Stereolithographic models for biomechanical testing

Variable properties and limited availability are pitfalls in using cadaveric bones for implant stability tests. Artificial bones avoid these, but tailoring them to specific studies may be difficult. Stereolithography (SLA) techniques produce tailor-made bones with realistic geometries, but their lower Young's modulus might affect outcomes. We investigated whether implant stability and cortical strains with SLA made bones match those with stiffer artificial bones and, if not, whether a thicker cortex to compensate the lower modulus gives a better match. Tibial trays were cemented in place and cyclically loaded while determining cortical strain and tray migration. Permanent and cyclic migration of trays in both types of SLA model (range: 13-28 and 58-85 mum) was within the range of those in composite models (range: 4-62 and 51-105 microm). Strains more distally were approximately inversely proportional to the material stiffness and cortical thickness of the tibiae. We conclude this first study provides a strong indication for SLA tibiae as a valid model for the biomechanical assessment of new techniques in knee surgery and compare favourably with previously utilised models.