The Effect of Torque Differences for All-Suture Anchor Fixation Strength: A Biomechanical Analysis

To investigate the biomechanical influence of differential loading of suture strands (torque) on the fixation strength of knotted and knotless all-suture anchors.

The biomechanical strength of 48 all-suture anchors was evaluated for 4 conditions in polyurethane foam blocks: (1) 12 knotted all-suture anchors loaded proportionately, (2) 12 knotted all-suture anchors with 1 suture strand bearing 50% of total force (partial torque), (3) 12 knotted all-suture anchors with 1 strand fixated and the other loaded (full torque), and (4) 12 knotless all-suture anchors with the loop kept open via a fixed rod. Force for 1 mm and 2 mm of displacement and ultimate failure load were assessed.

For 1 mm of displacement, groups 2, 3, and 4 showed significantly lower forces than group 1 (all P < .001), with no statistically significant difference between groups 2 and 3 (P = .516); for 2 mm of displacement, all groups showed significantly lower forces than group 1 (P < .001), which positively correlated with applied torque. No differences in the mean ultimate loads observed between testing groups 1, 2, and 4 were noted, with 93.3 ± 3.8 N, 91.4 ± 4.7 N, and 92.6 ± 5.6 N, respectively; however, group 3 exhibited a significantly lower mean ultimate load (62.3 ± 1.7 N) than all other groups (P < .001).

The ultimate failure load of knotted and knotless all-suture anchor fixation was partially affected by loading differentials between strands in this validated foam block model. Differential loading of knotted all-suture anchor fixation presented greater initial displacement when compared with symmetrically loaded knotted all-suture anchors. Despite an initial increase in displacement, knotless all-suture anchors showed similar ultimate failure loads to knotted all-suture anchors with strands loaded equally.

The role of suture strand loading imbalance on anchor fixation is variable and should be considered during placement and fixation of the repair constructs in a clinical setting.