Comparison of 3 Suture Constructs on Upper One-third Subscapularis Tendon Tear Healing: An Animal Study Comparing Biomechanical, Histological, and Imaging Characteristics of Different Techniques

Background: Although arthroscopic single-row repair is a common approach for treating subscapularis tendon tears, its tendon-to-bone healing efficacy remains to be fully validated, particularly in terms of collagen remodeling and local inflammatory response. The H-loop knotless technique aimed to simplify the procedure and enhance repair stability. However, its healing outcomes compared with either the single-row (SR) or modified Mason-Allen (MMA) technique require experimental evaluation. Purpose: The aim of the study was to compare single-row, MMA, and H-loop techniques for repairing upper one-third subscapularis tendon tears in a rabbit model. The study focused on the inflammatory response at the tendon-bone interface, collagen remodeling, biomechanical properties at different time points, and the magnetic resonance imaging (MRI) signal-to-noise ratio (SNR) of the tendon-bone interface. Study Design: Controlled laboratory study. Methods: A total of 63 New Zealand White rabbits underwent bilateral upper one-third subscapularis tendon injury. The animals were assigned randomly into 3 groups: single-row group, MMA group, and H-loop group. At postoperative week 0, a total of 3 animals from each group were euthanized for biomechanical testing. At weeks 4, 8, and 12, another 6 animals from each group were euthanized: 3 for histological analysis and 3 for MRI and biomechanical assessments. Results: At 12 weeks postoperatively, all groups showed evidence of tendon-to-bone healing, characterized by histological maturation with organized collagen fibers and fibrocartilage formation, improved biomechanical strength, and decreased SNR on MRI. At 12 weeks, the H-loop and MMA groups demonstrated significantly superior tendon-to-bone healing compared with the single-row group, with higher tissue maturity scores (H-loop 15.66 ± 0.51 and MMA 14.33 ± 1.03 vs single-row 12.00 ± 0.89; P < .0001), larger fibrocartilage formation areas (H-loop 0.17 ± 0.02 mm 2 and MMA 0.17 ± 0.003 mm 2 vs single-row 0.13 ± 0.003 mm 2 ; P < .0001), and greater maximum failure loads (H-loop 102.58 ± 1.69 N and MMA 103.31 ± 2.22 N vs single-row 97.44 ± 2.28 N; P < .01). The H-loop and MMA groups also exhibited improved inflammatory regulation, with significantly lower M1/M2 macrophage ratios and reduced expression of cluster of differentiation 86 (CD86) and interleukin 6 (IL-6), while maintaining higher expression of the anti-inflammatory markers cluster of differentiation 206 (CD206) and transforming growth factor β (TGF-β). Notably, the H-loop group had a more mature collagen remodeling pattern, with significantly higher type I collagen deposition at the tendon-bone interface compared with the other 2 groups. MRI assessments revealed a lower SNR in the H-loop group, suggesting better tissue integration. Conclusion: All 3 techniques achieved satisfactory healing. Of these techniques, the H-loop and MMA techniques were superior to the single-row technique for modulating the inflammatory response and providing biomechanical strength. In addition, the H-loop technique resulted in more mature histological structures and a lower SNR. Clinical Relevance: Although this study was conducted in a rabbit model, the findings suggest that the H-loop knotless repair technique may offer biomechanical and biological advantages for subscapularis tendon repair. These results provide a foundation for future translational research and may inform surgical decision-making upon further validation in clinical settings.