Facet joint ankylosis in r-axSpA: detection and 2-year progression on whole spine low-dose CT and comparison with syndesmophyte progression

Abstract

Objectives: To evaluate the occurrence and progression of facet joint ankylosis in the whole spine using low-dose CT (ldCT) in radiographic axial spondyloarthritis (r-axSpA) and compare progression of facet joint ankylosis and syndesmophytes.

Methods: Patients with r-axSpA from the Sensitive Imaging in Ankylosing Spondylitis (SIAS) cohort underwent ldCT at baseline (n = 60) and 2 years (n = 53). Facet joints (right and left, levels C2-S1) were scored as ankylosed, not ankylosed or unable to assess. Joints that were frequently poorly visible (>15% missing), were excluded. Inter-reader reliability on the patient level was assessed with intraclass correlation coefficients (ICCs) and smallest detectable change (SDC). Ankylosis was assessed at joint level and patient level for both timepoints. Syndesmophytes were assessed with CT syndesmophyte score.

Results: Levels C5-T2 were difficult to assess and excluded from all further analyses. Facet joint ICCs were good to excellent for status scores (0.72-0.93) and poor to excellent for progression scores (0.10-0.91). Facet joint ankylosis was detected at every level but most frequently in the thoracic joints. In total, 48% of patients showed 2-year progression. Most progression occurred in the thoracic segment. Using SDCs as cutoff, 18% of patients had progression of facet joint ankylosis only, whereas 20% of patients had progression of syndesmophytes only.

Conclusion: This is the first study evaluating facet joints in the whole spine by ldCT in r-axSpA. Facet joint ankylosis was detected most often in the thoracic spine. Assessing facet joints in addition to syndesmophytes detected substantially more patients with damage progression over two years.

Keywords: ankylosing spondylitis; low-dose computed tomography; outcomes research; spondyloarthritis.

Fig. 1

Percentages of patients with ankylosed facet joints Percentages are given per joint level for the left and right joint, per reader, for baseline (left) and 2-year follow-up (right).

Fig. 2

Cumulative probability plots of progression of facet joint ankylosis Plots are shown for the whole spine (A) and cervical (B), thoracic (C) and lumbar (D) segments

Fig. 3

Cumulative probability plot showing 2-year progression of syndesmophytes and facet joint ankylosis Syndesmophytes were scored with the Computed Tomography Syndesmophyte Score (CTSS). Facet joint ankylosis scores are mean progression scores of the two readers. The plot is ordered by the facet joint ankylosis progression scores. Dots and triangles on the same location on the X-axis belong to the same patient. The scale on the left side of the figure belongs to the facet joint ankylosis progression scores, the scale on the right belongs to the CTSS progression scores.