Mechanical Properties and Engineering Analysis of Intramedullary Bone Fixation Nails Made from Fiber-Reinforced Composites: A Review

Intramedullary nails (i.e., cylindrical or non-cylindrical rods) for bone fracture fixation are manufactured using titanium or steel, which are stiffer compared to bone. Yet, stiff metal nails can limit interfragmentary fracture motion, which potentially causes delayed callus formation and healing. Also, stiff metal nails may carry too much load relative to bone, which potentially causes bone ?stress shielding? adjacent to the nail, bone density loss, bone resorption, and nail loosening. As such, there have been previous attempts to develop flexible nails using non-metallic materials made from fibers (e.g., carbon, flax, glass) immersed in polymer resins (e.g., epoxy, poly-ether-ether-ketone, polylactic acid). The goal of prior research has been to produce composite nails with tailor-made mechanical properties and optimal engineering performance vs. traditional metal nails. Therefore, this is the first review to survey 40 years of previous literature on composite nails that reported mechanical properties of fibers and resins at the material level (e.g., elastic modulus, ultimate strength), mechanical properties of isolated composite nails at the material level (e.g., fatigue strength, surface hardness), and bone-nail engineering performance (e.g., fracture motion, nail stress). Moreover, applying design principles, improving study protocols, performing future research, and clinical considerations are also discussed to help future researchers to develop intramedullary nails from novel materials.