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Biomechanical Study: Determining the Optimum Insertion Angle for Screw-In Suture Anchors—Is Deadman's Angle Correct?

Published:September 14, 2014DOI:https://doi.org/10.1016/j.arthro.2014.07.010

      Purpose

      To assess the effect of the insertion angle and the angle of applied load on the pullout strength of screw-in suture anchors.

      Methods

      Screw-in metallic suture anchors were inserted into a 10–lb/cu ft synthetic cancellous bone block at 30°, 45°, 60°, and 90° to the surface. The suture pull angle was then varied in 30° increments between 0° and 180°. Five constructs were tested to failure (anchor pullout) for each combination of angles using a Zwick tensile testing machine (Zwick Roell, Ulm, Germany).

      Results

      There were a total of 25 combinations. The greatest pullout strength was seen with a suture anchor inserted at 90° to the bone block with a pull angle of 90° to the bone (mean, 306 N; standard deviation [SD], 9 N). The weakest pullout strength was seen with a suture anchor inserted at 30° with the angle of pull at 120° (i.e., opposite to the direction of insertion of the anchor) (mean, 97 N; SD, 11 N). A simulated deadman's angle of 45° with an angle of pull of 150° produced a pullout strength of 127 N (SD, 4 N). The pullout strengths for each insertion angle were greatest when the angle of pull was similar to the angle of insertion (P < .0001, repeated-measures analysis of variance).

      Conclusions

      The angle of applied load to a suture anchor and the insertion angle significantly influence the biomechanical pullout strength of screw-in suture anchors. The insertion angle of the suture anchor should replicate the angle of applied load to ensure the optimum pullout strength.

      Clinical Relevance

      The screw-in anchor insertion angle and angle of applied load may have an influence on pullout strength.
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      Linked Article

      • Can the Deadman Be Killed?
        ArthroscopyVol. 31Issue 2
        • Preview
          When I postulated the deadman theory of suture anchors in 1995,1 I had no idea that it would ignite such a firestorm of controversy almost 20 years later. It seemed such an innocent concept. However, for the second time in the past 12 months, I find myself defending this venerable and self-evident concept against a quasiscientific diatribe. First, there was a cyclic loading study by Clevenger et al.2 that used a nonphysiological methodology to “disprove” the deadman theory. Fortunately, I had the opportunity to point out the experimental misapplication3 in that study.
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