| Single articular surface | Either ilium: 87% (82–91) – 91% (87–95) | Either ilium: 46% (39–52) - 51% (44–58) |
| Either sacrum: 93% (89–96) – 94% (90 – 97) | Either sacrum: 19% (14–25) - 21% (16–26) |
| Any 2 articular surfaces | 96% (94–99) – 99% (98–100) | 10% (6–14) - 41% (35–48) |
| All 4 articular surfaces | 99% (8–100) | 14% (9 – 19) |
| Erosion of articular surface (s) involved | Specificity (95% CI) | Sensitivity (95% CI) |
| Single articular surface | Either ilium: 90% (85–94) | Either ilium: 77% (71–83) |
| Either sacrum: 94% (91–98) | Either sacrum: 65% (58–72) |
| Any 2 articular surfaces | 96% (93–99) – 100% (100–100) | 24% (18–31) – 67% (60–74) |
| All 4 articular surfaces | 100% (100–100) | 38.1% (31–45) |
| Ankylosis of articular surface (s) involved | Specificity (95% CI) | Sensitivity (95% CI) |
| Single joint | 92% (88 – 95) | 60% (53–66) |
| Both joints | 93% (89 – 96) | 58% (51–64) |