Development of an in vitro three dimensional loading-measurement system for long bone fixation under multiple loading conditions: a technical description.
Abstract: The purpose of this investigation was to design and verify the capabilities of an in vitro loading-measurement system that mimics in vivo unconstrained three dimensional (3D) relative motion between long bone ends, applies uniform load components over the entire length of a test specimen, and measures 3D relative motion between test segment ends to directly determine test segment construct stiffness free of errors due to potting-fixture-test machine finite stiffness.Intact equine cadaveric radius bones, which were subsequently osteotomized/ostectomized and instrumented with bone plates were subjected to non-destructive axial, torsion, and 4-point bending loads through fixtures designed to allow unconstrained components of non-load associated 3D relative motion between radius ends. 3D relative motion between ends of a 50 mm long test segment was measured by an infrared optical tracking system to directly determine its stiffness. Each specimen was then loaded to ultimate failure in either torsion or bending. Cortical bone cross-section diameters and published bone biomechanical properties were substituted into classical mechanics equations to predict the intact test segment theoretical stiffness for comparison and thus loading-measurement system verification.Intact measured stiffness values were the same order of magnitude as theoretically predicted. The primary component of relative motion between ends of the test segment corresponded to that of the applied load with the other 3D components being evident and consistent in relative magnitude and direction for unconstrained loading of an unsymmetrical double plate oblique fracture configuration. Bone failure configurations were reproducible and consistent with theoretically predicted.The 3D loading-measurement system designed: a) mimics unconstrained relative 3D motion between radius ends that occurs in clinical situations, b) applies uniform compression, torsion, and 4-point bending loads over the entire length of the test specimen, c) measures interfragmentary 3D relative motion between test segment ends to directly determine stiffness thus being void of potting-fixture-test machine stiffness error, and d) has the resolution to detect differences in the 3D motion and stiffness of intact as well osteotomized-instrumented and ostectomized-instrumented equine radii.
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The researchers developed and tested an in vitro system to realistically mimic and measure the three-dimensional movements and forces experienced by long bones in real life situations. The study indicates that this system reflects actual bone behavior accurately enough to determine the stiffness/flexibility of bone fragments without any errors from the device itself.
Techniques and Instrumentation
The study is based on the creation of an in vitro system that can realistically simulate in vivo loading conditions on long bones in three dimensions.
The system applies different types of load uniformly such as compression, torsion (twisting), and 4-point bending across the entire length of a test bone.
Using an infrared optical tracking system, it measures the relative movement at both ends of a test segment, which is about 50 mm long. This measurement reveals the stiffness of the bone segment.
The researchers used intact equine radii bones (from horses), which were then intentionally damaged (osteotomized/ostectomized) and fixed with bone plates, to test this system.
Procedure and Findings
The bones were subjected to non-destructive loading conditions, mimicking real life situations.
The relative movement between the bone ends was recorded under these different loading conditions.
The measured stiffness of the intact bone segment was comparable with theoretical predictions based on the properties of the bone and mechanical equations. This reinforces the system’s accuracy and integrity.
The bones were then loaded until they failed or broke, either due to bending or torsion.
The specific way the bone broke was consistent and repeatable, matching theoretical predictions.
Conclusion and Implications
The study concluded that the developed 3D loading-measurement system can accurately mimic real-life movements and forces experienced by long bones during different loading situations.
The system not only applies a uniform load but also measures the relative 3D motion between bone segment ends, resulting in precise stiffness measurements.
This system could play a pivotal role in advancing our understanding of bone behavior under different stress situations – an element critical for orthopedics and related fields of study. Moreover, it could be used to test potential therapeutic interventions or surgical fixes.
Cite This Article
APA
Janicek JC, Carson WL, Wilson DA.
(2007).
Development of an in vitro three dimensional loading-measurement system for long bone fixation under multiple loading conditions: a technical description.
J Orthop Surg Res, 2, 21.
https://doi.org/10.1186/1749-799X-2-21
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