3D Muscle Loss (3DML) assessment: A novel CT-based quantitative method to evaluate rotator cuff muscle fatty infiltration

International audience; IntroductionRotator cuff fatty infiltration (FI) is one of the most important parameters to predict the outcome of certain shoulder conditions. The primary objective of this study was to define a new computed tomography (CT)-based quantitative 3-dimensional (3D) measure of muscle loss (3DML) based on the rationale of the 2-dimensional (2D) qualitative Goutallier score. The secondary objective of this study was to compare this new measurement method to traditional 2D qualitative assessment of FI according to Goutallier et al and to a 3D quantitative measurement of fatty infiltration (3DFI).Materials and Methods102 CT scans from healthy shoulders (46) and shoulders with cuff tear arthropathy (21), irreparable rotator cuff tears (18), and primary osteoarthritis (17) were analyzed by three experienced shoulder surgeons for subjective grading of fatty infiltration according to Goutallier and their rotator cuff muscles were manually segmented. Quantitative 3D measurements of fatty infiltration (3DFI) were completed. The volume of muscle fibers without intra-muscular fat was then calculated for each rotator cuff muscle and normalized to the patient’s scapular volume to account for the effect of body size (NVfibers). Three-dimensional muscle mass (3DMM) was calculated by dividing the NVfibers value of a given muscle by the mean expected volume in healthy shoulders. Three-dimensional muscle loss (3DML) was defined as 1-(3DMM). The correlation between Goutallier grading, 3DFI, and 3DML was compared using a Spearman Rank correlation.ResultsInterobserver reliability for the traditional 2D Goutallier grading was moderate for the infraspinatus (ISP=0.42) and fair for the supraspinatus (SSP=0.38), subscapularis (SSC=0.27) and teres minor (TM=0.27). 2D Goutallier grading was found to be significantly and highly correlated with 3DFI (SSP=0.79, ISP=0.83, SSC=0.69, TM=0.45) and 3DML (SSP=0.87, ISP=0.85, SSC=0.69, TM=0.46) for all four rotator cuff muscles (p