Summary

First biomechanical tests with cyclically full unloading of different adjustable loop button shows greater construc lengthening in Chinese finger trap technique.

Abstract

Purpose

Despite good initial pullout strength, it is unclear whether adjustable button devices for anterior cruciate ligament soft-tissue graft fixation, which are based on the Chinese finger trap technique, resist cyclic loading. Furthermore, they have never been tested in a cyclic protocol including complete unloading.
We hypothesize, that the displacement of adjustable button devices with the Chinese finger trap technique will be greater than that of continuous suture loop devices and other available adjustable button mechanisms in a cyclic loading with complete unloading protocol.

Methods

Anterior cruciate ligament reconstruction was performed in a porcine knee model using three different types of cortical fixation devices: two different adjustable button devices that use the Chinese finger trap technique, one adjustable button device that uses a locked suture loop mechanism and two different continuous loop devices as control groups (n=40). Specimens were mounted in a material-testing machine (Instron Inc.) that permitted 2500 loading and complete unloading cycles to a maximum of 250 N, as well as continuous elongation recording. A one-way ANOVA was performed for statistical analysis (P=.05).

Results

The displacement of the Chinese finger trap devices (8.1 +- 1.5 mm and 6.1 +- 1.4 mm) was significantly greater than that of the locked suture loop device (4.7 +- 1.0 mm, P<.05) and CL devices (4.1 +- 0.5 mm and 4.4 +- 0.3 mm, P<.01). No significant differences were detected between the locked suture loop and the continuous loop devices.

Conclusion

Cyclic loading and unloading of adjustable button using the Chinese finger trap technique leads to significantly greater construct lengthening compared with other devices. The relevance of this finding depends on the in vivo forces acting inside the knee joint during rehabilitation, which remain unknown. Lengthening of the adjustable button device due to cyclic loading might be a potential mode of failure after anterior cruciate ligament reconstruction and therefore should be considered when choosing femoral fixation technique.