Comparative evaluation of additively manufactured PLA models as cost-effective, non-inferior alternatives to composite bones for pull-out testing

The purpose of this study was to perform biomechanical pull-out comparisons between composite bone blocks and additively manufactured bone models using locked plate and screw systems. The hypothesis posited that the mean pull-out force of the 3D-printed models would demonstrate non-inferior pull-out strength compared to standard composite bones within a clinically acceptable 15% margin. A standardized pull-out mechanism was developed to evaluate its biomechanical reliability and its potential as a customizable alternative. The study compared three groups: standard composite (Sawbones) blocks and two types of additively manufactured polylactic acid (PLA) blocks (grid and gyroid infill pattern), each measuring the same dimensions with 30% infill and mimicking a Sawbones block with 2 mm cortical thickness. A 6-hole LC-DCP titanium plate was fixed onto bone block models with dimensions of 29 × 170 × 42 mm using four screws, each measuring 36 mm in length, which were inserted perpendicularly and tightened to the same torque levels. Steel cables placed under the plate were connected to a mechanical testing setup, and pull-out tests were conducted to evaluate fixation strength. Seven replicate specimens were fabricated to ensure repeatability and reliability of the results. Mean pull-out forces were 1784.4 ± 79.9 N for Sawbones, 1698.5 ± 134.3 N for Grid PLA (n = 7), and 1908.7 ± 335.2 N for Gyroid PLA (n = 7). Statistical analysis using a one-sample t-test showed that both 3D-printed models were non-inferior to the standard Sawbones model within a clinical acceptance margin of 15% (p < 0.05). Additively manufactured models exhibit mechanical pull-out performance that is statistically non-inferior to traditional composite bone block models. These findings confirm that 3D-printed PLA-based grid and gyroid structures serve as reliable, cost-effective alternatives for orthopaedic mechanical research without compromising mechanical integrity.