Distinct characteristics and progression patterns of facet joint structural lesions in radiographic axial spondyloarthritis.

BACKGROUND

Both vertebral bodies and posterior elements of the vertebrae (facet joints, FJ) can engage in bone formation in radiographic axial spondyloarthritis (r-axSpA). However, little is known about the specific structural lesions and progression patterns of FJs in r-axSpA.

OBJECTIVES

To identify specific lesions related to r-axSpA and to investigate the distinct progression patterns by comparing the FJ changes of r-axSpA with that of diffuse idiopathic skeletal hyperostosis (DISH), osteoarthritis (OA), and control group (CG).

DESIGN

Single-center, retrospective study. Longitudinal imaging data were retrieved and collected.

METHODS

Age- and sex-matched patients with complete thoracic and lumbar spine computed tomography (CT) data were included and their bilateral FJs were assessed. FJ changes were divided into erosions, ankylosis, joint-space narrowing, osteophytes, subchondral sclerosis, subchondral cysts, and vacuum phenomena. Average progressed year was defined as "number of changed vertebrae × interval years"/number of changed vertebrae.

RESULTS

In all, 50 patients in each group were included. Subchondral cysts and vacuum phenomena were not observed. Bilateral FJ ankylosis (FJA)/erosions in the thoracic and lumbar spine, and unilateral ankylosis/erosions in T1-4, T9-12 were significantly more common in r-axSpA. Joint-space narrowing/osteophytes/subchondral sclerosis were significantly more common in DISH and OA. FJ lesions progressed in 56.34% of vertebrae of r-axSpA. The most common pattern was "FJ normal advanced to ankylosis" (17.54%) which required 2.63 years. It was followed by "erosions advanced to ankylosis" (12.3%) which took 2.05 years, and by "normal FJ advanced to erosions" (11.04%) which took 2.29 years, respectively. Degenerative changes could also progress to FJ erosions/ankylosis (24.83%). The majority pattern in DISH/OA was "FJ changes advanced to subchondral sclerosis/osteophytes/joint-space narrowing."

CONCLUSION

Bilateral FJA/erosions are r-axSpA-specific lesions. The specific progression pattern for r-axSpA was "FJ changes advanced to ankylosis/erosions." Repeated CT examination in intervals of at least 2 years will be more appropriate for monitoring FJ progression.