Adjustable buttons for ACL graft cortical fixation partially fail with cyclic loading and unloading

Abstract

Purpose Despite good initial pullout strength, it is unclear whether adjustable button (AB) devices for anterior cruciate ligament (ACL) 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. It was hypothesized, that the displacement of AB devices with the Chinese finger trap technique would be greater than that of continuous suture loop devices and other available AB mechanisms in a cyclic loading with complete unloading protocol. Methods ACL reconstruction was performed in a porcine knee model using three different types of cortical fixation devices: two different AB devices that use the Chinese finger trap design, one AB 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. Results The displacement of ABs with a Chinese finger trap loop (mean 8.1; SD 1.5 mm and mean 6.1; SD 1.4 mm) was significantly greater than that of AB with a locked suture loop (mean 4.7; SD 1.0 mm; p < 0.05) and devices with a continuous loop (mean 4.1; SD 0.5 mm and mean 4.4, SD 0.3 mm; p < 0.01). No significant differences were detected between the ABs with a locked suture loop and the continuous loops. Conclusion Cyclic loading and unloading of AB using the Chinese finger trap technique leads to significantly greater construct lengthening compared with other devices. Complete unloading of the ACL is very likely to occur during rehabilitation after ACL reconstruction. Lengthening of the AB device due to cyclic loading might be a potential mode of failure of the ACL graft fixation. Therefore, when using an AB femoral fixation technique, a locked suture loop design or a careful rehabilitation protocol should be considered.

Biomechanical Evaluation of a Novel Loop Retention Mechanism for Cortical Graft Fixation in ACL Reconstruction

“…When tested in combination with a tendon graft, however, MSLD outperformed FTD in cyclic elongation. In agreement with a previous investigation, 19 the finger trap mechanism displayed a substantial shortcoming when subjected to complete unloading during cyclic testing, with loop elongation exceeding 3 mm at approximately 200 loading cycles. As it is unknown whether CFDs experience complete unloading after implantation during early rehabilitation, the clinical significance of this finding remains unclear.…”

“…In the first technique—generally referred to as the “finger trap”—the tensioning suture is sheathed by an additional load-carrying loop, which tightens when load is applied, thereby securing the tensioning suture in place. 19 In the second technique, the loading loop slings around the tensioning suture, and the resulting pressure prevents loop elongation (hereafter, “sling lock” mechanism). Fixed-length devices (FLDs) either rely on a continuous loop or are pretied to the specified length before insertion.…”

“…Although clinical results are generally satisfactory, 5,7,13,14 multiple biomechanical studies have raised concern regarding inferior fixation characteristics of adjustable-length CFD alone when compared with interference screw fixation 25 and fixed-length suspensory fixation. 1,2,18,20,30 Moreover, in an ex vivo biomechanical study, Glasbrenner et al 19 pointed out that adjustable-length fixation devices that rely on the finger trap mechanism can be sensitive to complete graft unloading during cyclic testing, with partial failure of the fixation within 2500 cycles of loading. Adjustable CFDs based on the sling lock mechanism, however, have exhibited unsatisfactory mechanical performance even when subjected to moderately high-cyclic forces.…”

Evaluation of Adjustable Loop Suspensory Anterior Cruciate Ligament Fixation Devices

“…From the six tested ALD groups, only the new ALD and RigidLoop do not reach clinical failure. Glasbrenner et al [10] evaluated whether ALDs with a locking mechanism based on a chinese finger trap (CFT) resist cyclic loading and complete unloading. They determined significantly worse results for ALDs with a locking mechanism based on a CFT than for ALDs with a button lock.…”

“…Thus, for each sample 3000 cycles of loading and complete unloading with increasing load levels between 50 N and 300 N were performed. The maximum load level of 300 N was chosen according to previously performed studies [9,10]. Barrow et al [9] and Ahmad et al [11] defined an absolute displacement of 3 mm as clinical failure, this value was considered as failure criterion for the tested samples.…”