Does Increased Cortical Screw Adhesion on the Far Cortex Result in Higher Resistance against Pull-Out?

Year 2025, Volume: 7 Issue: 1, 16 - 20, 15.01.2025

Ortaç Güran , Batuhan Gencer

https://doi.org/10.37990/medr.1540822

Abstract

Aim: Cortical screws exert compression on the fracture line by applying pressure to the surrounding cortex, while the screw moves within the bone structure through the threads as a result of cyclic movement. To achieve this compression, the cortical screw threads must adhere to the far cortex. The aim of this biomechanical study was to biomechanically evaluate the effect of varying degrees of contact with the far cortex on the resistance against pull-out and to determine the ideal amount of cortical adhesion.
Material and Method: A biomechanical study was conducted on the diaphyseal portions of 12 synthetic femur bones without the formation of any fracture models. The synthetic bones were initially divided into three groups, as follows: partial contact with the far cortex, full contact with the far cortex, and passed through the far cortex. The prepared models were subjected to testing, and after the bone was affixed within the compression device, the head of the screw on the bone was grasped with the aid of a tool, and a tensile force was applied to the cortical screw head until pull-out (load to failure).
Results: A significant difference was observed when the pull-out strengths were compared between groups (p=0.021). Post-hoc analyses revealed that this statistical difference was due to the group in which at least three threads passed through the far cortex.
Conclusion: When choosing the cortical screw length, a stronger pull-out resistance can be expected with a longer cortical screw length and passing the distal end through the far cortex. However, this should be decided taking into account the characteristics of the anatomical region to be treated, the nearby neurovascular structures, and the risk of tendon-soft tissue irritation.

Keywords

Biomechanical study , cortical screw , far cortex adhesion , fixation strength , pull-out

References

• Orthopaedic Implants. https://www.orthobullets.com/basic-science/9063/orthopaedic-implants access date: 26.8.2024.
• Roberts TT, Prummer CM, Papaliodis DN, et al. History of the orthopedic screw. Orthopedics. 2013;36:12-4.
• Feng X, Luo Z, Li Y, et al. Fixation stability comparison of bone screws based on thread design: buttress thread, triangle thread, and square thread. BMC Musculoskelet Disord. 2022;23:820.
• Fletcher JWA, Wenzel L, Neumann V, et al. Surgical performance when inserting non-locking screws: a systematic review. EFORT Open Rev. 2020;5:26-36.
• Lin CC, Lin KJ, Chen WC, et al. Larger screw diameter may not guarantee greater pullout strength for headless screws - a biomechanical study. Biomed Tech (Berl). 2017;62:257-61.
• Ricci WM, Tornetta P 3rd, Petteys T, et al. A comparison of screw insertion torque and pullout strength. J Orthop Trauma. 2010;24:374-8.
• Chen MJ, DeBaun MR, Thio T, et al. Drilling energy correlates with screw insertion torque, screw compression, and pullout strength: a cadaver study. J Am Acad Orthop Surg. 2020;28:e1121-8.
• Feerick EM, McGarry JP. Cortical bone failure mechanisms during screw pullout. J Biomech. 2012;45:1666-72.
• Gustafson PA, Veenstra JM, Bearden CR, Jastifer JR. The effect of pitch variation and diameter variation on screw pullout. Foot Ankle Spec. 2019;12:258-63.
• Baumbach SF, Synek A, Traxler H, et al. The influence of distal screw length on the primary stability of volar plate osteosynthesis--a biomechanical study. J Orthop Surg Res. 2015;10:139.
• Fletcher JWA, Windolf M, Grünwald L, et al. The influence of screw length on predicted cut-out failures for proximal humeral fracture fixations predicted by finite element simulations. Arch Orthop Trauma Surg. 2019;139:1069-74.
• Schmiedl A, Buchhorn A, Schönberger M. The relationship between the subclavian vessels and brachial plexus and the overlying clavicle: Anatomical study with application to plate osteosynthesis. Clin Anat. 2023;36:377-85.
• Chuaychoosakoon C, Chirattikalwong S, Wuttimanop W, et al. The risk of iatrogenic radial nerve and/or profunda brachii artery injury in anterolateral humeral plating using a 4.5 mm narrow DCP: a cadaveric study. PLoS One. 2021;16:e0260448.
• van Dijk PA, Breuking S, Guss D, et al. Optimizing surgery of metaphyseal-diaphyseal fractures of the fifth metatarsal: a cadaveric study on implications of intramedullary screw position, screw parameters and surrounding anatomic structures. Injury. 2020;51:2887-92.
• Kati YA, Kose O, Acar B, et al. Risk of injury to the neurovascular structures in the pararectus approach used in acetabular fractures: a cadaver study. J Orthop Trauma. 2021;35:e13-7.
• Gümüştaş SA, Tosun HB, Ağır İ, et al. Influence of number and orientation of screws on stability in the internal fixation of unstable femoral neck fractures. Acta Orthop Traumatol Turc. 2014;48:673-8.