Recently, dual energy x ray absorptiometry (DXA) was presented by Murphy et al as a new method for assessing periarticular bone mineral density (BMD) at the knee joint.1 Precision errors for BMD measured at the patella, femur, and tibia were reported for 14 subjects. The paper highlights the emerging importance of measurement of radiological data and attention to regional density characteristics in bone and joint diseases. Subchondral bone mineral density of the proximal tibia has previously been assessed by dual photon absorptiometry (DPA)—the precursor of DXA. Relations between subchondral BMD of the proximal tibia and age, …