Purpose: Suture anchors used for reinserting soft tissue on bony structures have been studied with the purpose of evaluating hold in bone. There has not however been any work on the influence of the eye design on suture resistance. The purpose of this work was to examine this aspect of the question.

Material and methods: The following anchors were tested: Statak 4 (Zimmer, Warsaw, IN, USA), Corkscrew 3.5, Fastak 2.4 (Arthrex, Naples, FL, USA), PeBA C 6.5 (OBL, Scottsdale, AZ, USA), Mitek GII 5Mitek, Norwood, MA, USA), Harpoon 2 (Arthrotek, Warsaw, IN? USA), Ultrafix (Linvatec, Largo, FL, USA), Vitis 3.5 AND 5 (Tornier, St Isnier, France). The following suture threads were used: Vicryl dec 5, Flexidene dec 5, PDS dec 4. Three types of tests were performed on an Instron 8500+. To study loading at thread rupture, a loop with a constant length was placed under traction in the axis of the anchor until thread rupture. Two measurement modalities were used. For the first, static tension was applied to increase the linear load at the rate of 1.25 mm/s. In the second, cyclic traction applied tension five times at a frequency of 1 Hz with 10N loading increments. To study thread weakening in relation to each anchor, we imposed a back and forth movement on the strand running through the eye using a sinusoidal 10 mm movement at a frequency of 0.03 Hz, one end of the thread being fixed and the other supporting a constant 20 N load. Each thread was tested in each anchor and each type of test was run three times.

Results: Load at rupture of each thread was not affected significantly by the design of the anchor eyes. Rupture generally occurred at the knot level, sometimes at the eye (Harpoon, Fastak, Vitis) for the Flexidene dec 5 thread. Conversely, there were important differences in the thread weakness tests: a knitted thread such as Vicryl was much stronger than the two other threads tested, irrespective of the anchor. Furthermore, resistance for the dynamic test was very variable for the different anchors: 100±20 cycles for corkscrew 3.5 and 3±1 cycles for Vitis 3.5 with Vicryl or 6+/1 cycles for Harpoon 2 with Flexidene.

Conclusion: The design and finishing of each eye had an effect on the resistance of thread moving through the eye. For anchors which weakened thread after a few back and forth movements, it can be assumed that simple knotting damages the thread to a point where early failure occurs at reinsertion. The best results were obtained when the anchor eye had a bevelled groove.