AB1471-HPR The reliability and validity of a novel MRI-based tool for the evaluation of forefoot bursae in patients with rheumatoid arthritis: The “FFB-score”
Authors: L. Hooper, L. King, M. Thomas, F. Roemer, D. Culliford, C. Bowen, N.K. Arden, C.J. Edwards
Journal: Annals of the Rheumatic Diseases (2013)

<h3>Background</h3> We recently demonstrated forefoot bursae (FFB) are a clinically important feature in patients with rheumatoid arthritis (RA)<sup>1</sup>. However, there is a need for an observer-independent, reliable and valid method of characterising FFB. Magnetic Resonance Imaging (MRI) allows improved visualisation and characterisation of FFB in multiple imaging planes. <h3>Objectives</h3> To determine the reliability and validity of a novel MRI-based scoring tool for the evaluation of FFB in patients with RA. <h3>Methods</h3> A collaborative process of tool design was completed by a team of rheumatologists, radiologists, and podiatrists from centres within the UK &amp; Germany. In an iterative process of tool design, items to be included, grading criteria, overall utility and MRI sequences were determined. The <i>FFB-Score</i> assesses 9 distinct forefoot regions and contains 5 items; lesion presence, shape, enhancement and T1 &amp; T2 characteristics. The final tool was evaluated on 42 consecutive patients with RA, mean(SD) age 62.2(±12) years, disease duration 15.3(±10.3) years, &amp; DAS-28 3.1(±1.4), who were recruited from a UK rheumatology clinic. Images were obtained using a 1.5T whole body scanner and 4-channel flex extremity coil. The MRI protocol included coronal T1 &amp; STIR, coronal &amp; sagittal T1 post-gadolinium, and long axis 3D SPACE sequences. The intra and inter-reader reliability were evaluated using Percentage Exact/Close Agreement (PEA/PCA). Content validity was evaluated using Lawshes' Content Validity Ratio. Discriminant validity, with regards to differentiation between high/low clinical markers of disease activity (DAS-28), MRI-determined disease activity (erosion, bone marrow oedema, synovitis) or foot-related disability (Foot Impact Scale), was evaluated using receiver operator characteristic curves and area under the curve analysis. <h3>Results</h3> The intra-reader reliability was determined as moderate for intermetatarsal soft tissue lesion shape (PEA:40% PCA:50%) and T1/T2 characteristics (PEA:60% PCA:90%, PEA:30% PCA:80% respectively) and good for all other items (PEA:50-90% PCA:100%). Inter-reader reliability was determined as good for all items (PEA:50-90% PCA:100%). Content validity was determined as good (Lawshes' CVR:0.625). The <i>FFB-score</i> total lesion enhancement grading has good discriminant validity when differentiating between patients with high/low MRI-determined disease activity in the forefoot (erosion:p=0.011, synovitis:p=0.004, oedema:p=0.018). The <i>FFB-score</i> has good discriminant validity for high/low reported foot impairment and activity limitation (p=0.006, p=0.033 respectively). <h3>Conclusions</h3> The <i>FFB-Score</i> is a viable tool for the detection and evaluation of FFB in patients with RA, which demonstrates satisfactory intra/inter-reader agreement and validation. Further validation, assessment of responsiveness and refinement of the <i>FFB-score</i> is needed in order to maximize the potential utility in clinical trials and epidemiological studies. <h3>References</h3> Bowen CJ et al. The clinical importance of ultrasound detectable forefoot bursae in rheumatoid arthritis. Rheumatol. (Ox.) 2010;59:1:191-2 <h3>Disclosure of Interest</h3> None Declared