Biomechanical Evaluation of a 4.75-Mm and a 5.5-Mm Bone Anchor at Two Insertion Angles Using One and Two Strands of Suture.

OBJECTIVE To compare biomechanical strength of 4.75- and 5.5-mm suture anchors when pulled at 45 degrees or 90 degrees angles using 1 versus 2 strands of suture. SAMPLE 48 synthetic bone block samples. PROCEDURES Anchors were inserted into synthetic bone blocks and tested for pullout in 4 configurations (1 suture strand vs 2 strands and 45 degrees vs 90 degrees 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. RESULTS 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 degrees (mean, 300 +/- 15 N) and 90 degrees (mean, 295 +/- 24 N), compared with 4.75-mm anchors at 45 degrees (mean, 202 +/- 12 N) and 90 degrees (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 degrees had a higher maximum load to failure than those inserted at 90 degrees. Constructs with 2 strands of suture had a greater pullout strength regardless of the direction of pull. CLINICAL RELEVANCE The strength of the anchor construct is likely increased with the use of double-loaded anchors inserted at 45 degrees. Clinicians should consider using 2 strands in clinical cases.