The prospective evaluation of changes in fatty infiltration and shoulder strength in nonsurgically treated rotator cuff tears.

Background: The purpose of this study was to evaluate the relationship of fatty infiltration in rotator cuff muscles and shoulder strength in rotator cuff tears and these changes during nonsurgical treatment.

Methods: Fifty-three shoulders from 47 patients (mean age: 69.9 years) diagnosed with rotator cuff tears by magnetic resonance imaging (MRI) were treated nonsurgically. The degrees of fatty infiltration in supraspinatus (SSP) and infraspinatus (ISP) muscles were graded by the modified Goutallier classification (grade 0-1, grade 2-3, or grade 4). The isometric strength of the abductors (Abd) and external rotators (ER) were examined with a hand dynamometer. We analyzed the correlation of the modified Goutallier classification in SSP and ISP muscles with the strength of Abd and ER at initial visit. In addition, MRI and strength tests were repeated after 24 ± 6 months, and changes in fatty infiltration and strength were examined.

Results: Fatty infiltration of SSP and ISP muscles had a negative correlation with the strengths of Abd and ER at initial visit, respectively. Six of 45 shoulders (SSP grade: 0-3) and 7 of 43 shoulders (ISP grade: 0-3) had progression of fatty infiltration. Predictive factor of a progression of fatty infiltration during follow-up was decreased initial strength of Abd. There was no significant change in the strength of Abd, and the strength of ER showed significant improvement between the initial and post-treatment measurements. Even in the subgroup that had progression of fatty infiltration at follow-up, the strength of Abd and ER did not decrease significantly.

Conclusions: Although fatty infiltration of the rotator cuff muscles exhibited a negative correlation with muscle strength, fatty infiltration and muscle weakness did not progress at the same rate.