The ultimate pullout strength and fatigue properties of a screw-design
suture anchor implanted in the anterior glenoid rim were investigated
and compared with results from a nonscrew-design suture anchor. Twent
y-two cadaveric glenoids were harvested and one to two anchors were im
planted in the superior and inferior quadrants. Fifty-seven Statak 3.5
anchors (Zimmer, Warsaw, IN) were tested and compared with results ob
tained in a previous study on 50 Mitek GII anchors (Mitek Products, In
c, Westwood, MA). The specimens were mounted on an Instron fatigue tes
ting machine (Instron Corp, Canton, MA) and cycled between preselected
minimum and maximum loads until pullout. The Mitek GII maintained a h
igher pullout strength than the Statak 3.5 after cyclic lending. Corti
cal thickness at the implantation sites was measured, and found to dec
rease monotonically from superior to inferior positions. The ultimate
pullout strength, and subsequently the fatigue life, of both types of
suture anchors depended directly on cortical thickness. The significan
tly lower performance of both anchors when placed inferiorly emphasize
s the importance of correct anchor selection, number, and placement in
this region. All anchors settled during the first 10 to 100 cycles, r
esulting in partial exposure of the implant. Intraoperative cycling of
the anchors before suture tying may be necessary to achieve complete
settling and prevent subsequent loss of coaptation between capsule and
glenoid. The study shows that for the anchors to last 1,000 cycles or
more, less than 50% of the theoretical ultimate pullout strength shou
ld be applied cyclically. With aggressive early rehabilitation exercis
es, this significant decrease in fixation strength could shift reconst
ruction failure from suture breakage or soft tissue tearing to anchor
pullout.