Evaluation of Tendon Fastener Designed for Percutaneous Placement in an Ovine Model for Repair of Articular-Sided Rotator Cuff Tears

Introduction: Surgical treatment for partial-thickness rotator cuff tendon (RCT) tears often involves open or arthroscopic conversion to a full-thickness tear. A novel method has been developed that utilizes sutureless bone-to-tendon fixation using a percutaneous fastener. Purpose: This study characterizes the biomechanical stability of the fastener in a partial-tear ovine rotator cuff model compared to that of a screw-and-washer. Methods: The study included an ex vivo cadaveric phase and an in vivo pilot. During the ex vivo phase, the infraspinatus tendon was partially transected in 20 cadaveric sheep shoulders. Shoulders were allocated into three groups: fastener (FS) (n = 10), screw-and-washer (S/W) (n = 7), and an empty group without fixation (n = 3). In an in vivo pilot, three sheep underwent bilateral partial infraspinatus transection and repair, with the fastener in one shoulder and the screw-and-washer in the contralateral shoulder; animals were euthanized at 8 weeks for histological analysis. Both cohorts underwent biomechanical assessments, and the in vivo samples underwent histological dissection and analysis. Results: No significant biomechanical differences were noted among the three groups in ultimate load (FS: 2822 N, S/W: 2599 N, empty: 2924 N), ultimate displacement (FS: 15.9 mm, S/W: 15.5 mm, empty: 13.8 mm), stiffness (FS: 252.4 N/mm, S/W: 237.7 N/mm, empty: 279.9 N/mm), cross-sectional area (FS: 90.0 mm2, S/W: 93.0 mm2, empty: 78.8 mm2), ultimate stress (FS: 32.9 MPa, S/W: 28.3 MPa, empty: 37.8 MPa), ultimate strain (FS: 0.203 mm/mm, S/W: 0.183 mm/mm, empty: 0.183 mm/mm), or elastic modulus (FS: 231.1 MPa, S/W: 220.3 MPa, empty: 271.3 MPa). The mode of failure was most frequently a mid-substance tear. Both the fastener and the screw-and-washer demonstrated comparable histology across the graded parameters regardless of the evaluated animal or sample. Conclusions: The fastener offers similar biomechanical stability to that of a screw-and-washer construct in the treatment of partial rotator cuff tears in an ovine model. Clinical Relevance: The results of this animal model study provide evidence to consider further clinical testing.