The design process for orthopaedic implants : an introduction

Orthopaedic implants consist of engineered devices for various surgical uses, such as plates or nails used to fix fractures; plates, rods, or cages used for spinal fusion, total hip or knee arthroplasties, and osteoconductive bone scaffolds. The implant design process typically involves the complicated interaction of interdisciplinary teams, client consultation, concept generation, concept ranking, prototype fabrication, engineering analysis, etc. However, the process can also be described as having four major aspects, each of which has a feedback loop if modifications are needed. The first is the design and fabrication, which can include factors such as geometry, surface finish, special features, material selection, and methods of fabrication. The second involves mechanical/engineering analysis, which could involve factors such as stress risers, stress shielding, elastic stiffness, failure strength, and fatigue life. The third is biological/clinical analysis, which may involve factors such as biocompatibility, bioresorbability, bone remodelling, surgical simplicity, and clinical outcomes. The fourth is marketplace evaluation, which might involve factors such as cost-effectiveness, patent acquisition, regulatory approval, demographic suitability, and ecological sustainability. These aspects, or the specific factors within each aspect, can occur sequentially step by step, simultaneously side by side, in different orders, or by some combination of all of these options. This article is a brief practical introduction to the design process for orthopaedic implants.