Anatomy data driven mechanical adaptation of bone tunnel-screw interface in ACL reconstruction

Anatomical information about bone microstructure at the anterior cruciate ligament attachment sites could guide biomimetic strategies in anterior cruciate ligament reconstruction. This study intends to apply P45 plastination technology to overcome the limitations of conventional imaging techniques and quantitatively characterize the trabecular bone structure at ACL insertion sites. The research objective is to establish a biomimetic strategy for guiding the orientation and depth of bony tunnels and design functionally graded interference screw, thereby optimizing surgical outcomes.

Sixty human knee joint specimens were analyzed using P45 plastination technique, U-Net convolutional neural networks for image segmentation, and MATLAB digital processing to extract morphometric parameters (porosity, trabecular number, degree of anisotropy, and orientation) of trabecular bone at Anterior cruciate ligament femoral and tibial attachments. Based on the extracted trabecular parameters, four uniform and four functionally graded screw models (Double Gyroid, Diamond, Fischer-Koch S, and Octet) were designed in nTopology and use finite element simulation to evaluate the differences in mechanical performance between this method and traditional methods within the bone tunnel.

The trabecular bone at the Anterior cruciate ligament-attachment sites exhibited distinct, site-specific architectural patterns. The femoral attachment site formed a rectangular area (1.47 ± 0.18 cm length, 0.68 ± 0.07 cm width) with trabeculae oriented perpendicular to the insertion plane. Porosity showed a gradual transition (0.52 ± 0.05 to 0.47 ± 0.04), trabecular number averaged 2.45 ± 0.25 /mm, and anisotropy averaged 0.73 ± 0.07. The tibial attachment site formed a larger rectangular area (1.76 ± 0.21 cm length, 0.76 ± 0.21 cm width) with trabeculae aligned parallel to the ligament axis. Porosity transitioned from 0.53 ± 0.03 to 0.58 ± 0.05, trabecular number averaged 3.6 ± 0.63/mm, and anisotropy averaged 0.64 ± 0.09. Finite element analysis revealed that the gradient Double Gyroid screw exhibited superior mechanical compatibility (lowest average stress: 8.86 MPa) at the femoral site, while the gradient Octet screw performed best (lowest average stress: 12.26 MPa) at the tibial site.

An integrated mesoscopic approach for quantitatively analyzing Anterior cruciate ligament attachment site trabecular bone and applying these parameters to biomimetic screw design and bone tunnel positioning was presented. The findings provide a strategic framework for enhancing the anatomic and biomechanical compatibility of Anterior cruciate ligament reconstruction, potentially leading to improved surgical success rates.