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Objective—To evaluate the effects of pilot hole diameter and tapping on insertion torque and axial pullout strength of 4.0-mm cancellous bone screws in a synthetic canine cancellous bone substitute.
Sample—75 synthetic cancellous bone blocks (15 blocks/group).
Procedures—For groups 1 through 5, screw size-pilot hole diameter combinations were 3.5–2.5 mm (cortical screws), 4.0–2.5 mm, 4.0–2.5 mm, 4.0–2.0 mm, and 4.0–2.0 mm, respectively. Holes were tapped in groups 1, 2, and 4 only (tap diameter, 3.5, 4.0, and 4.0 mm, respectively). One 70-mm-long screw was inserted into each block; in a servohydraulic materials testing machine, the screw was extracted (rate, 5 mm/min) until failure. Mean group values of maximum insertion torque, axial pullout strength, yield strength, and stiffness were determined.
Results—Mean maximum insertion torque differed significantly among the 5 groups; the group 5 value was greatest, followed by group 3, 4, 2, and 1 values. Group 3, 4, and 5 axial pullout strengths were similar and significantly greater than the group 2 value; all values were significantly greater than that for group 1. Group 5 and 4 yield strengths were similar and significantly greater than the group 3, 2, and 1 values. Stiffness in group 3 was similar to group 4 and 2 values but significantly greater than the group 5 value; all values were significantly greater than that for group 1.
Conclusions and Clinical Relevance—These synthetic cancellous bone model findings suggested that tapping a 2.0-mm-diameter pilot hole when placing a 4.0-mm screw is the optimal insertion technique.
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.