Biomechanical evaluation of a 4.75-mm and a 5.5-mm bone anchor at two insertion angles using one and two strands of...

To compare biomechanical strength of 4.75- and 5.5-mm suture anchors when pulled at 45° or 90° angles using 1 versus 2 strands of suture.

48 synthetic bone block samples.

Anchors were inserted into synthetic bone blocks and tested for pullout in 4 configurations (1 suture strand vs 2 strands and 45° vs 90° insertion angle) for a total of 8 groups with 6 samples each. A 3-way ANOVA was used to compare effect of anchor size, strand amount, and angle of pull.

All constructs failed via anchor pullout. Anchor configurations with 2 strands of suture and 4.75-mm anchor (mean, 286 ± 24 N) or 5.5-mm anchor (mean, 300 ± 15 N) had greater pullout strength than configurations with only 1 strand of suture and 4.75-mm anchor (mean, 202 ± 12 N) or 5.5-mm anchor (mean, 286 ± 13.6 N). The 5.5-mm anchors had a higher maximum load to failure under axial pull at 45° (mean, 300 ± 15 N) and 90° (mean, 295 ± 24 N), compared with 4.75-mm anchors at 45° (mean, 202 ± 12 N) and 90° (mean, 208 ± 15 N). There was a higher maximum load to failure for the double-stranded constructs, regardless of anchor size, at both angles of insertion. Anchors inserted at 45° had a higher maximum load to failure than those inserted at 90°. Constructs with 2 strands of suture had a greater pullout strength regardless of the direction of pull.

The strength of the anchor construct is likely increased with the use of double-loaded anchors inserted at 45°. Clinicians should consider using 2 strands in clinical cases.