ASTM F1541 encompasses many different testing requirements for characterizing external skeletal fixation devices (ESFD’s). This specification is used for many fixation devices and applications, Joint prostheses, Modular prostheses, Osteosynthesis, Ring elements, Staples, Subassembly (frame), Synthetic bone, and other implant characteristics. Listed below;a summary of each Annex and recommendations for the type of Testing System needed to perform the test procedure.

ADMET Test Systems

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. See Fig A2.1 for test set up diagram. 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. offset yield plot

A4- Test Procedure for External Skeletal Fixator Joints

Testing joints is more complicated because 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. Reference Fig. 4.1. Measure load in x,y, and z directions.

Calculate Stiffness, Failure Load. XY Plot – Load vs. DeformationBiaxial Testing System

A5- Test Method for External Skeletal Fixator Pins

Static 4 point Bend Test– load fixator pins. Bending moment vs. Flexural Deformation Curve. Calculate bending stiffness, strength, and designated % flexural strain. With these results determine the bending rigidity. 4 point bend fixture

Static Torsion Test– grip both ends of the fixator pin.One end remains stationary while a torsional load is applied to the other end. Torque vs. Angle plot. Determine stiffness, strength, and then rigidity. (A5.3.1.8)

A6- Test Method for External Skeletal Fixator Subassemblies

Subassemblies are individual bridge and connector elements. These subassemblies can vary in material, size, and pattern. The bottom grip holds the subassemblies in a rigid position, and the top grip is at loading end.

A7- Test Method for External Skeletal Fixator- Bone Constructs

A fixator-bone construct is created. This construct 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 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. See Fig A7.1 and Figs. A7.3-A7.5. All calculations for stiffness, strength, and durability can be found in section A7.11.

Recommended system-The eXpert 2610 Biaxial equipped with MTESTQuattro integrated to perform Tension, Compression, and Torsion Tests. Special Fixtures for gripping rings, constructs, rods, pins, sub-assemblies, and other connectors available from ADMET.

The eXpert 2600 series can be equipped with varying load and torque capacities, special fixtures, baths, temperature chambers, and other accessories.

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