2015 ISAKOS Biennial Congress ePoster #2422

Change in the Pennation Angle of the Supraspinatus Muscle After Rotator Cuff Repair

Ikuta Hayashi, MD, PhD, Yonago, Tottori JAPAN
Makoto Enokida, MD, Yonago JAPAN
Takahiro Yamashita, Yonago City, Tottori Prefecture JAPAN
Tottori University, Yonago, Tottori, JAPAN

FDA Status Cleared

Summary: We evaluated the change in pennation angle of the supraspinatus muscle after rotator cuff repair. Preoperative pennation angle is directly correlated with the tear size and can be useful to predict repaired cuff integrity. Restoration of pennation angle after arthroscopic repair associate with the tear size.

Abstract:

Purpose

The pennation angle of the rotator cuff muscle is an important architectural and functional feature of pennate muscles. Several studies have reported on the pennation angles of intact rotator cuff muscles; however, few studies have reported on the pennation angles of rotator cuff tears. In this study, we evaluated the change in pennation angle of the supraspinatus muscle after rotator cuff repair.

Methods

Arthroscopic rotator cuff repair was performed in 107 consecutive patients by our senior surgeon between November, 2005 and March, 2014. The criterion for inclusion in the study was evaluability by magnetic resonance imaging (MRI) both preoperatively and at a minimum of 6 months after the repair. The criterion for exclusion was poor scan image quality due to artifact creation. Finally, 68 patients were enrolled. The size of the rotator cuff tear was measured under arthroscopic visualization. Using the maximum values of either the length or width, full-thickness tears were classified as small (<1 cm), medium (1–3 cm), or large/massive (3–5 cm/>5 cm). Tears with no exposure of their rotator cuff footprints were defined as partial-thickness tears. Shoulder MRI scans were analyzed in the T2-weighted axial plane and oblique coronal planes. The pennation angle (the angle subtended by the central axis of the intramuscular tendon and anterior muscle fiber in supraspinatus) was measured in a specific region extending from the articular surface of glenoid to 30 mm medially in the axial plane by MRI preoperatively and postoperatively. Repaired cuff integrity was evaluated using the criteria established by Sugaya et al. Types 1, 2, and 3 were defined as the repair types, and types 4 and 5 as the re-tear types.

Results

The mean age of all 68 patients (37 men, 31 women) was 63.5 years (range, 30–80) at the time of arthroscopic rotator cuff repair. The mean duration from surgery to postoperative MRI was 11.1 months (range, 6–13). The configurations of tears were partial in 17 patients, small in 10, medium in 24, large/massive in 17. Mean preoperative pennation angle was 8.6 degrees in partial, 10.0 degrees in small, 11.9 degrees in medium, 20.2 degrees in large/massive tear patients. Preoperative pennation angle increased significantly with enlargement of the tear size (p < 0.001). Rates of re-tear were 29% in medium tear and 59% in large/massive tear patients. The preoperative pennation angle over 20 degrees had a sensitivity of 88.9% and specificity of 84.7% for re-tear. For repair types, comparison between the preoperative and postoperative pennation angle showed that the mean significantly decreased 11.8 degrees to 9.9 degrees in the medium tear group (p < 0.01) , but had no significant difference in the large/massive tear group (15.1 degrees to 13.3 degrees) (p = 0.33).

Conclusion

Preoperative pennation angle is directly correlated with the tear size and can be useful to predict repaired cuff integrity. Restoration of pennation angle after arthroscopic repair is associated with the tear size.