Backfill is a specific sign of XXXX seen on MRI.

@entity1 @entity615 @entity1691
OBJECTIVES: To summarize the characteristics of backfill in @entity1 with @entity1691 (SpA) and @entity1 with @entity615 ( @entity615 ) and healthy controls, and to assess the value of backfill in diagnosing axial SpA. METHODS: Three readers blinded recorded backfill seen on T1SE MRI scans from 647  subjects: 297  @entity1 with @entity1691 ( @entity1691 ), 126  @entity1 with non-radiographic axial SpA (nr-axSpA), 147  @entity1 with @entity615 , and 77  healthy controls. The SPARCC SIJ Structural Score (SSS) method was used to assess backfill. The changes of backfill were evaluated by the follow-up MRI scans from 157  @entity1 . We summarized the characteristics of backfill and calculated its sensitivity and specificity for diagnosing axial SpA. RESULTS: Backfill was recorded in 78.8% @entity1691 @entity1 , 11.1% nr-axSpA @entity1 , 1.8% @entity1 with @entity615 , and no healthy control. Backfill affected more frequently at ilium bone, lower half of sacroiliac joints in axial SpA (both P<0.05). The SSS score of backfill was much higher in axial SpA than in @entity1 with @entity615 (both P<0.01) and it did not correlate with demographics and BASDAI, BASFI, and CRP (all P>0.05). The score of backfill only positively correlated with symptom duration in @entity1691 (r=0.251, P<0.01) and in nr-axSpA (r=0.743, P<0.01) @entity1 . Only 8.9% @entity1 had the change of backfill in an average follow-up time of 1.09  years. Backfill had high specificity (0.98) and moderate sensitivity (0.59) for diagnosing axial SpA. CONCLUSIONS: We summarized the characteristics of backfill and found that backfill is a specific sign of axial SpA seen on T1SE MRI.
