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

Lucca Lacheta; Jon Miles; Brenton Douglass; Peter Millett

doi:10.1016/j.asmr.2020.12.008

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

Arthrosc Sports Med Rehabil. 2021 Feb 25;3(2):e549-e554. doi: 10.1016/j.asmr.2020.12.008. eCollection 2021 Apr.

Authors

Lucca Lacheta^{1

2

3}, Jon Miles¹, Brenton Douglass¹, Peter Millett^{1

4}

Affiliations

¹ Steadman Philippon Research Institute, Vail, Colorado, U.S.A.
² Center for Musculoskeletal Surgery, Charitè Universitaetsmedizin Berlin, Berlin, Germany.
³ Department of Orthopaedic Sports Medicine, Technical University of Munich, Munich, Germany.
⁴ The Steadman Clinic, Vail, Colorado, U.S.A.

Abstract

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

Methods: 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.

Results: 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).

Conclusions: 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.

Clinical relevance: 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.