The hypothesis is that the all-suture anchor pull is less invasive and the cortical thickness affects the pull force. A study to assess the influence of the cortical and cancellous bone structure on all-suture and conventional anchor biomechanical properties was carried out and morphological bone damage after failure was compared.
30 human humeri were biomechanically tested as follows: starting with a load cycle from 20 to 50 N, a stepwise increase of the upper peak force by 0.05 N for each cycle at a rate of 1 Hz was performed. Analysis included maximum pullout strength for three different anchor implantation angles (45°, 90°, 110°) of the two anchor types. After anchor pullout, every sample underwent micro-CT analysis. Bone mineral density (BMD) and cortical thickness were determined at the anchor implantation site. Furthermore, the diameter of the cortical defect and the volume of the bone cavity were identified.
--The maximum pullout strength of all-suture anchors demonstrates a strong correlation to the adjacent cortical thickness with at least 0.4 mm needed to withstand 200 N.
--No correlation could be seen in conventional anchors. Moreover, no correlation could be detected for local BMD in both anchors.
--All-suture anchors show a significantly narrower cortical defect as well as a smaller bone cavity following pullout (4.3?±?1.3 mm vs. 5.3?±?0.9 mm; 141 mm3 vs. 212 mm3).
--The cortical defect is largest if the anchors are placed at a 45° angle.
Finally, the pullout power of all-suture anchors depends on the thickness of the humeral cortex, contrary to traditional anchors. In addition, stitching anchors shows a significant reduction in cortical defect and bone injury in the event of pull-outs. The practical implications of this study therefore are, because of their bone preservations, that all-suture anchors are favorable. Intra-operative decortication should also not be carried out and cortical thickness pre-operatively assessed to minimize the possibility of failure of anchor.