Scoring system used to evaluate 5 consecutive slices in the SPARCC SSS.
| Feature | Definition | Score per Slice |
|---|---|---|
| Fat metaplasia | Increased signal on T1W sequences; homogeneous increased signal that extends ≥ 1 cm from the joint surface | 0–8 |
| Erosion | Full thickness loss of cortical bone at its anticipated location and loss of normal bright appearance of adjacent bone marrow | 0–8 |
| Backfill | Complete loss of cortical bone at its anticipated location and increased T1 signal clearly demarcated from adjacent normal marrow by dark band with irregular contour on T1W sequence | 0–4 |
| Ankylosis | T1W bone marrow signal extending between the sacral and iliac bone marrow with full thickness loss of dark appearance of cortical bone | 0–4 |
| Sclerosis | Dark appearance of cortical bone on T1W sequence extending > 5 mm beyond the cortical margin | 0–8 |
SPARCC: Spondyloarthritis Research Consortium of Canada; SSS: Sacroiliac joint Structural Score; T1W: T1-weighted.