These authors investigates the change in the pennation angle of the supraspinatus muscle after rotator cuff tear repair in 68 patients who underwent arthroscopic rotator cuff repair and magnetic resonance imaging. The size of the tear was measured under arthroscopic visualization. The size of the rotator cuff tear was measured under arthroscopic visualization. By use of the maximum values of either the length or width, full-thickness tears were classified as small (<1 cm), medium (1-3 cm), large (3-5 cm), or massive (>5 cm).Tears with incomplete exposure of their rotator cuff footprints were defined as partial-thickness tears. Large and massive tears were grouped because a tear over 3 cm also includes the infraspinatus tendon.
The pennation angle of the supraspinatus both preoperatively and postoperatively and the integrity of the repaired cuff were determined by magnetic resonance imaging.
The preoperative pennation angle was significantly greater with enlargement of the tear size (P < .0001, analysis of variance).
The pennation angle (θ) is subtended by the anterior muscle fiber (thin line) and the central axis of the intramuscular tendon (thick line). The measured region extends 30 mm medially from the articular surface of the glenoid.
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 retears were noted in patients with partial and small tears.
The retear rate was 90.9% when the preoperative pennation angle was 20° or greater and was 12.3% when this angle was 19° or less, and the risk ratio for retear was 7.4 when this angle was 20° or greater. Comparison between the preoperative and postoperative pennation angles showed a significant decrease in the mean value from 11.8° ± 3.7° to 9.9° ± 3.0° in the medium tear group (P = .007, paired ttest) but no significant difference in the large or massive tear group (from 15.1° ± 7.0° to 13.3° ± 5.8°) (P = .33).
Comment: The retear rates were high for tears larger than "small". This article did not report clinical outcomes for the patients.
We wonder whether the pennation angle is affected by the degree of retraction, with more retracted tendons having a greater angle.
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