Citation: Hamandi, F.; Whatley, S.; Simon, G.; Venkatarayappa, I.; Goswami, T. Failure Analysis of a Femoral Cephalomedullary Nail. Metals 2023, 13, 506. https:// doi.org/10.3390/met13030506 Academic Editor: Ruslan R. Balokhonov Received: 10 January 2023 Revised: 13 February 2023 Accepted: 1 March 2023 Published: 2 March 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). metals Article Failure Analysis of a Femoral Cephalomedullary Nail Farah Hamandi 1 , Stephen Whatley 1 , Gerard Simon 2 , Indresh Venkatarayappa 3 and Tarun Goswami 1,3, * 1 Department of Biomedical, Industrial, and Human Factors Engineering, Wright State University, Dayton, OH 45435, USA 2 Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright Patterson Air Force Base, Dayton, OH 45433, USA 3 Department of Orthopedic Surgery, Sports Medicine and Rehabilitation, Wright State University, Dayton, OH 45435, USA * Correspondence: tarun.goswami@wright.edu Abstract: A fractured cephalomedullary femoral nailing system was investigated for the clinical and mechanical reasons responsible for its failure. Optical and scanning electron microscopes were utilized to investigate the fracture surface characteristics. Striations presented on the surface indicated mechanical fatigue. A qualitative material conformity test was conducted using available resources and found to be inconclusive, requiring more advanced testing of Ti-15Mo per ASTM standards in a third-party laboratory. In addition, the investigation showed that there is evidence of overloading failure once the fatigue-propagated crack reached a critical size. Based on the observed features, it is possible that nail and self-tapping helical screw interference may have occurred. The interior wall of the nail exhibited damage, allowing a surface crack to form. This surface crack was propagated due to cyclic loading occurring as a result of activities of daily living. The propagation of cracks formed the striations seen on the failed device. This continued for a period of time up until the crack grew to the point where the structure of the nail could no longer withstand the load and catastrophically failed by overloading. Keywords: cephalomedullary nail; finite element; fracture; fatigue; striations; crack 1. Introduction In the United States, nearly 300,000 people over the age of 65 suffer a hip fracture every year. Nearly 95% of these hip fractures are a result of fall [1]. According to a study presented in the American Society of Bone and Mineral Research (ASBMR) 2022 Annual Meeting, the number of global hip fractures is predicted to double by 2050 [2]. Currently, internal fixation devices are widely used to mend serious bone fractures. Unlike previous methods of repairing bone fractures, internal fixation devices offer several benefits, such as quicker recovery times and being without the immobility that comes using a cast [3]. Internal fixation devices cover a wide variety of devices that incorporate metal plates, pins, nails, screws, etc. [4,5]. In this study, the internal fixation device investigated is an intramedullary nail, which gets implanted within fractured long bones and secured with a series of pins and/or screws [6,7]. The body of the nail provides stability to the long bone while being able to help support external weight [8,9]. The device being examined is a fractured cephalomedullary (CM) femoral nailing system. In an accompanying paper, we reported the computational simulation of a femoral nail fracture. Since these nails are inserted into the bone itself, it has several advantages over previous methods of healing fractured long bones. The older methods of restoring long bones required the patient to be immobilized for long period of time [10,11]. Any movement on the part of the patient would cause the bone to shift, and the fracture would either heal incorrectly, causing a deformity, or fail to heal at all [12]. The intramedullary nail, on the other hand, is fixed to the bone itself with locked screws that share the load Metals 2023, 13, 506. https://doi.org/10.3390/met13030506 https://www.mdpi.com/journal/metals