Change in the pennation angle of the supraspinatus muscle after rotator cuff tear repair

Background: The pennation angle is an important architectural and functional feature of pennate muscles. The purpose of this study was to investigate the change in the pennation angle of the supraspinatus muscle after rotator cuff tear repair. Materials and methods: The study included 68 patients who underwent arthroscopic rotator cuff repair and magnetic resonance imaging. The size of the tear was measured under arthroscopic visualization. The pennation angle of the supraspinatus both preoperatively and postoperatively and the integrity of the repaired cuff were determined by magnetic resonance imaging. Results: The preoperative pennation angle was significantly greater with enlargement of the tear size (P < .0001, analysis of variance). The retear rate was 29% in patients with medium tears and 59% in patients with large or massive tears. No retear was noted in patients with partial and small tears. The retear rate was 90.9% when the preoperative pennation angle was 20 degrees or greater and was 12.3% when this angle was 19 degrees or less, and the risk ratio for retear was 7.4 when this angle was 20 degrees or greater. For repair-type tears, comparison between the preoperative and postoperative pennation angles showed a significant decrease in the mean value from 11.8 degrees +/- 3.7 degrees to 9.9 degrees +/- 3.0 degrees in the medium tear group (P = .007, paired t test) but no significant difference in the large or massive tear group (from 15.1 degrees +/- 7.0 degrees to 13.3 degrees +/- 5.8 degrees) (P = .33). For retear-type tears, no significance was found between groups. Conclusion: The preoperative pennation angle is directly correlated with the tear configuration and could be one of the prognostic factors for postoperative cuff integrity. To restore the pennation angle, primary repair is more appropriate in smaller rotator cuff tears than in medium-sized tears. (C) 2018 Journal of Shoulder and Elbow Surgery Board of Trustees. All rights reserved.