LAUSR

BACKGROUND The purpose of this study was to evaluate the mechanical, structural, and histological quality of rotator cuff repairs augmented with an interposition electrospun nanofiber scaffold composed of polyglycolic acid (PGA) and poly-L-lactide-co-ε-caprolactone (PLCL) in an acute sheep model. METHODS Forty (n=40) acute infraspinatus tendon detachment and repair procedures were performed in a sheep infraspinatus model using a double row transosseous equivalent anchor technique with either an interposition nanofiber scaffold composed of PGA-PLCL or with no scaffold. Animals were euthanized at 6-week (n=20 samples) and 12-week (n=20 samples) postoperative timepoints to assess the biomechanical and histological properties of the repairs and to compare differences with each group. RESULTS Within the scaffold-treated group treatment there was a significant increase in ultimate failure force (N) from 6 to 12 weeks (p < 0.01), a significant increase in ultimate failure load from 6 to 12 weeks (p < 0.01) and a significant increase in ultimate failure stress (MPa) from 6 to 12 weeks (p < 0.01). At 6 weeks, tendon-bone attachment was most consistent with an "indirect" type of insertion while at 12 weeks a visible difference in the progression and re-formation of the enthesis was observed. Compared to controls, animals in the scaffold-treated group displayed an insertion of the fibrous tendon with the humeral footprint that was beginning to be organized in a manner similar to the "native" direct/fibrocartilaginous insertion of the ovine infraspinatus tendon. In the majority of these animals treated with the scaffold, prominent perforating collagen fibers, similar to "Sharpey's fibers", were present and extending through a region of calcified fibrocartilage and attaching to the humeral footprint. There were no surgical complications in any of the 40 sheep, including delayed wound healing or infection. CONCLUSIONS In a sheep acute rotator cuff repair model, securing a nanofiber scaffold between the tendon and the bone using a double row transosseous equivalent anchor fixation technique resulted in greater failure strength. Additionally, at the enthesis Sharpey fiber-like attachments (i.e., collagen fibers extending form the tendon into calcified fibrocartilage of the humerus) were observed, which was not seen in the control group.