Fat Metaplasia and Backfill Are Key Intermediaries in the Development of Sacroiliac Joint Ankylosis in Patients With Ankylosing Spondylitis

摘要

Fat metaplasia in bone marrow on T1‐weighted magnetic resonance imaging (MRI) scans may develop after resolution of inflammation in patients with ankylosing spondylitis (AS) and may predict new bone formation in the spine. Similar tissue, termed backfill, may also fill areas of excavated bone in the sacroiliac (SI) joints and may reflect resolution of inflammation and tissue repair at sites of erosions. The purpose of this study was to test our hypothesis that SI joint ankylosis develops following repair of erosions and that tissue characterized by fat metaplasia is a key intermediary step in this pathway.