Mechanical assessment of tripled hamstring tendon graft when using suspensory fixation for cruciate ligament reconstruction

Similar biomechanical properties of four tripled tendon graft models for ACL reconstruction

PURPOSE

The present study tested and compared the biomechanical properties of four different triplicate graft tendon techniques.

METHODS

32 tripled tendons from the common extensor muscle of bovine fingers were tested on a material testing machine, passing the end loop over a metal rod of a clevis connected to the load cell on the upper side, and fixing the lower end to a clamp. The samples were divided into four groups: (A) tripled with a free end sutured only to one of the two fixed bundles (B) tripled with a free end positioned between the two fixed strands and sutured to both (C) tripled with an S-shape and all the three strands sutured together at the upper and lower extremities of the graft (D) partially quadrupled with the free end sutured together with the other three bundles at the upper extremity. Each sample was pretensioned at 50 N for 10 min and then subjected to 1000 load control cycles between 50 and 250 N. Finally, each sample was subjected to a load to failure test. Authors also present some preliminary results on the feasibility of a non-contact and full-field Thermoelastic Stress Analysis technique, based on Infrared Thermography, to evaluate the level of stress on the whole graft, and hence on each strand, during fatigue loading.

RESULTS

Eighty five percent of the samples failed at the level of the clamp. The cyclical elongation progressively decreased in all the samples and there was a simultaneous increase in stiffness. An increased stiffness was noted between Group 2 vs Group 3 and Group 2 vs Group 4 at the 500th and 1000th cycle. The failure loads were as follows: (a) 569.10 N, (b) 632.28 N, (c) 571.68 N, (d) 616.95 N. None of the parameters showed a statistically significant difference between the four groups.

CONCLUSION

This study reported similar biomechanical behavior of four different models of tripled grafts suitable for ACL reconstruction. In addition, the biomechanics of overall tripled tendon grafts seems more affected by the viscoelastic property of the tendon itself rather than the preparation method.

Viscoelastic and failure properties of two configurations of triple-folded hamstring tendons used for anterior cruciate ligament (ACL) reconstruction

BACKGROUND

Hamstring autografts are commonly used for anterior cruciate ligament (ACL) reconstruction. Different folding techniques exist in tripling the semitendinosus. Few anatomical studies exist in evaluating their viscoelastic properties. The purpose of this study was to characterize and compare the viscoelastic and failure properties of two hamstring graft configurations, the "Z" construct and "2" construct.

METHODS

Ten matched pairs of fresh-frozen cadaveric semitendinosus hamstring grafts were used to create the "2" configuration or "Z" configuration. The biomechanical testing consisted of four phases: preconditioning, where graft dimensions (mm) were measured; stress relaxation, where load, displacement and time data were collected and equilibrium relaxation (%) was calculated; dynamic creep, where the total construct elongation was calculated; and ramp-to-failure, where maximum failure load was recorded.

RESULTS

The "2" configuration demonstrated recorded forces (N) significantly greater at each time point when compared to the "Z" configuration during stress relaxation (p = 0.003). The "2" configuration exhibited significantly less construct elongation (mm) during dynamic creep at 10 cycles (p = 0.008) and 2000 cycles (p = 0.0001). The maximum measured load at failure was significantly greater in the "2" configuration constructs than "Z" configuration (p = 0.013). Moreover, the axial loads at 2, 3 and 4 mm of displacement were, on average, greater in the "2" configuration than "Z" configuration (p = 0.152; p = 0.080; p = 0.012), respectively.

CONCLUSION

The results of this study provide support for folding techniques for tripled grafts to provide higher viscoelastic and failure properties for techniques with less suture interfaces. Future studies can potentially evaluate the clinical significance of these findings.

Four-strand hamstring graft is stiffer than a tripled semitendinosus graft in anterior cruciate ligament reconstruction: a cadaveric study

Purpose

The aim of this study was to compare the biomechanics of a four-strand hamstring graft with a tripled semitendinosus graft, with and without adjustable extra-cortical button fixation, in a cadaveric model.

Methods

Four groups of 10 cadaveric hamstrings were tested: In group A, a tripled semitendinosus graft fixated with two adjustable extra-cortical buttons; in Group B, a four-strand semitendinosus and gracilis graft fixated with an adjustable extra-cortical button and a clamp; in group C, a tripled semitendinosus graft fixated to a steel hook and a clamp; in group D, a four-strand semitendinosus and gracilis graft fixated to a steel hook and a clamp. Each group was submitted to a cyclic loading test (1000 cycles between 50 and 250 Newton at a frequency of 0.5 hertz) and a load-to-failure test. Primary outcomes were ultimate failure load and stiffness. Secondary outcomes were graft elongation and graft diameter.

Results

There was no difference in ultimate failure load among groups. Group B achieved a median stiffness of 171 N/mm (interquartile range [IQR] 139–204) which was significantly higher than Group A (median 103 N/mm (74–119), p < 0.01). Group B showed more cyclic elongation (4.1 mm (3.4–5.7)) compared to group D (2.3 mm (1.9–3.0)), and also lower stiffness was noted (171 N/mm (139–204) vs 265 N/mm (227–305)). There was no difference in graft diameter among groups.

Conclusions

The results of this study indicate that higher stiffness can be achieved using four-strand hamstring tendon grafts compared to tripled semitendinosus grafts when using femoral extra-cortical buttons, despite comparable graft diameters. Thereby, the use of adjustable extra-cortical fixation devices may result in more cyclic elongation and lower stiffness of the graft.