Biomechanical comparison of different rotator cuff anchor repair techniques on osteoporotic bone model

The objective of this study is to evaluate the increase in anchor pullout resistance forces provided by different surgical methods such as adjacent anchor application, cannulated screw augmentation or autograft compression; which were defined to prevent anchor failure and improve fixation strength. And we also aimed to biomechanically prove that anchors with larger threads would enable a more durable repair. The study was conducted on 72 humeri obtained from 18-month-old lambs. After soft tissue removal all specimens were drilled in the same direction which the anchor would be applied with a 4.5mm drill-bit; to simulate an osteoporotic bone model. Specimens were divided into 6 groups each consisting of 12 humeri. In group 1, two 5-mm Fastin RC (DePuy Mitek, Raynham, MA) anchors were applied close to each other so that adjacent grooves were intertwined. In group 2 two 5-mm Twinfix titanium anchors (Smith & Nephew Endoscopy, Andover, MA) were applied in a similar manner as the first group. In group 3, spongious bone autograft were compressed before the application of a 5-mm Fastin RC anchor. Group 4 consisted of Fastin RC anchor with a cannulated screw, group 5 contained only Fastin RC anchor and group 6 only Twinfix titanium anchors. Each specimen was connected to AG-X Shimadzu device (Kyoto, Japan) by a specially designed holding mechanism with 135 ° angle to the ground plane. Cyclic pullout tests were performed in the axial direction. Additionally pullout test after maximum loading in the axial direction were performed. The data were recorded and statistically analyzed. After the experiments, cyclic elongation and peak-to-peak displacement under cyclic loading were evaluated and Fastin-Fastin group showed statistically significant (p<0.05) less displacement compared to other groups, while no statistically significant difference were observed between other groups. Pullout under maximum loading tests revealed that Fastin-Fastin group provided a statistically significant (p<0.05) more durable fixation, and again no statistically significant difference was seen between the other groups. The results of our study revealed that cannulated screw augmentation or autograft compression techniques did not provide any increase in fixation strength of anchors, whereas adjacent anchor application was found to increase fixation strength. Anchors with larger thread diameters should be the preferred anchor for adjacent application. These data could be interpreted as, for rotator cuff repair in osteoporotic bone fully threaded anchors with larger thread diameters should be used; and adjacent anchor application technique is the method of choice for augmentation.