Influence of initial biomechanical environment provided by fibrous composite intramedullary nails on bone fracture healing

Long bone fractures are primarily treated with internal fixation devices, and intramedullary (IM) nails are the most commonly used. Reamed and unreamed surgical procedures are commonly used to attach IM nails to fractured bones. It is believed that the use of flexible composites contributes to successful fracture healing because of the desirable initial interfragmentary movement (IFM) provided by the material. This finite element study was conducted to understand the influence of initial IFM on the healing process by using various IM nail materials (stainless steel, carbon/epoxy composites (WSN3k [0]2nT, WSN3k [±30]nT) and glass/polyprophylene (Twintex [0]2nT) composite). Reamed and unreamed IM nails were used to investigate the effects of mesenchymal cell activities, deviatoric strain, and body fluid flow in calluses on bone healing. The results showed that unreamed IM nails promoted healing because of a 40% increase in initial cells supplied to the central callus, compared to reamed nails. The most suitable initial interfragmentary strains (IFS) (18.3% and 6.85%, reamed and unreamed) were provided by the flexible Twintex [0]2nT IM nail and this induced 38% and 40.33% healing performances by the reamed and unreamed IM nails, respectively.