Objective: The microanatomic basis for formation of erosions in inflammatory arthritis is incompletely understood but is thought to be related to bare areas and the associated cartilage-synovium junction. The purpose of this study was to test the hypothesis that erosion-prone sites are associated with microdamage in macroscopically normal joints.
Methods: Histologic evaluation of erosion-prone sites was performed on 20 collateral ligaments (CLs) from the metacarpophalangeal (MCP) and proximal interphalangeal (PIP) joints of 5 normal cadavers. In addition, the MCP joints (n = 17) and PIP joints (n = 3) of 20 patients with rheumatoid arthritis (RA) were assessed by computed tomography (CT) to ascertain whether the topography of erosion formation in patients with RA corresponded to the cadaveric findings.
Results: Absence of a bare area was noted in cadaveric tissue at the periligamentous erosion-prone regions, especially in the distal MCP joints and both distal and proximal PIP joints. Nevertheless, these sites exhibited soft-tissue pathologic features and bony microdamage/cyst formation. Other significant findings included the presence of pannus without inflammatory changes in the regions in which a bare area was absent, and the replacement of bare area regions with fibrovascular synovial tissue in joints without inflammatory changes. The sites of cadaveric tissue microdamage corresponded to CT-determined erosion formation in the MCP and PIP joints of patients with RA, in whom erosions adjacent to the CLs were more common than dorsal or volar erosions.
Conclusion: Periarticular erosion formation may not necessarily depend on the presence of a bare area and has a propensity to occur adjacent to ligaments in which bone microdamage is common. These findings suggest that periligamentous locations prone to microdamage may critically influence the topography of erosion formation in inflammatory arthritis.