FRI0440 Presence of bone marrow edema on magnetic resonance imaging of the sacroiliac joints in military recruits before and after 6 weeks of intensive physical training

Background Studies have shown an increase of bone marrow edema (BME) on magnetic resonance imaging (MRI), especially in feet and ankles of professional athletes and in minimally active healthy controls after mechanical stress [1]. Although this has been described for several joints and across different sport activities, information concerning BME in the sacroiliac joints (SIJ) has not been studied. In axial spondyloarthritis (AxSpA), the presence of 1 BME lesion (characteristics typical for AxSpA) on 2 consecutive slices or 2 BME lesions on 1 slice is sufficient to fulfill the definition of a positive MRI as defined by ASAS. Although this definition should only be applied on MRI of symptomatic patients with suspicion of SpA, it is unknown whether BME lesions in healthy controls could meet this definition and therefore incorrectly be interpreted as BME in the context of SpA. Objectives Study the effect of intense physical training in healthy subjects on the presence of BME on MRI-SIJ, by investigating whether healthy subjects meet the ASAS definition of a positive MRI and whether this is modulated by mechanical stress. Methods Twenty-two military recruits underwent a MRI-SIJ before and after 6 week of intense and uniform physical training. BME lesions were scored by 3 trained readers (MdH, GV and TR) blinded for time sequence and clinical findings. Additionally, the agreement with the definition of a positive MRI defined by ASAS was evaluated. Regarding the number of lesions and fulfillment of the ASAS definition of positive MRI, a consensus was made by agreement of 2 out of 3 readers. Results In total, 86.4% (19/22) asymptomatic recruits were male (mean age of 25.0±0.8 years). At baseline, 40.9% (9/22) of recruits presented with at least one BME lesion, whereas this number increased to 50.0% (11/22) at week 6. Indeed, 3 recruits developed BME over time, whereas in one recruit the BME lesions disappeared over time. The mean number of BME lesions was 1.0 (±0.3) at baseline, compared to 1.9 (±0.7) at week 6. Median (25th, 75th percentile) BME lesions were 0.0 (0.0, 2.25) and 0.5 (0.0, 3.0) at respectively baseline and week 6 (P=0.109). Mean change in BME lesions was 0.9 (±0.6). When applying the ASAS definition of a positive MRI, BME was present in 22.7% (5/22) of recruits at baseline, and this increased to 36.4% at follow up, of which an additional 4 initially MRI negative recruits became MRI positive and one recruit no longer fulfilled the definition. Conclusions In this small exploratory study we could not find a statistically significant difference in BME on MRI-SIJ after 6 weeks of training. However, over 1/5 of asymptomatic recruits displayed BME lesions, that would meet the ASAS definition of a positive MRI, increasing to more than 1/3 at follow up. Thus, in young active patients, the interpretation of BME lesions should be cautious. References Kornaat PR, Van de Velde SK. Bone marrow edema lesions in the professional runner. The American journal of sports medicine 2014;42(5):1242–6. Acknowledgements ASAS research grant 2017. Disclosure of Interest None declared