Citation: Cost˘ achescu, B.; Niculescu, A.-G.; Grumezescu, A.M.; Teleanu, D.M. Screw Osteointegration— Increasing Biomechanical Resistance to Pull-Out Effect. Materials 2023, 16, 5582. https://doi.org/10.3390/ ma16165582 Academic Editors: Stéphane Durual and Laurine Marger Received: 23 June 2023 Revised: 3 August 2023 Accepted: 9 August 2023 Published: 11 August 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/). materials Review Screw Osteointegration—Increasing Biomechanical Resistance to Pull-Out Effect Bogdan Costăchescu 1,2 , Adelina-Gabriela Niculescu 3,4 , Alexandru Mihai Grumezescu 3,4,5, * and Daniel Mihai Teleanu 6 1 “Gr. T. Popa” University of Medicine and Pharmacy, 700115 Iasi, Romania; costachescus@gmail.com 2 “Prof. Dr. N. Oblu” Emergency Clinical Hospital, 700309 Iasi, Romania 3 Research Institute of the University of Bucharest—ICUB, University of Bucharest, 050657 Bucharest, Romania; adelina.niculescu@upb.ro 4 Department of Science and Engineering of Oxide Materials and Nanomaterials, Politehnica University of Bucharest, 011061 Bucharest, Romania 5 Academy of Romanian Scientists, Ilfov No. 3, 050044 Bucharest, Romania 6 “Carol Davila” University of Medicine and Pharmacy, 050474 Bucharest, Romania; daniel.teleanu@umfcd.ro * Correspondence: agrumezescu@upb.ro Abstract: Spinal disorders cover a broad spectrum of pathologies and are among the most prevalent medical conditions. The management of these health issues was noted to be increasingly based on surgical interventions. Spinal fixation devices are often employed to improve surgery outcomes, increasing spinal stability, restoring structural integrity, and ensuring functionality. However, most of the currently used fixation tools are fabricated from materials with very different mechanical proper- ties to native bone that are prone to pull-out effects or fail over time, requiring revision procedures. Solutions to these problems presently exploited in practice include the optimal selection of screw shape and size, modification of insertion trajectory, and utilization of bone cement to reinforce fixation constructs. Nevertheless, none of these methods are without risks and limitations. An alternative option to increasing biomechanical resistance to the pull-out effect is to tackle bone regenerative capacity and focus on screw osteointegration properties. Osteointegration was reportedly enhanced through various optimization strategies, including use of novel materials, surface modification tech- niques (e.g., application of coatings and topological optimization), and utilization of composites that allow synergistic effects between constituents. In this context, this paper takes a comprehensive path, starting with a brief presentation of spinal fixation devices, moving further to observations on how the pull-out strength can be enhanced with existing methods, and further focusing on techniques for implant osteointegration improvement. Keywords: bone fixation; spinal fixation devices; spinal screws; pull-out effect; reinforcement strategies; osteointegration; material optimization 1. Introduction Spinal disorders are among the most common medical conditions, covering a wide range of pathologies [1]. The increase in life expectancy has left the population exposed to different degenerative changes and deformities in the aging spine [2,3]. Moreover, various daily habits, posture conditions, comorbidities, and traumas are reflected in the health of the spinal column [4]. Management of spinal disorders may comprise physical examinations, plain radiography, computed tomography scans, and magnetic resonance imaging to correctly and efficiently assess the diagnosis, establish the treatment plan, and determine the prognosis [5]. Despite most patients being treated conservatively, a significant and growing part of the population with spinal issues is subjected to surgical interventions [1]. Surgical spinal procedures have been practiced since Jules Gerin first attempted surgical scoliosis Materials 2023, 16, 5582. https://doi.org/10.3390/ma16165582 https://www.mdpi.com/journal/materials