Background High Resolution peripheral Quantitative Computed Tomography (HR- pQCT) allows to detect very small cortical breaks, so called “microchannels” in the periarticular bone. These structures resemble an interaction between the bone marrow and synovial compartment potentially allowing communication of inflammation between these two compartments.
Objectives To quantify micro-channels in healthy individuals, ACPA-positive individuals and early rheumatoid arthritis (RA) patients.
Methods HR-pQCT (XtremeCT, Scanco, Switzerland) scans of healthy subjects, ACPA positive subjects without RA and ACPA positive early RA patients were assessed. Transversal, sagittal and coronal planes of the 2nd metacarpophalangeal (MCP) head were scored for microchannels. Analysis was performed by two independent and blinded readers. To search for a potential function these cortical microchannels we performed HR-pQCT measurements of cadaveric hands (n=6, Body Donation Program of the Institute of Anatomy, University Erlangen-Nuremberg) with contrast enhancement to display vessels. After defrosting at room temperature for 24h hours, the radial and ulnar artery was dissected and contrast agent (Imeron 350 Iod/ml, Bracco Imaging, Germany) was injected in both arteries followed by HR-pQCT measurement. The study was approved by the local ethics committee.
Results A total of 61 healthy controls (29 females; 32 males), 21 ACPA positive subjects (17 females; 4 males), 35 ACPA positive RA (25 females; 10 males; disease duration 0.66 yrs) were evaluated. Cortical channels were detected in all subjects with distinct localization (Fig. 1a). Most lesions were located intra-articularly at the palmar and radial side of the MCP 2 head. We found a significant difference (p=0.001) in the numbers of microchannels between the three groups with higher numbers in the early RA group compared to the healthy controls (Fig 1b). Using contrast enhanced HR-pQCT images of human cadaver hands we were able to display intracortical and medullar vessels with a size as low as 0.15 mm diameter (Fig. 2a/b). In addition, vascular trees around the wrist and MCP joints could be visualized after 3D segmentation (Fig. 2c). Despite good vascular visualization no contrast enhancement was observed in the intraarticular region of the above described channels.
Conclusions Micro-channels in the periarticular bone increase during the development of RA. Until now the function of micro channels is still unclear. If cortical channels reflect breaks, vessels from “inside-out”, cartilage anchors or nutritive channels still needs to be determined.
Disclosure of Interest None declared