Biomechanics of Polyhydroxyalkanoate Mesh–Augmented Single-Row Rotator Cuff Repairs
Polyhydroxyalkanoate (PHA) mesh is a bioresorbable scaffold used to reinforce the suture–tendon interface in rotator cuff repairs (RCRs). We conducted a study of cyclic and ultimate failure properties of PHA mesh–augmented single-row RCRs and nonaugmented RCRs. Eight pairs of fresh-frozen cadaver humeri (6 male, 2 female) were tested. Mean (SD) age was 61 (9) years. The supraspinatus tendon was resected and reattached in a single-row configuration using 2 triple-loaded suture anchors and 6 simple stitches. The opposite humerus underwent RCR augmented with 2 strips of 13-mm × 23-mm PHA mesh. Humeri were mounted in an Instron load frame, cycled 1000 times to 1.0 MPa of effective stress, and loaded to failure. Construct gapping and ultimate failure loads/displacements were recorded. Paired t tests compared augmented and nonaugmented RCRs (P ≤ .05 was significant). There was no difference in gapping over 1000 cycles (P = .879). Mean (SD) failure load was higher for PHA mesh–augmented RCRs, 571 (173) N, than for nonaugmented (control) RCRs, 472 (120) N (P = .042), and failures were consistent within pairs because of tissue failure at the knots or anchor pullout. This technique for arthroscopic augmentation can be used to improve initial biomechanical repair strength in tears at risk for failure.
Study Limitations
This study had several limitations. First, it was a cadaveric biomechanical study that evaluated only time-zero biomechanical properties. Loads were normalized to tendon size, specimens were randomized between sides, and paired specimens were used to minimize the effects of tendon and bone quality on outcome metrics. In addition, donor tendons were representative of otherwise healthy tissue. Chronic tears and associated resorption/atrophy could have affected the magnitude of forces and gapping detected in this study. Theoretically, over time the tendon tissue will adhere to and grow into the mesh, which could minimize potential differences. Studies are needed to determine the effects of healing on long-term repair strength in affected patients. Last, all constructs were performed in open fashion to improve repeatability of construct placement and provide accessibility for Instron testing. Our technique did not directly replicate the arthroscopic approach, but, unlike other augmentation techniques, it is so simple that transition to all-arthroscopic augmentation is realistic.
Patch augmentation increases the cost of materials and operative time and should be considered a limitation of its utility. We do not recommend augmentation in all RCRs, as it likely is cost-ineffective. Instead, we recommend augmentation in cases of poor tissue quality, which could lead to healing failure, revision surgery, and higher overall patient costs beyond the cost of adding augmentation. Similarly, we recommend augmentation for revision cases in which tendon healing has failed and tissue quality is poor. The goal is to prevent another failure.
Conclusion
PHA graft augmentation of single-row triple-loaded anchor repairs of the supraspinatus tendon improves the overall ultimate load to failure by 25%. There was no difference in gap formation after cyclic loading between augmented and nonaugmented repairs. This technique for arthroscopic augmentation can be used to improve initial biomechanical repair strength in tears at risk for failure.
Am J Orthop. 2016;45(7):E527-E533. Copyright Frontline Medical Communications Inc. 2016. All rights reserved.
