Proton-Density Fat Fraction of Rotator Cuff Muscles Is Associated with Isometric Strength 10 Years after Rotator Cuff Repair: A Quantitative MR Imaging Study of the Shoulder

Introduction: To investigate the relationship of proton-density fat fraction (PDFF) of the rotator cuff muscles with semiquantitative magnetic resonance imaging (MRI) scores, cartilage T2 relaxation times, and isometric strength measurements in patients 10 years after rotator cuff repair.

Materials and Methods: Bilateral shoulder MRI was performed in 13 patients (11 male, 2 female; age 72 ± 8 years) 10.9 ± 0.4 years after unilateral autologous periosteal flap augmented rotator cuff repair (26 total shoulders assessed). Goutallier classification, muscle atrophy, rotator cuff tendon integrity, and cartilage defects were determined based on morphological MRI sequences. A sagittal two-dimensional multislice multi-echo sequence was used for quantitative cartilage T2 mapping. A chemical shift encoding-based water-fat separation technique (based on a six-echo three-dimensional spoiled gradient-echo sequence) was used for quantification of the PDFF of rotator cuff muscles. Isometric shoulder abduction strength was measured clinically. Mean and standard deviation, Pearson correlation, and partial Spearman correlation were calculated.

Results: The mean PDFF of rotator cuff muscles was 11.7 ± 10.4%. High supraspinatus PDFF correlated significantly with higher Goutallier scores (R = 0.75; p < 0.001) and with lower isometric muscle strength (R = − 0.49; p = 0.011), also after adjustment for muscle area measurements and tendon rupture (R = − 0.41; p = 0.048). More severe cartilage defects at the humerus were associated significantly with higher supraspinatus PDFF (R = 0.44; p = 0.023). Cartilage T2 values did not correlate with muscle PDFF (p > 0.05).

Conclusion: Because MRI-derived rotator cuff muscle PDFF is associated with isometric strength independently of muscle atrophy and tendon rupture, it may provide complementary clinically important information in tracking rotator cuff muscle composition on a quantitative level.