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

Area of Science:

• Orthopedic surgery
• Biomedical engineering
• Sports medicine

Background:

• Adjustable button (AB) devices are used for anterior cruciate ligament (ACL) soft-tissue graft fixation.
• The Chinese finger trap technique is a common mechanism in some AB devices.
• The cyclic loading performance, especially with complete unloading, of these devices is not well understood.

Purpose of the Study:

• To evaluate the cyclic loading resistance of AB devices utilizing the Chinese finger trap technique.
• To compare the displacement of Chinese finger trap AB devices against other fixation methods under cyclic loading with complete unloading.
• To test the hypothesis that Chinese finger trap AB devices exhibit greater displacement than continuous suture loop devices and other AB mechanisms.

Main Methods:

• Anterior cruciate ligament (ACL) reconstruction was performed in a porcine knee model.
• Three types of cortical fixation devices were tested: two Chinese finger trap AB devices, one locked suture loop AB device, and two continuous loop devices.
• Specimens underwent 2500 cycles of loading (up to 250 N) and complete unloading in a material-testing machine, with continuous elongation recorded.

Main Results:

• AB devices using the Chinese finger trap loop showed significantly greater displacement (mean 8.1 mm and 6.1 mm) compared to AB devices with a locked suture loop (mean 4.7 mm) and continuous loop devices (mean 4.1 mm and 4.4 mm).
• No significant difference in displacement was found between the locked suture loop AB devices and the continuous loop devices.
• The study demonstrated that Chinese finger trap AB devices are susceptible to construct lengthening under cyclic loading and unloading.

Conclusions:

• Adjustable button devices employing the Chinese finger trap technique exhibit significantly greater lengthening under cyclic loading and unloading compared to other fixation methods.
• Complete unloading of the ACL graft is a common occurrence during post-operative rehabilitation.
• The lengthening of Chinese finger trap AB devices may represent a potential failure mode for ACL graft fixation, suggesting consideration of locked suture loop designs or cautious rehabilitation protocols.