The Effect of Dynamic External Rotation Comparing 2 Footprint-Restoring Rotator Cuff Repair Techniques

Abstract

Background Allowing for humeral external rotation while loading rotator cuff repairs has been shown to affect tendon biomechanics when compared with testing with the humerus fixed. Adding dynamic external rotation to a tendon-loading model using footprint-restoring repairs may improve our understanding of rotator cuff repair response to a common postoperative motion. Hypothesis A tendon suture-bridging repair will demonstrate better load sharing compared to a double-row repair, and there will be a differential gap formation between the anterior and posterior tendon regions. Study Design Controlled laboratory study. Methods In 6 fresh-frozen human cadaveric shoulders, a tendon suture-bridging rotator cuff repair was performed; a suture limb from each of 2 medial anchors was bridged over the tendon and fixed laterally with an interference screw. In 6 contralateral match-paired specimens, a double-row repair was performed. For all specimens, a custom jig was employed that allowed dynamic external rotation (0° to 30°) with loading. A materials testing machine was used to cyclically load each repair from 0 N to 90 N for 30 cycles; each repair was then loaded to failure. A deformation rate of 1 mm/s was employed for all tests. Gap formation between tendon edge and insertion was measured using video digitizing software. Results The yield load for the suture-bridging technique (161.88 ± 35.09 N) was significantly larger than the double-row technique (135.17 ± 24.03 N) (P = .026). The yield gap between tendon and lateral footprint was significantly greater anteriorly than posteriorly (1.62 ± 0.82 mm and 0.68 ± 0.47 mm, respectively) for the suture-bridging technique (P = .024) but not for the double-row technique (1.35 ± 0.52 mm and 1.05 ± 0.50 mm, respectively) (P = .34). There were no differences for gap formation, stiffness, ultimate load to failure, and energy absorbed to failure between the 2 repairs (P > .05). The anterior regions of the repair were the first to fail in all constructs. The suture-bridging repair remained interconnected for 5 of 6 repairs. Conclusions The tendon suture-bridging rotator cuff repair has a yield load that is higher than the double-row repair when allowing for external rotation during load testing. External rotation can accentuate gap formation anteriorly at a repaired rotator cuff footprint. Clinical Relevance Based on the tension of repair, there may be a role for reinforcing the repair anteriorly and limiting external rotation postoperatively.