BOSTON, Massachusetts—Expanding bone marrow lesions may add to knee pain in some patients but are not likely to be the only source of such pain. The study authors led by David T. Felson, MD, professor of medicine and epidemiology and chief of the clinical epidemiology unit at the Boston University School of Medicine in Massachusetts, found that bone marrow lesions can cause knee pain even in patients without radiographic evidence of osteoarthritis (OA). Their findings are reported in Arthritis & Rheumatism.¹

"Although our data suggest a consistent and moderately strong association of both the development of bone marrow lesions and enlargement of existing bone marrow lesions with the development of frequent knee pain, the findings do not identify bone marrow lesions as being the sole source of knee pain," Dr. Felson and colleagues wrote. The new findings suggest that many patients may develop knee pain caused by inflammation within the joint or enlargement of effusions.

The researchers studied patients aged 50 to 79 with knee OA or patients at high risk of developing the condition and asked them twice at baseline and twice at 15 months about the presence of knee pain, aching, or stiffness. There were 110 case knees without knee pain at baseline, but which became painful at follow-up. Case knees were compared with 220 control knees that were pain-free at both baseline and follow-up. The researchers scored MRIs for volume of bone marrow lesions in the medial, lateral, and patellofemoral knee compartments.

Dr. Felson reports that 54 of 110 (49.1%) case knees showed an increase in bone marrow lesion score within a compartment, compared with just 59 of 220 (26.8%) control knees (P <.001 by chi-square test). This suggests that enlargement of bone marrow lesions is common and may not be associated with pain in some knees.

Most case knees with increased bone marrow lesions already had a bone marrow lesion at baseline, with enlarging lesions at follow-up. New lesions were more common in case knees than in control knees among the subset that had no bone marrow lesions at baseline. However, new onset knee pain was strongly linked with an increase of two or more units in bone marrow lesions. The researchers found that 27.5% of case knees showed a bone marrow lesion score increase of at least two units, compared with 8.6% of case knees.
 
More lesions, more pain

The paper "suggests that patients with more and larger lesions are more likely to have increasing knee pain, however about 25% of patients (control case) with OA and no knee pain also had some bone marrow lesions," said Stephen Honig, MD, director of the osteoporosis center at New York University Hospital for Joint Diseases in New York City.

"The identification of the bone marrow lesions requires an MRI and this adds considerable expense to the management of OA and is not likely to be part of routine clinical management of this common condition," he pointed out.

There is evidence that suggests that bone marrow lesions may represent microfractures of bone and their presence in OA has helped to promote great interest in the role of bone and OA, a condition marked by loss of articular cartilage, some degree of synovial inflammation, and the development of osteophytes at joint margins," Dr. Honig explained. "If the bone marrow lesions represent devitalized bone and subsequently affect the overlying articular cartilage, the two processes may be pathophysiologically linked [and] preserving bone may then help preserve articular cartilage."

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