A biomechanical study on suture anchor insertion angle: Which is better, 90° or 45°?

Current surgical practices often rely on suture anchors for tendon or ligament repair. While the 90° insertion angle is commonly used, some surgeons prefer 45° for better anatomical fit. Prior research has shown that pullout strength depends on bone density and anchor design. However, the specific effects of insertion angle on anchor stability remain unclear. No prior work had resolved how angle alone influences failure loads across different bone densities. This gap motivated researchers to investigate whether 90° or 45° insertion provides better resistance to pullout forces. The study aimed to clarify how angle interacts with bone density in synthetic and biological models. It was already known that cortical thickness and cancellous structure affect anchor performance. That uncertainty drove the need for controlled mechanical testing in both synthetic and porcine bone models.

The goal was to determine whether a 90° or 45° insertion angle yields greater pullout resistance in suture anchors. The study focused on how angle affects anchor stability in different bone densities. Researchers aimed to compare failure loads under two pulling angles and three bone density conditions. They wanted to assess whether angle alone could predict anchor performance. The motivation came from clinical uncertainty about optimal insertion techniques. Surgeons often face decisions about angle based on anatomy or tissue quality. This study sought to provide biomechanical evidence for those choices. The specific problem addressed was the lack of comparative data on angle-specific pullout strength. The research aimed to clarify whether 90° insertion consistently outperforms 45° in various bone types.

The researchers used a universal testing machine to measure pullout strength in synthetic and porcine bone models. They selected three synthetic bone densities and porcine humeri as biological controls. Metallic anchors were inserted at 90° or 45° to the bone surface. Pulling forces were applied at the same angles to simulate clinical scenarios. The maximum load to failure was recorded for each condition. The study compared failure loads across insertion and pulling angles. Statistical analysis evaluated differences in strength between angles and densities. The experimental design allowed direct comparison of angle effects in controlled settings.

Anchors inserted at 90° showed higher pullout strength than those at 45° in all tested conditions. In low-density synthetic bone, 90° anchors had 534.6 ± 28.9 N versus 488.1 ± 25.3 N for 45° (p < 0.05). In medium-density bone, 90° anchors reached 636.8 ± 25.3 N versus 517.5 ± 27.4 N (p < 0.01). High-density synthetic bone showed 735.6 ± 45.1 N for 90° versus 557.0 ± 42.5 N (p < 0.01). Porcine humeri had 285.6 ± 47.2 N for 90° versus 181.4 ± 31.3 N for 45° (p < 0.01). When pulling at 45°, 90°-inserted anchors still outperformed 45°-inserted ones in low-density bone (651.1 ± 38.3 N vs. 529.4 ± 37.6 N, p < 0.01). Medium-density bone showed 711.4 ± 25.3 N for 90° versus 599.2 ± 29.8 N (p < 0.01). Porcine humeri had 265.3 ± 49.0 N for 90° versus 181.5 ± 29.4 N (p < 0.01). These results suggest that 90° insertion consistently provides better resistance to pullout.

The findings suggest that 90° insertion angle provides greater pullout strength than 45° in both synthetic and biological bone models. The results were consistent across low, medium, and high-density bone types. The authors propose that angle alone significantly affects anchor stability. They suggest that 90° insertion may be preferable for maximizing resistance to pullout forces. The data support the hypothesis that perpendicular insertion enhances mechanical performance. The study does not claim that 45° insertion is ineffective, only that 90° offers better strength in tested conditions. The researchers do not generalize these findings to all surgical contexts but emphasize their relevance to anchor placement in rotator cuff or labral repair. The results may guide surgeons in selecting insertion angles based on bone quality and anatomical constraints.