A Brief Introduction into Orthopaedic Implants: Screws, Plates, and Nails

Introduction: Bone, as a hard biological tissue, consists of cells resided in the bone matrix, which is made by an organic (primarily collagen (90%) and 10% amorphous ground substance) and a mineral phase. The main constituents of bone mineral are calcium phosphate and calcium carbonate. The mineral components consist mainly of hydroxyapatite crystals and amorphous calcium phosphate. Bone acts as a reservoir for our body's calcium, also serves as a protector for vital organs, as well as provides mechanical stability to our body, and makes locomotion possible. This hard biological tissue has a hierarchical structure and is designed optimally. There are two types of bone, at the macroscopic level, in our body: cortical (compact or Haversian) and cancellous (spongy or trabecular) bone (see Fig. 1). This specific classification is based on the difference in their microstructure and basic units, as well as in the extent of their porosities. Cortical bone's porosities are at the micro-scales (the size of voids are on the order of a couple of micrometers, and the porosity of cortical bone varies from 5 to 30%), while cancellous bones' porosities range from 30% to more than 90% [1].