In Vivo Assessment of a Load-Bearing Biphasic Osteotendinous Braided Collagen Scaffold for Reconstruction of Massive Irreparable Rotator Cuff Defects.

Massive, irreparable rotator cuff tears affect a significant patient population and often require invasive procedures such as allograft patch augmentation, superior capsule reconstruction, and muscle transfers due to the limited regenerative capacity and inability to reattach the rotator cuff to the humerus. Current surgical techniques primarily focus on mechanically reinforcing the tendon without promoting biological integration, leading to high re-tear rates and functional limitations. This study aimed to evaluate OsTend, a biphasic osteotendinous scaffold designed to span the MIRC defect by bridging the muscle to the bone footprint. As such, OsTend is designed to be conducive to supporting tendon and bone regeneration while enabling muscle tissue ingrowth. OsTend consists of electrochemically aligned collagen threads braided into a three-region scaffold: a proximal region for muscle integration, a midsection as a tendon regeneration template along with a polycaprolactone membrane as a suture rip-stop, and a hydroxyapatite-infused distal region to facilitate bone ingrowth. A total of 16 New Zealand White rabbits underwent unilateral infraspinatus tendon resection and repair with OsTend, followed by biomechanical testing, micro-computed tomography, and histological analysis at 1 and 3 months postimplantation. Results demonstrated a 65% increase in ultimate tensile strength from 1 month (102.1 ± 21.5 N) to 3 months (167.9 ± 62.3 N). Tendon retraction between 1 month (7.47 ± 2.61 mm) and 3 months (6.77 ± 1.91 mm) was < 2 mm during the study period. Bone volume fraction at 1 month (24.80% ± 8.30%) and 3 months (21.52% ± 4.97%) of the footprint reached approximately 75% of the intact bone (30%). Between 1 and 3 months, the failure mode of repaired shoulders shifted from pullout at the enthesis (80% at 1 month) to rupture at the mid-substance (100% at 3 months), indicating attainment of a functional integration between bone and scaffold over time. Histological analysis revealed collagen fiber alignment in the muscle and tendon regions and bone-like tissue formation surrounding the hydroxyapatite-infused region. These findings suggest that OsTend reestablishes tendon-bone attachment with structural integrity; thus, this multiphasic biotextile platform holds the potential as an off-the-shelf biomaterial for treating massive irreparable rotator cuff tears.