Anterior Talo-Fibular Ligament Tensile Properties Compared to Suture Tape, Allograft, and Copolymer Augmentation Elements: An Isolated Biomechanical Study

Abstract

Introduction/Purpose: The modified Brostrom-Gould (MB) technique incorporates the inferior extensor retinaculum for added strength of anatomic Anterior Talo-Fibular Ligament (ATFL) repair. A major limitation of the MB technique is the inability to restore native ATFL biomechanics. Surgical augmentation methods have been introduced to address the MB insufficiency. The purpose of this study is to investigate the isolated biomechanical performance of common MB augmentation elements including suture tape, allograft, and copolymer compared to that of native ATFL. Methods: A total of 24 samples were tested in this study, n=6 in each group. An electromechanical testing system (Instron, Norwood, MA) was used to investigate the biomechanical performance of native ATFL, UHMW-PE suture tape (FiberTape™, Arthrex, Inc., Naples, FL), allograft (Semitendinosus Graft), and copolymer (FlexBand™, Artelon, Marietta, GA). Native ATFL ligaments were isolated from cadaver specimens (mean age: 63 years; range: 45-80), semitendinosus allografts were obtained from LifeNet Health (Jacksonville, FL). Samples measured 20 mm between rigid fixtures and oriented parallel with the long axis of the load cell to simulate worse-case loading. Samples were loaded to failure at 305 mm/min. Biomechanical outcomes included elongation, stiffness, and ultimate load to failure. One-way ANOVA was used to evaluate significant effects of all biomechanical variables. If significance was observed, post-hoc comparisons of augment element and native ATFL were performed with either Tukey or Holm-Sidak test (SigmaPlot,14.0, Systat). Results: Stiffness was greatest for the suture tape group (246.4±52.1N/mm) and least for the copolymer (9.4±2.9N/mm). Significant differences were observed between all augment elements except when comparing ATFL to allograft (p=0.086). Ultimate load was greatest for the suture tape group (544.1±59.7N) and least for the copolymer (146.7±8.9N). Analysis revealed that suture tape ultimate load was statistically greater than copolymer (p < 0.001, Fig.1). Elongation at ultimate failure was greatest for the copolymer group (30.0±8.7mm) and least for suture tape (2.6±0.5mm). Significant interactions were detected for all ultimate load comparisons except for allograft and ATFL (p=0.691), allograft and suture tape (p=0.537), and ATFL and suture tape (p=0.436). See Figure 1 for all data and statistical outcomes. Conclusion: ATFL augmentation elements require thorough evaluation for clinical adoption. Copolymer was 79% weaker in ultimate load and elongated 131% more than the native ATFL. Conversely, suture tape group exhibited 47% greater ultimate load and 82% less elongation at failure compared to ATFL. Clinically, these results suggest the copolymer maintains elastic properties incapable of supporting ATFL ligament healing under load. ATFL augmentation with suture tape offers advantageous post- operative load-sharing support and may allow return to preinjury level activity sooner, as has been seen clinically.1 These results provide insight into how these augmentation elements perform in a static model. Elongation Under Load Figure. 1: Mean elongation data points by group at specified loads up to 550N as well as table that includes all load-displacement data mean and standard deviations. *All stiffness values statistically different from one another (p<0.086 for all comparisons) except for Native ATFL vs Allograft ***Copolymer elongation at failure was statistically greater than all other groups (p<0.001 for all comparisons) **Suture tape ultimate load was statistically greater than Copolymer (p<0.001)