Prevalence of red marrow around the knee joint in adults as demonstrated on magnetic resonance imaging.

RATIONALE AND OBJECTIVES: We determined the prevalence of red marrow around the knee joint in adults and evaluated variations with age, gender, and other variables. METHODS: One hundred ninety-nine adult patients presenting for routine knee magnetic resonance (MR) imaging completed a questionnaire that covered age, gender, menstrual history, past pregnancies, smoking history, and medications. The presence or absence of visible red marrow in the distal femur and proximal tibia on both coronal and sagittal MR images was recorded for each patient. Associations between the presence of red marrow and the other recorded variables then were evaluated. RESULTS: Red marrow was present in more than half of the women and less than one sixth of the men, a statistically significant difference. The age distribution of red marrow in men and women also was different. Red marrow was the most common in women aged 30-60 years. In men, there was no clear-cut age trend. Red marrow also was more likely to be present in obese individuals and smokers. No association was found between the presence of red marrow and any of the other recorded variables. CONCLUSION: There are clear gender, age, obesity, and smoking-related differences in the prevalence of red marrow around the knee joint in adults. Red marrow is relatively common in this site in all age groups, and its presence should not be a cause for clinical concern.