Hypothesis: A composite of multilayer tendon slices (COMTS) seeded with bone marrow stromal cells (BMSCs) may impart mechanical and biologic augmentation effects on supraspinatus tendon repair under tension, thereby improving the healing process after surgery in rats. Methods: Adult female Lewis rats (n = 39) underwent transection of the supraspinatus tendon and a 2-mm tendon resection at the distal end, followed by immediate repair to its bony insertion site under tension. Animals received 1 of 3 treatments at the repair site: (1) no augmentation, (2) COMTS augmentation alone, or (3) BMSC-seeded COMTS augmentation. BMSCs were labeled with a fluorescent cell marker. Animals were euthanized 6 weeks after surgery, and the extent of healing of the repaired supraspinatus tendon was evaluated with biomechanical testing and histologic analysis. Results: Histologic analysis showed gap formation between the repaired tendon and bone in all specimens, regardless of treatment. Robust fibrous tissue was observed in rats with BMSC-seeded COMTS augmentation; however, fibrous tissue was scarce within the gap in rats with no augmentation or COMTS-only augmentation. Labeled transplanted BMSCs were observed throughout the repair site. Biomechanical analysis showed that the repairs augmented with BMSC-seeded COMTS had significantly greater ultimate load to failure and stiffness compared with other treatments. However, baseline (time 0) data showed that COMTS-only augmentation did not increase mechanical strength of the repair site. Conclusion: Although the COMTS scaffold did not increase the initial repair strength, the BMSC-seeded scaffold increased healing strength and stiffness 6 weeks after rotator cuff repair in a rat model.
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