Glenoid suture anchor fixation strength: Effect of insertion angle

Purpose: The purpose of this study was to determine the effect of varying insertion angles on the fixation strength of screw-in devices placed in the glenoid rim. Type of Study: Cadaveric biomechanical analysis. Methods: Eighteen cadaveric glenoids had 3.0-mm cannulated screws inserted for a depth of 10 mm in all 4 quadrants: anterior superior (AS), anterior inferior (AT), posterior superior (PS), posterior inferior (PI). Screws were inserted along the orthogonal to the glenoid rim at the point of insertion or at angles that deviated from this vector by 20degrees and 40degrees. Load to failure was performed at 10 mm/s along the orthogonal to the point of insertion. Results: For screws inserted orthogonal to the glenoid rim, the average load to failure was highest for the PS quadrant (733 +/- 369 N) and lowest for the AT quadrant (272 69 N). The AS and PI quadrants showed intermediate values (549 +/- 334 N and 484 +/- 141 N, respectively). Deviation from orthogonal correlated with decreased fixation strength. This decrease was statistically significant in the AS and PI quadrants, with deviation of 40degrees, and in the AT quadrant, with deviation of 20degrees, as well as 40degrees. Conclusions: Insertion angles for screw-in fixation devices should be orthogonal to the glenoid rim at the point of insertion to maximize strength. Deviation of 40degrees from orthogonal compromises fixation in most quadrants and deviation as little as 20degrees can compromise fixation in the AT quadrant. Clinical Relevance: To maximize strength of labral reattachment to the bony glenoid, screw-in type fixation devices should be inserted as orthogonal to the glenoid rim as possible. This is especially true for Bankart repairs, because device pullout occurs at significantly lower loads in the anteroinferior quadrant compared with the other 3 quadrants. Deviating as little as 20degrees further decreases fixation strength significantly.