needing its own treatment.
• Insufficiency fracture or osteonecrosis. Protected weight-bearing and medical follow-up, decided by your doctor or an orthopaedic surgeon. Physiotherapy fits around that plan rather than leading it.
• Drugs aimed at the lesion. A small trial found that a bisphosphonate infusion reduced pain and lesion size at six months (Laslett et al., 2012), but a larger two-year trial in 223 people found no benefit for pain or cartilage loss (Cai et al., 2020). It is not a routine treatment.

I start with the story, because it sorts the causes faster than the scan does: whether there was an injury, whether training or activity changed, how quickly the pain came on, and whether you can put weight through the leg. If the picture suggests an insufficiency fracture, infection or osteonecrosis, I say so and send you to your doctor before anything else. I cannot order imaging myself; when further imaging would change the plan, I flag it to your family doctor or specialist and refer you.

On examination I look at alignment and how you walk, check for swelling and warmth, measure range of motion, test the quadriceps and hip, and look at how you load the knee in the movements that hurt. I read the rest of the report alongside that: the cartilage, the menisci and the ligaments usually tell me more about the plan than the marrow signal does.

Treatment follows the cause. For an arthritic or overloaded compartment that usually means strengthening, particularly the quadriceps and hip, with walking or cycling, changes to the loads that flare it and attention to weight where it is a factor. After an injury it is the rehabilitation for that injury. Pain is tracked in what you can do, and the scan is not repeated to check on the lesion unless your doctor has a reason to.