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From the Southern California Permanente Medical Group, Woodland Hills Medical Center, Department of Orthopaedic Surgery, Los Angeles, California, the Kerlan-Jobe Orthopaedic Clinic, Los Angeles, California, and the Orthopaedic Biomechanics Laboratory, VA Long Beach Healthcare System, Long Beach, California, and University of California–Irvine, Irvine, California
* Address correspondence to Maxwell C. Park, MD, Southern California Permanente Medical Group, Woodland Hills Medical Center, Department of Orthopaedic Surgery, 5601 De Soto Avenue, Los Angeles, CA 91365 (e-mail: mcp16{at}columbia.edu).
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.
Key Words: rotator cuff • double-row • transosseous-equivalent • rotation • biomechanics
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