Review Article Proc IMechE Part H: J Engineering in Medicine 2019, Vol. 233(3) 295–308 Ó IMechE 2019 Article reuse guidelines: sagepub.com/journals-permissions DOI: 10.1177/0954411919827044 journals.sagepub.com/home/pih Intramedullary nailing biomechanics: Evolution and challenges Natacha Rosa 1 , Miguel Marta 2 , Ma ´rio Vaz 1,3 , Sergio M O Tavares 1 , Ricardo Simoes 4,5 , Ferna ˜o D Magalha ˜es 6 and Antonio Torres Marques 1 Abstract This article aims to review the biomechanical evolution of intramedullary nailing and describe the breakthrough concepts which allowed for nail improvement and its current success. The understanding of this field establishes an adequate back- ground for forthcoming research and allows to infer on the path for future developments on intramedullary nailing. It was not until the 1940s, with the revolutionary Ku ¨ntscher intramedullary nailing design, that this method was recognized as a widespread medical procedure. Such achievement was established based on the foundations created from intuition- based experiments and the first biomechanical ideologies. The nail evolved from allowing alignment and stability through press-fit fixation with nail-cortical wall friction to the nowadays nail stability achieved through interlocking screws mechanical linkage between nail and bone. Important landmarks during nail evolution comprise the introduction of flex- ible reaming, the progress from slotted to non-slotted nails design, the introduction of nail ‘dynamization’ and the use of titanium alloys as a new nail material. Current biomechanical improvement efforts aim to enhance the bone– intramedullary nail system stability. We suggested that benefit would be attained from a better understanding of the ideal mechano-biological environment at the fracture site, and future improvements will emerge from combining mechanics and biological tools. Keywords Bone biomechanics, intramedullary nailing/plugs, implants/ prosthetics, orthopaedic procedures, bone fracture, trauma Date received: 17 October 2017; accepted: 12 December 2018 Introduction Intramedullary nailing is an effective and reliable stabi- lization system and has been the preferred treatment for a wide range of long bone fractures. Some of its advantageous features when compared with other sta- bilization methods include small operative scars, low infection rate, 1 early patient ambulation, decrease blood loss, minimal disturbance to the fracture site and surrounding soft tissues 2,3 and an overall high rate of successful results. 1 The current intramedullary nails’ remarkable designs, materials selection, functional sim- plicity and effectiveness were achieved after a long and conflicting theoretical path characterized by an increased understanding of the biomechanical laws and their relations to the sequential bone healing complex overlapping events (see Figure 1). This article aims to provide an analysis of the intramedullary nail fixation method evolution and the understanding of the theore- tical biomechanical concepts behind the important turning points in its history. The evaluation of the intramedullary nail biomechanical concepts evolution will help infer on the future progress of this stabiliza- tion method and help to establish the adequate back- ground knowledge for research studies. 1 Department of Mechanical Engineering, Faculty of Engineering, University of Porto, Porto, Portugal 2 Department of Orthopaedics, Centro Hospitalar de Sa ˜o Joa ˜o, Porto, Portugal 3 INEGI, Faculty of Engineering, University of Porto, Porto, Portugal 4 Polytechnic Institute of Ca ´vado and Ave, Barcelos, Portugal 5 Institute for Polymers and Composites IPC/I3N, University of Minho, Guimara ˜es, Portugal 6 LEPABE–Faculdade de Engenharia, Universidade do Porto, Rua Dr. Roberto Frias, Portugal Corresponding author: Natacha Rosa, Faculty of Engineering, University of Porto, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal. Email: natacharosa22@gmail.com