Biomechanical performance of rotator cuff repairs with humeral rotation: a new rotator cuff repair failure model.

BACKGROUND Traditional biomechanical evaluations of rotator cuff repair techniques employ cyclic loading of the supraspinatus tendon in an isolated medial direction. PURPOSE This study was conducted to evaluate 2 different rotator cuff repair techniques that are currently the subject of debate with cyclic loading and with internal and external humeral rotation to better simulate postoperative rehabilitation. STUDY DESIGN Controlled laboratory study. METHODS Nine fresh-frozen paired human cadaver shoulders (18 shoulders) were studied. A single-row repair with 2 suture anchors was compared with a double-row repair with 4 suture anchors. The shoulders were tested in a custom device to position the shoulder in neutral, 45 degrees of internal rotation, and 45 degrees of external rotation. Cyclic loading of the supraspinatus tendon was performed with an MTS material testing machine. Gap formation was measured and analyzed for each rotational position using the MTS device. RESULTS For the single-row repair, average gap formation per 100 cycles in the positions of neutral, internal, and external humeral rotation was 1.47 +/- 0.63, 3.11 +/- 1.55, and 2.24 +/- 0.94 mm, respectively. For the double-row repair, average gap formation per 100 cycles in the positions of neutral, internal, and external humeral rotation was 1.25 +/- 0.54, 2.29 +/- 1.10, and 1.57 +/- 0.48 mm, respectively. For gapping averaged over all positions, the double-row repair had significantly less gapping than the single-row repair (P = .0109); gapping was greatest for internal rotation, followed by external rotation, and least for neutral (P < .0001). CONCLUSION The testing method of including a rotational component in biomechanical rotator cuff repair testing is a more realistic model of the loading conditions experienced by a repaired rotator cuff as the patient participates in postoperative rehabilitation. Double-row repair has better fixation strength than single-row repairs when exposed to cyclic loading and changes in humeral rotation position. CLINICAL RELEVANCE Humeral rotation affects rotator cuff fixation and should be considered in postoperative rehabilitation.