Mapping the bare area and transcortical pores in finger joints: co-location with bone erosions in rheumatoid arthritis.

OBJECTIVE

Transcortical pores and the bare area have been suggested as structural determinants of bone erosions in rheumatoid arthritis (RA). We aimed to map the spatial distribution of transcortical pores and bare areas in whole finger joints of postmortem subjects and to determine the anatomical relationship between erosions in patients with RA and the bare areas.

METHODS

This was a descriptive, cross-sectional study including the second and/or third fingers from deceased individuals (n=8), obtained postmortem, for mapping the number, size and spatial distribution of transcortical pores in four quadrants using micro-CT (n=33 joints). The extent of the bare area at the erosion-prone radial and ulnar quadrants (n=12 joints) was mapped histologically and pores assessed intra-articularly and extra-articularly. In patients with RA (n=22), bone erosions were identified using high-resolution peripheral quantitative CT of the second metacarpophalangeal (MCP) joint.

RESULTS

In postmortem subjects, transcortical pores were located both intra-articularly and extra-articularly. The spatial pore distribution along the finger at the MCP, proximal interphalangeal (PIP) joint and distal interphalangeal (DIP) joint was comparable. The radial quadrant did not show more or larger pores compared with the other quadrants. The number of pores was not consistently higher in joints and areas prone to erosion. The bare area was more frequently and more extensively present in joints commonly affected by erosions. In RA, all erosions (n=26) were confined to or overlapping with the bare areas.

CONCLUSIONS

These findings support the bare areas, but not transcortical pores, as structural determinants for erosion location in finger joints in RA.

TRIAL REGISTRATION NUMBER: NCT04645381 and NCT03429426.