Purpose To determine the degree of preoperative fatty degeneration within muscles, postoperative longitudinal changes in fatty degeneration, and differences in fatty degeneration between patients with full-thickness supraspinatus tears who do and those who do not experience a retear after surgery. Materials and Methods This prospective study had institutional review board approval and was conducted in accordance with the Committee for Human Research. Informed consent was obtained. Fifty patients with full-thickness supraspinatus tears (18 men, 32 women; mean age, 67.0 years ± 8.0; age range, 41-91 years) were recruited. The degrees of preoperative and postoperative fatty degeneration were quantified by using a two-point Dixon magnetic resonance (MR) imaging sequence; two radiologists measured the mean signal intensity on in-phase [S(In)] and fat [S(Fat)] images. Estimates of fatty degeneration were calculated with "fat fraction" values by using the formula S(Fat)/S(In) within the supraspinatus, infraspinatus, and subscapularis muscles at baseline preoperative and at postoperative 1-year follow-up MR imaging. Preoperative fat fractions in the failed-repair group and the intact-repair group were compared by using the Mann-Whitney U test. Results The preoperative fat fractions in the supraspinatus muscle were significantly higher in the failed-repair group than in the intact-repair group (37.0% vs 19.5%, P < .001). Fatty degeneration of the supraspinatus muscle tended to progress at 1 year postoperatively in only the failed-repair group. Conclusion MR imaging quantification of preoperative fat fractions by using a two-point Dixon sequence within the rotator cuff muscles may be a viable method for predicting postoperative retear. (©) RSNA, 2016.

An increase in supraspinatus fatty degeneration was statistically significantly correlated with severity of supraspinatus tears and moderately correlated with muscular atrophy. Fatty degeneration tends to progress more rapidly than muscular atrophy in female patients, with statistically significant sex differences.

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