Background Bone damage in rheumatoid arthritis (RA) typically emerges at certain anatomical hotspots corresponding to the so-called “bare area”, an intra-articular region between the cartilage and the insertion site of the joint capsule (1,2). We hypothesized that this region exhibits certain micro-anatomical properties, which facilitates the emergence of bone erosions.
Objectives To find the micro-structural correlate of the origin of bone erosions in the bare area of the human joint
Methods Bare areas of human joints were analyzed for early microstructural changes by in-vivo high-resolution peripheral computed tomography (HR-pQCT). First, bare areas were exactly defined by scanning 6 cadaveric hands for localization of the bare area in the human metacarpal head. Bone lesions found in the cadaveric hand by HR-pQCT were additionally by super-resolution ex vivo micro-CT (μCT40). Then, number and distribution of the type of bare area bone lesion found in cadaveric study were analyzed in a cohort of 105 healthy individuals and 107 anti-citrullinated peptide (ACPA) positive RA patients with similar sex and age distribution.
Results HR-pQCT combined with adaptive thresholding allowed the definition of a new type of bone lesions in the bare areas of the human joint termed “COMIC” standing for “cortical micro-channel”. Their existence in the bare area was additionally validated by microCT (Figure 1). RA patients showed significantly (p<0.001) more CoMiCs (112.9±54.7/joint) than healthy individuals (75.2±41.9/joint) with 20–49 years old RA patients exhibiting similar CoMiC numbers as observed in over 65 year old healthy individuals. Importantly, CoMiCs were found in RA patients already very early in their disease course with enrichment in the erosion-prone radial side of the joint.
Conclusions CoMiCs represent a new structural feature of the joint, which is characteristic for the bone of the bare area. COMICS at low level are also found in young healthy individuals but they significantly increase with age and particularly with RA. COMICs develop much earlier and much more pronounced in RA patients than in healthy individuals and therefore represent an interesting new early indicator for erosion development in ACPA positive RA patients.
Stach CM, Bauerle M, Englbrecht M, Kronke G, Engelke K, Manger B, et al. Periarticular bone structure in rheumatoid arthritis patients and healthy individuals assessed by high-resolution computed tomography. Arthritis & Rheumatism. 2010;62(2):330–9.
Simon D, Kleyer A, Stemmler F, Simon C, Berlin A, Hueber AJ,Haschka J, Renner N, Figueiredo C, Neuhuber W, Buder T, Englbrecht M, Rech J, Engelke K, Schett G. Age- and Sex-Dependent Changes of Intra-articular Cortical and Trabecular Bone Structure and the Effects of Rheumatoid Arthritis. J Bone Miner Res. 2016 Oct 27. doi: 10.1002/jbmr.3025. [Epub ahead of print].
Disclosure of Interest None declared