UCLA

Preclinical evaluation of orthopaedic implants typically employs a comprehensive approach, including animal models, cadaver studies, computational analyses, and composite surrogates. Cadaveric models have been integral to the in vitro biomechanical testing of orthopaedic implants and surgical techniques, yet natural anatomic variations in size, shape, and bone quality often overshadow differences due to the experimental variables in these studies. Over the past three decades, commercially available composite bones have been widely accepted as surrogates for biomechanical testing. These epoxy and polyurethane-based models are typically made by injection molding and have been validated by numerous labs for long bone models. However, these models have not been validated or widely adopted for small bones. One explanation may be that they may not have the resolution needed for biomechanical models of small bones, such as the carpal bones of the upper extremities, which have unique size and mechanical properties. Therefore, the present study investigated the use of additive manufacturing to develop a model of the most commonly fractured small carpal bone, the scaphoid, for the purposes of biomechanical testing.

Scaphoid morphology and bone density were measured through computed tomography to replicate in the model. The strength of three commonly used additive manufacturing materials, polylactic acid, polycarbonate, and resin, was measured at different infill densities. A nonhomogeneous, anisotropic scaphoid model was additively manufactured with polycarbonate, which may be the material most representative of the scaphoid bone from those tested. This model may enable better testing and characterization of surgical implants for the scaphoid.