Screw pullout strength in osteoporotic bone: A comparative study of synthetic femur surrogates

Synthetic bone models are frequently used in biomechanical research to assess the fixation strength of implants. Due to their inherent material properties they often overestimate fixation performance - especially in osteoporotic bone, where reduced trabecular density and cortical thickness diminish fixation strength. This study aimed to evaluate new custom-made polyurethane resin bone (PuReBone) surrogates designed to replicate mechanical characteristics of osteoporotic human femora. Their screw pullout performance was benchmarked against human femurs, standard commercial surrogates, and epoxy tubes. Custom-made polyurethane resin-based surrogates were evaluated in screw pullout experiments using 4.5 mm cortical screws. Their mechanical performance was compared to osteoporotic human femora, a widely used commercial synthetic surogate (Sawbones), and Krülit epoxy tubes. Pullout force and displacement, failure patterns and cortical thickness were analyzed to assess the biomechanical performance of PuReBone. Pullout forces of PuReBone with a hollow intramedullary canal (855 ± 307  N) were in close agreement with values reported in the literature for osteoporotic human bone (835 ± 444  N, p = 1.000), whereas our experimental results for epoxy-based surrogates (1,905 ± 375 N, p < 0.001) and Krülit (3,234 ± 291  N, p < 0.001) showed significantly higher values. Displacement at failure and stiffness differed across surrogates, with PuReBone showing similar values to the commercial epoxy-based surrogates but lower stiffness than Krülit. Concluding, PuReBone represents a promising alternative to current synthetic bone models for biomechanical testing of screw pullout in osteoporosis research. Its ability to more accurately replicate osteoporotic bone mechanics enhances the reliability of orthopaedic implant testing and surgical fixation studies.