ASTM F1541 | External Skeletal Fixation Devices | Mechanical Properties
ASTM F1541 is a testing standard that characterizes external skeletal fixation devices (ESFD) and provides test methods with performance criteria to measure the mechanical characteristics of ESFDs and their fixation to the bone. ESFDs are used for the fixation of the skeletal system in orthopedic surgery. Their clinical success usually depends on suitable mechanical integration with the host bone or limb.
ASTM F1541 covers multiple test methods. Manufacturer should select and run the test methods applicable to the particular device design. Tests may cover individual elements (for example, anchorage elements, bridge elements); subassemblies of elements (for example, connectors, joints, ring elements); or the entire fixator. Refer to the entire specification in the relevant ASTM publication for more information.
ASTM F1541 | External Skeletal Fixation Devices | Mechanical Properties
A1- Classification
Describes each part of the external skeletal assembly, definitions of the relationships between parts, description of the calculations and analysis needed for evaluation, and the reason for the need for testing.
A2- Test Method for External Fixator Connectors
This annex tests the strength of the external fixator connector itself as opposed to the strength of the connection to bridge and anchor elements. Axial or Torsional Load is applied to connector via an input platen that is rigidly bonded to the connector.
A3- Test Method for Determining In-Plane Compressive Properties of Circular Ring or Ring Segment Bridge Elements
Apply compressive quasistatic loading on the ring at points 180 degrees apart until failure. Plot load vs displacement. Compressive Stiffness (n/mm) In-plane compressive strength (n) and compressive yield at a designated offset yield. This will determine the in-plane compressive properties of a circular or ring segment bridge elements.
A4- Test Procedure for External Skeletal Fixator Joints
Testing joints is more complicated as these parts are meant to move and during the test, we want to determine the stiffness and durability of the connector. Gripping should minimize the elastic flexure in the loading input element. Calculations include stiffness, load at failure, and an XY Plot – Load vs. Deformation.
A5- Test Method for External Skeletal Fixator Pins
Run static four-point bend testing on load fixator pin samples as described in the standard to obtain a bending moment vs. flexural deformation curve. Calculations include bending stiffness, strength, and designated % flexural strain. Bending rigidity is determined from these results.
This annex also covers a static torsion test where both ends of the fixator pin is gripped and one end remains stationary while a torsional load is applied to the other end. Torque vs. angle is plotted. Calculations include stiffness, strength, and rigidity. (A5.3.1.8)
A6- Test Method for External Skeletal Fixator Subassemblies
Subassemblies are individual bridge and connector elements and may vary in material, size, and pattern. This method includes procedures in various force loadings (axial, medial-lateral shear, anterior-posterior shear), or under moment loadings (torsion, medial-lateral bending, anterior-posterior bending), or a combination thereof. The bottom grip holds the subassemblies in a rigid position, and the top grip is at loading end. Calculations include Chord stiffness, yield strength and ultimate strength of external skeletal fixator subassemblies.
A7- Test Method for External Skeletal Fixator-Bone Constructs
This annex establishes a universal fixator-bone construct’s minimum configuration and set tests for evaluating performance characteristics. For testing, a fixator-bone construct assembly is created that consists of individual bridge and connector elements anchored to bone analog.
Static tests subject the construct to linear and angular load conditions. The construct strength and stiffness are determined.
Fatigue (multi-cycle dynamic) tests subject the construct to repeated loading conditions. The durability is determined.
Loading conditions may vary with the construct set up depending on the connector elements and bridge dimensions. Refer to Figure A7.1 and Figures. A7.3-A7.5 in the standard for further details. All calculations for stiffness, strength, and durability can be found in section A7.11 of the standard.
ASTM F1541 | External Skeletal Fixation Devices | Mechanical Properties
| ASTM F1541 | Recommended Equipment |
|---|---|
| Testing System | |
| Fixturing |