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

Abstract Introduction Rotator 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 Methods 102 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. Results Interobserver 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 The mean values of 3DFI and 3DML were 0.9% and 5.3% for Goutallier-0, 2.9% and 25.6% for Goutallier-1, 11.4% and 49.5% for Goutallier-2, 20.7% and 59.7% for Goutallier-3, and 29.3% and 70.2% for Goutallier-4, respectively. Conclusion The Goutallier score has been helping surgeons by using 2-dimensional CT-scan slices. However, this grading is associated with suboptimal interobserver agreement. The new measures we propose provide a more consistent assessment that correlates well with Goutallier’s principles. As 3DML measurements incorporate atrophy and fatty infiltration, they could become a very reliable index for assessing shoulder muscle function. Future algorithms capable of automatically calculating the 3DML of the cuff could help in the decision process for cuff repair and the choice of anatomic or reverse shoulder arthroplasty.