Reduced Trabecular Bone Mineral Density and Cortical Thickness Accompanied by Increased Outer Bone Circumference in Metacarpal Bone of Rheumatoid Arthritis Patients: a Cross-sectional Study

Introduction: The objective of this study was to assess three-dimensional bone geometry and density at the epiphysis and shaft of the third meta-carpal bone of rheumatoid arthritis (RA) patients in comparison to healthy controls with the novel method of peripheral quantitative computed tomography (pQCT).

Methods: PQCT scans were performed in 50 female RA patients and 100 healthy female controls at the distal epiphyses and shafts of the third metacarpal bone, the radius and the tibia. Reproducibility was determined by coefficient of variation. Bone densitometric and geometric parameters were compared between the two groups and correlated to disease characteristics.

Results: Reproducibility of different pQCT parameters was between 0.7% and 2.5%. RA patients had 12% to 19% lower trabecular bone mineral density (BMD) (P<or=0.001) at the distal epiphyses of radius, tibia and metacarpal bone. At the shafts of these bones RA patients had 7% to 16% thinner cortices (P<or=0.03). Total cross-sectional area (CSA) at the metacarpal bone shaft of patients was larger (between 5% and 7%, P<0.02), and relative cortical area was reduced by 13%. Erosiveness by Ratingen score correlated negatively with trabecular and total BMD at the epiphyses and shaft cortical thickness of all measured bones (P<0.04).

Conclusions: Reduced trabecular BMD and thinner cortices at peripheral bones, and a greater bone shaft diameter at the metacarpal bone suggest RA specific bone alterations. The proposed pQCT protocol is reliable and allows measuring juxta-articular trabecular BMD and shaft geometry at the metacarpal bone.