Integration of locking screw fixation into 3D-printed patient-specific porous titanium implants enhances osseointegration: an <i>in vivo</i> study in a rabbit bone defect model.

Abstract

<h4>Importance</h4>Three-dimensional (3D) printing enables fabrication of patient-specific implants (PSIs) tailored to complex bone defects. Although locking screw fixation offers mechanical advantages in conventional plating, its integration into 3D-PSIs is technically challenging and has not been evaluated for biological outcomes.<h4>Objective</h4>This study aimed to assess whether locking screw fixation enhances osseointegration compared to nonlocking fixation when directly integrated into 3D-printed porous titanium implants.<h4>Methods</h4>Segmental femoral defects (20 mm) were created in ten adult rabbits, and customized porous Ti6Al4V implants were designed based on preoperative computed tomography (CT) scans. The implants incorporated threaded holes replicating the ARIX locking system and were fabricated via selective laser melting. Animals were randomly assigned to locking (n = 5) or nonlocking (n = 5) screw fixation groups. After 12 weeks, implant osseointegration was evaluated using radiography, micro-CT, and histological analyses.<h4>Results</h4>All implants remained stable without failure. Micro-CT revealed significantly higher bone volume fraction in the locking group (27.8% ± 3.7%) than the nonlocking group (23.8% ± 1.7%; <i>p</i> < 0.05). Histology showed more extensive and homogeneous bone ingrowth in the locking group, whereas fibrous tissue formation was observed in some nonlocking cases. The bone area percentage was significantly greater in the locking group (24.4% ± 9.9%) than in the nonlocking group (12.2% ± 7.1%; <i>p</i> < 0.05).<h4>Conclusions and relevance</h4>This study demonstrates that integrating locking screw fixation into 3D-printed porous titanium PSIs enhances osseointegration by improving primary stability. These findings suggest that locking fixation in PSI designs may improve outcomes for load-bearing bone defect reconstructions in veterinary and potentially human applications.