In vitro comparison between cortical and cortico-cancellous femoral suspension devices for anterior cruciate ligament reconstruction: implications for mobilization.

Purpose: To analyse the capability of cortical and cortical-cancellous suspension devices to provide a strong fixation in order to follow an aggressive early mobilization protocol.

Methods: Anterior cruciate ligament (ACL) reconstruction was performed in vitro on 40 porcine femurs employing a high-strength braided cord as a graft. Four femoral suspension devices were analysed: the cortical suspension devices Endobutton and XO Button and the cortical-cancellous suspension devices Biosteon Cross-pin and Cross-pin ACL. Two kinds of biomechanical testing were carried out: static and post-fatigue failure strength tests. Stiffness, failure load, elongation at failure load, elongation after 20 cycles and elongation after 1,000 cycles were assessed. The bones were cut after testing to analyse the failure pattern.

Results: All of the devices exceed 50 % of total elongation in the first 20 cycles of fatigue. In the static failure tests, there were significant differences (p < 0.05) in elongation to failure between the cortical-cancellous suspension devices Biosteon Cross-pin and Cross-pin ACL and the cortical suspension device Endobutton. No significant differences were found in the failure tests after 1,000 cycles of loading. The failure mode of the cortical devices comprised breakage of the cortical bone, accompanied by introduction of the device into the tunnel. The failure mode of the cortical-cancellous devices was pin breakage accompanied by tunnel enlargement.

Conclusion: The first cycles of mobilization are critical for elongation. This mobilization process does not significantly diminish the mechanical characteristics of the reconstructions. All the fixations support an intensive early mobilization protocol, with loads of over 500 N.