Relationship Between Rigidity of External Fixator and Number of Pins: Computer Analysis Using Finite Elements

Abstract

Objective: To analyze the rigidity of a platform-type external fixator assembly, according to different numbers of pins on each clamp. Methods: Computer simulation on a large-sized Cromus dynamic external fixator (Baumer SA) was performed using a finite element method, in accordance with the standard ASTM F1541. The models were generated with approximately 450,000 quadratic tetrahedral elements. Assemblies with two, three and four Schanz pins of 5.5 mm in diameter in each clamp were compared. Every model was subjected to a maximum force of 200 N, divided into 10 sub-steps. For the components, the behavior of the material was assumed to be linear, elastic, isotropic and homogeneous. For each model, the rigidity of the assembly and the Von Mises stress distribution were evaluated. Results: The rigidity of the system was 307.6 N/mm for two pins, 369.0 N/mm for three and 437.9 N/mm for four. Conclusion: The results showed that four Schanz pins in each clamp promoted rigidity that was 19% greater than in the configuration with three pins and 42% greater than with two pins. Higher tension occurred in configurations with fewer pins. In the models analyzed, the maximum tension occurred on the surface of the pin, close to the fixation area.

TThe Effect of Dynamic Interfragmentary Movement on the Mechanical Performance of External Fixation Devices for Open Tibial Fractures

“…Mesic et al (18) , and Tananan et al (15) by approximately 62.92%, 43.55%, and 23.35% respectively, and lower than device by Koo et al (19) , and Marcelo et al (7) by approximately 16.55% and 33.26% respectively.…”

“…The model of the external fixation device was analyzed to take into consideration the assembly requirement of the ASTM (American Society for Testing and Materials) technical standard F1541-standard specification and test methods for skeletal fixation devices (7,8) . The details of the assembly are represented in Fig 3 and Table 1.…”

Fracturas apendiculares en caninos politraumatizados, complicaciones asociadas y tratamientos actuales

“…Los fijadores externos se han utilizado desde la época de Hipócrates, sin embargo, fue después de la Segunda Guerra Mundial cuando se hicieron grandes avances; el moderno fijador externo se produjo en la década de 1970, durante las últimas décadas se han producido avances significativos en la fijación externa, teniendo como principal característica la estabilidad (Sternick et al, 2012).…”

Design, analysis and testing of an external fracture fixation device manufactured from composite materials

“…Similar approach to FE modeling was presented in [11] and [21] for example, but the main goal of the works was different. Even the material of fixators analyzed in [11] and [21] was different than in our case (both were manufactured from metal), the methodology of modelling, type of elements, linear elasticity, use of coupling, contact definitions, etc., can be used in our solution.…”