Effects of different cortical all-suture anchor (Y-Knot RC) insertion points and deep vs. flat insertion on its biomechanical properties.

Abstract

To evaluate the minimal distance of the all-suture anchor (ASA) insertion point to the decorticated cortex-cancellous interface without compromising biomechanical properties and to evaluate the biomechanical differences of deep vs. flat anchor insertion depths. Thirty ASAs (Y-Knot RC) were tested. The artificial bones were designed to mimic the cortical-cancellous bone interface of the humeral head after footprint decortication and were therefore half covered with a 1-mm thick layer. Anchor insertion points were defined within the cortical layer at 0 mm, 2 mm, and 4 mm distance to the cortical-cancellous artificial bone edge. Furthermore, 2 different anchor insertion depths (25 mm vs. 35 mm) were tested. After an initial preload of 10 N, a cyclic testing protocol was conducted with a stepwise increasing pullout of 5 N for each cycle. Recorded data included maximum pullout force, construct stiffness, and the load at which first anchor motions were registered. The maximum pullout force was reached when the ASA was placed at a 4-mm distance to the cortical-cancellous interface, while the lowest pullout force was registered at the 0 mm position directly at the interface (184 ± 38 N vs. 144 ± 6 N, P = .041). The 2 mm position showed a maximum pullout force of 148 ± 6 N (not significant). No differences were noted regarding construct stiffness and registered load at the first anchor motion. Deep anchor insertion showed a similar maximum pullout load and load at the first sign of anchor motion compared to the flat anchor insertion. Construct stiffness was significantly higher in the deep insertion group (16 ± 4 N/mm vs. 11 ± 1 N/mm). ASA insertion within the cortical layer should respect a minimum 4-mm distance to the cortical-cancellous interface to secure optimal pullout strength. Pullout strength of the ASA remained unchanged with greater insertion depth, whereas construct stiffness increased.