Mechanical comparison of cold-worked versus cold-worked hot-forged dynamic hip screw system

Abstract

Purpose: Dynamic hip screw (DHS) plate fabrication has a crucial role in success rate of surgeries for fractures of the proximal femur. Our research focuses on comparing microstructure and mechanical properties of DHS plates fabricated through two distinct processes. We aimed to compare the mechanical cold-worked (CW) DHS plate versus a DHS plate that fabricated through the cold-worked hot-forged (CWH) DHS plate. Methods: The CW and CWH DHS plates had similar topology, however, tested under different loading scenarios. To make the results comparable, the test for the CW DHS plate was simulated and validated utilizing the finite element modeling (FEM) approach. Then, the model (i.e., the CW DHS plate) was analyzed applying the loading scenario of the CWH DHS plate test. Finally, the results of the FEM analysis for CW and the actual test for CWH DHS plates including compression bending stiffness/strength and proof load were compared. Furthermore, the chemical combination of the two plates was analyzed to investigate if they meet the requirements for ASTM F138 standard. Results: Our analysis showed the amount of “Proof Load” and “Compression Bending Strength” of the CWH DHS plate significantly improved by ∼87% in comparison with the CW DHS plate that both fabricated with ASTM F138 material. On comparison between their grain sizes, the CWH DHS plate has a finer grain size (∼55% smaller than CW DHS plate) which leads to larger yield stress. Conclusion: Although the cold-working process according to ASTM F138 leads to enhance the mechanical performance of a DHS plate, adding hot-forging to the process improved the mechanical performance of DHS plate. The outcome of this study could facilitate the development of the optimal fabrication process for surgical implants which in turn will increase the long-term success rate of the relevant surgeries.