OBJECTIVETo evaluate the diagnostic value of pelvis bone marrow fat depositions (BMFD) displayed by magnetic resonance imaging (MRI) in patients with ankylosing spondylitis (AS).

METHODSEighty-eight subjects undergoing pelvic MRI examinations were enrolled in this study, including 44 with clinically confirmed AS (39 male and 5 female patients with a mean age of 26.41∓8.09 years) and 44 control subjects without AS (37 male and 7 female subjects with a mean age of 29.32∓7.31 years). The incidence of BMFD in the bilateral sacroiliac (SI) joints and acetabulum were compared between the two groups. The distribution features of BMFD of the periarticular cancellous bone marrow in the pelvis and in other regions of the pelvis were analyzed for the AS patients, and the incidence of BMFD was determined in different stages of sacroiliitis and hip arthritis.

RESULTSThe incidence of BMFD in the SI joints and acetabulum was significantly higher in the AS patients than in the control subjects (P<0.01); The incidence of BMFD was significantly higher in the periarticular cancellous bone marrow than in the other positions of pelvis (P<0.01). The incidence of BMFD ranged from 40.0% to 45.9% in early stages of sacroiliitis, significantly lower than the incidence in later stages (58.3%-73.1%, P<0.01); the incidence showed no difference between different stages of hip arthritis (P>0.01).

CONCLUSIONSAS patients have a higher incidence of BMFD in the pelvis than control subjects. BMFD is distributed mainly under the articular surface, seen throughout the stages of AS, indicating that BMFD is an important pathological change of the bone marrow in AS to potentially allow early diagnosis of AS.